Align Boring the Crankcase, Help educate this amateur... Options

[stephenaki]

OK, I understand the reason WHY you align bore the case, got it. My question with the 914 case is bearing selection after it is done.

Now, rebuilding my MG engine and selecting bearings was easy, measure the journals and choose the size needed. The 914 case however has a set on the journal and a set on the case.

If I have to align bore the case is there a special consideration on bearing selection or do I just measure journals and get a bearing set that accounts for the difference based on balancing of the crank.

May be an obvious question to some but I am confused and want to make sure I rebuild the engine correctly and order the right parts.

[Jake Raby]

It is IMPERATIVE that if the case is to be align bored that you have the main bearings BEFORE the boring process is done..

This is because the oversize bearings as well as the stock bearings no longer have the stock dimensions that work with the stock main bore dimensions dictated in the Bentley manual.

There are few people that align bore TIV cases correctly, most simply apply the same tunnel dimensions as stock and thats incorrect for today's bearings that can vary as much as .002 from stock.

Oversize OD bearings are available .020 on the OD and as much as .030 undersize on the crank. I do have a very limited supply of 1mm+ thrust cut bearings, but they are pure gold.