Posted by John R. 2nd Question. Since you recommend checking the old 84mm crank and line boring the crank bores to do it right, why not go one step further, okay 2 steps, and buy and install a 86mm crank and new stroker rods? Maybe the new 96mm bore pistons can be mfg to dimensionally accommodate the old rod length by having the distance above the piston wrist pin be 2mm more rather than just new stroker rods. Aaahh...wishful thinking? I am sorry Zane, but I may be just repeating myself... But it seems that the extra cost for the bigger bore 96mm pistons is very small. But it would be another increment up in cost for the later 3420cc/86mm (used) crank and another increment up in cost if I have to get new longer stroker rods. So in summary, the bigger 96mm bore is a small cost but 86mm crank and rods is a bigger jump in price. Key question - Is that extra stroker pricing worth having a 3.8-3.9 liter motor? By the way, the car itself is nice enough,interior/exterior/accessories/etc to have won 1st place Show&Shine at Pacific SharkFest in 2003. So perhaps it deserves/worth the investment. Thanks again for your expertise/experience, john, Farmington, UT
on 1/13/2004, 11:38 am, in reply to "Re: Euro M90 rebuild - Power boost"
63.228.201.220
I appreciate your response. I think the big expense on the rebuild would be the head work and I have that covered with the new MM head. So, I also figure I will probably have to bore and install new pistons (I have read that the M90 3453cc motor had "suffered a service problem with the 93.4mm bore" per BMW Six Series book by Jeremy Walton). I think it would be overly optimistic (read "dumb") that I could use the old pistons, hone and just install new rings. So the 1st question is..if new pistons are needed, why not go to the maximum bore possible (96mm) rather than just the next avaiable/workable piston oversize - not much difference in Piston cost.
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