Frank,

I have had a similar problems with getting the mains done.

With the mains now properly torqued, ask the shop to shoot for the minimum number on the spec (not so easy to do).

To make the bore clean up all the way around it ends up to big since you canÆt bring the edges in. If you hit the max number the bore ends up round and pretty with the sides cleaned up but you can have too much clearance when assembled.

The only thing that works is a mild egg shape. It's only at the far edges. The bearings have this same taper to avoid pinching as the housing flexes.

Basically on a line hone / line bore the sides of the bearing bores are going to be large no matter what to get to the housing right verticly. ThatÆs OK since the loading horizontally is minimal.

In my experience if they hone the bore to the max number thatÆs in spec you can still end up with too much clearance on the mains. Granted the spec only allows for about .0005" of tolerance but in my experience that adds directly to your bearing clearance.

If you have a crank that's been polished itÆs likely that itÆs a couple of tenths under where it started. Combine that with max sized housing bores and you have a tolerance stackup that gets your mains out of spec or to the high side.

Getting the block done again should help; again ask if they can go to the low side of the spec. There is not a lot to work with. All you care about is the up and down dimensions.

I know on some motors they have select fit bearings available, does yours? On engines that donÆt have select fit bearings I have fine tuned the clearance by sending the crank out for ion nitriding. It takes about a two weeks to turn the part around costs about $120 and the crank should be lightly polished when you get it back.


It also adds about .00015ö -.0003ö per surface. Since there are two sides to a journal that drops the clearance by .0003ö-.0006ö and gets you a super tough bearing surface. I donÆt know if your crank is hardened or not or if you have select fit bearings available. I also have used coated bearings with good results. Get the clearances right without the coatings. The coatings thin out and burnish in on the vertical surfaces (they end up super polished and shiny) but stay close to full thickness on the sides.

Kevin