MTFCA Forum

Getting ready to set up a block to Babbit and bore and ran into a problem.
I placed my boring bar frame on the block pan rails and noticed a rocking of the boring
bar frame.
Took a feeler gauge and checked the clearance to be about .030 with cam side clamped down with
the frame resting on the opposite side of the block at the front.
The .030 gap was measured at the opposite side flywheel end.
I checked my homemade boring bar frame on a surface plate and came up with .002 to .0015 rock.
I looked at the block pan surface and can see variation in the surface from milling at the flywheel
end.
Henry apparently did not make any scrap.
I have the capability of cleaning up this surface on the mill.
Should I clean up this surface or go ahead and place the boring bar frame on the block and shim up the frame
accordingly and proceed ?

Thank you

Johnr

I had come across a block once that had been, machined/ground, on the pan surface, the problem it presented in assembly was that the ball cap no longer was in alignment, had to use 2 pan gaskets.

If you machine the base, your crank will end up too close to your cam for that critical gear mesh dimension. And you have created a hybrid bastard with more problems to come.
A good boring bar fixture picks up the cam bore front & back to ensure this critical dimension.
If you can clean the block base, maintain the cam/crank location & make a correct thickness gasket shim, it could work.
If its not a scarce(early) block, I would lean toward replacing it.

Any amount taken off the pan rail, you might have to compensate for when setting up the boaring bar in order to keep the center to center for the cam to crankshaft by adding shims to bring it back up.

I'm wondering if there wasn't some localized damage somewhere on the pan rail that's causing the rock, rather than a gradually "twisted" surface. Have you run a file across the pan rail, trying to highlight any raised areas?

Do you know the history of the block?
Was it involved in a fire? That will cause a twist. Just a possible answer to your problem.