The International Cessna^® 170 Association

I have the solid aluminum mounts on my 170 and 180. The solid aluminum bushing makes a solid connection between the engine mount and the firewall and when torqued properly clamps the mount to the firewall and does not move. You will feel more vibration with the solid mounts.

The rubber mount is a rubber bushing in the firewall with the engine mount bolt floating in it. If the rubber bushing wears out to the point the bolt contacts the firewall, the firewall hole will be elongated due to wear and neither mount will work properly.

The solid mount bushings are Cessna part numbers and can be interchanged with a logbook entry. Most owners in Alaska change them out.

Just my thoughts on the fire wall mounts.....You pull them up to torque, and after the first flight toque, is crap....then, no one looks at them again, until they look like the pic I sent. My personal thoughts are, they are a bad idea. I'm sure the engineers thought this through to the utmost. But after about 5 years you have a solid mount. Cuz the rubber goes to crap.

Of course, on my '48 Ragwing, there are no rubber bushings there.
64 years, and so far so good..........

Brad Brady wrote:Just my thoughts on the fire wall mounts...........after about 5 years you have a solid mount. Cuz the rubber goes to crap.

That is true, the rubber bushings are a bad idea unless replaced regularly.

However, the washer being solid up against the firewall does not make a solid mount when the rubber is gone. The bolt is smaller than the hole thru the firewall so the engine mount is not constrained radially. Like putting a 1/4" bolt in a 1/2" hole it can wallow out the hole eventually making it where even the solid aluminum bushing won't work properly.

Understood, Richard... I'm just saying after about five years, or so you have solid mounts due to the hardening of the rubber.. I'm sure we are on the same page......

Rubber tires are also a bad idea unless you replace them regularly. That is why you replace them regularly. Maybe I should try solid aluminum tires so I won't have to air them up. Just kidding. Unless everyone is having their mounts wear out every five years, I don't think the problem is the design. Has this happened more than once? Maybe you just got some bad rubber mounts. They could have been contaminated by some chemical or maybe sat on a shelf for ten years before you bought them. They could even be making them in china now from inferior materials. They should be lasting more than 5 years though as most are.

Tried to ballance the prop on the old engine could not duplicate the readings. Haven't tried on this one I do not plan on changing back to rubber. Maybe next time the engine is off. The vibration isn't bad just different than it was with the other engine and mounts.

mit wrote:Tried to ballance the prop on the old engine could not duplicate the readings. Haven't tried on this one I do not plan on changing back to rubber. Maybe next time the engine is off. The vibration isn't bad just different than it was with the other engine and mounts.

mit-
Did the prop go back on the new engine with the exact same orientation as the old engine? The reason I ask is after one annual, my O-300-D had an odd vibration I had not felt before. The prop had been removed during the annual so we reversed the prop 180 degrees and the odd vibration went away.

hilltop170 wrote:

mit wrote:Tried to ballance the prop on the old engine could not duplicate the readings. Haven't tried on this one I do not plan on changing back to rubber. Maybe next time the engine is off. The vibration isn't bad just different than it was with the other engine and mounts.

mit-
Did the prop go back on the new engine with the exact same orientation as the old engine? The reason I ask is after one annual, my O-300-D had an odd vibration I had not felt before. The prop had been removed during the annual so we reversed the prop 180 degrees and the odd vibration went away.

Prop was overhauled by Dominion and reinstalled like I always do. Going to try to balance it again when I get time.

FredMa wrote:Rubber tires are also a bad idea unless you replace them regularly. That is why you replace them regularly. Maybe I should try solid aluminum tires so I won't have to air them up. Just kidding. Unless everyone is having their mounts wear out every five years, I don't think the problem is the design. Has this happened more than once? Maybe you just got some bad rubber mounts. They could have been contaminated by some chemical or maybe sat on a shelf for ten years before you bought them. They could even be making them in china now from inferior materials. They should be lasting more than 5 years though as most are.

I think 5 years was just thrown out as an example, the point being the rubber mounts won't last 60 years without failing and unless owners/mechanics check them and change them when needed, they will fail and damage the firewall eventually. No one says they must be changed at any certain interval or ever if that's what someone wants but they do get soaked with oil, baked with elevated temperatures, stressed repeatedly, and wear out eventually. Hopefully the discussion will inform those not aware of the problem and offer a permanent solution if desired.

Well said Richard, sometimes my points don't come across clearly

Now this is funny, I really wanted the solid mounts, so I would never have to look at the firewall mounts again. I figured that the solid mounts will last longer than me!(since I'm in my mid 50's) That is a given, cuz Dan would kill me if I installed the solid mounts I have never used Hill Aircraft, (Cessna Parts.com) but they had both. (solid....652.00, rubber...53.62) guess how I went

No kidding, $652.00 divided by 5 is a long time!

hilltop170 wrote:No kidding, $652.00 divided by 5 is a long time!

Yep...

Where can I get rubber mounts Bushing number 0550155 4 ea and Pad number 0550154 4 ea?
Gary