Motor mount shims
Posted: Mon Nov 21, 2011 9:30 pm
by Andy Walker
Hey all…
I know a lot of folks have to shim their motor mounts…but what size shims are we talking here? My lower motor mounts fit tightly (almost too tightly), and my uppers have a really big gap. Even when I make sure the width at the top is the specified 32", the gap between the mount brackets and the mount itself is easily 1/8" or more on each side. The only way I could get it to fit tightly against the motor mount would be to shave the upper crosstie enough that the upper width is less than the specified 32".
What am I missing here?
Re: Motor mount shims
Posted: Mon Nov 21, 2011 11:50 pm
by fastj22
I had to shim both top and bottom a bit. I think its just variations in all the different components coming together. Check with Kerry but I think you are within specs.
Re: Motor mount shims
Posted: Tue Nov 22, 2011 12:50 am
by MichaelFarley56
I’ve heard of lots of people needing several shims, with .025 and .032 sizes being used but you can go thicker if needed. I can’t remember how thick is allowed but I remember some people going .090 or higher total thickness.
And yes, it’s normal for the upper and lower shims to be different thicknesses.
Re: Motor mount shims
Posted: Tue Nov 22, 2011 1:19 am
by Andy Walker
MichaelFarley56 wrote:I’ve heard of lots of people needing several shims, with .025 and .032 sizes being used but you can go thicker if needed. I can’t remember how thick is allowed but I remember some people going .090 or higher total thickness.
And yes, it’s normal for the upper and lower shims to be different thicknesses.
Yeah, I’m talking I’d need 1/8" or 3/16" thick shims! I just checked the mount, and the distance between the upper mounts are about 1/8" less than specified in the plans. I e-mailed Sonex, we’ll see what they say.
I guess it’s my week for weird problems. 
Re: Motor mount shims
Posted: Tue Nov 22, 2011 3:08 am
by 142YX
Yea, i got the 32" dimension dead-nuts on and i probably have about a 1/8th total gap. My guess is the precision of the motor mounts aren’t very high. I wouldn’t deviate from the 32" dimension, as this will mess with the fit of your firewall and cause a nasty chain reaction of nothing fitting correctly
Re: Motor mount shims
Posted: Tue Nov 22, 2011 10:42 am
by N111YX
Here’s a pic of mine. While the pic shows four shims, I did end up doubling up a couple. I used all kinds of different metal thicknesses. The largest combination may have been near 1/8 inch.
Sorry to hear about your trouble, Andy.
I do have your solid rivets next time we meet…
Kip
Re: Motor mount shims
Posted: Tue Nov 22, 2011 11:12 am
by Andy Walker
N111YX wrote:Here’s a pic of mine. While the pic shows four shims, I did end up doubling up a couple. I used all kinds of different metal thicknesses. The largest combonation may have been near 1/8 inch.
Sorry to hear about your trouble, Andy.
I do have your solid rivets next time we meet…
Kip
Thanks Kip! If you guys are getting near 1/8" shims, maybe I’m not as for off as I think.
If you’re going to be around over the long weekend, maybe we can get together. Did you get your rivet gun back as well?
Re: Motor mount shims
Posted: Tue Nov 22, 2011 11:58 am
by N111YX
Andy, I may be flying around on Sunday. No rivet gun yet but maybe within a week or so…
Re: Motor mount shims
Posted: Tue Nov 22, 2011 12:16 pm
by Andy Walker
N111YX wrote:Andy, I may be flying around on Sunday. No rivet gun yet but maybe within a week or so…
Cool, give me a call if you have the time and inclination to get together.
Re: Motor mount shims
Posted: Tue Nov 22, 2011 3:02 pm
by Andy Walker
Kerry says that the welding process is not perfect, hence the small variation from plans. He thinks big fat shims is the answer, and seemed to indicate there is no upper limit to the thickness of the shims you can use.
Re: Motor mount shims
Posted: Sun Dec 04, 2011 3:26 am
by 142YX
I ended up attaching my engine mount today.. and i used .090" shims on all four corners. Fit like a glove with that thickness, and just for reference, i did nail that 32" dimension dead on.
Re: Motor mount shims
Posted: Sun Dec 04, 2011 11:31 am
by N111YX
That looks really good! It’s fun to see all of the updates…!
