Kitfox 4 + HKS, the saga continues

[rwaltman]

Abstract:
I got my KF back from, or should I say, I rescued my KF from the A&P at the end of week 4 of the annual inspection. I don't understand what happened, this person has a good reputation and already did some minor work in the KF after I bought it.

Background:
The task at hand was, (1) condition inspection, (2) after a fuel leak, change the hoses in both wings, (3) after thinking about it, change all fuel and oil lines.
I asked for (1), (2) and (3) in successive days starting the week of July 4th , so we had a slow start, but still, this is a three day job, plus the time spent waiting for the hoses to arrive. One week and a half tops, two being very patient?
I got it at the end of week 4 for, after telling them I am not willing to wait any longer and I am taking it back regardless of the work being completed or not.

Last reports from the battle field:
I stopped briefly on my way to work on Thursday, was told “it's ready to go”.
I say I'm taking it the following day, they ask me to be there not later than 3pm. They also ask me to bring the cowlings from my hangar to run the engine with the right cooling, etc. I do that before leaving on Thursday.
Following day I call in the morning to make sure every thing is OK. (It is, of course.) I tell them I'll be there at 2:30. (No problem, we are ready.)
At 4pm I am still waiting while they are working on the plane #$*&%^! !
The cowlings on the floor, as I left them.

Finally they are done, I get the logbooks updated, load the cowlings in my car, pull the plane out of the hangar, unfold the wings (good, no leak.) The engine starts with a 2 second crank. They close the shop and leave.
I begin my own inspection, planning to do some taxi testing. Go around with paper towels cleaning the engine compartment, including the oil tank, the bottom is dirty. (They replaced one of the fittings)
I see a few minor things I asked were not done. In the logbooks, “HKS-700” is misspelled as “Rotax” (I printed all the manuals for them. HKS is all over the place)
I start and stop the engine a few times, (some problems here but not the A&P's fault, details later.)
A last check before taxiing out, one last go around with paper towels. The oil tank bottom is dirty. Again?
I look closer and find the oil drain bolt loose, not even “finger tight”, and not safety-wired …
Planning to have a serious talk with these guys on Monday.
Other than that,

Taxiing:
Next to impossible. The tailwheel unlocks and points sideways with very little side force, then the plane chooses which way to go without consulting with me.
Yes, I know the theory, a quick blast of power and use the rudder to straighten things out.
Yet, with untested brakes and taxiway lights plus other airplanes nearby did not want to try that theory.

The solution was already provided by Av8r3400 and others:

... Remove the unlocking cam from your Maule tailwheel until you are much more comfortable with the ground handling of your Kitfox. ... This cam unlocks the wheel allowing full swivel. If the rudder stops were not sized perfectly, the tailwheel will go to full swivel too easily and you'll have an instant ground loop.
Keeping the steering lock always engaged is much safer, at first.
Done, and now I can taxi. Just need to get one of those truck stickers: “Caution, this vehicle makes wide turns”

Engine:
To save some typing, just read Geowitz reports here [ http://www.teamkitfox.com/Forums/showthread.php?t=2995] and here [ http://www.teamkitfox.com/Forums/showthread.php?t=3803 ]

Relevant quote:
...on subsequent starts everything is rather violent and shakey until the prop gets up to speed. I mean bucking bronco type engine violence... Idle should be around 1600 rpm. At this speed the prop will go back into bucking mode with violence. Around 2000 rpm is somewhat bearable, but my panel is shaking like it's doing the jig. Above 2000 I can almost feel numbness in my body from the vibrations and see the panel shaking. It smooths out relatively above 3000 rpm and gets better the higher I go.

The numbers for me are different, but the tooth loosening vibration is the same. Unfortunately the Powerfin hub is 3-blade only, can not reconfigure it for 2 blades, to try a smaller MOI.
May bite the bullet and order a two-blade hub until I decide what to do. Anybody has an unused 2 blade wooden prop I could buy cheap?

A couple of bright spots:
(1) The battery survived the 2+ years deep discharge.
(2) The engine starts in 2-3 seconds when cold. Slightly warm, it starts instantly. Not fast, not quickly, instantly. I don't think the propeller does more than 1/2 a turn from turning the starter to running on its own.

Next steps:
1st, the quality of the inspection being in doubt I'll do my own using the Kitfox Aircraft provided item list as a guide. May recruit some more knowledgeable friends.

2nd, the engine vibration issue. The previous owners flew from small grass fields with zero traffic, minimizing the time the engine needs to run at idle or low power. I have a longer taxi, may have to wait for other traffic, etc., needing to be above 2400 or 2500 to stop the shaking.
At this high idle rpm the propeller generates too much thrust. Not only staying put requires using the brakes, I need to brake also to keep the taxi speed at a reasonable level.
I see a new propeller in the future...

To be continued.

[napierm]

Sorry the condition inspection went so bad. When I got the KFIII I spent several months (I'm slow) changing out all the rubber, re-sloshing the tank, changing out the crank in the 582, replacing worn hardware, cleaning and re-greasing anything that moved, etc. Stripped and repainted a few things as well. Then the condition inspection was a retired A/P I knew who gave it a once over and kept commenting on how nice it looked and then told me what all to write into the log book before he added his language to it. I think being able to do all the work on these planes and being sure its done right is one of the best perks.

Then when it started flying (yes!) I had to spent more time figuring out how to set up the jets and and tuning lots of other things that had never been done on that plane plus learning how to fly it (slow feet). Well worth it, put over 200 hours in the KF and had a great time. Crap, I wish I had something flying right now....

