Engine Mount

[6843]

Hi All,

The rubber engine mount bushings (Continental part # 2387) have deteriorated and I have new bushings on order from spruce. The C-90 mount has a sleeve in the bushing that stop the compression at a defined spot. The C-85 bushing does not and, I suspect, you could squeeze the poop out of them long before you'd reach a torque value. So... how tight do I tighten the mounting bolts on a C-85?

Thanks,
Dave

[6643]

Warning! Can of worms...

There are two styles of mount, often called "conical" an "Lord" mounts. The mounts shown above are Conical mounts and fit all C85 and C90 engines except the -14 (e.g. C90-14) variants. The Lord mounts fit the C85-14, C90-14 and all O200 engines. (The Continental overhaul manual says the -16 variants also use the Lord mounts, but I have found that to not (always) be true.) The lord mounts are made up of 8 pieces, including a steel tube that runs through the center. The steel spacer is inside a rubber bushing (another one of the 8 parts) in the photo.
.

lords_on_the_left_208.jpg (92.8 KiB) Viewed 2391 times

To add to the confusion, Cessna lists a steel spacer that runs through the center of the conical mounts. Continental does not, and more than one person has mentioned problems using them since thee is no provision in the conical cushion for a spacer between the cushion and the bolt.

Here's the Continental drawing, including the torque spec (60-80 in-lbs.):
.

Conical mount.jpg (37.66 KiB) Viewed 2391 times

The Cessna part number for the steel bushing is 0450195. This is not the same spacer as used in the Lord mount, which is 0450200-502.

I'm sorry, what was the question?

[6898]

Yes can of worms, (like wheel extenders) So my findings some 10-15 yrs ago as follows ; Thinking the steel tube spacers were meant to keep the mounts from smashing and also how can you get a correct torque with just rubber and nothing to bottom out on? Then thinking I was told the new conical mounts were a smaller dia. inner hole which could make sense because i hunted all over, found 4 tubes and theirs no way to get them in the rubber and through the case mounts? The call out for washers also seams too thin of a washer , after time they will start to pull and cave so we used a thicker large washer.

[6643]

found 4 tubes and theirs no way to get them in the rubber and through the case mounts

It's possible, with a lot of dish soap and blue language. However, it compresses the material in the narrow part of the engine case so much that it wears through pretty quickly. I ended up putting the spacers in the spare parts bin and going with the Continental recommended configuration. [And I stopped torquing at 60 inch-pounds.)

Continental says to adjust the torque between 60 and 80 inch pounds to achieve minimum vibration. I'm not sure how that could work...

The call out for washers also seams too thin of a washer

Yeah, my interpretation of the parts catalog is that you use two AN970-6 washers in front of each mount (8 total). I think I've seen other manufacturers calling for the same thing. The AN970s are each 1/16" thick. Continental part 21530 is a washer intended for the same purpose and is about twice as thick (as one AN970).

[Edit]The drawing above may imply they are 3/32" thick.

[atypicalguy]

So a c85-12 would use the conical mount, and not the Lord mount.

Warning! Can of worms...

There are two styles of mount, often called "conical" an "Lord" mounts. The mounts shown above are Conical mounts and fit all C85 and C90 engines except the -14 (e.g. C90-14) variants. The Lord mounts fit the C85-14, C90-14 and all O200 engines. (The Continental overhaul manual says the -16 variants also use the Lord mounts, but I have found that to not (always) be true.) The lord mounts are made up of 8 pieces, including a steel tube that runs through the center. The steel spacer is inside a rubber bushing (another one of the 8 parts) in the photo.
.
lords_on_the_left_208.jpg

To add to the confusion, Cessna lists a steel spacer that runs through the center of the conical mounts. Continental does not, and more than one person has mentioned problems using them since thee is no provision in the conical cushion for a spacer between the cushion and the bolt.

Here's the Continental drawing, including the torque spec (60-80 in-lbs.):
.
Conical mount.jpg

The Cessna part number for the steel bushing is 0450195. This is not the same spacer as used in the Lord mount, which is 0450200-502.

I'm sorry, what was the question?

[edidin]

It seems that the 120/140 have the steel spacer down the middle for their C-85 (-12) installations. I know of three that certainly do, and the Cessna manual calls it out. The exact same engine in a Cub (J3) does not seem to have the spacer, just he conical mounts facing each other with a bolt through it.

Another variable have seen is whether or not there's a plain washer under the bolt head where it abuts the engine mount. Seems reasonable to have one there, but not all do, and some have it only on some of the bolts and not the others...

Have been buying the mounts themselves from Continental of late.

[8281]

So it may seem confusing as to why the J-3 does not use the steel bushing
is because the engine mount Bolt is Larger in Dia. !

[6643]

The Cessna bolt and the Continental specified bolt are both AN6 bolts. The ID of the bushing matches the OD of the bolts. There is no provision for the spacer.

There is a very similar-looking conical mount for Lycomings that takes an AN8 bolt. Maybe that's where the confusion comes from.

[edidin]

As far as I can tell, the C120 parts manual calls out the spacer for all models (1946-1948) of the C120 and C140. Here is the excerpt from the 1946 C120 page - the spacer is Cessna part number 0450195.

Spacer Callout C120140.jpg (164.22 KiB) Viewed 1144 times

[6643]

Yeah, I think the enduring question is "why does Cessna add the spacer when Continental and all the other airframe manufacturers don't?"

When I removed mine, the rubber around the sleeve was worn away and the sleeve was bearing on the ID of the ear of the engine case. Reinstalling them with new mount was an exercise in round peg in too small hole.