1098cc maximum overbore?

[jcrcleeman]

I've aquired a 10ma 1098cc engine and when I stripped it down I noticed the pistons were 30 thou oversized which I can't understand as the Haynes manual says only 20 max is possible ?
Is there a reasonable explanation for this size overbore and is it reliable?

[philthehill]

In some ways you have already answered your question in that the engine has already been bored to plus 0.030".
Pistons are available for a plus 0.060" re-bore
https://www.morrisminorspares.com/engin ... -4-p830161

Is a 0.060" re-bore reliable? If the re-bore is done properly it is no less reliable than an engine with a standard bore.
I would ignore what you have read and if necessary re-bore the block in question.

[jcrcleeman]

Thanks again Phil.
Should I supply the pistons myself or is there an advantage in the engineering firm supplying them?
(£140 from ESM etc.)

[philthehill]

So long as the bores are sized to the pistons it will not matter if you or the engineering firm supply them. Check that the pistons are of a good quality.