crankcase stress on stand?

gigem75 · 09-22-2007, 04:48 PM

Maybe I'm over analyzing this but in looking at the crankcase and putting it on a engine stand I'm sensing there will be quite a bit of stress on the case since it is only supported at one end. I realize the ring adaptor will spread out the stress on the supported end but it just seems that with adding the crank, rods, and the other half there has got to be quite a bit of stress on the case. It would seem to me that one would want to join the halves under a condition equalized or no stress to insure the best possible seal between the halves. Am I just thinking to much or could this possibly be a valid concern?

304065 · 09-22-2007, 05:08 PM

The factory assembled 917 engines in the same fashion, they are twice as long.

Nobody worries about it.

cgarr · cgarr's Garage

Just make sure its bolted tight to the adapter, it then becomes one.

356RS · 356RS's Garage

Your engine stand is supporting the case on three points right? I have seen some engine stands with only two mount points.

BoxxerSix · 09-22-2007, 07:18 PM

Quote:

Originally Posted by john_cramer

The factory assembled 917 engines in the same fashion, they are twice as long.

Nobody worries about it.

Not that it really matters here but from pictures I've seen of 917 builds the nose of the motor was supported as well, as seen here:

http://www.pbase.com/917carl/image/21933404

JFairman · 09-22-2007, 10:04 PM

I think your thoughts might have some merit.
I don't know if it makes any difference though.

but here's some other things about metal and gravity and torque...

You're supposed to store crankshafts upright because if you store them on their side gravity will bend them and they won't be straight after a while...

and,

I remember the mid 80's chevy ilmor engine was the most powerful engine in indy cars at that time because they moved the cam drive from the front of the crankshaft to the back of the crankshft next to the flywheel, because cam timining was not affected by crankshft twist there.
They found that the crank would twist a little bit under heavy load and cam timing would retard because they were taking the cam drive from the opposite end from the flywheel and clutch.

trivia,, i know.

304065 · 09-23-2007, 04:12 AM

Yeah, I saw those photos and considered them before posting my answer. Carl Thompson putting a piece of wood under one end. What I was thinking of are the really cool photos of the Factory in 1971, the one that ran in Pano (I can't find it online) where they had the white tubular rails in the workshop that the P201s attached to, and a few 917 engines were cantilevered out. Also, the Factory welded some gussets to the tubes on the P201 where they join the ring to take the weight of the bigger engine.

Bullet Bob · 09-23-2007, 07:50 AM

With the engine bolted to the stand it is being supported in the same manner as when it is in the car, though when it is in the car it is supporting the tranny's weight as well. When bolting to the stand only torque the bolts slightly tighter than finger tight because the only way these are going to fail is if they pull out of the case. The more you torque, the greater the chance of that happening.

gigem75 · 09-23-2007, 09:56 AM

There are only two points of attachment on each case half which is what got me to thinking about this in the first place. When the engine is in the car it is supported at the pully end as well as the gearbox end.
I think I'm going to join the case on the bench. I've got a jig in my head that shouldn't be to hard to fabricate.
Thanks for the replys, they are appreciated.

BoxxerSix · 09-23-2007, 10:08 AM

These motors were also designed as stressed members in various chassis, such as the 956/962. They can hold their own weight on a stand. The tensile strength of the securing studs into the case is probably over 10,000psi on their own, coupled with the half-rim support of the stand itself and it's pretty stout. I wouldn't go bouncing it around on a stand though trying to move it to a fro..

I'd personally be more concerned about the stability and strength of the base stand itself vs the actual strength of the case bolted to the adapter.

gigem75 · 09-23-2007, 01:32 PM

I'm pretty sure the stand will be fine. Last on it was a 351W from a 1982CorrectCraft.

I understand the stressed member, but that's with the halves together. I'm sure either way would be fine but I'll sleep better at night knowing I joined two unstressed halves together rather than one being under stress and the other one not under any stress.