What gear ratio do you have? I sold off my Powerfin (it was a pusher) but it was a pretty good match for my HKS 3.47 gearbox according to the previous owner. I do recall that the Powerfin is pretty light weight. You could measure the inertia to see if it is over/near the limit. One guy is running a 74" 2-bladed wood prop on his Avid Flyer using a 2.58 ratio HKS with good success. He is on the Yahoo HKS group.

I keep collecting new/used props. I've got a 70" Kiev, a 70" 2-blade IVO medium (minus the front hub, anybody have one?), and a 70" 3-blade tapered Warp Drive (supposedly came off a Subaru, but has a 100mm bolt circle and a 1" hole). When I ever get to fly I'll have a few to try.

You have the Lost Hills motor mount as well, yes? You might call MNFLYER and trade notes. He's been pretty helpful to me. He used to have the 3-bladed warp drive prop on his and I know mine is pretty heavy. I don't recall him mentioning the vibration you have. Are the carbs synced? From your description I wouldn't count on those mechanics and would check it myself. That can make it shake.

Can also check the balance, pitch, and tracking of the prop. If I recall right the Powerfin had a 1" hole front and back. If so, checking the balance is easy: a 1" tube and two lawn chairs work very well. Mine are all different and so had to make a few spacers. If these are off only slightly it is not going to give the hard vibration you are describing but its worth a check.

Best of luck,

Mark

[Geowitz]

I would second the motion on the carb sync. Perhaps you already did this, but I don't recall you noting that as being done. That's always first on the HKS engine vibration check list.

As Mark said, the powerfin's are pretty light and there are a lot of people using them on the HKS's. I wouldn't give up on it just yet.

[Mnflyer]

Hi Robert, also when starting the engine I only turn on the electic pump to fill the carb bowls and to hear that its running then I turn it off when cranking the engine I have notice significant engine smoothness starting this way the electric pump tends to flood the engine when starting and until the excess fuel is cleared out the engine runs extremely erratic / ruff, and syn the carbs.

[rwaltman]

Are the carbs synced?

I would second the motion on the carb sync.

and sync the carbs.

OK, OK, I got it. ;) I'm buying a Carbmate.

Roberto.

[rwaltman]

1 ... What gear ratio do you have?
2 ... I do recall that the Powerfin is pretty light weight.
3 ... You could measure the inertia to see if it is over/near the limit.
4 ... You have the Lost Hills motor mount as well
5 ... Are the carbs synced?
6 ... check the balance, pitch, and tracking of the prop.
7 ... Best of luck


1 - I believe is the 3.47:1 - Will check
2 - That's the claim. Around 0.75 Kg per blade.
3 - In my to-do list - From Powerfin's web site:
"POWERFIN Propellers are 2,500 kg/cm2 for a big three-blade model and 1,800 kg/cm2 for a two- blade model."
4 - Yes.
5 - In my to-do list - I asked this to be done, don't know if it was done, and wouldn't trust the answer anyway.
6 - Did check the tracking (with a very rudimentary setup), waiting on a new torque wrench to do more.
7 - Thank you!

Roberto.

[rwaltman]

Today's update - Did around 25 minutes taxiing, without the tailwheel unlock it felt very much under control. Of course, I did not run very fast or rise the tail. And most of the time dragging the brakes.
Can make a U-turn in two fuselage lengths (roughly, less?)
I was paying more attention at the taxiway lights than at the turn radius, believe could make it better with some practice.

Found the previous owner(s) check list. It says after engine startup, warmup while idling at 2000 rpm. Cannot do that without "the shakes".
At 2200,2300 rpm begins to be OK.

But it did not feel as bad as last time. Followed Mnflyer suggestion of not using the fuel pump; was more proactive correcting the throttle; also let the engine reach higher temps.

More squawks: One CHT stoped working. The oil temp is erratic, goes up and down, shows zero, climbs again. Neither one of the fuel gauges (installed in the wing roots, not the panel) work.
The tension spring on the pilots side left rudder pedal falls. (too long? overstretched?)

[ Still thinking if I should stop payment on the check with which I paid for the inspection etc. Probable have only a few more hours to do so. ]

I am planing to do several hours taxiing, will try to put at least 45 minutes every day after work. Can/should I log this time as PIC, even though I have no intention of taking off?

To be continued.

Roberto.

PS: Added pics of the engine installation here: http://www.teamkitfox.com/Forums/album.php?albumid=117

[tommg13780]

Roberto,
Have you considered putting a little more time into problem solving rather than typing??????????

[Geowitz]

OK, OK, I got it. ;) I'm buying a Carbmate.

Roberto.


:D Especially with the 3.47 gear box you should be silky smooth with that prop.

[rwaltman]

... should be silky smooth with that prop.

Hopefully, but I never read of anybody idling at 1600 rpm with that engine/prop combo ...

Roberto.

[rwaltman]

Have you considered putting a little more time into problem solving ...

No, but I think is a great idea! Added it to my to-do list, item #2643 ;)

More seriously, I'm getting the process rolling. The more I learn, (and I know very little,) the more I'll be able to do on my own.
The plane had to go to an A&P for an annual anyhow, asking him to do these repairs instead of doing them myself before the annual was an attempt to get back to flying in a reasonably short time, while I learn what I don't know, buy the tools that I don't have, etc.
One other option, with which all of us are familiar, is a project progressing steadily but slooooowly, ending in estate sale.

