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Bell Housing Runout Question

1K views 6 replies 2 participants last post by  bandhmo2 
#1 ·
I am swapping a Ford NP435 behind my 4.0 using a T-150 bell housing. Just to be on the safe side I check the runout of the face of the bell housing and the bore. The face is very good 0.002" TIR, the bore is not so good 0.012" TIR, it needs to go straight up.

The more I look on line the more different versions of what is acceptable I find. Some say the bore needs to be with in 0.010" some say 0.005" and others 0.0025". Most of the time they do not specify if the numbers are TIR or the offset of the bore. The only thing I have noticed is that the closer the source is to someone who sells off set pins the tighter the tolerance they list. It does not help that most of the sites I find that even talk about this are high RPM car racing sites, so I do not know how much of this applies to low RPM jeeps let alone 40 year old 4 speed truck transmissions.

All the offset pins I have found are solid which will not work for me as bolts go through the pins in this setup. My gut instinct is to say the hell with it close enough, especially since I have never checked this in other bell housings and they have worked fine, but I hate to have to redo things down the road.

I know there are some on here that are into high performance engines in general and some into AMC engines in particular. Could anyone comment on how close they consider close enough and how they adjust runout on AMC engines given how the dowel pins are hollow? Also am I just being silly even worrying about this?
 
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#2 ·
According to the '78 FSM you check face runout 1/8" from the edge of the bore, and it's not to exceed 0.010" total. If it does, correct it with shims under the mounting bolts.

Bore runout is not to exceed 0.010" also. Changing the face alignment obviously also changes the bore alignment. If it's impossible to get both within the limit, replace the housing.

If you shoot me your e-mail address I'll scan the section and send it to you.
 
#3 ·
PM sent, thanks Jim.

I checked the face near the edge of the hole (about 1/8") so that one is definitely ok. However, I did not think to note, what side the high side was on. I will recheck that.
 
#5 ·
Got the pages, thanks Jim. It is nice to have some real specs to work with.

I spent about 2 hours today checking the bore and face. The face is on average dead true. It does seem to walk around about 2 thousandths but not in a consistent way, I think it is just unevenness of the surface. The bore also seems rather uneven checking up down and side to side shows one thing. Checking rotated 45 degrees shows a somewhat different thing. I found that if I taped the housing in the direction It needed to go when the bolts were snug I could bend the alignment pins a bit and then if I forced it in that direction when tightening the bolts, it would repeat to the same spot.

It is far from perfect but it is now just within spec. I am going to just call it good.
 
#7 ·
The bore is at 0.010" TIR right now, which is the spec., the face is at no real runout, though there is some random unevenness of a few thousandths.

I am just going to call it good. I really hate to start playing with shims between the bell housing and block if there is anyway out of it. I am just going to hope that this is one of those cases where; Close enough is a lot faster then perfect, and just as effective. :)
 
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