Main and rod bolt replacment

[a_thomasmr23]

I'm doing an emergency rebuild and am wonder if the main and the connecting rod bolts have to be replaced? I know one of the sets is outrageously expensive and the funds are tight. If you have reused them did you engine explode? A M50 swap in the work in a 2-3 year time frame so this engine doesn't need to run forever and I don't really drive like an asshole or track the car.

[strad]

I know at least one of those is torque to yield. Might be both. I would not reuse torque to yield bolts.

[a_thomasmr23]

I though that might be the case but the bentley has no warnings about replacement like it does for head or flywheel bolts. Thats what lead to the confusion

[Hallen]

None of them are really torque to yield. However, you do use an angle torque on the rod cap bolts and that will probably stretch them some.

Reusing the rod cap bolts isn't advised. However, you can probably get away with it if you torque them properly (15ftlb then 70° if I recall correctly). If you start to hear a nasty clattering sound after running the engine for a while, well, some of those bolts have backed out. It is extremely noticeable.

The main bolts can be reused.

(torque to yield being when the bolts are stretched just to the point where they won't shorten back up when the tension is released. It is the highest level of holding power that can be applied without breaking the bolt. It is rarely actually used from what I understand, but the term is used a lot.)

[nando]

rod bolts are DEFINITELY torque to yield! replace them for sure, don't even ask questions. They are stretch bolts and are only designed to be used once, just like E30 head bolts.

main bolts can be reused. However, they are pretty cheap. Sometimes it's better to just buy new ones instead of spending hours cleaning old bolts. But it's up to you.