Van's Air Force
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Sagging engine
- Thread starter redhawk
- Start date
akarmy
Well Known Member
After about 300 hours my engine started sagging. Eventually it was down about 3/8". I first tried swapping the mounts around. Didn't do anything for my situation. I waited a bit longer until I ended up with a small cut in the lower fiberglass cowl from the alternator pull wheel. Decided it was time to tackle the project. I used the same large washers that come with the engine mount kits. I took 2 of them and cut slots into them. Loosened up the lower mounts and lifted the engine up enough to get the washers started into the gap. As hard as it was to get them in, there's no way they are going to slip out unless the bolts fall out first. I was able to tap them into place, retorque the bolts and put the cowl back on. Fingers crossed... It raised the engine about 1/4" so now it's 1/8" low which is just fine.
The only problem is the pivots the engine upward on an arc (as would be expected) and now I had some interferences with areas of my baffles that were really too close already. How did I know? The first test flight I had new vibration... So I trimmed the nose of the baffles back a bit and trimmed the fiberglass on the intake snorkel (carb engine) a bit until I had good clearances all around. Everything working great now.
The only problem is the pivots the engine upward on an arc (as would be expected) and now I had some interferences with areas of my baffles that were really too close already. How did I know? The first test flight I had new vibration... So I trimmed the nose of the baffles back a bit and trimmed the fiberglass on the intake snorkel (carb engine) a bit until I had good clearances all around. Everything working great now.
[email protected]
Well Known Member
I did this exact thing about a year ago on my Rv-6A 0-360 c/s prop
I put a three 3/8" fender washers under the 4 bottom bolts of the mounts. Works great. I didn't slot the washers, just pulled the bolts out and slipped them in. I did have to use longer bolts in a couple holes so's the castellated nuts would still get their cotter pins.
It brought the engine up very nicely.
I actually drew up the lift factor on a large piece of heavy paper before I started.
It was faster and way cheaper than new mounts
My luck varies Fixit
I may be getting to the point of doing this...very slight sagging from perfectly in line to just a bit low after 11 years. I would NOT cut a slot in the washer, as that seems like a guaranteed way for it to rotate around (heavy side down) and drop out...LOTS of motion on startup and shutdown, plus vibration in flight. Seems like a bad idea to me, but YMMV.
I agree, only had thought to ask if anyone had done it. The risk is just too great for the additional trouble to pull the bolt out enough to put the washer.
Slotting the washers works fine. It gets tightly clamped between the engine and the aft half of the isolator, so there is no chance in it coming out.
The arm length ratio between the engine mount to spinner distance ,and the top of the engine mount to the bottom of the engine mount, is about three to one, so you’ll get about three times the vertical movement at the spinner as what the thickness of the spacer washer is.
Gotcha, and I can see that now. Also, there are two options: put it on the aft side of the top mounts, or the forward side of the bottom mounts. Any reason to do one or the other?
No, if you’re going to make an elevation adjustment of the spinner relative to the cowl, it has to be done with spacers between the bottom isolators and the engine case.Gotcha, and I can see that now. Also, there are two options: put it on the aft side of the top mounts, or the forward side of the bottom mounts. Any reason to do one or the other?
Adding spacers to the backside of the top isolators will just space the head of the bolt further aft, but it will do nothing to change the position of the engine relative to the engine mount.
Doh! Of course. I see that now.
I was just thinking of using a AN970-7, any reason that it needs to be STD619?
If they are sagging, they are loosing/have lost some elasticity. The related energy has to be absorbed somewhere else. I’d strongly consider this point before making my final decision. Anecdotal experience that others may add to the contrary won’t be relevant here. My worthless $0.02
I need to do this in the near term also. Can you give me the outer diameter of that washer? I am going with 1/8" and will just make the washer on the lathe.
Agree. The isolators will eventually get severely deformed and loose all elasticity. The shimming trick may last a year. Depends on the intensity and frequency of flying of course.
blaplante
Well Known Member
Sorry, washers are at my hangar and it'll be two weeks before I get there again.
