Engine to firewall bushings (1948)

[IdahoPilot]

So, while checking torque on all important attach bolts. We noticed there are rubber bushings on engine side, and on the cabin side. The IPC does not show them. From research on here, I don't see that a SN before 19200 is supposed to have them. Do I need to remove them, or is there some approval for adding them? Thanks a ton!

[Brad Brady]

So, while checking torque on all important attach bolts. We noticed there are rubber bushings on engine side, and on the cabin side. The IPC does not show them. From research on here, I don't see that a SN before 19200 is supposed to have them. Do I need to remove them, or is there some approval for adding them? Thanks a ton!

Ken,
I see what your saying. I just opened the IPC, for straight 170's. It shows a pad of some kind, yet the part numbers are convoluted. The A and B IPC shows the rubber mounts and define them as P/N 0550355 (fire wall) and 0550154-2 (cabin). I'm of the mind that is the part numbers you want for your's.....I'm just not sure. BTW...There is no specified torque for these mounts. The 100 series manual. (which is the only resource I know of) states that the rubber is to be pushed out till there is a slight bulge in the rubber mounts. (Mechanic torque) I wanted to change out the rubber mounts with, (float plane) AL. mounts for a B model I was working on....Yet at a price of 650.00 for the AL. mounts, and 70.00 for the rubber, I can change out a lot of rubber mounts. This is a point of contention for me. I really think that people neglect these mounts. To me they need to be looked at, more.

[IdahoPilot]

Ken,
It shows a pad of some kind, yet the part numbers are convoluted. The A and B IPC shows the rubber mounts and define them as P/N 0550355 (fire wall) and 0550154-2 (cabin).

Does it say AN960-616 and AN970-6? That's what mine says, AN960 is a normal washer, and AN970 is a large area washer. That is all I am seeing. Its all so confusing. Dang people messing stuff up.

[Bruce Fenstermacher]

There is no engine mount bushing prior to serial number 19200. There is just an AN 970-6 and an AN960-616 washer.

If I had installed bushings per a 19200 or later serial number I wouldn't remove them until some wise guy aircraft judge deducted points from my pristine restoration.

[IdahoPilot]

Ok, Didn't think so. Next question, this makes it an illegal installation... Is there a downside to having these installed? Any real reason for them to be installed? I have a feeling our IA will say to remove them.

[Bruce Fenstermacher]

Ken this sort of thing comes up all the time. Is it correct the way it came from the factory? No. It is airworthy from a safety standpoint? Yes. Is it an improvement? We would think probably. Is it a major alteration? I won't say. Some folks say since our Cessna's were approved under the same TCDS that any improvements can be incorporated in older airframes. Lots of folks say make the change and no one will know but of course you know.

You have to do what you think is the right thing to do.

[IdahoPilot]

Bruce, Thank you for your Candor. I guess it all depends on who is signing the paperwork huh. Thank you so much for your insight.
It's great to see this old bird almost back to flying condition. Couldn't have done it without information like this.

Ken

[Brad Brady]

Ken,
If the part numbers mentioned earlier are installed, they probably should be re-installed. just cuz, they are there... The holes in the fire wall are there to include the mounts.....anything else will not fill the void......Just my thoughts.....

[Brad Brady]

Ken,
It shows a pad of some kind, yet the part numbers are convoluted. The A and B IPC shows the rubber mounts and define them as P/N 0550355 (fire wall) and 0550154-2 (cabin).

Does it say AN960-616 and AN970-6? That's what mine says, AN960 is a normal washer, and AN970 is a large area washer. That is all I am seeing. Its all so confusing. Dang people messing stuff up.

Yes

[GAHorn]

Ok, Didn't think so. Next question, this makes it an illegal installation... Is there a downside to having these installed? Any real reason for them to be installed? I have a feeling our IA will say to remove them.

I have a feeling that 999 out of 1000 IA's will not notice the difference unless you point it out to him/her (because they never noticed early airplanes didn't have them) and the one that does notice will reason that since Cessna altered later airplanes to have them ...they must be a good thing with a purpose...(an "update", if you will.)

[IdahoPilot]

George, He is the one that noticed them. Asked me to do some extra research. He is just deciding whether he feels ok about them being there.

[Brad Brady]

Ken,
I'm not looking at your aircraft. But if the firewall is drilled out to accept the later rubber mounts, you have no recourse,except to put in the later mounts. I think your IA will agree. Pics would help.

[Bruce Fenstermacher]

Ken, Brad is of course correct. Though I'd not sure there is a modification required for the bushings. Brad would know better, he's probably seen the firewall with no mount more that I have.

I would suggest to your IA that this is a minor alteration and was an upgrade through the 170 model run and not make a big deal of it.

[Brad Brady]

Ken,
Haven't been on in a wile, so haven't read any new posts. Your situation intrigues me. From what I see on the IPC you should have a 3/8 inch hole in the fire wall. If you have a (roughly) 5/8 hole in the fire wall you need the later mounts. The rubber from the engine side fits into the cabin area, and is encapsulated by the rubber washer in the cab. (you already have the part numbers) Each held in place with large area washers. These need to be brought into the torque I mentioned earlier. If there is something in between the mount and the firewall, (with a 3/8 hole) I'm thinking it should be removed. If you go with the mount to fire wall, there is a torque. I just don't know it. I would use the 100 series torque recommendations in the torque ledger.

[mongo2]

I've searched high and low for a vendor to get P/N 0550355 (fire wall) and 0550154-2 cabin , but still no luck. Checked most of the usual Cessna vendors. Anybody know of a source?