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68niou1
10-10-2013, 09:35 PM
How can you tell if your prop is out of balance? Would you notice it more at higher rpm vs. lower rpm? The reason I ask is because I am at a dead end. I have performed everything I can think of but my 80hp Rotax UL still idles rough and makes massive gearbox ratcheting noises below 2500 rpm. I am wondering if my prop is out of balance/and or bent. However- It runs smooth from 2500 on up all the way to 5200, so in my mind I am thinking if the prop was bad it would get worse at higher rpm- not better. I had the gearcase rebuilt so that takes it out of the equation, and the engine only has 150 hours since new. I know the original owner ground looped the plane so I have a lot of unanswered questions. Any input would be appreciated-

Thanks,

Scott

DesertFox4
10-10-2013, 09:55 PM
I know the original owner ground looped the plane so I have a lot of unanswered questions.

Was there any mention of a prop strike in this engine's history?

68niou1
10-10-2013, 10:19 PM
None in the logs. I was not told about the ground loop when I bought the plane- I found out about it from the grand old interweb when the builder of the plane(the original owner commissioned him to build it) mentioned in another forum how he had to go rescue the owner when he(the owner)ground looped it. A couple of posts later there is a picture of my plane so no question about whether or not it actually happened. Also I found a bent rim in the trailer- and there is scarring on the tail-further evidence:mad:

Av8r3400
10-11-2013, 05:31 AM
I haven't commented on my progress lately because I haven't finished, yet. I will (hopefully) be doing a test run today.

But...

1. How many hours do you have on the motor? Check.
2. Do you know if Kitfox service bulletin # 54A (http://www.kitfoxaircraft.com/support/service_bulletins/sb54.htm) has been complied with?
3. Has the gearbox ever been serviced? Check.
4. How about the prop?


Does the motor move easily in the rubber mounts? Mine did. Complying with the bulletin helped that a lot. I have not run it yet to see if that cured or helped the problem.

68niou1
10-11-2013, 06:26 AM
I haven't commented on my progress lately because I haven't finished, yet. I will (hopefully) be doing a test run today.

But...

1. How many hours do you have on the motor? Check.
2. Do you know if Kitfox service bulletin # 54A (http://www.kitfoxaircraft.com/support/service_bulletins/sb54.htm) has been complied with?
3. Has the gearbox ever been serviced? Check.
4. How about the prop?


Does the motor move easily in the rubber mounts? Mine did. Complying with the bulletin helped that a lot. I have not run it yet to see if that cured or helped the problem.

1. Engine only has 150 hours on it.
2. SB 54A Has been done.
3. Gearbox was just done by Aircore Aviation.
4. Prop has never been messed with as far as I can tell.

I have been chasing this same problem since I got the plane in July- I did not have much Rotax experience- so did not know what was "normal". Since then I have listened to quite a few and mine is not right compared to everyone else. That only leaves the prop- or I am wondering if there is too much spacing in the gears in the gearbox???:confused:

Dorsal
10-11-2013, 09:09 AM
One quick question is does it change much on one ignition or the other?

Slyfox
10-11-2013, 09:52 AM
I am going to throw this out here. there is always one side when checking the mags that is always a little rougher.

next, when starting these things if you choke a slightest bit to much, you WILL have a low end roughness. to choke mine I have mags off , pull throttle all the way off, with choke on crank for a count of 3 or 3 cycles, can here it (compression) . I than stop release choke, turn on mags, start engine. after start up I go to 3000 rpm. the rotax manual actually says to run at High rpm until it smooths out. I generally keep it above 2500 all the way out to the runway. After my flight and land, the low rpm is nice and smooth.

Now with that said, I have choked it just a little to much, like count of six, that thing will not run at low idle for nothing. At least until I pull the plugs and clean them, than It's back to normal.

these engine hate too much fuel. I've flown behind the ul and uls for 1800 hours now, rich starts always affects the low end.

68niou1
10-11-2013, 10:02 AM
One quick question is does it change much on one ignition or the other?

Does not change on either side. Both ignitions are within 50 rpm of each other at drop- and I do not use the choke to start it.

