Tech Tips Changing Engine Mount Rubber Isolators

[edidin]

Going to change the isolators. Just wondering if there are any tips and tricks from someone who has done them recently. Standard AN6 bolt version.

[6643]

Support the engine with a hoist, and don't over tighten the bolts. If you have the Cessna spacers than stop when you "hit" them, otherwise 60-80 inch lbs is the spec. Use two AN970-616 washers in the front of each mount, or one Continental part 21530.

[6298]

Like John says, use a hoist. I usually remove the nuts and washers on the bottom two mounts. You can remove and replace the lower rubbers, tighten them, and then replace the uppers by gradually lowering the hoist. Don’t over torque.

[V529]

Going to change the isolators. Just wondering if there are any tips and tricks from someone who has done them recently. Standard AN6 bolt version.

Just curious, why are you changing the isolators?
Time? dry rot? vibration? something else?

[edidin]

Thanks John and Randy for the tips, torques, and order of operations.

The rubber is quite dried out in my opinion, likely on the aircraft for several decades, assuming they were even replaced the last time the engine was off its mount!

Have all new hardware coming tomorrow and should give it a do on Thursday.

[V529]

Thanks John and Randy for the tips, torques, and order of operations.

The rubber is quite dried out in my opinion, likely on the aircraft for several decades, assuming they were even replaced the last time the engine was off its mount!

Have all new hardware coming tomorrow and should give it a do on Thursday.

Thank you, I'm just trying to keep track of "trends" and was wondering if you were experiencing vibrations or any other abnormalities. My own isloators (0-200) will be getting replaced soon........why? cuz it's "time".

[edidin]

I decided to replace all the isolation in the aircraft. First did the panel isolators since they were sagging and causing the Av-30 to sometimes contact the structural airframe which would really annoy the MEMs gyros inside. Found that two were the crappy $4 ones so changed to a full set of real Lord mounts.

Looked over the engine and the bottom conical isolators looked tired. Pulled all 8 isolators and also replaced all the hardware (AN6, 616s, and 970s). This install, unlike a J3/C-85 did recently had the bushings inside the isolators, which are specified in the Cessna parts manual (along with an asterisk to see Continental manual which does not seem to show the bushings...).

The old isolators were pretty tired and the bushing had worn the bottom ones quite asymmetrically and to a rather thin condition. Of course without the bushings might not have had that failure mode.

Tightened to about 75 in-lb and all was well. In particular, the vibration previously felt when reducing power to about 1400-1600 at say key position on downwind was gone. Cruise seemed a little nicer too. C-85 stoker.

[edidin]

Support the engine with a hoist, and don't over tighten the bolts. If you have the Cessna spacers than stop when you "hit" them, otherwise 60-80 inch lbs is the spec. Use two AN970-616 washers in the front of each mount, or one Continental part 21530.

What's the best way to determine if you've hit the spacers? Sudden increase in torque? I'm at about 75 in-lb but wondering if that might be a little low given I did re-install the spacers.

[6643]

What's the best way to determine if you've hit the spacers? Sudden increase in torque?

Yes. You go from compressing rubber to compressing steel tubing.