And I'm not typing, I'm venting.

Roberto.

[Mnflyer]

Roberto, the HKS will never run smooth at 1600 R's with the carbs synd and after it completely warmed up it will run smooth at 1700, but on warm up from cold 2000 is the number to shoot for, the HKS with the oil cooler mounted were yours is (same set up as mine) will take a min. of 5 to 7 minutes to warm up and that will be an oil temp of approx 110*F the erratic instrument reads could be do to a poor ground.

[rwaltman]

Carbmate finally arrived, torque wrench and digital angle meter ready, but not my other tools.
The type of tools I use in my hobbies are not really suitable for maintaining an airplane. (Soldering iron, wire cutters, multimeter)
So, to complement them, I got a Craftsman box full with some 200-plus shiny metallic objects. (They are really cute. No colored glass beads, unfortunately).
Complemented it with a few more metric sockets and wrenches for the HKS and off we went to the airport, to sync the carbs.

The HKS docs say the carburetors can be balanced without a prop installed, so I decide to remove it.
Mainly for safety, in a compact engine like the HKS the propeller is not too far away from the carbs, I would be working alone, hot and muggy day, etc.
But also I wanted to get a feeling for how much of the vibration I observed was due to the engine 2 opposite cylinders configuration and how much was due to the props torque reaction.

Before removing the prop I verified the blades pitch and tracking, to see if they were contributing to the problem. They were not.

Pitch: Measured with a digital meter, all three blades were between 1/2 a degree of each other. That speaks volumes for the mechanical steel-pin and feeler method that Powerfin used.

Tracking: It was perfect. Put a laser pointer on the ground aiming up, moved it until the dot was just on the edge of blade #1. It stayed there when I rotated blades #2 & #3

Then, off with his prop! Hooked up the Carbmate, started the engine.
With the throttle all out it idled at over 2000, and the vacuum balance was way off. (Shaking, of course.)
After adjusting both carbs back and forth for a few minutes I got the RPM down to just under 1700, (Mnflyer: right on the mark!), with the Carbmate showing balance. HKS docs say 1400 RPM, 1450 without prop. Doubt I could go that low.

Two unexpected problems showed up.

(1) Without the prop to circulate some air through the oil cooler, the oil temp was climbing fast and was already around 190 when I finished the idle setup. I don't think I can run it at 3000 RPM without overheating. (I heard a few hissing noises when I stopped the engine that I never heard before.)

(2) At this low RPM the generator was not properly charging he battery, and the Carbmate (hooked to the plane's battery) begun showing a low-voltage warning.
This is easy to fix. Just ignore it or use a 2nd small battery for the Carbmate only.

#1 is more complicated. I don't want to reinstall the prop to continue. It is really really close to the carbs. Was thinking of getting some kind of fan to force air through the oil cooler.
Was still thinking when it begun to rain. I have a 1/2-T hangar, which forces me to work outside. If it rains hard, work stops.
Barely finished folding the wings and pushing the plane, pulling the plane, pushing the plane, until it was at just the right angle to fit in the available space, when the rain became torrential.
Closed the hangar door and spent some time marking the wheels position on the ground with duct tape, to know where to aim next time.
Tomorrow's forecast is rain. Tuesday looks good, could put 1 and 1/2 hour after work, so I have two days to think about the oil temp problem.

Any suggestions?

Roberto.

PS: I just noticed the date stamp in the camera is one month off.

[SkySteve]

Roberto,
Thanks for the pics showing your use of the handy "guage clamps". You just solved my problem of holding my digital gauge solid and the same in each blade when I set mine. Ta-da!!

[rwaltman]

Thanks, but not my idea.
See http://powerfin.com/instructions.html

My only contribution was to use the bubble level on the blade's edge, instead of just "putting the blade in the same position."
I also used the level to make sure the meter was vertical when measuring the hub's slope, otherwise small errors will be introduced.

Roberto.

[rwaltman]

Yesterday caught a window between the passing thunderstorms and gave the Carbmate a second chance to prove itself.

Set up the plane as usual, still sans propeller, but this time with a couple fans in front of the cylinders and oil cooler, to be able to run for longer times without concerns about heating.

Was able to set the balance correctly at a lower idle, ~1600 RPM, and balanced again at ~3000 RPM. Oil temp reached around ~170
No noteworthy shaking or vibrations.

Before mounting back the propeller checked its balance. (Pitch and tracking verified earlier.) The only thing I could use as an axis was a wooden rod with a somehow rough finish, that didn't really allow the prop to rotate freely, so small imbalances may go unnoticed. But after several cycles of rotating the prop some 30 degrees and nudging it both ways I was satisfied it was OK.

Propeller back on, engine on, shaking and vibration are back. Maybe less than before, but far, far away from running smoothly. Before, I could smooth it out by pushing above 2400 RPM, now there is a band where it shakes badly above the 2400 mark.

I'm wondering if the engine/prop/mount combination is making the whole structure vibrate at some natural resonance frequencies. If that is happening, I doubt there is anything I can do, other that learn what RPM bands cause it and avoid them.

The Carbmate shows good balance up to ~3300 RPM. Trying to throttle it up above ~3500 RPM causes the following: (a) shakes really, really bad. (b) Carbmate shows vacuum going out of balance. (c) One of the EGT readings goes down (a lot!).
Fuel flow problems in one the carburators?

