 |
Matronics Email Lists
Web Forum Interface to the Matronics Email Lists
|
| View previous topic :: View next topic |
| Author |
Message |
malannx(at)bigpond.com
Guest
|
 Posted: Thu Mar 12, 2009 11:22 am Post subject: Rotax 921ULS rough running(420 hoursTSN) |
 |
|
Over a period of a couple of months the engine/plane has developed significant vibration that was related to engine revs and was like it was running on 3 and a half cylinders-not actually missing.
After much head scratching and all the usual things such as carby balancing, plugs etc. a leak down test was performed with the following results:
Cyl 1: 73/80
Cyl 2: 64/80
Cyl 3: 63/80
Cyl 4: 73/80
By listening I determined the intake valves in cyl. 2 and 3 were leaking. Subsequently all 4 heads were removed and sent for service.
All 4 intake valves were too badly damaged on their valve seat mating surfaces to be repaired. So 4 new valves. The Rotax mechanic had no explanation for the damage. Have used mostly Mogas premium unleaded. The mechanic said he would expect to see that damage on an engine that had done 1200 hours exclusively on Avgas.
No damage to the valve seats in the heads. Talk of sending the valves back to Rotax. I liked the lack of head gaskets. There would be good heat transfer from the top of the cylinder barrels to the heads.
The mechanic also suggested that some people had vibration problems at around 3000 revs that could not be cured. It was discovered that the nut holding the small gear(gearbox) on the crankshaft was loose. This proved to be the case on mine. It was well below the required 200nm(146 ft/lb). The serrated bellville washer under the nut was badly worn and was replaced. The nut is supposed to be put on with Loctite. On my engine it appeared that Loctite had been applied after the nut was tensioned up and had wicked in only a couple of threads. I was impressed with the simplicity of the Rotax gearbox and its ease of disassembly. I loved the use of bellville(cupped) washers and shims to get the required torsion in the “dog clutch”.
After carby disassembly 2 damaged O rings were found on the idle mixture screws, after renewal the idle improved marginally.
Engine has always run much smoother on one mag than the other, although rev drop difference between the two was only 30-40 revs at 4000, much less than the roughness indicated.
Trigger coils checked and tested okay with an ohm meter. Trigger coil plugs reversed at the ignition modules, but roughness stayed with the same mag circuit eliminating the trigger coils. Then switched plugs that connect the ignition modules to the coils(4 of) and voila the problem changed mag circuits, indicating a problem with 2 coils or their leads and plug caps. Both coils test okay, both primary and secondary circuits. One spark plug cap tested okay until a slight tension was applied, then went open circuit. It was replaced and engine test run. Still the same problem. The ignition modules/coil pack are an absolute dog’s breakfast to get at, compact but a terrible design for access.
So the saga continues. I have found several major problems I would not have found for a while. Have just priced a coil. Hard to imagine how a tiny little coil could cost more than a set of tyres for my car or a bottle of Australia’s premier red wine-a bottle of Penfold Grange(over $500). Incidentally, I priced an ignition module and I could get a one way airline ticket to London for less. So I just need a few days to pluck up the courage to order a new coil then try to work out which coil is crook.
On a more serious note the ignition modules are supplied with power from 2 charging coils. The schematic shows 2 seperate wires from the charging coils to the ignition modules. On my engine there is only one wire, jumpered to each module. The failure of that wire at either end results in the loss of both ignition systems, a very serious design flaw and one I'm glad I found.
Malcolm Ferguson
Esqual, 912ULS, Rospeller CS
[quote][b]
| | - The Matronics RotaxEngines-List Email Forum - | | | Use the List Feature Navigator to browse the many List utilities available such as the Email Subscriptions page, Archive Search & Download, 7-Day Browse, Chat, FAQ, Photoshare, and much more:
http://www.matronics.com/Navigator?RotaxEngines-List |
|
|
|
| Back to top |
|
 |
N117FA
Joined: 19 Sep 2008
Posts: 6
Location: Gaithersburg, Maryland
|
| Posted: Tue Aug 25, 2009 3:03 am Post subject: Re: Rotax 921ULS rough running(420 hoursTSN) |
|
|
Has a solution been found for this problem?