68niou1
10-11-2013, 10:05 AM
I am going to throw this out here. there is always one side when checking the mags that is always a little rougher.

next, when starting these things if you choke a slightest bit to much, you WILL have a low end roughness. to choke mine I have mags off , pull throttle all the way off, with choke on crank for a count of 3 or 3 cycles, can here it (compression) . I than stop release choke, turn on mags, start engine. after start up I go to 3000 rpm. the rotax manual actually says to run at High rpm until it smooths out. I generally keep it above 2500 all the way out to the runway. After my flight and land, the low rpm is nice and smooth.

Now with that said, I have choked it just a little to much, like count of six, that thing will not run at low idle for nothing. At least until I pull the plugs and clean them, than It's back to normal.

these engine hate too much fuel. I've flown behind the ul and uls for 1800 hours now, rich starts always affects the low end.

Slyfox I need you to stop by and listen to it. Brendon is right behind me and I have listened to his- Chad's and Kelly's, none of them sound like mine. Let me know when you are available-

Slyfox
10-11-2013, 10:25 AM
are you back out at felts? what times are you generally there? You can also take the plugs out and look at them. chances are the front plugs I believe might be black, that's not good. although it can be normall, for these generally are darker than the others. If need be I have a spark plug cleaner. quick clean and back in. Do you have a key switch for mags, or flip switches. I have flip switches and I feel that's the only way to go on the 912.

The other day when doing a check over, I found my cable slipped out at the carb for the choke, that can kick the choke on just a little. the fix is to put a wire from the carb to the wire to keep it in place.

Slyfox
10-11-2013, 10:35 AM
One more thing, if you choose to be able to crank the motor with the mags off, you should be able to install a starter button seperate from your keyed mags switch, that is if you have a keyed switch for everything. I have a starter button on my rv. makes for bring up oil pressure with the mags off, very usefull.

68niou1
10-12-2013, 05:07 PM
Well Slyfox came over and listened to it- he found one of my chokes slightly open, cleaned the plugs and tried again- same issue as before. So now he has loaned me a prop to try- and the warp drive tool to check mine. Thanks Slyfox!! I will try to get to it on Monday- will update the results.

DesertFox4
10-12-2013, 05:32 PM
Well Slyfox came over and listened to it- he found one of my chokes slightly open, cleaned the plugs and tried again- same issue as before. So now he has loaned me a prop to try- and the warp drive tool to check mine. Thanks Slyfox!!


Steve's a good man.:)

Hope you get to the bottom of this problem.



I agree on the ignition switches and start button. Love that setup.

Slyfox
10-12-2013, 06:28 PM
I didn't point out when listening to the engine, but the older 912ul engines had a distict whirl noise. My old one did it and I heard it out of yours. I still say that prop of yours has a problem. it sure had a nasty wobble when watching it from the side. really hope we can get to the bottom of your problem.

68niou1
10-14-2013, 08:31 PM
Well- checked the pitch on the warp, and it was perfect. So I pulled it off and put on Slyfox's known good prop(powerfin), crossed my fingers and fired it up- and got no where:mad:

Went back to the basics, compression check, pulled valve covers, rechecked plugs, out of ideas. About ready to order a 100 horse and start over:confused:

So next stop Jim Scott Aircore Aviation on Friday hopefully as I am at a complete loss.

DesertFox4
10-14-2013, 09:18 PM
Scott- do you know the history of this engine such as did the first owner run 100LL or auto gas? I heard tell of a 80 hp Rotax up in Utah that had lots of trouble after running 100 LL without using the lead scavenger additive and experienced a lot of rough running issues. He finally did a tear down and found lots of lead deposits causing the problems. Just food for thought. I know your getting frustrated as all the tried and true fix's are not helping.
Best of luck. Keep us updated.

68niou1
10-15-2013, 07:15 AM
Scott- do you know the history of this engine such as did the first owner run 100LL or auto gas? I heard tell of a 80 hp Rotax up in Utah that had lots of trouble after running 100 LL without using the lead scavenger additive and experienced a lot of rough running issues. He finally did a tear down and found lots of lead deposits causing the problems. Just food for thought. I know your getting frustrated as all the tried and true fix's are not helping.
Best of luck. Keep us updated.

