Has anyone discovered better, more resiliant, longer lived bushings for aerovee engine mount bushings, instead of original sonex items, that have the identical physical dimentions for proper fitment?
Edit: these are Super Pro SPF2092BK bushings. Available in the US and Australia it would seem. Some of the old links are broken but if you search for “Super Pro SPF2092BK” you will find their USA or Australia website, plus ebay sellers and so on.
As mentioned in other threads: The SuperPro bushings are shorter in length than the original rubber bushings. So you’ll need to add extra washers/shims to get sufficient compression and to properly space the engine forward to give clearance between the prop and the cowling.
Note that the Sonex plans/instructions describe a maximum thickness of washers/spacers for the engine mount bushings; but this isn’t a true “hard limit”. I know this because I mentioned it to a Sonex employee, and they pointed out that in some publicity photos of the “Red One” factory airplane you can spot some additional spacers on their engine mount. [Obviously you want to approach this carefully and intelligently, though]
I had the benefit of skipping the stock rubber bushings and going right to the Super Pro ones. So, my cowl fits. I made a bunch of aluminum washers on the lathe for alignment.
Super Pro SPF2092BK is not the correct part number. I just ordered them, have them in front of me in a package, with that part number, and they are 1” diameter, where 1-1/4” is required. They have only a single shoulder where two are required. And they are only 5/8” deep, where 7/8” is required (can’t make up 1/4” which washers).
Its true that the SuperPro units lack the “second shoulder”. And yes, this means there’s a small air-gap in the center of the stack-up (between the front and rear bushings). But its the compression and the first shoulder that really carries the load. As long as you add shims/washers to get good compression, it’s worked out fine for several of us.
The major issue is the ones I have are too small in diameter. I took them to the airport today and they are much too small. The engine mount recess is much wider than these bushings, so they would just slide to the top of the engine mount recess under the weight of the engine. I often pull 4-g’s on some aerobatic maneuvers, so that makes that issue even more pronounced.
It feels like we have the same part number, but very different physical dimensions from what y’all have installed. If anyone has an unused one on hand, I’d be curious to know the diameter.
Exactly. If you tried to get a bushing between the tube and the through hole of the mount, the psi on the bushing would be high and the bushing would get torn up.
@Sonex439 , are you worried about the through hole? I wouldn’t be.
I’m going to yield the the wisdom of those who have been there and done that. I’ve got the bushings, so when I do my condition inspection later this year, I’ll give them a go. I replaced the bottom ones last year with the factory bushings, and was going to change out the top ones this year. I’ll likely replace all of them, now. In for a penny, in for a pound!
All good! Double-checking anything you learn on the internet is smart.
When you do install them, definitely keep in mind that you’ll need additional shims. I didn’t shim mine enough and the engine is starting to sag a bit. Gonna have to pull the engine and re-mount it sometime this spring/summer (a major chore with the turbo and all its associated plumbing).
