I’m looking to figure out what size the oil drain plug in the case is. e.g. M12 x 1.25

The PO helicoiled the case for the drain plug on my engine. I don’t know if the bolt in there is the original bolt that the helicoil was sized for or if they just put a helicoil in what was left of the original threads and put a smaller bolt in. As it is right now, the helicoil was done pretty poorly so something has to change.

I saw another thread discussing options for timeserts, helicoils, or pipe plugs too, so just want to figure out what nominal should be and go from there. Thankfully the engine is apart so all options are on the table.

My recollection is that the original threads were 14 x 1.5 but I don't know that for sure.

I had a bus case with the same issue and I recut the thread for a 911/944 drain plug and liked how it worked out. The 911/944 drain plug is something like 18mm diameter. I had the engine apart at the time some chips and shavings were not a problem.

Jim

Thanks Jim -
I think the original is actually an M12, but I’m not entirely sure. I may go with the 944 plug after all. I’ll see what my machinist has to say first.

12 x 1.25

Without pics or seeing the plug that was in your engine, my guess is it got stripped and whoever did the repair used (or tried to use) whatever they could easily source, which isn't stock.

Putting a helicoil in the stock threads would result in a much smaller plug.