Engine Mounting torque

Ralph

Senior Member
Joined
Apr 12, 2004
Messages
404
Location
Mason, MI
Aircraft
Gyrobee gyro, BB trike
Total Flight Time
1000+
Can anyone quote chapter and verse on the proper torque when installing a 503 to the egine mounting bearers using the standard 10 mm bolts?

Ralph
 
For AN fine-thread bolts, the torques would be:

AN3 (3/16 dia): 20 - 25 in.lbs
AN4 (1/4 dia): 50 - 70 in.lbs
AN5 (5/16 dia): 100 - 140 in.lbs
AN6 (3/8 dia): 160 - 190 in.lbs
AN7 (7/16 dia): 450 - 500 in.lbs
AN8 (1/2 dia): 480 - 690 in.lbs

Hope this helps.
 
Richard,

Thanks for the information. The 3/8-inch bolts are 9.53mm so unless somebody comes up with a Rotax spec, it looks like we would be safe shooting for about 175 inch-pounds.

Ralph
 
Ralph HOLD ON!!!

According to the latest Rotax parts manual, the torque on those 10mm mounting studs (or bolts if that's what you're using) is only 90 inch pounds (10 Nm). Because the crankcase is aluminum alloy, it obviously can't handle the same torque rating of steel.

I hope I caught you in time.

John L.
 
I believe the 10 Nm spec if for the Rotax studs into the case. The nuts would then torque to 38 Nm. The stud torque is less because the stud "bottoms" in the hole and you don't want load the case. IE: push the bottom out of the hole.

Bolts would need to be torqued between 35 and 45 Nm depending on the bolt. Grade 8.8 or 10.9. I believe the hole is almost 24 mm deep and bottom taped. 12mm or so thread engagement is good.

Just a little dab of loctite doesn't hurt.
 
Thanks guys. One should always read the latest Forum input early in the morning! :=) Anyway, you caught me before I trashed the case, so all is well!

Added later:

I just found some torque specifications for aluminum 3/8-inch bolts - 75-110 inch pounds. Since the aluminum threaded section on the block that is engaged by the bolts is 2-3 times the threaded thickness of a standard nut, it would seem that doubling the aluminum torque range (150-220) would be OK. We will shoot for somewhere between 150 and 175 inch pounds and will let everybody know what happens.



Ralph
 
Last edited:
Ralph, I hope you're planning on putting your installation info on your website. I'm looking at the 503 as well and I would be greatly interested in your experience.
I also look forward to seeing what gearbox/muffler setup and prop you decide to use.
I'm a somewhat larger than average (205 lb) guy that will be flying in Texas where the temps can range fairly high and I want to make sure I have enough go to get in the air and stay there :)
Thanks
 
Ralph, I may have misunderstood but are you thinking about using aluminum bolts to mount the engine?

Four M10 aluminum bolts will NOT hold the engine to the mount.
 
No, I wasn't planning to use aluminum bolts, but was using the torque data for such bolts to look at limits for the aluminum case. In any case, here is how it all worked out:

(1) Set up a test fixture and 150 in-lbs would not fully compress the lockwasher.

(2) Manually torqued the bolts to the point where they had fully compressed the lock-washers and left them solidly engaged but no excessively so. Then went and measured to torque - 41 Nm or 30 ft-lbs or 360 in-lbs. Papa Smurf gets the prize!

Just for the record, the 30 mm-long bolts are a perfect fit, engaging all the threaded zone in the case with about 2 mm to spare.

Ralph
 
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