Engineers / smart people of r3v, are my flywheel bolts too short

[e304me]

well i bought a never used jb flywheel from a guy and he did not have the bolts. Im thinking that it probably came with special bolts because i dont think the stock ones are quite long enough for this flywheel the first pic is the stock flywheel and the second is JB. Remember that the threads in the crank do not start right at the face. I have also emailed JB but im guessing they wont sell me shit without a complete rebuild of the flywheel. (this was the case until the guy i bought it from found the ring for the bolts)

[Nick325is]

I'm 99 percent certain that the jb racing flywheel I brought came with bolts that were the same size as the ones that I removed.

Let me see if I can find a pic.

-Nick

[kowalski]

just counter sink the bolts into the flywheel.

[kronus]

just counter sink the bolts into the flywheel.

Pff, why even bother with that? Just coat the mounting surface with Elmer's white glue and slap on :D

[netcsk]

I don't know how many of those threads will be caught, but you need at least 3 threads to get 90% of the clamping. In other words, put some loctite on them and you should be fine.

[e304me]

yeah jb wants 50 bucks for theres and they are not even 12.9

[AndrewBird]

Why not go to the hardware store and buy longer bolts?

I suppose the heads are flatter then normal. Would regular bolts stick out too far?

[matt]

Why not go to the hardware store and buy longer bolts?

I suppose the heads are flatter then normal. Would regular bolts stick out too far?

Gaaahhhh. NEVER do this. Get the right bolts, get them from BMW.

BMW is way smarter than the hardware store!

[AndrewBird]

Dude. They are bolts. The simplest part on the entire car. If you are worried about them shearing, get grade 8's and call it a day. The only issue is if the thinner heads are actually needed or not.

[NC325iC]

Dude. They are bolts. The simplest part on the entire car. If you are worried about them shearing, get grade 8's and call it a day. The only issue is if the thinner heads are actually needed or not.

they are bolts yes, they are coated specially, shorter heads and yellow loctite on the ends of them, and they may be stretchers im not sure there. i wouldnt trust any vital part of my engine to any old bolt.

In these pictures did you use the spacer that goes btw the bolts and the flywheel? does the jb fly rquire its use?

[Garageaholic]

You have plenty of thread on there to handle the shear load. Not to mention, you have 8 bolts.

Those bolts must be at least grade 5, which means it can handle a shitload of shear forces.

[Hick]

Thats not shear, thats a bearing stress for how far 'sunk' the bolts are into the crank.

Shear = [2 x torque x bolt diameter from center] / [Number of bolts x Bolt area]

that dosent take into account factors of safety, which would be a muliplier.

dont remember bearing off the top of my head

In short, buy the proper studs from the dealer or vendor. Not hardware bits

[LINUS]

as a ex-mechanic in an acid refinery, for steel we had to have 5 threads engaged in the opposite fastener, bolt-n-nut, or stud & 2 nuts. You had to have 1 thread exposed through the fastener if it was a stainless application. Generally that meant ~8 threads in a nut, and then the exposed.

Motorcycle dealerships are a good resource for hardware if you can get in good enough to rummage their bolt bins. Swing arms/suspension use a lot of good size, high grade hardware.

[matt]

Dude. They are bolts. The simplest part on the entire car. If you are worried about them shearing, get grade 8's and call it a day. The only issue is if the thinner heads are actually needed or not.

What? NO. This is not true at all.

There is a TON of engineering behind almost every nut, bolt, stud and washer that BMW puts on your car.

Plus, grade 8 is an SAE standard, and doesn't even apply to metric bolts. Those are either 10.9 or 12.9, both of which are stronger than grade 8!

And for god's sake torque them properly.

[nando]

flywheel bolts rank right up there with rod bolts, main bearing bolts and head bolts. don't fuck around - just get the right hardware. I know i've seen threads where people have sheared/broken the flywheel bolts because of improper hardware or not torquing them right. unless you really enjoy pulling your transmission to redo something as "simple" as 8 bolts..