I am officially out of my depth. Suggestions?

Roberto.

[GDN]

Yes make a dynamic balancing

[Mnflyer]

Hi Roberto, I see you have a Lost Hills engine mount, check the torque on the bolts going thur the rubber biskets to the engine, do not torque more than 10 ft lbs mine are between 6 and 10" lbs. make sure they are safety wired at those low torques they will back out.
You will also need to syn the carbs at 5000 to 5400 R's when I do mine I secure the plane by tying the tail down with a cable to my truck trailer hitch than sit in the plane with the carbmate with you (prop on).

[Dave F]

I have zero HKS experience but I will say that you might be expecting more than acceptable. I have no problem with a 503/582 idling at 2000 to 2300 rpm with a 2.58 or a 3 to 1 gear box.
So a HKS with 3.47 gear box idle at 2000 would be acceptable in my opinion.

Also I wold not accept 1/2 degree variance in pitch amongst the 3 blades -- 1/4 Degree MAX. This is not likely your culprit for shaking. Might just the nature of the beast plus a fw more contributing factors?
Engine mounts too tight ?
Wrong stiffness - measure with a durometer.


Here is an article on HKS http://www.lightsportaircraft.ca/excalibur-aircraftreview/aircraft-performance.html
And states my thoughts as well .........

The Rotax 503 and 582 will idle comfortably at 2,000 to 2250 rpm while the HKS depending on prop will come in between 1750 and 2000 rpm. The standard prop is a two blade ground adjustable 68 inch, my preference for a 582 is a three blade 66 inch and for a 503 a three blade 64 inch.

Hope this helps - more fun flyign that fixing EH !

[rwaltman]

Thanks for the replies.


Yes make a dynamic balancing
I plan to do it, but as a "final polish". There seem to be some fundamental problems I need to solve first.


check the torque on the bolts going thur the rubber biskets to the engine
Good point, will do.


syn the carbs at 5000 to 5400 R's when I do mine I secure the plane by tying the tail down with a cable to my truck trailer hitch than sit in the plane with the carbmate with you (prop on).
OK, I can see the logic on this. If there is a small balance error at 3000 RPM it will be "amplified" at higher RPM settings. Conversely, any remaining error at high RPM should be smaller at lower RPM's (I think.)
One problem now is, (I did not write this clearly,) that the engine will no go above 3400-3500 RPM, one cylinder "faints". (I assume the one cylinder loosing power causes the shaking, and not the other way around.)
I'm not sure I want to do the sync at high power if I am alone, and I can not recruit any help were the plane is now. We'll see ...
Using the car as a tie-down is a good tip. Solves one problem: I was planning to do high-power runups tying the plane to posts set up to protect the hangar's electric meters from cars. That is almost on an active taxiway between the hangars. Can take car and plane to the end of the hangar road away from everything.


I have zero HKS experience
That makes two of us.


I will say that you might be expecting more than acceptable. I have no problem with a 503/582 idling at 2000 to 2300 rpm with a 2.58 or a 3 to 1 gear box. So a HKS with 3.47 gear box idle at 2000 would be acceptable in my opinion.
I was following the HKS docs. The installation manual says idle at "1400 to 1750", "1900 if needed for low vibration." And yes, from several sources 2000 seems more realistic.
I don't care what the actual number is as long as at idle RPM, (a) The engine runs (relatively) smooth. (b) The engine does not overheat. (c) The plane does not move without applying the brakes. I could not get (a) and (c) together.


Also I wold not accept 1/2 degree variance in pitch amongst the 3 blades -- 1/4 Degree MAX. This is not likely your culprit for shaking
Just curious - What accuracy can be achieved with a conventional (non electronic) protractor? I thought 1/2 a degree was quite good.


Might just the nature of the beast plus a fw more contributing factors? Engine mounts too tight ? Wrong stiffness - measure with a durometer.
Yes, maybe, maybe. Great! Another tool I didn't know existed.


Here is an article on HKS http://www.lightsportaircraft.ca/excalibur-aircraftreview/aircraft-performance.html
And states my thoughts as well ...
Saved for future reference.


Hope this helps - more fun flyign that fixing EH !
I guess is a rite of passage I need to go through. No pain, no gain. The French say it better: "Il faut souffrir pour etre belle"

Roberto.

[foxfever]

Thanks for the replies....

Just curious - What accuracy can be achieved with a conventional (non electronic) protractor? I thought 1/2 a degree was quite good.

Roberto.

I have owned and flown 3 blades of several manufacturers.

The 3 I had that adjusted similar/same as yours are warp drive, gsc, and powerfin props.

I can say that within 1/2 degree is acceptable and likely not contributing to your problem.

When I was in a hurry and re-pitching, within 1 degree was good enough for me.

I would then try to get it within 1/4th later, and found no significant difference in smoothness.

Also, of the 3, I felt the PF was the smoothest.....

[CDE2FLY]

Roberto - I suggest trying to isolate the problem. In general, the source of the vibration is either due to engine operation or pitch/tracking/balance of the propeller.

With the prop off, it sounds like the shaking is not nearly as bad. Does the substantial drop in EGT occure when the prop is off? If so, sounds like a cylinder is not firing properly. I assume you have two carbs, 4 cylinders, and you're monitoring EGTs on two cylinders not fed by the same carb. Would it be possible to monitor EGT on all 4 sylinders to determine if both cylinders fed from a particular carb were dropping? This would suggest something is going on with the carb supplying fuel to the cylinders with the low EGTs.

