Budman II

iTrader: (1)

I have a question about the main bearing bores on my 489 that I am rebuilding. Engine had only 30 hours on it with previous build - had to redo the lower end due to metal from cam spalling.

I was checking bearing clearances this week using a vernier micrometer and a dial bore gauge. Clearances were checked by measuring main journals with the mic, zeroing out dial gauge on micrometer, and then measuring bearings. I got .0026, .0026, .0030, .0035, .0041 front to back.

Questioning this, I pulled the bearing shells and measured the main bearing bores with the caps torqued down to the specified 110 ft lb. I got 2.939, 2.939, 2.9394, 2.9399, which jibes with the variance in bearing clearance readings. These measurements were taken by setting the mic to the low side of the spec for the main bearing bores (2.970) and then zeroing out the mic against it.

This block was supposed to have been line honed when it was rebuilt the first time. Should I be seeing these variances with a proper line honing?

Big question is, does this need to be corrected? We are talking about a normally aspirated, 550ish HP motor that won't likely see the other side of 5500 RPM.

MER Performance

2.937/2.938 is spec. for the mains. Looking at you measurements, it tells me the hones, shoes or stones are tapered allowing the bore size to increase from front to rear. Being the crankshaft journals, measure the same diameter, I would be more concerned about the taper and main alignment of housing bores. I can assure you this, each time you torque the mains, you will come up with a sightly difference in measurements. I would be looking at the wear pattern on the old main bearings, if possible to see if the bearing was side-loading at all. If in question; I would re-cut the caps and re align-hone the mains.

Budman II

iTrader: (1)

Yeah, I guess I didn't quite get my money's worth on that $250 align hone job with the first build...

MER Performance

Wow! $250 to line hone, I charge 125-150, depending what the conditions are at the start. Obviously; that $250 was made without much effort, he could have done 2 blocks for that. That block should have been PERFECT, for that. SORRY

Budman II

iTrader: (1)

Yep, that's what the ticket said on it. Taking the block to him tomorrow or Thursday so he can mic it in my presence. Lucy, you have some 'splainin' to do!

MER Performance

Please tell us, what his explanation is; for the bore stepping in size. Either the crank is oversize and use a HX bearing, Std, or a for undersize .001, than size the main bearing bores to accommodate the bearing oil clearance you want.

Budman II

iTrader: (1)

Crank measured 2.743 across the 4 front main bearings. The rear main measured smaller, can't remember the exact number - need to check at home. I think that is generally common for the rear main to have a little more clearance for the thrust.

I would rather get the bores straightened out and within spec so I can keep my standard sized bearings. I should not have to be shelling out more cash for over / underside bearings after paying to have the thing align-honed!

blue thunder

I'd probably make a go of it with x and .001 bearings as needed to get .003-.0032. If you have it re line bored you may need an .005 under timing set or whatever appropriate. That isn't cheap either. It also changes the pushrod geometry a bit. Just food for thought...

Budman II

iTrader: (1)

Are the x bearings available for the rear main? Seems like I recall reading that these were only for the front four mains. Is the .0041 clearance on the rear main excessive?

blue thunder

I'd do 1/2 shell of x on 1,2 uppers, std on 3 u+l, .001 1/2 shell on 4 upper, and .001 rear upper and lower. Yes you can get x/.001 in all caps. End with .0031,.0031, .003, .003, .0031. You could aslo consider just a half shell of .001 in the upper of the rms if you'd like a little more clearance there. Lots of guys look for .0035 in the rms but I'd rather have say .0032 than .0037 if falling in between.