I’m seeing lot’s of progress being made in the colder months… 
Re: Motor mount shims
Posted: Sun Dec 04, 2011 3:47 pm
by 142YX
While i am on the subject.. what are people using to corrosion protect the exposed 4130 steel when you drill through that nice powder coating? I was thinking of just touching it with some automotive engine (high temp) stuff from a rattle can.. i also thought about epoxy primer but am favoring a simpler/cheaper method as i dont quite think that will be necessary.
Re: Motor mount shims
Posted: Mon Dec 05, 2011 4:36 pm
by Andy Walker
142YX wrote:I ended up attaching my engine mount today.. and i used .090" shims on all four corners. Fit like a glove with that thickness, and just for reference, i did nail that 32" dimension dead on.
Thanks for the pics…based on the gaps I’m seeing now, my shims will be similarly sized.
Re: Motor mount shims
Posted: Tue Dec 06, 2011 9:48 pm
by N111YX
You’re in the desert. I would not sweat it… :lol:
I would imagine that touch up paint would be adequate. I’ll bet that our airframes will all last longer than all of us and the next guy or the guy after that will have to worry about all corrosion…
142YX wrote:While i am on the subject.. what are people using to corrosion protect the exposed 4130 steel when you drill through that nice powder coating? I was thinking of just touching it with some automotive engine (high temp) stuff from a rattle can.. i also thought about epoxy primer but am favoring a simpler/cheaper method as i dont quite think that will be necessary.
Re: Motor mount shims
Posted: Tue Dec 06, 2011 11:13 pm
by Andy Walker
N111YX wrote:You’re in the desert. I would not sweat it… :lol:
I would imagine that touch up paint would be adequate. I’ll bet that our airframes will all last longer than all of us and the next guy or the guy after that will have to worry about all corrosion…
142YX wrote:While i am on the subject.. what are people using to corrosion protect the exposed 4130 steel when you drill through that nice powder coating? I was thinking of just touching it with some automotive engine (high temp) stuff from a rattle can.. i also thought about epoxy primer but am favoring a simpler/cheaper method as i dont quite think that will be necessary.
Sounds about right. I used NAPA 7220 self-etching primer on my elevator horn, seemed to work well.
Re: Motor mount shims
Posted: Wed Dec 07, 2011 1:43 am
by 142YX
Yea i don’t sweat it on the aluminum at all.. but the steel makes me nervous. What i think i am going with is some Rustolium rattle can high temp engine block paint.. Home Depot’s finest. Should be enough to prevent rust.
Re: Motor mount shims
Posted: Wed Dec 07, 2011 2:18 am
by 142YX
Andy Walker wrote:Sounds about right. I used NAPA 7220 self-etching primer on my elevator horn, seemed to work well.
Careful.. you will probably need to apply a “sealer” to that primer for it to provide any corrosion protection. The primer alone dosen’t provide much of anything other than a good surface for a sealer or top cote to bond to.
This is off topic for this tread, but i did the whole corrosion protection flip flop for several months and eventually decided not to do anything to the aluminum itself. I strongly believe i will still have a 50 year airframe.
Re: Motor mount shims
Posted: Wed Dec 07, 2011 9:26 am
by fastj22
I owned a 1966 Cessna 150. Zero corrosion in 2011.
Re: Motor mount shims
Posted: Wed Dec 07, 2011 12:05 pm
by Andy Walker
142YX wrote:
Andy Walker wrote:Sounds about right. I used NAPA 7220 self-etching primer on my elevator horn, seemed to work well.
Careful.. you will probably need to apply a “sealer” to that primer for it to provide any corrosion protection. The primer alone dosen’t provide much of anything other than a good surface for a sealer or top cote to bond to.
This is off topic for this tread, but i did the whole corrosion protection flip flop for several months and eventually decided not to do anything to the aluminum itself. I strongly believe i will still have a 50 year airframe.
I’m with you on the aluminum, not doing anything to it. On the steel I really just wanted something to cover the bare steel. Between the bare primer and the fasteners in the holes I’m confident it will survive with the small amount of water it will be exposed to (plane will be in a hangar). If there is a problem with steel corroding you will see long before it’s a structural issue if you are even half awake during pre-flights and condition inspections.
