prop sag--new mounts or shim existing mounts?

[rbridges]

My prop has a slight sag (maybe 1/4-1/2 inch.)  Just enough to get a little rubbing on the 201 cowl with the bottom portion of the hub.  I took the top and bottom cowl off today, and there is a little paint that's been rubbed off the fiberglass.  It looks like the last overhaul was >10 years.  I would assume that's how old the mounts are since no other mention is made about them.

So, should I go ahead and get new mounts or try shimming the existing ones?  The plane feels smooth as it is, not much vibration during flight.  I don't mind shimming the mounts, but I don't know if it will sag shortly afterwards.  On the other hand, it's only $350 for 4 new mounts at aircraft spruce, but I'm thinking that new mounts would eventually start to give with time.  I want to do whatever will hold up best.

What would you guys do?

[M016576]

I'd shim them.  In fact I did about 2 years ago, and they are holding up just fine.

[jetdriven]

Maxwell posted an article on his site says the same thing.   Shim it.  

 

[bnicolette]

Probably no problem with just shimming it.

My airplane was showing a tiny bit of sag and it had been 11 years since they were changed so I decided to just change out the Lord mounts and then have it shimmed correctly when I took it in to have it rigged.  There is no good way to check the "rubbers" other than to visually inspect them.  I will say that when I replaced mine, I noticed less vibration in the airplane.  They were fairly easy to change and me and my mechanic had them in within 3 or 4 hours.  I am happy I did them.

[rbridges]

I just wasn't sure about shimming since the existing mounts are 10-15 years old.  Is it obvious when you inspect them if they need replacing or not?

[Sabremech]

I'd change the mounts. It's not that expensive and shimming is just a temporary fix. I did mine in September for the same reason. No issues with cowling rubs now. I think you can bypass the inspection of them since they're sagging and obviously need to be replaced due to the age. Just my .02

 

[Mooney_Allegro]

I had my 12 year-old mounts changed out last year due to a leaking mount and collapsed mount.  Total cost to replace the mounts w/labor $1808.68.  I told them to shim the engine up so it would line up with the cowling, but they never did line them up, so I still have about 1/4-1/2" difference.  It's almost time for overhaul, I'll just wait. 

[bnicolette]

I purchased my Lord mounts and new bolts/nuts from Spruce which was approx. $550.  It took us no more than 4 hours from start to finish to install them and the shop rate is $65/hour which is $260.  So total cost was approximately $810.

However, I let the shimming up to my local MSC so there was at least another 1 to 2 hours in there at $85/hour.  At least they are done and off my list of "to do's" for many years.  Seems like the rubber mounts would be about equally important as the landing gear shock discs as far as keeping them "fresh"?

 

 

 

[jamesm]

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Well .... I am going to take the opposite side of  what most others are saying. I have a   67 M20C that has same symptoms of what you have described. Since the  Lord mounts, rubber gives and metal shims don't typically the engine vibration(s) and could cause problems prop balance and I would think that the engine baffles are more pron to cracking if the engine was shimmed whereas rubber gives.

In my case the engine was  shimmed prior to the cowl enclosure installation. I wound  up paying for the engine being shimmed later. The cowl enclosure had been rubbing from the  spinner on  lower right side of the cowl enclosure.  About ten years ago,  My IA and I were able to change the lord (engine) mounts without having to pull the engine and I think we did in about 4 hours.  One thought would be to replace the lord mounts this year say and if decide to replace/overhaul the engine in two years  just reuse the mounts  that you replaced this year.

I had to repair the cowl enclosure a  couple years ago since  I had the engine overhauled  otherwise I would have had to buy a new cowl enclosure and start all over with the painting  hole drilling  and .... which would have been a real pain and time consuming.

Nothing is cheap in aviation anymore... :-(

 

James M.

[jamesm]

One more thing....  Should you decide to replace your engine mount/mounting hardware and if you have a O-360 A1D wide deck engine like mine make Darn sure that the engine mount nut are 5/8" wrench size and NOT 11/16" wrench size  I am told that they come both wrench sizes for the same part number. I found out the hard way and had  11/16" wrench size nuts  and  I doubt that I would have been able to pull the bolts with larger engine mounting nuts.  fortunately I had the engine off for other reasons though it was still a real stinker to the nuts off even with the engine off the airplane.

Lycoming engine case have litte wells / depression  (well is what I call them) where the engine mount nuts are located it can be a real bastard to get a wrench on the engine mounting nuts in the first place and the larger wrench size makes thougher. Not metion that these are nuts that hold the engine to the  engine mount.

I had to grind / make harbor frieght wrench to fit into engine case to get to the engine mounting nuts.

James M.

'67 M20C

[PTK]

I would go the extra mile and do it right by replacing them. I'm a firm believer in "do it right or don't do it at all." having said that this is one of those decisions that could easily be influenced by whether you are going to overhaul the engine soon or not. But still I would replace them now. Even if you pull the engine the mounts are done!

[rbridges]

thanks for the replies.  I think I am going to replace the mounts.  I looked through the logs, and it's actually been 16 years since overhaul.  Should I still get my hands on some washers to shim the new mounts if necessary?

