Improved speed with re-shimmed engine

[Bartman]

I had my engine mounts re shimmed this annual. I had been doing 136kts at 65% power LOP. Today on my first flight I now get 145kts at the same power setting. This was using FF x 14.9 for percent power. I usually cruise at 8-10 K and today was at 6,500 so not exactly the same, but the percent power was about the same. I am pleased with the results so far.

By the way the spinner was very much out of alignment with the cowl before, nearly 3/4 inch droop. Now it's perfect.

[jetdriven]

That seems a little optimistic I can believe 2-3 knots.

The only way to know is do a real speed run on it and GPS ground speed in a couple different directions isn't very good. The NTPS file i posted is deadass however. Try that.

[Guest]

It never hurts to have the thrust line and the longitudinal axis the same. Next is parasitic drag from gears doors and anything that sticks out.

Clarence

[M20S Driver]

Fixing the sagging prop (.5 inch) on my M20S gave me an extra 3 or 4 knots at max power at 10,000 feet.  The pitch stability was improved a lot.

[Bartman]

Well I'm not exaggerating. Just posting my results, but the conditions are not exactly the same. But I can definitely say I have not see over 138 while LOP in a long time.

[kerry]

I'd like to get mine done.  What's the average cost to have the mounts shimmed. 

[N201MKTurbo]

About $10 worth of washers.

[Guest]

I'd like to get mine done.  What's the average cost to have the mounts shimmed.

Kerry,

Check out Don Maxwell's site, he has a small piece on shimming the mounts.

Clarence

[Wakeup]

How do you know if you need shimmed ?? Thanks. Troy

[N201MKTurbo]

How do you know if you need shimmed ?? Thanks. Troy

Good question. The cowling can sometime ride up and make it look like the engine is sagging. I'm not sure exactly how to measure if.

[carusoam]

Examples of centered, and some not so centered, and others...

Bartman's is easy to see...the curve of the spinner matches the curve of the cowl and is centered in the hole... Very nice!

My C was not as easy because the hole was a big guppy mouth. When it broke a weld on the motor mount the sag was about a 1/2 inch. It didn't look right, but was challenging without a ruler to tell. Not so nice!

George posted pictures of his M20S. The curvature of the cowling has a 1/4" step between it and the spinner (same as my O). His engine is properly shimmed, centered in the round hole of the cowl... Not as pretty as bartman's machine!

Causes, worn rubber parts, broken welds and funny design characteristics...

Bartman, is that a Bravo?

Best regards,

-a-

[kerry]

I read Don Maxell's article.  It says there should be 1'' between the lower cowling and the starter and the spinner should look centered.  My starter is about 1/2'' above the cowling.  According to Maxwell's article it will require 1/8'' washer which will raise the engine a 1/2''.  I was wondering how big of job is it or how much does a shop charge on average? 

[kerry]

My mounts seem fine

[carusoam]

Expect to decowl, support the engine with a hoist. Loosen some hardware, add some shims...

Tighten, measure, recowl...

Possibly repeat.

Check the age of the rubber mounts. If they are decades old...

Consider swapping them out since you are doing the work already.

Benefit of new rubber mounts...less vibration...

Know, I am only a PP, not a mechanic....

Ask your mechanic how many hours he thinks for this? A good time to ask is when you are doing the owner assisted annual...

[Piloto]

Air temperature and aircraft weight can easily makes a 5Kts difference on indicated air speed. Running at LOP speed slow down for just a 10deg difference on the mixture setting. When comparing speeds use the same density altitude, weight and mixture setting.

 

José  

[M20J26]

I spoke with Don Maxwell and his opinian is engine shimming has nothing to do with the ships speed

[cliffy]

Typically a sagging engine is due to old sagging engine mounts. The front of the lowers and the rear of the uppers. Shimming a sagging engine with old mounts is only masking the real problem.

any speed run comparison needs to be done at the same density altitude and power to be valid.

[Guest]

I read Don Maxell's article.  It says there should be 1'' between the lower cowling and the starter and the spinner should look centered.  My starter is about 1/2'' above the cowling.  According to Maxwell's article it will require 1/8'' washer which will raise the engine a 1/2''.  I was wondering how big of job is it or how much does a shop charge on average?

Kerry,

It's not really a big job, ask your shop if they have any old Lord mount washers. If they do you will need to cut a slot the same width as the hole 7/16" bevel and smooth the slot.

With your shop remove the top and side cowls, loosen the lowere engine mount bolts, support the engine by the front with some rope or a sling, raise the front of the engine making a space between the lower mount and the engine, slide or tap the new washers into place, lower the engine and re torque the bolts. You may have to remove washers frommunder the nut to maintain proper safet of the nut and bolt. reinstall the top cowl and check the fit.

As some have pointed out the mount rubbers may be old and squeezed, in many cases washers were lost in. Prior engine removals. Mooney also used 1/16" washers for finer fitting.

Clarence

[PaulB]

I paid about $300 for Maxwell to fix mine. Didn't notice any speed difference but it looks a lot cooler.

[N201MKTurbo]

The motor mount bolts don't usually go in and out happily. They will fight you the whole way and the nuts and bolts are hard to get to. So, normal for a Mooney.

[Awqward]

Bartman, I notice that you don't have doublers on your spinner....is this by design?

[Bartman]

That spinner was installed about 5 years ago. The old one cracked, right under the doubler plate. Anyway, the IA got a new one and installed it and I have flown it exactly the way it is since then.

 

When I first got the plane I used to push into the hangar with one hand on a prop blade and one on the spinner. I doubt that had anything to do with it cracking, but after seeing just how thin, fragile, AND EXPENSIVE these things are I no longer touch the spinner.

[Hank]

I push into the hangar with one hand on the tow bar and one hand on the corner of the cowl. I only touch the spinner with polishing rags. (Yeah. I like this shot.)

[ArtVandelay]

One hand on the prop close to spinner, one hand on tow bar, I figured the prop is designed to handle forces on it, the cowling isn't

[OR75]

How big of a job is it to change all 4 rubber mounts on a J ? 

Any special tools required ? (apart from being able to hoist the engine)

What accessories come on the way ?