It did run 100LL exclusively from day one, but it only had 145 hours on it when I got it, and now it has 154. I guess I can't count anything out at this point. Dynamic comp test shows #1 124, #2 136, #3 126, #4 135 and differential shows 78/80 all around. Like I said, I am at a loss, multiple people have looked at it so now its down to the Rotax expert:D I still think I might have the same problem as Larry-

Danzer1
10-16-2013, 08:45 AM
Scott,

Steve mentioned, your prop had a "nasty wobble" when looked at from the side - did his known good prop also have the same problem?

You mentioned the problem went away after having the gear box rebuilt. Is this the same , identical problem you had prior to that (reoccurred)? Or is this something that has cropped up since?

Greg

68niou1
10-16-2013, 11:32 AM
His was the same- I think it was just the light playing tricks on us as it was getting kind of dark out when we were running it up. This is the same problem I had originally before the gearbox rebuild, however it is much smoother than it was before. When I got it back I still had not been able to listen to some other examples so compared to what it was before the rebuild, it was much smoother(before it shook so bad the carbs puked fuel out of the breather hose), however, now that I have been around a few other Rotax's, it is not as smooth as it should be. I am impatiently waiting for Larry's parts to come in so he can be the guinea pig:D

Danzer1
10-16-2013, 02:59 PM
You and Larry may have 2 completely different problems. He keeps describing vibration and you seem to generally refer to rough running. Although either could be symptomatic of a prop, gear box, crankshaft issue and/or a fuel, fuel/air mix, detonation problem.

If you want to rule in or out the vibration aspect, I'd suggest the same thing as I did for Larry - checking the prop hub and crankshaft for true/endplay and runout.

Very few issues originate with the gear box, but that is what gets damaged 1st, due to other balance, true, vibration source issues. Unless of course you have high time and it's simply wear. Yours has very low time.

Can you find out from Aircore what was worn, out of spec, replaced when they rebuilt the gear box? Did they give you any explanation on what was wrong with it and their thoughts as to why? Did they actually rebuild it or just inspect it?

You could be "chasing your tail" and might end up rebuilding it again if the source of the problem originates either in front of or behind it.

Can you video (with sound) and post to YouTube - it's awfully hard to get a good idea from descriptions.

Good luck, I know how frustrating these things are.
Greg

68niou1
10-16-2013, 03:23 PM
When I pulled my gearbox off- I checked to see if the prop shaft was bent, which it was not. I did not check the crank, my logic was if the prop shaft was straight the crank should be straight too. When Aircore rebuilt the gearbox I am pretty sure he replaced the spring washers behind the dog gear(there was a update on those I think) and when I talked to him a couple of days ago he remembered some galling(or marks) on the dog gear. My rough running issue is vibration, started by gearbox chatter below 2500 rpm. I will try to get some video of it so it can be better understood. Thanks again for all your input.

Scott

Danzer1
10-16-2013, 03:49 PM
We may be talking semantics here, maybe not but, the prop shaft being straight is different than the prop hub being true and within spec for runout. If the prop hub is not true and/or runout is not within spec it could be caused by a bent prop shaft or the hub itself or within the gearbox or the proper alignment of any of them.

The prop shaft being straight, does not mean the crankshaft is true or within runout spec as you have the gearbox in between.

I still think both are worth checking. If it were a gear design issue (even though they may have improved it), I'd think we would have heard about a lot more issues than just the few here, out of the thousands running.

Greg

Av8r3400
10-16-2013, 06:07 PM
Danzer, you need to understand that my (and Scott's) engines are early 912 UL motors. The new gear set that I have coming is a complete redesign, the material, pressure angles and oil control are completely different.

This vintage gearbox, per Rotax, is supposed to be rebuilt at 300 hours. (Meaning these parts get replaced then.) Most do not get this done because it isn't needed.

I have checked runout of the prop flange, prop shaft and crank gear. These are all fine. I'm sure Scott's is too. The combination of many variables has caused this issue. I'm sure the high mass index of the Warp Drive prop that I have is part of it. I'm also sure that the sitting my motor did from the time it was new in 1993 to the first flight of the plane in 2007 has something to do with it.

From all of the Rotax people I have spoken with, who are very much in the know, this is a gearbox issue.

