Bell-housing alignment help

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Did some math....If your dial indicator is 20 degrees off from perpendicular, a true 10 thousands off will show 10.64 thousands on the dial. So if you can't get it perpendicular, you can use a little math to get the true number.
 
OK. So I clipped the mag mount to the block and dialed the face and the edge of the crank. Fine.

Then, I clipped the mag mount to the crank, and I dialed the face of the block, where the bell mounts.
Block%20Dial%20Indication.jpg


At 3:00 on the block, I zero it.
By 2:00, I'm at -18 thou.
At 12:00, I'm at -24 thou
At 11:30 I'm at -27 thou.
At 10:00 I'm at -14 thou.
At 9:00 I'm back to -5 thou.

I did the same thing with the block plate mounted, thinking surface irregularity or anything like that. (I do have a little-- about 4 thou of bounce as it goes over ridges in the paint) With the block plate mounted and dialing the plated but unpainted surface of the plate, I get identical results.

I turned the crank by 90 degrees and re-dialed it, thinking anything with the flange being bent or anything. Exact same results. That tells me the problem isn't in the crank.

The entire flange that the bell mounts to is not in the same plane as the face of the crank!

If the block is machined 24 thou shy at the top of the block, then that cocks the entire bell forward... and the lever arm to the ring where the tranny mounts is more or less the same as the lever arm from the crank out to the flange -- So, no surprise, the ring is cocked upwards and forward by about the same -- about 25 thou. Giving me 52 thou of total runout.

My freaking block is machined out of square.

Even if I abused the crap out of the bell to get it dialed in "right", it would still be tipped forward, and there would still be an angular misalign between the line of the crank output and the line of the tranny input, which I can't imagine does anything good.

I think it's time to get a new block. :(
 
Been down this road, paint on the mounting surface of the block will mess up your readings.
 
But.... but.... but..... Mammoth Motors TOLD you they factory would never have done that..... LOL. Golly, that is something. Good work to find this out.

It is a fair assumption to say that the trannie mount flange is parallel to the front flange of the bell housing. It probably IS parallel when the bell housing is torqued in place. But with this being so far off, I think it would be wise to torque the bell in place, and run the indicator around the trannie mount surface to be 100% sure. It is a smaller surface, so the amount of deviation from a flat plane will be considerably smaller than the block surface.

If you don't have the heads on but do have the pistons in, or ready to go in, then I'd first take the same piston/rod and mount it in holes 1, 7, 2, and then 8. Look at the piston-to-deck height relative to the location and see if there is a pattern of the deck piston-to-deck heights. I just wonder if the mains bore is off. Of course, it would have to be waay, waaaay, waaaaaay off for the back plane of the block to be that far off though, so it is not likely.

And there is another possibility.... that the side flanges of the back of the block have been tweaked backwards. But I'd think that the deviation would mostly be gone by the time you reached the areas of the block where the water jacket joins the rear flange, and that is not quite the case with your measurements.

If the bore is basically straight relative to the decks, then I would look at the shims like suggested. And I would consider putting the block to bell braces in place on this one.
 
if the block deck is parallel with the crank c/l, when you swap piston and rods to 4 corners, I am wondering what kind of trouble could you get in if you milled rear face perpendicular to crank c/l?
 
I would think you could stand a .025-.030" cut in the back without pushing the trannie snout or TC snout too far into the crank. All doable.... but finding a machinist who can set it up right will be the trick; I don't imagine that is a typical setup for engine work.
 
nm9stheham said:
I would think you could stand a .025-.030" cut in the back without pushing the trannie snout or TC snout too far into the crank. All doable.... but finding a machinist who can set it up right will be the trick; I don't imagine that is a typical setup for engine work.
Click to expand...
if you have a lot of money in the block, it might be worth investigating. There are probably some garage machinists out there who would do it for $100, maybe $150.
 
When you indicated the face of the block, did you take into account the end float of crank? Every time you rotate for a reading, you need to float crank to same end stop. There is about .004" clearance so it will affect some.
 
3406pk said:
When you indicated the face of the block, did you take into account the end float of crank? Every time you rotate for a reading, you need to float crank to same end stop. There is about .004" clearance so it will affect some.
Click to expand...
good point. there is crank end play, it may or may not have affected your numbers
 
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