Conical engine mount bushings

[Steve Pierce]

Aircraft Spruce now sells Lycoming OEM parts. I have had great service out of the OEM shock mounts.

[fabricman]

Installing new motor mount rubber bushings in the 0320. Steves spec posted earlier calls for compression of the donuts between the motor mount boss and the washer on the engine side to a measurement of 1.840, if Mark and I read it correctly. Here is a photo of the top mount on the RH side. Nut is run up to far to engage the cotter key, is very tight and only measures 1.91 in.. What is going on? Do I have the wrong rubber bushings? Invoice shows the correct ones and they look correct.


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[Steve Pierce]

Taks an AN8-44 bolt and no AN washers. The drawing is on the first page of this thread. Just replaced the mount bushings on a Pacer. The measurement is rubber to rubbber per that same drawing.
IMG_20180519_141122.jpg

IMG_20180519_140912.jpg

IMG_20180519_141225.jpg

[fabricman]

Taks an AN8-44 bolt and no AN washers. The drawing is on the first page of this thread. Just replaced the mount bushings on a Pacer. The measurement is rubber to rubbber per that same drawing.
IMG_20180519_141122.jpg

IMG_20180519_140912.jpg

IMG_20180519_141225.jpg

Thanks, Steve! Appreciate the repost. By the way......Happy Birthday!

[J Ryd]

During removal of my muffler, i noticed it was less than 1/8" from the firewall. In fact, the carb heat cable wore a nice hole in the heat muff because it was pinched. Remembered reading on this forum that it could be a symptom of worn bushings. They all appear in good condition, no cracks, etc. Checking specs as noted above, they are all correctly tightened. Since the muffler is on its way to Dawley, i guess now would be a good time to change them anyway!? Univair wants $11 bucks each.
Jan

[andya]

When I bought my 22-20 some 30 years ago, we found the mount had a dent in it that I decided needed fixed.
We pulled the engine and pulled mount and sent it to the outfit in Atlanta that had a good reputation for
repairing mounts. We re-assembled and noticed my muffler shroud was very close to the firewall.
It was like that before we sent the mount off. I would bet yours and mine aren't the only ones.

[Subsonic]

My muffler shroud is about one eighth of an inch, to maybe 0.150" clear of my firewall on the right side and about one quarter inch clear on the driver side. Just for info. My muffler and rear stack were replaced with new hardware from Wicks 4 years ago but my front stack was/is perfect after 2700 hours TT. Engine conical rubber mounts replaced in early 2018, and only about 70 hours since then. I've seen about 0.130" sag in the front oil cooler in that time. (2 years) These planes are not super easy to maintain in my experience. Partly because they're so old. Partly because of design. Fun to fly, tho. I'm just trying to stay in the air. So getting to the gritty part - regarding load bearing designs, the cantilevered exhaust and Very heavily loaded conical mounts will be ongoing problem areas. I blame Lycoming for the crappy mounts. Rubber parts are relatively cheap, but changing them is not easy. Engine hoist involved and lots of finger pinching, grunting. yanking, pulling, pushing, sweating, and cussing. Sight unseen, I'd say change your engine mounts then measure your muffler clearance. Others will have their opinions...
-Subsonic

[Steve Pierce]

Aircraft Spruce sells genuine Lycoming engine mount bushings for $9.90 each. https://www.aircraftspruce.com/catal...3-19_71032.php

[smcnutt]

I don't notice it as much on the muffler but we often have an issue with the chin mounted oil cooler rubbing on the cowling. We've replaced the mount bushings a couple of times over the years. It's a nuisance and can involve a lot of cussing but doable swapping them out one at a time. Definitely go with the genuine Lycoming bushings. they've held up the best.

[rgoering]

I have 1950 PA-20 with O-320. What is the proper torque, or compression length when tightening bushing bolts (engine to mount)?
Thanks!