Crank End Play Issue

[toojeeps]

I've been rebuilding our M38A1's F134. Just got it back from the machine shop who did some honing on the cylinders and such. Put in the new(ish) crank and shimmed it with 3 shims to begin with (as according to the manual) and had 21 thousandths of end play. All parts are accounted for. Removing all the shims I still have about 12 thousandths of play.

The crank I got was a remanufactured one from Autozone. Price was right, came with appropriate bearings and everything. Might have been a mistake, though.

My question is, can I have the crank machined down 11-12 thousandths and add a couple of shims and make this work? The book says 4-6 thousandths is spec (I think). The crank itself looks decent, it just appears to have been either cut down too much behind the front bearing, or built up too much on the end.

Also, this is Deino on dad's SN...he doesn't want me signing out because he says it won't sign back in with the dial-up here.

[53a1]

I had the same problem but mine was around .010 with no shims so I left it alone with no shims. It's hard to explain to people what is happening but I think you got the idea. Basically the shim condition assumes you have negetive clearance to start with and the shims loosen things up. If you your starting with clearance greater than .004 with no shims than your SOL.

I think the concensus was that you have to turn the face on the crank or the front bearing is not thick enough. Sounds like you have new bearings so you may not have that option.

Maybe thay are aftermarket bearings and maybe out of spec?

FYI, when I say bearing thickness I mean the frace of the front bearing that controls the thrust of the crank.

[toojeeps]

I was considering leaving it as is if I was around 8-9 thousandths, but my gut tells me I should "adjust" it given the 12 thousandths. Before the rebuild, it was around 30 thousandths, and it ran, but it made a heck of a noise. Dunno if that's what caused it, though.

I'll check the bearings, but they'd better be good...it's a good brand.

[jam51m38cdn]

53a1 is exactly right, the face of the crank has to be turned down. What happens is there is a raised ridge on the face of the first journal by the counter weight. When the cranks get turned down many machine shops also clean up the face as this is where the rear side of the front main rides. When you clean this and take metal off it makes it too long. In order for the thrust shims to work, this has to be shorter than the width of the front main bearing. Another thing that comes into play is that excessive end play will wear out the sides of your connecting rods and the sides of your cylinders and pistons. This is very critical as it controls everything

[toojeeps]

Should get the crank back from the machine shop Friday. Thanks for the help!

[Deino]

Whew, back on my own SN.

I think I got lucky with the connecting rods. All measure to spec. Apparently the engine hadn't ran much after its "rebuild" years ago. Cylinders still had cross-hatching marks. So basically I'm just fixing what someone fixed long ago.
_________________
- Dan

1952 M38 (MC56474, 33 108M HQ6)
1953 M38A1 (MD54216, 40-I-160I B-35)
1954 M170 (MD-A10513)
1964 M416 1/4 Ton Trailer (35-138F CT-12)