318is resto w/ built turbo M42

[econti]

I don't know shit about thread inserts really, but I imagine any reduction in grip length/thread count has huge strength implications.

Losing 3 of ~12 threads is a pretty large percentage. Yes the larger thread should bear more, but you're probably net negative on this.

Same sort of situation as the aluminum block M52/M54 guys who run the shorter engagement iron block studs or thread insert to M11 and have them rip out of the block, but kind of wild to see it happen with an iron block.

In theory the bigger stud method is for the stud strength, not the block thread strength as it is in the butter blocks. The quoted torque spec for ARP is 62ft/lb for M10, and 112 for M12. Something to do with the cross sectional area increase I would assume.

I've also done some learning on timeserts and apparently if the bottom of the insert isn't engaged with the studs it can rip it apart. It definitely was when I put it together, however the machine shop that bored it with the torque plate perhaps did not, so I'm leaning towards that being the reason why.
Anyway, the new insert turned up along with the tap and drillbit so I'll see if I can salvage it. God I hope so. I am too poor to put it all in another block.

[varg]

What a pain. Did the stud bottom out in the block and jack the threads out?

The thread engagement length from the stud to the timesert is fine, it stripped the threads in the block. Engagement looks fine there too since it's the entirety of the timesert's external thread, you couldn't get extra engagement out of it anyway. The gotcha is that guidelines for engagement length in cast iron require more length than high strength steel, but with the larger threads you should have excess strength. If you have the thread specs and engagement depth it's not hard to calculate if it's inadequate for the load you're putting on those studs but I don't see any reason why it would be a problem unless the thread quality is poor or the stud bottomed out and jacked the insert out.