PDA

View Full Version : 912 let me down, again...



sdemeyer
03-28-2010, 07:25 AM
Was out enjoying the nice PNW weather yesterday and my 912 started running like crap, again. Lately, this seems to be the case more often than not. Further investigation revealed a broken carb boot. I just replaced these six months ago to the tune of $100.00 ea. Lucky for me the carbs have retainer springs or the whole $#^&^ carb would have fallen off.

I'm becoming less and less impressed with Rotax and am seriously considering replacing with something a little more reliable, like a VW or even the Boxer motor off my BMW motorcycle.

I rarely see any Internet posts about problems with Rotax 912. Am I the only person alive with 912 issues, Sheesh?

cap01
03-28-2010, 11:36 AM
scott , sorry to hear about the engine problem . awhile back there was a post on here about a place in ohio that makes and sells the rotax cab sockets . supposed to be some super rubber that makes them better than rotax . i think they were around 60 bucks , if you want ill email the address .
cliff at flying b

SkyPirate
03-28-2010, 11:39 AM
If I ever use a 912 ,.that is one part I will re make out of aluminum or 308 stainless ,..seems allot have the same problem,..find a shop that has a mandrel bender and get a 10 inch piece of tubing the same size at the outlet ..ID measurement being the crucial,.have them bend up a tight 90 degree bend then cut the 2 radius sections out on each end where the bend starts and weld them to a flange that will fit properly ..use a straight hose that is fuel compliant from the new piece to the carb tube,..shouldn't have that problem again.

if you can not find a shop that has a mandrel bender ,.. propane fired roof furnaces have 308 stainless or inkanel tubes in them with a series of 90 degree bends in them,..a scrap yard might possibly have one or 2 kicking around ..cut a section of the tubing out that fits your need.

inkanel can be welded with stainless or nickel rod or wire,..best with tig.

Chase

sdemeyer
03-28-2010, 12:18 PM
Do you have the 7 mm spacer on the hose clamp?
To me that looks like it has been tightened to hard on the clamp.

W

Well, I don't know what length the spacer is but it's the one that came with the new $100.00 sockets. Looks overtightned but I don't know how that could be the case, with the spacer installed.

sdemeyer
03-28-2010, 12:24 PM
If I ever use a 912 ,.that is one part I will re make out of aluminum or 308 stainless ,..seems allot have the same problem,..find a shop that has a mandrel bender and get a 10 inch piece of tubing the same size at the outlet ..ID measurement being the crucial,.have them bend up a tight 90 degree bend then cut the 2 radius sections out on each end where the bend starts and weld them to a flange that will fit properly ..use a straight hose that is fuel compliant from the new piece to the carb tube,..shouldn't have that problem again.

if you can not find a shop that has a mandrel bender ,.. propane fired roof furnaces have 308 stainless or inkanel tubes in them with a series of 90 degree bends in them,..a scrap yard might possibly have one or 2 kicking around ..cut a section of the tubing out that fits your need.

inkanel can be welded with stainless or nickel rod or wire,..best with tig.

Chase

I'm guessing the reason for the rubber sockets is to absorb minor engine vibrations. I'm not sure how the carbs would hold up if they were solidy mounted. But, what do I know.... I'm the one with the broken engine :)

sdemeyer
03-28-2010, 12:37 PM
scott , sorry to hear about the engine problem . awhile back there was a post on here about a place in ohio that makes and sells the rotax cab sockets . supposed to be some super rubber that makes them better than rotax . i think they were around 60 bucks , if you want ill email the address .
cliff at flying b

Thanks, Chuck. When I purchased the new sockets, to make a long story short, I ended up purchasing three. I was going to send the unused one back but I never got around to it. Thankfully I kept it so I'm back in business. However, due to the number of issues I’ve had, my confidence in the motor is deteriorating rapidly. I’m near the point where flying the KF is no longer fun and exciting. I went to Pt Townsend for lunch yesterday and I couldn’t help but notice the lack of emergency landing sites between here and there.

