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Had just scrapped an early 998 cooper block due to off set bored a little to increase the clearance between 1 & 2, 3 & 4 cylinders, for the max +100 thou flat top pistons!
Anyone had the same experience?

Al

I think that's the oil passage to feed the cylinder head.....I believe Vizard mentions it in his books.....

Could that not be sleeved and re-cut to save the block? It looks further down than the rings would go?

JR

My 998/1098 12A479 block was overbored to +0.100" without any problems. Offsetting not necessary unless you're going bigger.

Graham Russell mentions the possibility of breaking into the oilway when using 68mm pistons and suggests it can be fixed by sleeving.

https://russellengineering.com.au/project-68mm-part-1/

bwaminispeed wrote: ↑Wed Jan 26, 2022 4:46 pm I think that's the oil passage to feed the cylinder head.....I believe Vizard mentions it in his books.....

That rings a bell with me……..Aralditing a piece of brake pipe in or something….???

Seems fairly normal on big overbites to small bore blocks. You can save it by sleeving. Its generally below the ring lands so not to much of an issue

Thanks for all your advise, had found another 998 block to over bore again without off set bore , just a lesson learnt to avoid off set at all for small bore block!


Al

When offsetting a 998, you don't go as far on the oilway end of the block - it's in the Bibles.
From memory it's 10 thou less than the distance of the other movements (.025"/.025"/.025"/.015")

I should have studied the Bible more frequently before I machine the block, never though of 998 block will cause an issue.
Finding another 998 block may be more cost effective than have the block sleeved and re bore.

Al

Looking at that pic, I'm pretty sure even at .010 less, you still would have been into that gallery....