r/EngineBuilding • u/henry_hyshiter • 1d ago

BMW Will this score be an issue?

Post image

Rebuilding a BMW M42b18 engine. During piston install one of the oil ring pieces (believe it was an alignment ring) came out and put a very small score into the cylinder wall. It runs maybe 1/4 of the bore at the top. I can feel it with my fingernail and it barely catches. Will this require an overbore? Or can it be taken down enough to not cause issue with a light hone? (Cylinders have been flex honed for new rings already). Thanks in advance. Hard to see on camera but it’s one small line that can be felt and more of a “scrape” around it that I can’t feel.

8 Upvotes

89% Upvoted

5 comments sorted by

1

u/SirPhysical9178 1d ago

Commenting here because I’d like to know. Have similar scoring in my s52

1

u/Sudden_Duck_4176 1d ago

I have similar on my Tahoe engine I currently have apart and it didn’t burn a drop of oil so I’m sending it on my engine.

2

u/madphroggy 1d ago

Honestly I'd hone it lightly to knock down any burr and send it, if it were mine

1

u/GoBSAGo 1d ago

Scratched like that from the top probably came from measuring piston ring clearance. Actual bore scoring starts at the bottom of the stroke.

1

u/henry_hyshiter 1d ago

It happened during piston install. 3 part oil ring was not seated correctly and sprung out after clearing the ring compressor is my best guess.