912ULS Engine Vibration

by Andrew Pawlak in 912 / 914 Technical Questions 6 years ago

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Re: 912ULS Engine Vibration

by Roger Lee » 6 years ago

Roger Lee

126 5.14k 4.58k

If all you see is 240-270 in/lbs that's way too low. The average I see at annuals is 440 - 490. Your gearbox shouldn't be used any more until it gets inspected and shimmed. If it's that low maybe the phenolic washer gave up the ghost and allowed the lose compression.

Roger Lee
LSRM-A & Rotax Instructor & Rotax IRC
Tucson, AZ Ryan Airfield (KRYN)
520-349-7056 Cell

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Re: 912ULS Engine Vibration

by Andrew Pawlak » 6 years ago

Andrew Pawlak

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SO the gearbox was under spec and was sent for repair. I got it back, reinstalled as per specification and after letting the Loctite gasket material cure for a day tried to fire her up. Tried being the operative word. After a few attempts she started but was now running far worse than ever. After 30 seconds I noticed the ODD side of the engine had no EGTs while the EVEN side was normal. After shutdown, the Even cylinder headers were too hot to touch while the #1 cylinder header was hot and the #3 cylinder was cool (EGT probe is on that header). No more chatter from the gearbox so that is good. Clearly I had nothing firing on Cylinder 3 and Cylinder 1 seems to be running cooler than the rest. I swapped the HORIZONTAL ignition module plugs (plug in sideways) to see if the problem would migrate to the other side/different cylinder - nothing changed. Pulled plugs - look like they did at the annual 4 months ago. Clean and gapped right ~ 0.026. Replaced anyway on #3 with new gapped to 0.025. Boots check out at 5K ohms. Re seated all boots and ensure they are on good (have not checked for current in the wires yet - will do that tomorrow with voltage sensor/timing light). Pulled the valve cover off and rotate the prop by hand - lifters and valves moving as expected - nothing looks stuck/open valve. Did differential compression check on #3 - 78/80 on calibrated gages - Last conditional all cylinders were same. Pulled the carb off to inspect and ensure all is in order. Might be a fueling/mixture problem. Will disassemble and inspect tonight. Running out of patience and options. Open to any suggestions or ideas. Need to get this engine back to running. Any input is welcome. Will report back with updates as they occur. Thanks in advance.

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Re: 912ULS Engine Vibration

by Andrew Pawlak » 6 years ago

Andrew Pawlak

1 4 11

After stripping down the carb on the odd side again and cleaning it thoroughly - I think the idle jet might have been partially blocked but didn't find anything in it or the bowl. After re-assembling everything all seems well! My guess is I had a really lean condition on the odd side and Cylinder 1 was burning what little fuel there was. Cylinder #3 got nothing.

Ran it again today and all seems normal. Power is good to 5000RPM. Will take her for a pattern run after the winds die down and see how she is. Bowl is super clean with no residue. Will follow up after a few days to confirm all is well.

Lesson learned - These carbs have really tiny passages. If it ain't running right...even if you can't see anything....double check. the slightest blockage will cause all sort of havoc.

Thank you said by: john gunn

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912ULS Engine Vibration

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