m50/52 crank bolt torque

[jessezipper]

ok , ive got my m52 goin back together. the front crank bolt that has to come off to get the timing cover off, is there a certain torque to tighten to goin back on???

ive looked for torque specs, dont know the proper name for the bolt either..

[WhoNew]

Search Jesus bolt. Seriously.

It's high, if I remember correctly, it's 325ftlbs.

[Jackson42]

I looked it up in the BMW TIS and the spec is 410Nm (300 ft-lbs). The TIS says to replace it rather than reuse it. It is really important that it be torqued correctly because if it comes loose it destroys the keyway on the crankshaft, which will cause one very expen$ive repair.

[jessezipper]

Dealer item only?? I can't find it at oriels, autozone or advanced autoparts ..it's a 97 motor is the dealer gonna have it still

[bubba966]

Yup, dealer only. Doubtful it'll be in stock. Most likely have to get it ordered for you.

[HE53]

Just reuse it, I've done it many many times and never had any issue.

[Jackson42]

Just reuse it, I've done it many many times and never had any issue.

So have I. I just reported what the TIS said because I wouldn't want it on my conscience if I suggested reusing the bolt, he did, and the engine grenaded.

[HE53]

So have I. I just reported what the TIS said because I wouldn't want it on my conscience if I suggested reusing the bolt, he did, and the engine grenaded.
Understandable, but its not a stretch torque bolt so go for it.

[5mall5nail5]

Just reuse it, I've done it many many times and never had any issue.

It's torque to yield. You can measure the bolt stretch. Re-use it if you like punishment.


Understandable, but its not a stretch torque bolt so go for it.

Yeah it is. Measure the diameter of the unthreaded shaft, look up on a torque table and you'll see that the bolt is almost into plasticity at 300 ft lb.




OP do not reuse it. It's $5 - $6. Replace it.

We see them back out/loosen ALL the time when reused over in the FI section. When that happens the crank pulley can move, shears the woodruff key off, and then the engine runs all the wrong timing and can be damaged. Remember, on these motors this is not only your harmonic balancer (which means you really want it tight and not move if you value your bearings) but it's also how the ECU times the engine.

[Jackson42]

5mall5nail5 - "Knipex Addict?" Me too, brother - me too!

[5mall5nail5]

5mall5nail5 - "Knipex Addict?" Me too, brother - me too!

:D

[jessezipper]

i will not reuse it , but ill call the local bmw dealer, and get it ordered as well as the seal near it as it looks old ..

[djb2]

It's torque to yield. You can measure the bolt stretch. Re-use it if you like punishment.

The bolt may be torqued to near is plasticity limit, but that doesn't make it TTY (torque-to-yield).

It's unlikely to be a torque-to-yield bolt with just a torque spec. TTY fasteners typically have a spring-preload/stretch specification specified as how much of an angle to turn after initial clamping pressure is reached.

If the bolt is near is plasticity limit, the thread pitch should be measured to check that the bolt hasn't stretched.

[5mall5nail5]

The bolt may be torqued to near is plasticity limit, but that doesn't make it TTY (torque-to-yield).

It's unlikely to be a torque-to-yield bolt with just a torque spec. TTY fasteners typically have a spring-preload/stretch specification specified as how much of an angle to turn after initial clamping pressure is reached.

If the bolt is near is plasticity limit, the thread pitch should be measured to check that the bolt hasn't stretched.

It's hard to get a TTY on a crank bolt because you usually need to use an extremely long torque wrench to get the figure. Most shops will not ever have a 36" torque wrench with an angle gauge. In fact, most shops use a standard 1/2" torque wrench with a multiplier, which of course does not have an angle gauge.

If you look at the bolt specs it will likely say X ft lb +- Y ft lb. I believe that to be due to the bolt being into the stretch area whereas it doesn't much matter if its 300 or 310 ft lb. I bet BMW would do an angle on that bolt if you could do it practically.

Either way, TTY or not, it's consumable.