I just finished installing the plog from zzp. Took er for a spin and.. Well, smooooother for sure! I don't expect massive gains but I am happy my engine will breath better now!

One of the studs came out with the nuts. It is warped and bent and looks a bit cross threaded (which is odd because nothing has been done to the motor since I got it new. Factory cross threading?)

Do we know the size of stud I need to get? M8 doesn't seem to fit right and I think the others are metric. Any advice here would be great.

3800 Series II in a 2001 Monte Carlo SS.

 

Ok, after many hours on the phone, the answer came with some prying at the dealership.

It turns out the hole in the block (head?) is a 5/16"-18 hole. The 5/16th end of the stud/nut goes into there. The other end of the stud (the side that faces out) is an M8-1.25mm.

VERY odd how they have imperial on one side and metric on the other.

I ran a 5/16th tap into the hole to straighten out the edge of the cross thread and it took it very well. I replaced the messed up stud with a 5/16 stainless bolt, washer & lock. Done!

 

SAE to Metric studs are actually more common then you may think. That's why a set of pitch gauges became a part of my tool arsenal a long time ago. Glad to hear you got it figured out.