Here’s some headbolt choices. It’s not my intent to make editorial comments here, so I’m not pushing one choice over another. This is just info from various sources to give you a feel for what different folks have said.
- OEM TTY headbolts. They run ~$25 for a set. Theoretically you should use them only once, but I’ve read where there is a way to test for re-use, and also a different tightening protocol if you re-use them. The re-use test is to see if the length has increased. If <2mm (I’d be inclined to half that), then they’re ok to re-use. The re-use tightening protocol is tighten in 3 stages to ~53ftlbs. Those two ideas came from different sources so I’m not suggesting that the 3 stage re-tightening protocol is the natural next step if the bolt has not grown more than 1mm.
I’ve never snapped a headbolt before, but I figure that if one did snap it would snap above the threads and getting it out wouldn’t be too much of a crisis. $25 isn’t a bad rate for insurance tho.
When you put in OEM TTY bolts using the normal 22ftlbs, 90deg, 90deg protocol, you get 53-55ftlbs. You have to be careful about this tho. If you aren’t pretty familiar with what a bolt feels like when it’s starting to “give” shy away from this.
Early M20 engines had standard bolts, not TTY bolts. The M10 motor uses standard bolts. I’ve not came across anything that explained why BMW shifted to a TTY bolt for later M20 motors. Sure, the early bolts had a history of breaking, but they could have fixed that with stronger bolts. But instead they went to TTY bolts. Some folks say that a TTY bolt provides better control over clamping force resulting in a head that is fastened to the block with the right pressure and a more homogeneous distro of pressure. The guys that boosting M20’s generally don’t use the TTY bolts, but that doesn’t mean that they know what they are doing.
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ARP headbolts. These are reusable and IIRC run $200-$230. They have their own tightening protocol and are popular among the M20 boosters. I’ve not used them.
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Metric Mechanic headbolts and Metric Blues. These are reusable. They look pretty similar, but I don’t know if they really are the same. I’ve used both and they seem to work fine. I’d use a 3 stage tightening sequence to 55ftlbs. They are significantly cheaper than ARP bolts. Once the ARP bolts came out the boosters started dissing Metric Blues, but I don’t know if that had any basis in fact. Contact MM for their bolts. The Metric Blues can be found here: http://www.mcmaster.com/#91303a306/=b9b5k3
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Headstuds. This is probably the primo solution because studs take the cast iron threads out of the equation. I don’t recall the cost, but I think it’s a little less than ARP headbolts. A little searching around will find them, or call RaceWare. I’ve not done this either.