SkyPirate
03-28-2010, 12:58 PM
sdemeyer,..
if your connecting a rubber hose to this flange,..the rubber hose is what is suppose to take out the vibration,..I'm sure that the reason for the plastic goose neck or flange is cost of manufacturing ,..it's allot cheaper to inject a one time made casting/mold for every flange made then it is to farm out the job to a shop that makes each piece individually.
I owned 2 of the shop's that did that type work,..plastics and injection molding pretty much took that type of production application away from the job shops,..with exception to fuel blocks ,..I did allot of filling for pre machined teledyne aluminum pump and valve castings,.
with some applications ,..plastics just don't cut it ,..luckily :)

have you got the 582 set up? if you do then the connection is pretty short between carb and flange,..you can move the carb out a little with a hose between carb and flange ,..it would if nothing else give a little more performance to your engine sort of like a tunnel ram,..


Chase

sdemeyer
03-28-2010, 01:07 PM
sdemeyer,..
if your connecting a rubber hose to this flange,..the rubber hose is what is suppose to take out the vibration,..I'm sure that the reason for the plastic goose neck or flange is cost of manufacturing ,..it's allot cheaper to inject a one time made casting/mold for every flange made then it is to farm out the job to a shop that makes each piece individually.
I owned 2 of the shop's that did that type work,..plastics and injection molding pretty much took that type of production application away from the job shops,..with exception to fuel blocks ,..I did allot of filling for pre machined teledyne aluminum pump and valve castings,.
with some applications ,..plastics just don't cut it ,..luckily :)


Chase

Chase, I just went back and reread your original post. I missed the part about connecting the rubber hose from the new flange to the carb. If I have this problem again, I will definitely explore your idea as it sounds pretty good.

Thanks,
Scott

SkyPirate
03-28-2010, 01:14 PM
if you want even more HP for the buck ..inside of the flange put 3 vorticy generators set at about 30 degree's,..just little fins about 3/8" tall that enhance the air as it is drawn into the engine,.. like a tornado so to speak,..more evenly distributed fuel to air mixture ,..almost all carburated auto engines have this either incorperated into the ventury or in a plate between carb and intake manifold ,..some after market intake manifolds use this as well pre built into it.

Chase

Mnflyer
03-28-2010, 01:39 PM
Hi Scott, there were a bunch of crap Rotax/Bing carb sockets made a few years ago that cracked even the HKS engine experienced them cracking I had to replace both of my original sockets in less than 150 hrs of operation. I replaced them with the sockets from JBM products and so far no cracks. If the carb or airfilter rubs / contacts anything it will also cause them to crack much sooner, I can't say enough good about the JBM sockets and I know of other guys with the HKS engines that had the same problems and his cured the problem. heres a link to his carb socket page.
http://jbmindustries.com/ROTAX.htm

SkyPirate
03-28-2010, 02:17 PM
on the 912's I've seen ..there is a flange then a tube about 8 inches long then the carb, carb being mounted close to the firewall. sounds like you've got your's connected like the 582's do ..flange to carb?

Chase

sdemeyer
03-28-2010, 03:11 PM
I wish I would have known about JBM products last year!

Chase, my carbs are mounted directly to the socket. I only have maybe 1" clearance between the air filter and the firewall on right carb and zero clearance on the left carb. The right socket is the one that broke. If I had 8" tubes the carbs would be in my lap. But, that may make them easier to adjust :)

SkyPirate
03-28-2010, 03:19 PM
That may be the answer Scott~! less chance of carb ice too :) ha ha

Chase

Dorsal
03-28-2010, 03:21 PM
Are you using the factory airbox or straight to an air filter? I ask because I have read of others having this problem with the carbs but it appears not when using the airbox. The box appears provides some support for the carbs and prevents a cantilevered filter. Not sure if any of this matters but it looks more secure to me. Again I have limited information and only a few run-up hours on my engine.

