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Engine mount bolts too short??

bertschb

bertschb

Where's my engine????
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I installed the engine mount today and it appears to me that the two lower/inner bolts (AN6-20A) are too short as shown below. The upper two bolts (AN6-24A) have 2 threads showing and the lower outside bolts (AN6-22A) have 3 threads showing.

Should I replace these lower inside bolts with AN6-22A?

IMG_4200.jpg

Screenshot 2025-04-30 at 3.44.36 PM.png
 
Definately too short. Mine have 2-3 threads showing. Are you sure they're 20's? Using the correct 0663P washers?
PS did you clean the powder coat from the surface under the bolt heads to get a good ground to the fuselage?
 
Halleffect said:
Are you sure they're 20's? Using the correct 0663P washers?
PS did you clean the powder coat from the surface under the bolt heads to get a good ground to the fuselage?
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Yes, using 663 washers on both sides. As far as being positive they are 20's - no, I'm not positive. What I am positive about is they are the only bolts that could be 20's. What I mean by that is all other bolts are accounted for. Sooooo, if they aren't 20's, Vans sent me the wrong length. Hope that makes sense. I'll remove one of them and measure it.

It looks like an AN6-22A bolt should be 2.078" long.

I did not clean the powder coating from the surface under the bolt heads. It's not in the tricycle gear plans. But, I did read about it in the wiki. I also read Scott's opinion of it.
 
That’s definitely to short - you want 1-1/2 threads at least - but more than three is excessive. Is there room to grind off any engine mount tube under the bolt head? I don’t know what the engine mount looks like on the -14 where those bolts go in, but if there is a tube welded in that the bolt goes through, and it sticks out forward a bit, you can grind some of that off, allowing the bolt to go further into the firewall. Show a picture of what is under the bolt head.

Engine mounts frequently have minor tolerance issues that require a little grounding or slightly longer (or shorter) bolts.
 
Just measured both of the bolts in question. They are 2.15" long which is slightly longer than the 2.078" I found online for the length of an AN6-20A bolt. So, it appears to be the proper AN6-20A bolt - it's just too short. I would think everybody building a -14 would have the same problem. That is, unless the engine mount I have has changed slightly.

I will order AN6-22A bolts and try again.
 
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Ironflight said:
That’s definitely to short - you want 1-1/2 threads at least - but more than three is excessive. Is there room to grind off any engine mount tube under the bolt head? ...Engine mounts frequently have minor tolerance issues that require a little grounding or slightly longer (or shorter) bolts.
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There isn't enough material to remove on the lower inner mount tubes. I ordered some AN6-22A bolts. Those should work.

Good to know there are variances in the engine mount that might require changing the bolt lengths. I always check the threads on the back of nuts to make sure the bolts are long enough. Since this was the engine mount, I thought FOR SURE the spec'd AN6-20A bolts would be the proper length. Glad I checked!

It seems there is always something waiting to trip up new builders :mad:
 
I'm always interested in the design of the 14 vs 10 and this has peaked my OCD for years. First why does the 10 nuts mount FWF vs the 14 FWR? Next for the 14 there is a note to use washers on the upper bolts only, why? This would obviously add a few threads to the lower bolts if the note is used. But why? Seems washers on all would better distribute the load? I guess when you have your bolts FWR you can use Nylok.

Finally look at the 14 vs 10 wing attachment bolts, washers used and not used very different for basically the same wing attachment design.

Screenshot 2025-04-30 203351.jpg
 
dmattmul said:
..Next for the 14 there is a note to use washers on the upper bolts only, why?
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Actually, the plans call for 632 washers on the back of the upper bolts only. The lower bolts use 663 washers on the back. All the bolts have 663's on the front.
 
Is there a reason for the nut to be placed in that location?
For ease of inspection, wouldn't it be better if the nut was on the engine side and a castle nut used...... Like the RV6.
 
gasman said:
Is there a reason for the nut to be placed in that location?
For ease of inspection, wouldn't it be better if the nut was on the engine side and a castle nut used...... Like the RV6.
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I seem to remember someone (Scott?) saying the RV-14 mount was designed and attached differently to the other mounts.
 
Brian,

I had the exact same issue on my -14. Purchased longer bolts and moved on. As I recall, I also moved to AN365 all metal lock nuts. In retrospect, I'm glad to see that I'm not the only one that had the issue. Apologies to all for not reporting the problem. I imagine there are countless little "gotchas" in many builds that aren't brought to light.

Fred
 
bertschb said:
lower outside bolts (AN6-22A) have 3 threads showing.
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I never had that problem with the 20A bolts. I did have that same isssue with the lower outside bolts though, so I added a .032 washer on those bolts. If you take a nylok and thread it on to those AN6 bolts you’ll find that when the nut is bottoming out on the grip, there’s only about 3 threads showing. If you have 3 threads showing on yours, it’s very close to giving a false torque reading because you’re tightening against the grip and not the stack up.
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On the top bolts, my build advisor didn’t like the way the bolts wandered off centre. It resulted in not having 100% bearing on the motor mount bolt bushing. So he made me a couple insert bushings to hold them centred. Keep an eye on those, as you tighten, so that they don’t wander off to one side. If they were tightened off centre, with engine vibration you would lose your torque, eventually.
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mc607 said:
I never had that problem with the 20A bolts. I did have that same isssue with the lower outside bolts though, so I added a .032 washer on those bolts. If you take a nylok and thread it on to those AN6 bolts you’ll find that when the nut is bottoming out on the grip, there’s only about 3 threads showing. If you have 3 threads showing on yours, it’s very close to giving a false torque reading because you’re tightening against the grip and not the stack up.
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This is very helpful Todd. Thank you! I will take a closer look at the bottom outside bolts to see exactly how many threads are showing.
 
I think you could use a .032" (NAS1149F0632P) washer on the fore and aft sides and the 20A bolt length will be fine.

Also, be careful if you ordered AN6-22A bolts, they may be too long and you will "bottom out" the nut against the shank of the bolt. Maybe you should have ordered AN6-21A bolts???

AN6-20.png
 
Tony Kirk said:
I think you could use a .032" (NAS1149F0632P) washer on the fore and aft sides and the 20A bolt length will be fine.

Also, be careful if you ordered AN6-22A bolts, they may be too long and you will "bottom out" the nut against the shank of the bolt. Maybe you should have ordered AN6-21A bolts???

View attachment 86650
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I ordered AN6-21A bolts as well as the AN6-22A (and a few other assorted sizes to have on hand for future issues like this). Thanks for the head's up. I will be paying special attention to possible "bottoming out" issues after seeing how short the threaded section is on these bolts.
 
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