Engine mount-to-firewall bushing removal for seaplanes

LakeHood170B · Post by **LakeHood170B** » Thu Jul 13, 2006 10:03 pm

In the course of the first real annual of my 170B floatplane (the one at the time of purchase turned out to be a joke), the following strange subject has come up. It is being suggested that there is some requirement or recommendation to replace all the rubber bushings (Items 4, 6, and 11, total of 8 parts, on page 84 of the 170B parts catalog) between the engine mount and the firewall with some solid metal part. The justification is that this prevents the engine (and mount) from getting into some bizarre oscillations during rough water operations.

The sounds like nonsense to me, particularly considering you don't have tires to absorb surface roughness when operating on water.

Any knowledge on this subject would be most welcome. This is holding up completion of my annual.

mit · Post by **mit** » Fri Jul 14, 2006 12:25 am

Sounds bogus to me.

c170b53 · Post by **c170b53** » Fri Jul 14, 2006 1:19 am

I use solid mounts (172) on the firewall for my straight mount 0-320, its no big deal. Rubber mounts work well as long as they are cared for and if the original engine is installed, probably adds to that super smooth feel. If the rubber mounts have excessive wear, then rough operations may cause the bolts to wear into the structure. (The round hole turns into an oval)

hilltop170 · Post by **hilltop170** » Fri Jul 21, 2006 9:07 am

The aluminum bushings bolt-up solid to the firewall preventing any relative movement between the engine mount and firewall, especially important on floats because there are no tires and spring gear to absorb the shock loading of rough water. Rubber bushings will deform and beat-out, letting the bolts eat into the firewall, leaving the engine mount loose. The engine lord mounts are huge in comparison to the firewall bushings and are meant to cushion the engine. I think its a good idea to replace the rubber bushings with the solid mounts on wheel as well as float aircraft.

bradbrady · Post by **bradbrady** » Sat Jul 22, 2006 1:04 am

Hilltop 170,
IMO the Al. bushings are the only way to go, every 170 or 172 that has rubber bushings, that I see, need the bushings replaced on average every four years (due to cracks or deteriation). The AL. bushings (if maintained properly will last forever), just my opinion.

brad

mit · Post by **mit** » Sat Jul 22, 2006 1:11 am

ok, so whats the P/N on these?

c170b53 · Post by **c170b53** » Sat Jul 22, 2006 1:47 am

There's nothing wrong with rubber but like anything it requires keeping on top of and I guess the $60 bucks for a new set now and then. Becasue they are a trouble to get to, they are ignored and then things get expensive, who would have guessed? I'm at the convention away from my parts books will reply when I get home. By the way this is my first party and I'll make a full post post party report later.

alaskan99669 · Post by **alaskan99669** » Sat Jul 22, 2006 2:17 pm

I just looked at mine, and for what it's worth they are aluminum.

hilltop170 · Post by **hilltop170** » Sat Jul 22, 2006 6:54 pm

[quote="mit"]ok, so whats the P/N on these?

[/quote]

Tim-
I just had the rubber bushings changed to aluminum bushings on 1715D. We luckily caught it in time, the bolts had just started to touch the firewall. The shop is closed on the weekends but will get the p/n for the aluminum bushings Monday.
Richard

spiro · Post by **spiro** » Tue Jul 25, 2006 10:32 am

Tim, I think what you're looking for is:

0751004-1 BUSHING
(List Price: $ 38.70) Stock Available $ 30.96 (EA)
0751004-2 PAD
(List Price: $ 20.90) Stock Available $ 17.77 (EA)

these would replace the stock:

0550155 BUSHING
(List Price: $ 6.56) Stock Available $ 5.58 (EA)
0550154-2 PAD
(List Price: $ 3.49) Stock Available $ 2.97 (EA)

the pricing is from CessnaParts.com

I don't think I've ever seen a Cessna floatplane w/o metal bushings. I replaced the rubber ones on my 170 at 1st annual, even though it's just a landplane. Tying the mount and firewall together strengthens the whole assembly.

- paul

hilltop170 · Post by **hilltop170** » Tue Jul 25, 2006 8:47 pm

Spiro-
Thanks for supplying the p/ns for the aluminum bushings, I was just headed out to the valley to get the numbers off my plane. I forgot to look yesterday.

I agree tying the whole airframe and engine mount solidly together strengthens both and even small alignment changes in the engine can cause differences in performance. I know some Super Cub guys who put just one thick washer under the bottom motor mount attach points and claim it makes a big difference. Having the engine hang semi-loose with rubber bushings could do the same thing only in a negative way, not to mention the potential for the loose bolts damaging the firewall.

Richard

4-Shipp · Post by **4-Shipp** » Wed Dec 06, 2006 3:20 pm

I am replacing my mount bushings during annual and have several questions:

What is the tried and true procedure for replacement? I assume something like:

1. support engine with hoist.
2. remove/replace either tops then bottoms, or left then right.

Am I close? Any gotchas?

Where are the torque values found for the rubber and metal bushings found? I have the 100 series service manual but not in front of me to look myself.

I almost hate to ask this (you know; if you can't stand the answer, don't ask the question...). What is the approval basis for replacing the rubber bushings with the aluminum parts?

Thanks.

Jr.CubBuilder · Post by **Jr.CubBuilder** » Wed Dec 06, 2006 4:21 pm

We just replaced my rubber bushing on the firewall, and the specs a rather vague. They said something to the effect of torquing the nuts down till the rubber compresses slightly. So we did exactly that and it left about three threads exposed out the top of the self locking nuts.

There was a torque spec in the manual for solid mounts, ie metal to metal, but the mechanic has that.

wsknettl · Post by **wsknettl** » Mon Feb 03, 2014 4:33 am

I know this is an older post but can anyone tell me if there is any change in the bolt size when switching to the aluminum bushings? Original bolts were AN6-22A top and AN6-32A bottom. Also is there any publication such as a service kit instruction or service letter/bulletin that covers this conversion?

Also to update pricing this is what Yingling is now asking:

0751004-1 BUSHING
(List Price: $ 156.00) Stock Available $ 132.60 (EA)
0751004-2 PAD
(List Price: $ 38.60) Stock Available $ 31.85 (EA)

these would replace the stock:

0550155 BUSHING 4 Ea.
(List Price: $ 12.10) Stock Available $ 9.98 (EA)
0550154-2 PAD 4 Ea.
(List Price: $ 6.40) Stock Available $ 5.28 (EA)

the pricing is from http://www.cessnadirect.com Yingling

mit · Post by **mit** » Mon Feb 03, 2014 5:56 am

I used the same bolts. I did notice more vibration, but I can't say for sure it was the mounts since it was a different engine.

The International Cessna 170 Association

Engine mount-to-firewall bushing removal for seaplanes

Engine mount-to-firewall bushing removal for seaplanes

Re: Engine mount-to-firewall bushing removal for seaplanes

Re: Engine mount-to-firewall bushing removal for seaplanes