My best guess is that the prop balance is the problem and you can only know for sure by using a dynamic prop balance tester like the Dynavibe. The broom handle approach will not provide nearly enough "resolution" to be useful. I was amazed how much smoother my engine was after dynamc balancing. A very noticible difference was achieved with several very small flat washers installed on the spinner back plate approximately 6 inches from the center of the prop. A very small imbalance can make a very big difference when "multiplied" by the length of the prop blade(s).

Again...try to isolate potential sources of vibration and rule things out one variable at a time. One additional thought - have you contacted the engine manufacturer? Chances are they've had customers with similar issues and might have some valuable insight.

Good luck and keep us posted.

[Timberwolf]

HKS is a 2 cyl engine

[CDE2FLY]

Yes - I should have looked at the pics more closely...clearly a 2 cylinder engine!

Couple of additional thoughts....with the prop off the engine ran smoothly up to 3000 rpm but with the prop on lots of vibration above 3500 rpm. Can you run the engine at 3500 with the prop off to see if the vibration returns?

You mentioned with the prop on there is a bad shake at 2400 rpm but up to 3000 rpm with prop off the engine with smooth. That would suggest the prop is causing at least some of the vibration.

Also, the drop in EGT has me thinking there is something else going on as well...a significant drop in EGT would suggest you're not firing on that cylinder which would cause a significant vibration in a two cylinder engine.

Again....best advise would be isolate the variables. Dynamically balance the prop if all all posible. Once the prop is balanced, if there continues to be a vibration, it's likely due to the cylinders not generating equal power...carb, fuel delivery, ignition, and compression are all possibilities.

[rwaltman]

There are two separate problems,

(a) Vibration
(b) Engine not developing full power.

Taking (b) here, (a) in a separate post. [ It is going to be long, even for my standards... ;) ]
In previous episodes I did not want to run the engine above 3000 RPM without the propeller, so I don't know if the problem shows up or no.
Went to the airport today planning to do just that, and to redo the carb balancing more carefully and at higher RPMs. (more below)
Couldn't do either. The oil temperature gauge stopped working. Without a reliable oil temp reading I didn't want to do anything with the engine beyond starting it and running at low RPM for a couple minutes.
Spend a lot of time trying to figure out how to get to the wiring and maybe remove the oil temp gauge itself, without much luck.

[ The most productive thing I did today was to assemble a tool cart that has been waiting in its box for 1 week.
When my wife saw it ( < http://www.homedepot.com/buy/storage-organization/garage-storage/2-tray-steel-utility-cart-99980.html > ) she asked if I'm going to serve tea in the hangar. ]

My suspects are:

(1) A fuel flow restriction in one of the carbs. Did open the top and cleaned the needle in the carb that, (from memory,) was feeding the cylinder that quits at > 3K RPM. Did not change anything (pushed it briefly to 3300 RPM)
(2) A bad carb sync that is noticeable only at higher RPM.
I'm not sure I did the procedure correctly with regards to the vacuum balance tube between both sides. I remember pinching it close when I did the idle point, not sure I did it when I balanced again at 3000 RPM.
(3) Like (1), but not a restriction but an "abnormality" in the fuel flow due to engine (and carbs) vibration.
(4) Bad compression in one cylinder. The compression was checked when the plane went for its annual and it was OK. (First day, I was there) Of course something may have happened between then and now. A stuck valve?
I will ignore the last two for the time being.

So, the steps now are (a) fix the oil temp reading problem, then (b) balance again the carbs and, if the problem is still there, (c) send the carbs to somebody for a full disassemble and clean-up.
There aren't many people familiar with the HKS engines, but the carbs are the same Bing 64 used in the Rotax 900s, so this should not be a problem.
Hopefully there will not be a (d), scratch head vigorously and go back to empty drawing board...

[ I did ask the mechanic to check the carbs when he had the plane, and he told me he did,but I'm not sure what that means and I wouldn't trust it anyway. ]

This is beginning to be frustrating. Due to work, travel time to the airport, weather, etc. I've been able to work a little on weekends only. Anything I can not solve on the spot (such as ordering a new oil temp sender or gauge) means instantly an additional 1-week delay ...

Roberto.

[pedro10012000]

Roberto - it seems the issue with one cylinder must be the first thing to resolve. Have you discounted that the rough running over 3000rpm could be something as basic as a bad or poorly gapped spark-plug. An easy way to check is to switch the plugs from one cylinder to the other.

Likewise you can may be able to switch over the leads from each CDI to check nothing is amiss with them (it could even be a grounding problem with one of them)

Otherwise strip and clean the offending carb, plus make sure the throttle and choke cables are running freely.

Did you see this discussion re the issue of the Bing carb vent tube length and locations - possibly similar symptoms to yours so worth checking ..... http://www.teamkitfox.com/Forums/showthread.php?t=3869

Does the aircraft have a genuine HKS rev counter? It seems a lot of non-genuine ones are prone to incorrect readings, meaning the pilot may pitch the prop incorrectly, which allows the engine to overrev by about 1000rpm. This can cause bending to the pushrods, which if slight, may only become evident (thru rough running) at higher revs.

I think from your pictures that you have a 2.58 ratio gear box - if so it is only specced to a MOI of 3000kg/cm2. That should be ok with the 3 blade Powerfin, provided you solve the engine running issue.

