Engine Mount Washers

[N2709P]

Jason, I would install the mounts and engine without any washers. Once the engine is mounted, put one leg of an 18 inch carpenters square against the firewall and the other at the aft section of the upper case split line. You can use a protractor to measure the angle between the square and the case split line. Should be 2 degrees right angle. Use an 8 inch digital level along the upper case split line. This should be 4 degrees down angle. These measurements will give you the thrust line of your engine to airframe. If it is out of tolerance, you can place washers as need to improve the thrust angle. Make sure that you have properly torqued the engine mount rubbers prior to checking the angles. It takes about 5 minutes to check with the upper cowling off. If you need more than a washer or two to bring it into line, you probably have something bent pretty good. Rebuilt motor mounts are a common issue. Some jigs are not so accurate, if they jig them at all.
N2709P

[Steve Pierce]

I check firewall to zero and then put the digital level across the two rocker covers if the engine is mounted. If not put the firewall side of the mount on a flat surface and being it is a conical mount the digital level should give you the angles when layed on the engine conical mount washers.

[Subsonic]

My Tri-Pacer engine mount appears to be twisted/bent down and counter clockwise as viewed from the pilot seat. The angle is 6.1 degrees down on cylinders 2, 4 and 4.1 degrees down on cylinders 1, 3, when referenced to the firewall. When you stand in front of the plane and look through the nose bowl holes, the cylinders slope down to the right a couple degrees. I rechecked the torque on all my conical bushings to 40 inch pounds, then tightened the upper pilot side to 60 inch pounds and it raised the engine about 3/16" as measured at the front mounted oil cooler gap to the nose bowl inlet. I can't see any bulges or bends in the engine mount tubes, but it must be there. Is it possible to adjust this misalignment out with washers under the lower left engine mount at the firewall?

[Jim]

Hi,

I don't think the mount bolts are tightened to a torque, it should be a distance between the washers the rubber is compressed to.

https://www.shortwingpipers.org/forum/showthread.php?4892

[N2709P]

Piper SL 349 allows the mount bolts for the rubber bushings to be torqued to 40”#’s rather than a specific linear measurement. If the recommended torque does not align the engine in the mount properly, either the rubber bushings need to be replaced or there is an issue with washer placement or the mount itself. Attempting to correct for a motor mount that is out of alignment by over or under torquing bushing bolts or adding washers between the bushings and engine is probably not the best solution. The welding shop in Wisconsin that bought a well known shop has serious issues with production. Their quoted cost to rebuild my motor mount that had a compression bulge on one leg was more than the cost of a new Univair mount. A lot of these airframes have been damaged in their lifetime. It might be acceptable to use a washer between the mount and firewall to correct minor powerplant alignment discrepancies.
N2709P

[Jim]

Hi again,

Piper SL 349 is Interesting. It doesn't read like there's rattle room to adjust, 40# it is.
SL-349.jpg

[Steve Pierce]

I would suspect the engine mount rubbers. I have pulled way too many that looked fine but were elongated. As far as 40 inch lbs of torque vs 1.84" of distance, from my experience they come out the same. The AN8-44 with an AN310-8 nut and the Lycoming washer come out perfect every time.

IMG_20190911_173431.jpg

[Subsonic]

I have new rubber bushings on order. I'll do that first and measure again.

[Steve Pierce]

That is what I would do.

[PACERGUY]

Bushings going bad is a common issue as is engine sag. Easy to spot on preflight as the oil cooler or spinner starts to rub on the cowling. Seems to me I remember hearing about it happening mid flying season to a guy and he simply tighten the top nuts about two turns which corrected the problem until he had a chance to replace the bushings. Ben a while so not quite sure who that was.
DENNY