Danzer1
10-16-2013, 07:14 PM
It could be - I'm just pointing out possibilities. And to play devils advocate - If they are completely different, new and improved and Scott's was just rebuilt, and Rotax knows of his issue (vibration) and other issues with the older gears on other engines - why didn't Aircore replace the gear set when they rebuilt it? Or, at least recommend that the gear set be replaced? Would have made sense, if that was thought to be an issue or the cause of the problem. Is he supposed to wait until 300 hours to fix the problem (if that is the root of it)?

Just possibilities and food for thought.
Greg

Av8r3400
10-16-2013, 07:33 PM
I appreciate the out of the box thinking. Really. That's why this forum is great!


There are three Rotax authorized service stations in the US. Lockwood, LEAF and California Power Systems. If one of them had done the gearbox rebuild they would have, no doubt, replaced the gears and dog ring if they showed any spauling.

I don't know Aircore. I'm sure they are very competent mechanics. But they are not Rotax. Speaking with the shop manager (a friend of mine) at LEAF he told me that if there is ANY wear or damage showing on the drive dogs the parts would be rejected immediately. This is a known problem.

Like a recall done by an auto manufacturer, there needs to be enough failures to make the action (Service Bulletin) economically feasible. These parts are taking care of themselves by attrition. My and Scott's problem are outliers.

Danzer1
10-16-2013, 09:17 PM
Aircore is a Rotax factory authorized repair center, this type of work does not in any way require the use of a "service center".

Maybe Scott should ask Aircore why they did not replace (or even recommend replacing) the gear set when it was apart. If, what you say LEAF says "the parts would be rejected immediately" and the guy at Aircore "remembered some spalling" then the gear set should have been replaced under that scenario. Not suggesting either LEAF or Aircore are wrong, but the way I see it, under this scenario, they can't both be right.

Scott, it would be very interesting to hear what Aircore thinks about it (and LEAFs opinion).

Greg

68niou1
10-16-2013, 09:36 PM
Jim Scott (Aircore) will be here Friday. Like Larry said, both of our UL's are very early examples, and both have sat a lot. Jim did the known AD on the gearbox which was replace the spacers and reshim I believe. And like Larry has shown us, the wear on the dog gear does not look that bad. If Jim had called me and given me the choice of $200 and taking a chance or $1500 I would have picked the first option every time:D Both Larry and I have talked to multiple Rotax experts and we are getting the same story. Could we both have different problems? Absolutely. That is why I am having Jim come work on my plane on Friday. However I will not be surprised if he tells me it is the gearbox. Here is the cool thing- I will update everyone what I find out, and so will Larry, that way we all can learn and know what to look for.

Scott

SkyPirate
10-16-2013, 10:20 PM
Just curious what are the series #'s or serial #'s on your 912? Mine starts 440.... And its also a ul

SkyPirate
10-16-2013, 10:22 PM
From what Larry has said in another post im pretty sure i
Have the wider gear set

SkyPirate
10-16-2013, 10:26 PM
If my rpms drop short of about 2300 she gets a little rough, but other then that, 2300 to 5400 she is smooth

68niou1
10-17-2013, 06:38 AM
mine is 4152298, and Larry's is pretty close if I remember correctly.

Danzer1
10-17-2013, 11:01 AM
Okay guys, You've both got me pretty frustrated, so I'm going to tell you why and leave it alone from here on out. Please bear with me until the end and then do what you want.

These forums/threads are for us to help each other out. Scott, this is the 2nd thread you've started supposedly attempting to find and fix your vibration issue. Apparently that also includes it fitting into some cost/risk/reward formula. Sometimes when it comes to safe and proper operation - that formula might not be the best choice, particularly if you invite others into your aircraft. You can choose to nickel and dime it, you can choose to take risk, you can choose to attempt to find and fix the problem or not. Heck, that's why we all choose to run un-certificated, experimental in the 1st place.

But as a reminder, others (passengers) may not have your same view. So here's why I'm frustrated as you've asked for assistance and some have spent considerable time attempting to help and it seems you guys just don't get it!

#1: Scott, you've stated you and Larry are both getting the same information from Rotax. You are not!