PS the HKS gauges often seem to have grounding issues - it may be worth checking the ground of your Oil Temp guage

[rwaltman]

pedro10012000 wrote:
-- the rough running over 3000rpm could be something as basic as a bad or poorly gapped spark-plug. An easy way to check is to switch the plugs from one cylinder to the other.
Plugs have 0-time - Changed when I bought the plane, even though they had only 80 hours. Still, valid point, will check. I kept the previous set.

-- strip and clean the offending carb, plus make sure the throttle and choke cables are running freely.
By "strip" you mean remove from the plane? Yes. Cables feel OK.

-- Did you see this discussion re the issue of the Bing carb vent tube length
Yes, and you mentioning it just brought something else to mind: I have been doing these experiments without the cowlings, that is, with an altered air flow. Should put then back.

-- Does the aircraft have a genuine HKS rev counter?
Yes, I am looking for a cheap optical tach to double-check it.

-- I think from your pictures that you have a 2.58 ratio gear box"
Thought I had the 3.47, but seems you are right. Found this in Yahoo's HKS group:
"look at the side of the gear housing. The 2.38 has 3 reinforcements in the casting on each side. The 3.47 has 4."
Next time I remove the plugs for any reason I'll check it turning the prop and counting piston cycles.

-- the HKS gauges often seem to have grounding issues - it may be worth checking the ground of your Oil Temp
Will do. By the way, this (grounding, wires shaking loose) is the kind of problems I'm concerned the excessive vibration may cause.

Roberto.

[Dave F]

How does this engine run at wide open static?
or at 5000 rpm. ?


possibly nature of the beast?

you would not be the first to think that is is very bad when it is just normal.


I would round up another HKS owner to evaluate.

[rwaltman]

Loaded with the propeller does not go past ~3300 RPM.
But now I know, or think I know, why. Did some progress this weekend.

[rwaltman]

Finally, a light at the end of the tunnel.

First - Fine tuning the prop.
My first attempt was more of a sanity check than a careful measurement.
I measured the pitch at the blades tip, that is, with the angle meter on top of the leading edge protection tape, something that Powerfin specifically says not to do. Also the plane was outside, on a windy day, with the wings rocking all the time.
I did it again, twice, inside the hangar, more carefully, not on top of the tape, and found a larger error than before. Two blades within 0.2 degrees, the third 0.8 degrees from the lowest of the first two.
Also, measuring from the hub's edge to the blade's tip, one blade was 1/32" longer than the other two.
The assembly instructions say to pull out the blades (as centrifugal force would) when assembling the hub, apparently this was not done consistently.
Prop was removed, disassembled, cleaned, reassembled and re-pitched correctly.

Second - My carb balancing was worthless.
There is a "vacuum balance tube" linking both air/fuel inlets, that needs to be closed when doing the carb balance. I overlooked the fact that in my setup it is not a tube, but a "T", with the center section feeding the fuel vacuum pump. So, one cylinder drove the carburetor on its side, while the other drove its carburetor and the fuel pump. Not really balanced.
Process repeated with the balance line removed from both ends, holes plugged, electric fuel pump on.
As before, 1st balance without prop, idle at ~1900 , high power at around 4000 RPM.
Then the prop went back on. Idles at 900! So the HKS recommended 1400 RPM is perfectly reachable.
At 900 - 1000 RPM is shaky but stable, doesn't try to quit. There is still some vibration until going above 2000 RPM, but much less intense than before.
So far so good. Further away, not so good.
As before, trying to go above ~3300 loaded with the prop causes shaking, vacuum unbalance, 1 EGT diving down.
This time I had reinforcements. "Rotax guy that knows" was by my side. He is convinced there is a carburation problem. The suspect carb is removed and disassembled, he says something "doesn't look right" but we had to leave it like that, was getting late in the day (yesterday)
We meet again today, the other carb is removed to compare and we find out that:

Third - Bing carburetors do not work correctly when not all the parts are there.
One of the bronze thingies is missing. (Will call it by its proper name when I get the manuals and learn it.) Not a clue how this did happen, I can only suspect the A&P from hell.
So, tomorrow I'll order the Bing manuals, the missing part, a rebuild kit if available, (gaskets, O-rings etc.) By next weekend should (one more should) have everything back and running, and bring back my attention to the CHT and fuel gauges.

Hey, at this rate I may greet 2013 with an airworthy Kitfox ...

Roberto.


Find the differences:

[Geowitz]

Sounds like you're making definite progress and it makes sense - Just giving you a hard time :D, but as we said before, the opposed 2 cylinder motors are extremely picky about carb balance/sync and if one is missing parts that would definitely make that impossible. Glad to hear you're getting closer.

[Av8r_Sed]

It looks to me that your missing carb part is a needle jet. That would certainly explain the poor running with increasing throttle.

You can find exploded parts diagrams for the Bing carbs on most Rotax supplier's websites.

[Timberwolf]

Good to see you're getting things worked out. However, I would have a huge bone to pick with the A&P and would be going over his head. It may be someone else's life you save. Really can't believe he would leave a part out of a carb. Just seems like careless workmanship. Attention to detail isn't a plus with an A&P, it's a necessity.

[napierm]

Wow. Yeah, that is the advantage of learning how to do the work yourself. You know how it was done -> right.

Good luck,

Mark

[rwaltman]

Carb kit arrived - Not as pretty as akarmy's tailwheel, but will keep me equally busy for a while. Will be working on the engine over the weekend.
Ah, the thingie was indeed a 2.70 needle jet.

