David,
I'm sure the engine mount issues that John Cooper is addressing are
much more important for your particular vibration issues, but thought
I'd share a few additional things that were corrected on my plane at
various times and made big differences in reducing vibration when
each was done:
1. Repositioning that exhaust pipe where it had been contacting the
edge of the hole where it exited the cowling made a surprising
difference.
2. Cleaning spark plugs
3. Dynamic balancing of the prop
4. The prob balancing man also showed me a spot under the cowl on
the co-pilot side where the longeron was contacting baffling; he said
that that is very common on Ercoupes and recommended having the
contact spot shaved just a hair to separate them.
(When ## 2, 3, & 4 were done all together in June, the difference was
very noticeable; it felt like the difference in a car before & after
tune-up!)
5. During the annual that just finished last week, the A&P found
several places where cowl & longerons and the other "framing" members
like the big ring at the very front around the nose bowl (can't
recall the correct terms, but if it was a house, they'd be structural
beams) were not fastened together in all of the places they should
have been. Correcting this made the whole front end feel like it's
tighter, more unitary, and with barely any vibration left. Even the
vibration that regularly used to sjhow up at pattern RPMs was gone.
The flight home was quite smooth.
HTH,
Linda
N3437H (Sky Sprite)
L.A.
________________________________________________________________________
1a. Engine Vibration
Posted by: "drdlhammond" [email protected] drdlhammond
Date: Sat Aug 14, 2010 7:36 am ((PDT))
1967 Alon A-2 with C90
History: I noticed what seemed to be excessive engine vibration
between 1500 and 2200 RPM. Propeller tracking checked during the
plane's annual and was found to be true. Following the advice of
previous Ercoupe Tech e-mail, my AP and I replaced the rubber motor
mounts and I had another shop conduct a dynamic prop balance. The
old rubber motor mounts were in good shape and the prop did not need
balancing (i.e. it was well within tolerance according to the AP who
performed the work). I printed out and followed the instructions
previously offered on Ercoupe Tech for replacing the motor mounts (my
AP had experience replacing motor mounts on other aircraft with
Continental engines but not in Ercoupes/Aircoupes). We could NOT
tighten the mounting bolts to the prescribed 60 inch pounds (we had
metal to metal contact between the engine and the mount). At 45 inch
pounds there was very little clearance so we settled on 40 inch pounds.
Current situation: After almost 15 hours of flying time, the engine
vibration is worse than when I started. Should we try tightening the
mounting bolts or loosening them? Any other suggestions? Cruising
at 2250 RPM is smooth but I need to fly slower at times, especially
in the pattern.
Thanks for your help!
David
N95CV