I'm working on a Rotax with the same symptoms and have performed the carburetor synchronization, have disassembled and cleaned the carburetors, and checked the prop for equal pitch of the blades. It isn't affected by running on either mag individually.
Thank you,
Younis Forsyth
Forsyth Aviation
| | - The Matronics RotaxEngines-List Email Forum - | | | Use the List Feature Navigator to browse the many List utilities available such as the Email Subscriptions page, Archive Search & Download, 7-Day Browse, Chat, FAQ, Photoshare, and much more:
http://www.matronics.com/Navigator?RotaxEngines-List |
|
|
|
| Back to top |
|
|
Roger Lee
Joined: 10 Jan 2006
Posts: 1464
Location: Tucson, Az.
|
| Posted: Mon Aug 31, 2009 8:05 am Post subject: Re: Rotax 921ULS rough running(420 hoursTSN) |
|
|
Use this type of 120V AC circuit tester and you can track down a bad plug or wire right up to the coils in a matter of minutes. With the engine running you run the tester along the plug wires and it lights up, if you have a bad plug or wire it blinks erratically or quits flashing.
| | - The Matronics RotaxEngines-List Email Forum - | | | Use the List Feature Navigator to browse the many List utilities available such as the Email Subscriptions page, Archive Search & Download, 7-Day Browse, Chat, FAQ, Photoshare, and much more:
http://www.matronics.com/Navigator?RotaxEngines-List |
|
| Description: |
|
| Filesize: |
1.23 MB |
| Viewed: |
6031 Time(s) |
|
| Description: |
|
| Filesize: |
729.88 KB |
| Viewed: |
6031 Time(s) |
|
_________________
Roger Lee
Tucson, Az.
Rotax Instructor & Rotax IRC
Light Sport Repairman
Home 520-574-1080 TRY HOME FIRST
Cell 520-349-7056 |
|
| Back to top |
|
|
N117FA
Joined: 19 Sep 2008
Posts: 6
Location: Gaithersburg, Maryland
|
| Posted: Wed Sep 02, 2009 1:38 pm Post subject: Re: Rotax 921ULS rough running(420 hoursTSN) |
|
|
Roger,
I really appreciate the suggestion. Sounds like a great way to check the ignition integrity without risking damage. I'll let you know what I find.
Thanks,
Younis Forsyth
Forsyth Aviation
http://www.ForsythAviation.us
[quote="Roger Lee"]Use this type of 120V AC circuit tester and you can track down a bad plug or wire right up to the coils in a matter of minutes. With the engine running you run the tester along the plug wires and it lights up, if you have a bad plug or wire it blinks erratically or quits flashing.[/quote]
| | - The Matronics RotaxEngines-List Email Forum - | | | Use the List Feature Navigator to browse the many List utilities available such as the Email Subscriptions page, Archive Search & Download, 7-Day Browse, Chat, FAQ, Photoshare, and much more:
http://www.matronics.com/Navigator?RotaxEngines-List |
|
_________________
www.ForsythAviation.us |
|
| Back to top |
|
|
Roger Lee
Joined: 10 Jan 2006
Posts: 1464
Location: Tucson, Az.
|
| Posted: Wed Sep 02, 2009 4:46 pm Post subject: Re: Rotax 921ULS rough running(420 hoursTSN) |
|
|
I have used it numerous times. You can pin point a bad wire or plug. Makes finding anything from the plug back to the coil easy.
| | - The Matronics RotaxEngines-List Email Forum - | | | Use the List Feature Navigator to browse the many List utilities available such as the Email Subscriptions page, Archive Search & Download, 7-Day Browse, Chat, FAQ, Photoshare, and much more:
http://www.matronics.com/Navigator?RotaxEngines-List |
|
_________________
Roger Lee
Tucson, Az.
Rotax Instructor & Rotax IRC
Light Sport Repairman
Home 520-574-1080 TRY HOME FIRST
Cell 520-349-7056 |
|
| Back to top |
|
|
|
|
You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot vote in polls in this forum
You cannot attach files in this forum
You can download files in this forum
|
Powered by phpBB © 2001, 2005 phpBB Group
|
Get Email Distribution Too!
FAQ
Search
Memberlist
Usergroups
Register
Profile
Log in to check your private messages
Log in