Roberto.

[rwaltman]

I would recommend tearing down / cleaning the carbs thoroughly.
Prophetic words ...

Problem solved! (After a day long dance practicing the 2-forward,3-backward step.)

Remove both carburetors, disassemble, check, there is a little dirt in the bottom of one of the fuel bowls, practically nothing in the other. Clean it. (Why only one?)
Remove almost everything than can be unscrewed (but not the main shaft.)
Clean everything (bodies and small parts) with a carb-cleaning spray can, rinse with lukewarm water, blow dry with compressed air.
Most things look OK, (engine has only 80 hours,) so we decide (Rotax-guy-that-knows is with me again, as Guy-that-knows-Bing-carbs,) to reassemble without replacing the O-rings and gaskets.
Carbs are put back together, making sure the missing needle jet goes where it belongs.
Install in airplane, hook up everything, fire the engine, and it runs exactly as badly as before.

Scratch heads, discus other possibilities. Check ignition. I saved the previous set of plugs, and with 80 hours they look cleaner than the new ones with a few hours under 100LL. Replace plugs, no change.

Check and re-check all connections to both carbs, specially the "bad" one, (the one that was missing the jet, the one where the EGT decreases after some point.)
Run the engine a few more times. At some point Rotax-guy pulls by hand the throttle in the "bad" carb. Engine speeds up as it should. Pull the throttle in the "good" carb, engine speeds up a little, and then coughs, EGT goes down etc.
Either the EGT senders are cross-wired or I cross-read the EGT's gauges. Which one is the right one? The one with the scale to the right, or the one with the needle axis to the right?

So, the suspect is now the other side of the engine. We just cleaned the carb, could there be a problem with the left cylinder or valves? We swap the carbs, the problem moves with the carb to the other side. Good, no top-end engine problems.

Newly-bad carb is removed, disassembled again, inspected more carefully. The main jet is blocked by an orange, crystalline like substance that survived previous spraying and blowing. (And my poor inspection.) This time all parts go into the heavy-duty carb cleaning stuff, the one that you soak the parts in.

...Fast forward to engine run-ups...

No problems at all starting or speeding-up. Went several times to 4500 RPM, briefly to 5000.
Held 4500 (78% of max continuous RPM) a couple times for more than 3 minutes without a hiccup and with the EGT's identical at 1200. The vibration at RPMs below 2000 is still there, but at acceptable levels. There is some lack of balance, of course, after touching the control cables so many times. I'll take care of re-balancing the carbs tomorrow, as well as doing run-ups at full power and re-pitching the prop for the correct static RPM.

( I believe now that I got the airplane already without that needle jet. Apparently it missing has a relatively small impact on the engine, at least at low altitudes.)

All this not for free... (a) One of the choke springs went missing in action. I never needed to use the choke to start the engine, so we safety-wired it in the closed position until I get a new one.
(b) I left the scene for a few minutes, and in that time another airplane came back to its hangar, with the Kitfox partially blocking the way. Guy-that-knows-Bing-carbs does not know Kitfoxes, at least not the wing folding bit. He pulled the pin and begun folding one wing without disconnecting the flaperon first. So now I have slightly bent flaperon control horn and push-pull tube to fix.

Roberto.

PS: Spell checker insists that "flaperon" should be "chaperon"

[Esser]

Guy-that-knows-Bing-carbs does not know Kitfoxes, at least not the wing folding bit. He pulled the pin and begun folding one wing without disconnecting the flaperon first. So now I have slightly bent flaperon control horn and push-pull tube to fix.

Man you just cant get a break.

[rwaltman]

Well, it is beginning to look as if I do have an airplane after all.
Run 1.5 hours on the Hobbs today. Some 20 minutes taxiing, re-setting the carbs idle balance, checking the gauges for normal readings.
For the rest, took the plane to the end of the road, tied the tail to my car, and run more than one hour non-stop, going from idle to full power and back. Spent 15 minutes at full power, (in slices of 2 to 3 minutes) Temps, pressures and EGTs were OK. Carbmate readings at highest sensibility:

0 2000 RPM (Idle)
-1 2500 RPM
0 3000 RPM
+1 3500 RPM (Some shaking)
+1 4000 RPM (Some shaking)
0 4500 RPM
0 5000 RPM
0 5500 RPM
0 5600 RPM (WOT)

Cannot do better than that. Did a shorter run after removing the Carbmate and connecting back the vacuum balance tube. Was expecting some improvement in the vibration, but if there was one, was not noticeable. Guess that helps only when the carbs are out of balance.
The last 1/2 inch or so of throttle travel does not increase RPM, was expecting a smaller "dead zone"
The 5600 RPM full static is a tad high, did not have the time today to re-pitch and try again.
Will do the same run tomorrow, but with the cowlings mounted.

I still see a few weekends of work taking care of small things, but things are definitely looking good.
Thanks everybody for your help, advice and support. (And no, I am not done bugging you guys yet.)

Roberto.

[Dorsal]

Roberto,
Glad things are looking up, you will certainly know your plane when you fly it.

[rwaltman]

Another day, another 1.5 on the Hobbs. As before, that includes a continuous run of more than one hour with my car as anchor. The rest taxiing around.
Before starting, I added 1 degree to whatever pitch the prop had.

The good - That brought down the static RPM from 5600 to ~5250, which is about right. Not a hiccup during the hour long run.

