Here is a question for those in the know - process on Rave but not final torque value.
P38 2.5 diesel
Cylinder head bolts.
Tightening sequence
Stage I tighten to 80 NM ( as per laid down sequence.
Stage 2 Loosen 180 degrees.
Stsge 3 Tighten to 50 NM
STAGE 4 TIGHTEN 90 DEGREES.
STAGE 5 Tighten a further 90 degrees.
STAGE 6 Run engine for 20 minutes till operating temp is reached.
STAGE 7 Let engine cool down.
STAGE 8 Tighten a further 90 degrees.
Now for the question. What is the final torque value on completion of stage 8 ???
Assistance appreciated.
Bloody tight. I assume the diesel has stretch bolts hence the 90 degree at a time rather than to a specified torque. The theory is that the bolts stretch and the 'springyness' in them clamps the head down tight which works as long as you have bolts with the correct amount of give in them. Too soft and they either snap off or stretch too easily, too hard and you run the risk of pulling the threads out of the block, so make sure you get decent quality ones. As it's a BMW engine I would suggest getting genuine BMW bolts.
I am slowly building up a BMW M51 engine and I have been looking at alternatives to stretch bolts, which I am not keen on.
The bolts are M12x1.5x147mm and there are 14.
It doesn't help you, but to give you a ball park idea of the torque, if the bolts were substituted for 12.9 grade high tensile bolts they could be torqued up to a maximum of 100 ft lbs. You would however not tighten stretch bolts to this.
12.9 grade or EN16T has a yield strength of 180,000 psi.
I looked at ARP bolts which are expensive. ARP8740 is a chrome moly steel and the threads are rolled again after hardening. It is 180,000 - 210,000 psi. A newer ARP alloy seems to be 625+ which is 260,000 - 280,000 psi.
Are the ARP ones for the diesel studs rather than bolts like the V8 ones? If they are, although expensive, they make the job so much easier. They have the coarse thread on one end where they screw into the block and a much finer thread at the other end for a washer and nut. It's so easy to simply do them up in stages up to the max of 60-65 ft/lbs (80-85 Nm). I go 40 - 50 - 65 on the torque wrench, none of this heaving on a long breaker bar trying to get 90 degrees which you never can as there's always something in the way.
Yes, the ARP ones for the M51 diesel are studs @ £360 for a set. I can't justify that.
I would be happy going to ordinary 12.9 studs or bolts, even so they are going to be around £10 each. They are metric fine 1.5mm while most you see online are metric coarse 1.75mm.
I have got plans for the engine. A variable vane turbo off an M57 L322 and a replacement FIP with a 14mm plunger. I want to run 2 bars boost.
Target 250bhp.