Slyfox
03-28-2010, 03:26 PM
There are a couple things that you have to do with a 912 in a model 4. The reason the model 4 has such trouble is the fact that the intakes are switched and the swing arm of the carb is great. so two things need to be, the small one is the filters, they must be the RU2700. Next you need to have the idle right. Meaning, and this is always ignored from me, the idle needs to be almost to about 500rpm. Yes I know you are not suppose to idle that low, I don't, but for shut down and startup you have to close the throttle off so there is NO kick back on shut down and you start the engine with throttle all the way off and push in throttle as you start, this will give you nice smooth operations. A side affect is you now have the ability to slow the airplane real nice on final, I actually pull the idle way back on the flare as well, as soon as I touch I put the idle back up to 1800 and ground runs are at 1800. But for start up and shut down the idle WILL be at closed throttle or about 500 if I let it sit there and run.

How I adjust this is just take the idle stop after 1800rpm is set up and turn the screw on each side back 1/2 turn. This will give you the proper spot and works great. I haven't had problems with my carb sockets since I started doing this. I also haven't had problems with landing short since I've had a lower rpm as well. I don't have problems with the gear case either because I never let it run on the ground with low rpms. Just my 2 cents worth on this situation. In years past I could count on replacing the sockets all the time or have the carb come all the way off. Now I do nothing but fly the airplane.

napierm
03-28-2010, 05:06 PM
Hey Scott,

I used the JBM sockets on my 582. The stock ones showed signs of fretting after only 10 hours since new. The replacements ran another 200 with no problems at all. I think they are still running on the engine now in a Kolb.

BTW, I agree that 912 is no good. Please let me know how much you want for it and I'll take it off your hands. :)

Good luck with your teething problems,

Mark Napier

sdemeyer
05-31-2010, 08:37 AM
I thought I would post a follow-up on my 912 saga. Over the course of a few months, my 912 started running bad. The symptoms were very rough mid-range ( 2500rpm - 3500rpm), Hard starting when cold, occasional dieseling on shutdown, Carb boots failing, Carbs falling off, wires breaking......etc.

I tried everything I could think of to fix including rebuilding carbs, replacing ignition system, triple checking carb balance, triple checking propeller pitch.

I finally gave up and took the KF to Aircore Aviation in Arlington,WA. After a quick diagnostic, Jim thought the problem was the gearbox. There was no noticeable "play" in the gearbox and I was very skeptical it could be the problem.

The gearbox was overhauled and to my surprise, ALL the problems went away. The motor now starts good, runs good and no longer vibrates.

My log book indicates the gearbox has just under 400 hours.

My 912 is now happy and so am I!

Scott

Slyfox
05-31-2010, 09:11 AM
that's interesting, is there any report on what they found wrong with the gear box. You said no end play, I think there should be a little. The only problem I have ever seen in a gear box is too much end play. I would be very interested in knowing what went wrong.

sdemeyer
05-31-2010, 07:50 PM
There was nothing dastardly wrong. It was not on the edge of self destruction. He said the gearbox was very old, as in years. So old that the parts had not been made in 12 years. He said the gearbox was worn to the limits, whatever that means. I think the disc springs were the main issue.

The parts he replaced were:

(1) Spacer 847689
(2) Step Collar 847785
(2) Disk Spring 838215
(1) Spacer 847687
(1) Bushing 933362
(1) Thrust Washer 827992
(2) Ring Half 926035
(1) Oil Seal 950470
(1) Bearing 832235

When I got the plane, the prop was all out of whack (blades were not equal pitch) but I did not detect this until I had 75 hours or so. I think that may have contributed to the accelerated wear.

Scott

DesertFox4
05-31-2010, 09:26 PM
Scott, I read your post and it brought back memories. I ran through a period where I was getting progressively harder and harder starts on my 912S. Fought it for a couple months trying everything in the book electrical and fuel wise. Rebuilt both carbs twice to no avail. Finally talked to our local Rotax guru (should have done it first off) and he diagnosed my problem over the phone. "Gearbox". Had about 400 hours on mine also. Took it off and dropped it off with him and when he disassembled it he discovered I was missing a slipper clutch that was supposed to have been on this engine. I had him install a clutch and re-shim the gearbox. Installed it and the engine starts and runs as new ever since. I think the clutch will help in the longevity of the gearbox but I will not hesitate to get it serviced if I start to see similar symptoms again.