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Sagging engine

tracy

Well Known Member
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My 8 is showing some motor sag ( alternator pulley is touching lower cowl) after 16 yrs of hanging and 750 hrs. It’s the standard dynafocal Mount with o360a1a engine. I am aware of shortening the alternator belt, but I understand that the lower bolts are a little longer than the upper bolts so that a washer can be added. Is this standard practice and how hard is the procedure? Would it be better to replace all mounts? They still appear to be in good shape from a visual perspective. If a washer is all that is needed, what part number is it?
 
Washers would probably work, but after 16 years, new rubber engine isolation mounts would be SWEET! :cool:
 
I wonder if new mounts would be smoother?

Can't offer a true comparison regarding smoothness since my experience between my 4 with about 14 year old isolation mounts (to which I added washers on the bottom) and my 7 with new mounts, have different engine / prop combinations. I didn't really notice a big difference in vibration between the two.

I can say it was not too much trouble to add the washers to the 4. Removed the nuts on the bottom bolts. Took the weight off the engine with a hoist. Pulled the bolts back far enough to add the washer one side at a time. Getting the cotter pins in was the biggest PIA. I understand you can use new metal nuts so you don't need the pins. Maybe some else knows if that is ok.

ACS washers - Dimensions of part # 08-03640: Thickness = 5/32", Hole Diameter = 17/32", Outside Diameter = 1-3/4".
Vans washers - WASHER STD-619 1/2 1.745 $12.50

If money is a concern I would just add the washers. If not replace the isolators. FWIW.
 
My 8 is showing some motor sag ( alternator pulley is touching lower cowl) after 16 yrs of hanging and 750 hrs. It’s the standard dynafocal Mount with o360a1a engine. I am aware of shortening the alternator belt, but I understand that the lower bolts are a little longer than the upper bolts so that a washer can be added. Is this standard practice and how hard is the procedure? Would it be better to replace all mounts? They still appear to be in good shape from a visual perspective. If a washer is all that is needed, what part number is it?

The mounts should still be OK after 750 hours unless you’ve been flogging the plane with aeros. Engine sag is normal. One extra washer at the lower mounts will do the trick.

However, as per Vans drawings the lower bolts are 1/8” longer than the upper bolts because the upper bolts go through 1 washer and the lower bolts go through 2 washers. Now you will be adding a 3rd washer to the bottom mounts so you will need to buy new bolts that are 1/8” longer than the existing lower bolts.

I highly recommend that when you buy the new longer bolts you drop the castle nuts because the cotter pins are going to be extremely difficult to install. Get standard AN7 bolts with AN363-720 metal locknuts. Many certificated aircraft use metal lock nuts on the engine mount bolts.

Incidentally, the extra washer you need is a Lord J-221861
 
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Thoughts?

Thoughts on swapping tops to bottoms and vice versa or changing orientation of each (if non-directional isolator)? Only half of each is under continuous compression. Yes, it is a temporary "fix" but should buy you some life/extend the parts life cycle. Managed to get a few more years out of my old Mooney EMs. Still have the scars from the removal/install.

Of course it is best to change them. Unfortunately, the new parts don't seem to last as long as the old ones of supposedly the same material. Best of luck.
 
VIPs, swapping tops to bottoms and a washer was a great sag fix. Bolts on bottom were long enough. 60 cuss jar quarters later and cotters were in.
 
Update

I went ahead and changed the rubber mounts out and found a much smoother ride with a 10 to 20 degree cooler number 3 cylinder head temp. The new mounts raised the engine ( more specifically the alternator pulley which started to rub cowling) one inch. Upon installing the cowling after mount replacement, the top of spinner was barely touching the top cowl. I removed the cowl and ran engine and found the engine settled just enough to provide clearance. I’m glad I swapped the mounts instead of just adding spacers on bottom mounts. Since I wasn’t the builder, I now know what the relationship between spinner and cowl should look like....centered. These mounts were 16yrs old with 750 hrs on them. One more thing, there is no more play in cowling.
 
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Glad to hear you got your sag fixed with new rubber mounts. Are these the ones you used? I was surprised they cost THAT much each! https://www.aircraftspruce.com/catalog/eppages/lordenginemountscessna_08-00380.php?clickkey=5922011

How long are these mounts supposed to last? My -4 only has about 650hrs on it and already I am seeing significant sag since I bought it. I've had it for about 4 years and put about 400hrs on it. I'm trying to decide if I'll need new mounts or it'll be ok to just rotate and/ or switch the mounts top and bottom.

I'm sure aerobatics will shorten their life, but does anyone know by how much?

I went ahead and changed the rubber mounts out and found a much smoother ride with a 10 to 20 degree cooler number 3 cylinder head temp. The new mounts raised the engine ( more specifically the alternator pulley which started to rub cowling) one inch. Upon installing the cowling after mount replacement, the top of spinner was barely touching the top cowl. I removed the cowl and ran engine and found the engine settled just enough to provide clearance. I’m glad I swapped the mounts instead of just adding spacers on bottom mounts. Since I wasn’t the builder, I now know what the relationship between spinner and cowl should look like....centered. These mounts were 16yrs old with 750 hrs on them. One more thing, there is no more play in cowling.
 
Barry

No, I used the Barry mounts from Vans. Around $130x4. Replacing them took most the day for two of us, but we had never done it before.
 
I went ahead and changed the rubber mounts out and found a much smoother ride with a 10 to 20 degree cooler number 3 cylinder head temp. The new mounts raised the engine ( more specifically the alternator pulley which started to rub cowling) one inch. Upon installing the cowling after mount replacement, the top of spinner was barely touching the top cowl. I removed the cowl and ran engine and found the engine settled just enough to provide clearance. I’m glad I swapped the mounts instead of just adding spacers on bottom mounts. Since I wasn’t the builder, I now know what the relationship between spinner and cowl should look like....centered. These mounts were 16yrs old with 750 hrs on them. One more thing, there is no more play in cowling.
Good call. With rubber parts it's a combination of the mileage (engine hours) and calendar age taking their toll. 16 years is a long time!
 
I added a 1/8” washer, but I put it under the engine mount on the firewall at about 200 hours. That corrected the sag, which has since been stable with no additional sag, and it was much easier than dealing with the rubber isolation mounts - which looked like new still.
 
I added a 1/8” washer, but I put it under the engine mount on the firewall at about 200 hours. That corrected the sag, which has since been stable with no additional sag, and it was much easier than dealing with the rubber isolation mounts - which looked like new still.

Sure, it’s easier to put washers at the firewall but there are a couple of potential problems with that approach. One problem is that it’s tilting the whole engine mount and therefore displacing the nose gear leg. On many RVs this can cause conflict problems between the gear leg fairing and the lower cowl intersection fairing, depending on how tight it was set up in the first place. The best solution generally is a washer at the rubber engine mounts.
 
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