[Cruiser]

since the weight of the engine causes different pressures on the lower mounts than the upper mounts you can have them rotated and shimmed and they should work fine.

[rbridges]

well, the mounts were changed today.  I wasn't there, but I was told that the lower ones were pretty worn.  We still need to put stuff back together, so I won't know how well things are lined up until tomorrow.

[M20S Driver]

Does anyone know if the engine mount on io550 installed on Ovation or Eagle could be shimmed? I could not find anything on-line for the shimming of the mounts on the newer Mooneys.

Thanks,

Masoud

[harrispa]

I would also be interested in hearing about experiences with the IO550 mounts.  Mine has sagged some and I am trying to decide what to do if anything.  2001 only 13yrs old and visually the rubbers look fine, but you can see they flex some when lifting the engine by hand via the prop.  Tried to do this lift test on friends Columbia and no give at all.  I did check the torque.

 

Paul

[jetdriven]

My boss was talking about the engine mounts on the 2002 Ovation he takes care of.  The ones in the catalog crush down after a couple years, while Lord makes a more durable mount that fits in the same place, its not approved for the Ovation.  Or as he understands it to be.

[Bob_Belville]

When we installed the engine (IO360) after my prop strike event we installed new Lords. The old Barrys were new with the engine in 2002 and were badly worn out. The engine sagged enough for the spinner to brush the cowl. The sagging was apparent when I bought the plane in 2012 and the previous owner told me He thought it was like that in 2006 when he bought the plane.

 

I understand the A&P had to take the cowl on and off several times to get the mounts shimmed correctly, I had insisted that the engine had to wind up centered on the cowl opening. (I have a 201 style cowl with a close fit to the spinner.)

 

I am of the opinion these mounts ought to be changed more like @ 5 years rather than 12 though Lords are supposed to be better and last longer than Barrys. In addition to scraping against the cowl, worn out mounts allow more vibration which cracks cowls, a misaligned engine should lose some thrust.   

[harrispa]

I checked the pictures of Ovations for sale on Controller.  Most look just like mine with the spinner below the cowl by about 1/2" or so.  The Part numbers listed in the Mooney parts manual are Lord mounts.  However, as I noted before, my friends Columbia has much stiffer rubbers than the Ovation with about the same engine, so my conclusion which may be wrong is that the Mooney Ovation mounts are softer and probably sag quicker due to this.

Paul

[jetdriven]

I had my 12 year-old mounts changed out last year due to a leaking mount and collapsed mount.  Total cost to replace the mounts w/labor $1808.68.  I told them to shim the engine up so it would line up with the cowling, but they never did line them up, so I still have about 1/4-1/2" difference.  It's almost time for overhaul, I'll just wait. 

So they charged you 18 hours of labor to replace the mounts and they didn't shim them to align them to the cowl?   FWIW, it takes one hour to replace the top mounts, perhaps 3 to replace the bottom, and 1-2 hours to shim, because I have done it myself.

[OR75]

FWIW ... 3 reasons for the spinner to look sagging: 

 

• old crushed mounts
• shims
• cowling moves up in flight

 

 

shimming is very easy to do once you have the tool to lift the engine. The most difficult is actually to have the right thin enough wrench to be able to re-torque the bolts.

 

I heard the bottom mounts are a pain to replace.

 

some replace the camlocks to rigid (non floating) to prevent the cowling from moving in flight but I don't like that option.

[jetdriven]

I am reworking the LASAR cowl fix kit on my plane. The kit installs a strap and nutplate with a solid screw on the bottom corners of the cowl, and fixed nutplates on the top cowl to prevent movement. Problem is, the threaded shank of the screw cuts into the lower cowl and the fixed nutplates transfer the shear load to the camloc holes which wears them out faster.

 

I did replace the lower nutplate screws with structural screws which have a smooth shank to avoid cutting into the cowling.

 

After reading a thread here, i got an idea. Put the fixed nutplates back in the boot cowl on top. Also block in some 1/4" high glass stoppers on the upper cowl and add some angle aluminum on the boot cowl to absorb the shear load.

[flyingvee201]

Ok, so my prop is sagging too.

The engine was overhauled a few years ago by the previous owner, but I cant find any record of the engine mounts being replaced.

I would like to replace them for piece of mind.

If that doesn't fix the sagging, what are these shims I keep hearing about?

Are they like big washers?

Where exactly do you put the shims?  On the outside of the rubber mount them put the bolt on?

Shim the fore or aft side of the pair of mounts?

 

Is it possible to replace one mount at a time without using an engine hoist?

 

Looking for some details.

thanks

Vic

[OR75]

doubt you can do something without a hoist.

 

picture of the shim between the AN bolt and the rubber mount.

 

Those are Mooney parts and exist in different thickness

 

the top are easy to get to.

bottom ones are a pain in the bottom !!

 

 

 

 

[Sabremech]

On my 66 C model, I used my engine hoist and changed the uppers together, left them loose and lifted up on the engine and replaced the lower mounts. I then torqued them. All without disconnecting any of the cables, etc.

David