The bad - the badvrations are back. I suspect the reason is that I removed the leading edge protection tapes, (one was damaged and needed to be replaced) and that may have thrown the prop out of balance. So, add to todo list - 1st, statically balance prop. 2nd, dynamically balance prop. (Is there a Dorsal in the room?)

The ugly - a new problem is that with the new propeller pitch and the need to keep RPM above 2000, (to avoid really really bad vibrations,) the Kitfox really wants to move and to move fast, too fast for my current skill level.
Taxing became an exercise in controlled braking. Need to find a way to bring down the MSR. (Minimal Smooth RPMs) In addition to the prop balancing I still need to retorque the engine mounts, per Mnflyer's suggestions. If that doesn't help, I may switch to a two blade prop even if that means a performance hit.

Yesterday's run was done using only the electric fuel pump. (Had the Mikuni disconnected to use the Carbmate.) Today the Mikuni was back on the job and the electric was not used. So both pumps are OK.

This time I brought my headset - Radio works, intercom works, (at least the pilot's side,) PTT button on the stick works. Microphone, not good enough. KMGJ has an automated transmit check. With the engine on I could not understand my own voice. Need to experiment with microphone shrouds/covers. Any suggestions?

One CHT doesn't work. Seat cover tends to slide forward. Removed cargo bag and liners, (want to keep it that way.) Need some cover on the cargo area so things don't fall in and go to the tail. Need to make sure the missing liners do not expose wires or hoses that could get entangled with my shoes. Fuel consumption from both tanks is far from even. Rudder cable tension spring keeps falling off. Flaperon push/pull rod still bent. And the engine vibrations. I think that's the complete squawk list. For a machine that did not run for 2 and 1/2 years could be much worse.

Roberto.

[Mnflyer]

Hi why do you want such a low static RPM?? My static RPM setting is 5900 +/_ 50 rpms. You want at least 6000 RPM's for take off and a 2 blade prop will not decrease performance if fact it will improve TO / climb performance.

[rwaltman]

Hi why do you want such a low static RPM?? My static RPM setting is 5900 +/_ 50 rpms.
Fear of overreving the engine in straight and level flight. Was aiming for 5400.
The baseline I'm using is the prop testing shown in Green Sky Adventures web site: 15 props combinations on two airplanes, 9 on a Zippy Sport and a 6 Kitfox II. (Both with HKS-700's, 2.58:1) The Kitfox II static RPM range from 5200 to 5800, average is 5533. The Zippy Sport static RPM range from 3820 to 5840. Average is 4987. The average of the whole lot is 5205.

On the other hand, just searched for static to max RPM ratios for several other planes & engines, and found a range from 86% to 95% For the HKS, 90% of 6200 Max would be a static 5580 RPM, right where I was before.


You want at least 6000 RPM's for take off
How much additional RPM do you get from static to take-off and climb-out speeds?


a 2 blade prop will not decrease performance if fact it will improve TO / climb performance.
If the prop is chosen correctly. The advice received is to go to 70" or more. For a 68", max prop tip speed would be ~0.63 Mach. (2400 RPM with the 2.58:1 reduction. I do not have the 3.47 unit as I originally thought)
That means there is a lot of room to increase speed and/or diameter. Cannot do either.

As usual, trying to make sense of what I learn while drinking from a firehose.

Roberto.

[Mnflyer]

As I posted my static RPM is 5900 and I have never come close to over reving the engine, when I release the brakes and push the throttle to full throttle the R's go to 5900 and stay there thur roll out and climp when I get to the altitude I want I pull the throttle back to 5500 and cruise, the engine has a 2.58 GB and I have a 2 blade 68" Warp Drive which far out preformed the 3 balde 66" GSC I started with.
If you check the Operators manual you see that at 5400 R's the HKS will be producing only 52 hp that is not enough for decent to roll and climb you'll need 2000' of runway and climb will be about 250 FPM, you have already noted that the increased pitch cause more idle vibes.
Once again there is little or no Rpm increase from static thur TO roll and climb only time would be in straight and level and that's when you pull the throttle back, you will aslo want the higher Rpm capabilities in the event you should need to make an emergency go around.

[rwaltman]

Gary, thanks for all the information. Will re-pitch for 5900 static.

[napierm]

Static balance, yes. Use a tube and good parallels. Pair of level chairs backs will work. Pretty sensitive too.

Dynamic balance... Has anyone done a dynamic balance on the HKS?

The balance master would be a better use of your dollars. It sounds like junk but they are using a similar system in tires now - a bunch of loose balls inside the tire. The balls will shift to balance the wheel. It is counter intuitive (to me, at least) until you've seen a demonstration - it works. The balance master uses mercury as the balancing medium.

[Dave F]

looking at the HKs chart -- you max power is 5800 to 6200 rpm .
I would set static RPM 6000 to start
you better off with a too fine then courser the pitch 1/4 degree at a time.
Static below 5800 would not be an option.

Running at 5400 static would likely give you 80 to 90% power so about 50 HP only
plus you be lugging the engine and using more fuel.


You can statically balance your prop well. This should be pretty close.

[rwaltman]

Went to the airport once earlier in the week and repitched the propeller to 9.1 degrees. Went back today to try it, slightly delayed by having to replace the band clamps holding the muffler.
The new setting gave exactly 6000 RPM static. The idle rpm went up with the lower propeller load, so another Carbmate session is due to bring it back below 2000 RPM. And still need to chase that CHT ...

Roberto.


Another static flight into the sunset ...