whilst oversizing the drain back holes in the heads I have struck the adjacent head bolt hole . Is this a problem ?? Personally, I would have thought not as there nowhere the oil can go . I don`t know if it is the front or rear head bolt hole `cos , excuse the ignorance , the heads look kinda 'ambidextrous'.to me and I don`t know the difference !!!Trust the engine builder knows
The holes were enlarged from 9.5 mm -close to 3/8"- to 11mm -close to 7/16 "
I have cleaned around the breakout , do I have to get a sleeve inserted or is all ok ??
Thanks
mike

 

Not sure what you mean by front or rear head bolt hole. The heads are the same from side to side. Breaking through is a bad thing, since it will affect how the head bolts clamp.

 

well I drilled out the 2nd head but only to 10mm and guess what --into the head bolt hole --only 1/2 a mm extra. So 3 out of 4 drainback holes went through to the head bolt hole .
(Info just for those who may be concerned about this possibility --in fact ,it appears , probability ----B heads.)

 

I have heard of others drilling the drain holes into the head bolt holes without an issue. The oil can't go "anywhere" and the head bolt boss should not rely much on that little piece of wall. I'd debur and run them. I have never personally done this modification, however.