If Larry's statements are correct, you would have been told you needed to replace your dog gear and gear set - you weren't told that.

You were not even given the choice as you've alluded to. In fact, you were not even told there was any spalling at all, so you didn't even have a choice to make. Or the spalling information to even make an informed decision.

So I don't see how you can state you are getting the same story.

#2: Larry, you stated: "I have checked runout of the prop flange, prop shaft and crank gear. These are all fine. I'm sure Scott's is too." and further stated "I appreciate the out of the box thinking".

As if my suggestions are not ordinary and inferring that Scott doesn't need to check his.

Scott has no way of knowing that unless they are checked and correct. So you can't eliminate them as a possible cause unless and until they are checked.

Further, these checks are not out of the box, off the wall ideas I've simply thrown out there. They are REQUIRED checks by Rotax whenever the gearbox is removed, inspected and reinstalled!

Please refer to the Rotax 912 Heavy manual chapter 72, page 39. Checking the propeller hub (flange) for runout is the 1st thing to be checked - it's not a suggestion.

Refer to the chapter 72 page 53. Checking the crankshaft for runout is not a suggestion.

Refer to chapter 72 page 54. Checking the prop hub for true (radial gear backlash) is not a suggestion.

So, before you guys jump all over me - I do realize that in a way anything Rotax says are really just optional suggestions, as you are running un-certificated, experimental aircraft and that allows you to make whatever choices you want. But those items are there for a reason and should be checked.

Do what you want to - that's why we choose to be in the experimental category, but do me a favor: If you choose not follow this or any other manufacturers "suggestions" for the proper and safe operation of your aircraft - please don't invite anyone else to participate with you - either in a forum or in your passenger seat - their tolerance for risk may not be the same as yours!

Thanks for listening, I'm done with this issue, I'm sure you'll follow up with the responses to this post and maybe the eventual solution to your issues.

Good Luck,
Greg

68niou1
10-21-2013, 10:16 PM
I am going to try to answer this as politically correct as I can, however it really fries my a$$ when someone who doesn't know me at all assumes from one or two posts he does.

First of all- Jim Scott from Aircore came out and worked on my plane on Saturday. Doublechecked everything I had done, looked everything over for himself, and came to the conclusion the dog gear is bad. Told me it is not a normal failure, and normally reshimming the gearcase takes care of any vibration/chatter issue. Then I pulled my gearcase apart, checked the runout on the propshaft(perfect), prop flange(perfect), crank(perfect), looked at all the gears and bearings and did not find anything abnormal. I did not get a chance to press the dog gear out of the case yet but when I do I will shoot photos of my dog gear and post it up. I then called CPS and spent $1300 on the gearset(backordered) and dog gear.

I am not going to comment on anything else.

Slyfox
10-25-2013, 08:27 AM
scott I hope soon you can have a decent running fox. Sunday was quit a day. I started up my fox and was in a hurry. It didn't want to start, banged and farted. I know better and kept it banging and farting. It did start, but I should have used more choke. I should have had it plugged in. It was cold. Anyway, I flew it to deer park and landed, now it's running really bad. I was joking when I said you gave me a virus. I was parked close to your fox. I went and flew back to felts with no problems. after landing it ran rough again. I made the right decision, grabed the rv and went for the flyout, which I had a great time. later that night I looked at the kitfox and found what I thought was the problem and I was right. the right carb socket was cracked open. monday I ordered the carb sockets from jbm. I recieved them yesterday and put them on last night. while putting them on I found the left cable, new style, was broken where the outer housing joins with the carb. OH man, you really got me on this one :). just kidding. I fly this thing so many times a week and now I have all kinds of problems:p.

anyway I connect the cable and tie it up good. now to order a new cable. John, when do you get back in the office so I can order parts.

pyolet
12-28-2013, 10:01 PM
Scott, I had similar symptoms on my recently acquired KF2, and couldn't perform a carb balance due to the extent of the shaking below 2500rpm. Talked to John at Kitfox and he suggested checking the motor mounts. Kitfox Service Bulletin #54 explains how to shorten the mount bushings. Took me half a day to perform the adjustment. Smoothed out my 750hr 912UL so that I can cold idle at 1000. FWIW. Woody.