Motor mount problem?

[Amelia]

My 1980 M231 is in the throes of an annual inspection, which was to be a relatively straightforward and painless affair, except it seems the motor mounts look rather ugly....rusty, flaking paint, etc. The engine itself, being relatively new, (6 years old, <700 hrs, TSIO 360 LB, factory reman) is in fine shape.

So, what wisdom might y'all share? Wonder why the steel tubing seems to be so unsightly in such a short time? Should I find a new one somehow? Get this one sandblasted and repainted? Put the cowling back on quickly? Natch, option3 is my favorite, but might be unwise. Mechanic says he will give it a very close look today, but I would appreciate some insight.

[AndyFromCB]

Be careful, too close of a look can end up costing you quite a pretty penny. If any of the tubes are less than 90% original thickness then off the mount goes. Ask me how I know ;-)

[Marauder]

There is a tolerance on how much material can be lost before the structure is declared unairworthy. It can be cleaned up and repainted if the corrosion is surface only.

[AndyFromCB]

Yes, 10%, in case of a mooney mount, 0.16mm, aka a spec of rust. It really doesn't take much to make an engine mount "unfair worthy"

[N201MKTurbo]

I have never done an engine swap on a K, but on a Lycoming, it is easier to remove the engine mount from the firewall with the engine still attached. By default you have the engine mount off the plane.

You are crazy not to strip and re-paint it at that time.

Strip it with sand blasting or chemical stripper, or both. A wire wheel helps also. Inspect it while stripped.

Prime it with anti-corrosion paint. Zinc chromate works the best but it is getting hard to come by. Zinc phosphate works OK but it takes a long time to dry.

I prefer to paint it with Tempo aircraft paint.

[jetdriven]

We didnt take any chances on our mount. It was rusty and crappy like many of them out there after 12 years, and I think it was just brushed on with Rust-oleum or rattle-canned, It sure wasn't finished professionally. We bead-blasted the mount, inspected it visually for grooves or cracks. If it failed that it was going to be sent off for the 1100$ fix and certification. Luckily it looked good. Then we washed it in metal-prep (acid solution), and rinsed and dried well. Then primed with epoxy 2K primer, then coated with2 coats of Nason unrethane Matterhorn white urethane paint, the same that goes on your wings. I color-matched it to an inspection panel on the bottom to have a quart of touch-up paint. The total labor on that deal was about 6 hours. Of course the new engine and mount paint maked the firewall and all the hoses and clamps look like crap, so, might as well......

[1964-M20E]

We didnt take any chances on our mount. It was rusty and crappy like many of them out there after 12 years, and I think it was just brushed on with Rust-oleum or rattle-canned, It sure wasn't finished professionally. We bead-blasted the mount, inspected it visually for grooves or cracks. If it failed that it was going to be sent off for the 1100$ fix and certification. Luckily it looked good. Then we washed it in metal-prep (acid solution), and rinsed and dried well. Then primed with epoxy 2K primer, then coated with2 coats of Nason unrethane Matterhorn white urethane paint, the same that goes on your wings. I color-matched it to an inspection panel on the bottom to have a quart of touch-up paint. The total labor on that deal was about 6 hours. Of course the new engine and mount paint maked the firewall and all the hoses and clamps look like crap, so, might as well......

Byron

Quite right while you have it off clean inspect and paint far easier and cheaper than trying to do it later same with hoses and clamps. However, I do disagree on over painting the mount paint it but, the extra layers of paint could mask cracks. This may sound picky but if I remember correctly NHRA made the top dragesters stop painting the chrome moly tube steel frames so as to be able to detect cracks sooner. Now of course they will only use a frame for a few years so no paint is not that bid of an isssue.

All I'm syaing is do not put too many layers of paint that might hide a crack.

[Amelia]

Oh, dear. Looks as if my engine mount is too far gone (yep, left front corner pitted beyond acceptable limits, and many layers of paint on the rest of it, hiding who knows what) and I'll have to find another one. Anybody know where a decent one can be found? Thanks for the thoughts!

[jetdriven]

Byron

Quite right while you have it off clean inspect and paint far easier and cheaper than trying to do it later same with hoses and clamps. However, I do disagree on over painting the mount paint it but, the extra layers of paint could mask cracks. This may sound picky but if I remember correctly NHRA made the top dragesters stop painting the chrome moly tube steel frames so as to be able to detect cracks sooner. Now of course they will only use a frame for a few years so no paint is not that bid of an isssue.

All I'm syaing is do not put too many layers of paint that might hide a crack.

One issue with too little paint is it rusting and going below limits within 12-15 years. On the other you have paint hiding cracks. FWIW, urethane paint cures very hard and will crack along with the metal, and 2 coats of primer and 2 coats of urethane is standard practice. It only leaves 3-5 mils of paint on the surface.

[jetdriven]

Oh, dear. Looks as if my engine mount is too far gone (yep, left front corner pitted beyond acceptable limits, and many layers of paint on the rest of it, hiding who knows what) and I'll have to find another one. Anybody know where a decent one can be found? Thanks for the thoughts!

Amelia, sorry to hear about the mount. Make sure it is actually below limits, as I have seen plenty of rusty mounts pass annaul and 6K is a lot of cash. Someone in trade-a-plane advertises a 1K flat-rate engine mount repair and recert. I'd go with them.

[N201MKTurbo]

I believe Lake Aero Styling can repair the mounts.