Guys, ref 360, thrust bearing cap to block alignment. I have ARP mains studs, without bearings fitted I noticed the surfaces front and rear of the #3 bearing cap to block have a slight miss alignment/step front to back, installed the bearing and others in the block and dropped the crank in without caps, measured crank end float at 0.018”, then installed the #3 cap with thrust bearing, re measured crank end float is now 0.001”.. Block has been align bored and prepped however should the #3 main cap have such an offset? I would have thought the front and rear surfaces should have had a smooth transition?
Thrust bearing cap offset
- Thread starter crash520
- Start date
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yellow rose
Overnight Sensation
They should.
Sometimes, depending on core shift and other things (like how accurately the bolt holes are drilled and if they are drilled perpendicular) you may have to oversize the holes in the main caps or just run an end mill down the hole and offset the hole so the cap can go to where it belongs.
I know guys do it but I never install main studs without a line hone.
You need to either over size the holes or offset them. Either way but .018 off may as well be 10 miles.
Sometimes, depending on core shift and other things (like how accurately the bolt holes are drilled and if they are drilled perpendicular) you may have to oversize the holes in the main caps or just run an end mill down the hole and offset the hole so the cap can go to where it belongs.
I know guys do it but I never install main studs without a line hone.
You need to either over size the holes or offset them. Either way but .018 off may as well be 10 miles.
rustycowll69
Well-Known Member
good catch. uuuhhh, yeah, that's a problem. Did the machine shop use your ARP studs to bolt the bottom end together prior to machining? If not, maybe the difference is (IIRC) factory main cap bolts are necked down slightly between the head and threads compared to the ARP studs. Get your machining receipt, and pay another visit to your machine shop. He may have some 'splaining to do.
moper
Well-Known Member
This is why attention needs to be paid beyond threading in main studs. The studs are "fitted" to the block (which in this case means clearancing the hole(s) in the caps) and then the main bore is then corrected because the studs will deform the caps when properly fit and torqued.
nm9stheham
Well-Known Member
OP, did you move the crank back and forth front to rear with some force and with the caps lightly torqued down to make sure the thrust bearing were setting equally distanced from the fron tof the block? (At least as equally as they can be..)
Yes I have done this now and have 0.005”, more the issue is without caps installed I have 0.018”, which means all the thrust is taken by the cap rather than the block which in my mind is not ideal. More to follow
MOPAROFFICIAL
Oogliboogli
Take the cap side thrust bearing and clearance it with some 400 grit paper, re checking till you get the .0018 like the saddle side thrust bearing gives.
Fyi If you are using a stroker crank, you need a narrow main bearing set, the felpro full groove version, because the wider bearing keeps the crank from moving.
nm9stheham
Well-Known Member
Well, not really. It's likely that the block is taking the thrust in one direction and the cap is taking it in the other direction, and the cap and block surfaces are a bit offset from each other, as you noted. I can't recall the max thrust movement but IIRC it is not nearly .018". So some of the thrust movement is going to disappear with the cap in place anyway. I'll guess that the studs versus the mains bolts (with the reduced diameter bolt shanks) are reducing it by several thousandths....refer to post #2
Thanks that’s about what I have, I know with the cap correctly aligned with the block I can’t screw studs or bolts in, if I was to use bolts I d prob have to put the bolts in, almost home, tap the cap into the registers and do the bolts up then smack the crank back and forth, I’m using the narrow clevite full groove bearings
famous bob
mopar misfit
Lotta diff. between .018 and .0018 !! Almost sounds like the machine work was done w/ # 3 on backwards.
Like stated above, do u have a full fillet crank, w/ narrow bearings ?
MOPAROFFICIAL
Oogliboogli
Thanks for catching what I obvously missed.
.018 is out of spec, it'll run... but i believe it's .0015-.010
Maybe the cap was flipped, the bearing locators should be on the same side, check for that.
Marcohotrod
Well-Known Member
if the cap was right over the block the thrust would be .018" = too much. should be .005" - .010"
nm9stheham
Well-Known Member
So if the crank has a .005" thrust play with the caps aligned as well as they can be as is being reported now..... is this any longer a problem? There is nothing that actually guarantees that the cap and block side surfaces are actually going to be perfectly aligned that comes to my (tired) mind....
It may depend on how the factory set up the machining of theses side surfaces. But, even if they are factory machined while being torqued together, I can't see anything that makes sure they will stay so aligned once they are removed and re-torqued in place the 2nd time. Only something like alignment sleeves extending into the holes (like in many rod caps) can control that.
And then on top of that, is some clearance between the sides of the thrust bearing and the cap and block. Hence the 'delicate' alignment procedure of smacking the crank back and forth LOL
It may depend on how the factory set up the machining of theses side surfaces. But, even if they are factory machined while being torqued together, I can't see anything that makes sure they will stay so aligned once they are removed and re-torqued in place the 2nd time. Only something like alignment sleeves extending into the holes (like in many rod caps) can control that.
And then on top of that, is some clearance between the sides of the thrust bearing and the cap and block. Hence the 'delicate' alignment procedure of smacking the crank back and forth LOL
Well I’m starting to agree!!! I guess in my mind and in a perfect world I’d prefer for the block to take the forward thrust load of the crank and in this case it’s not. When I get a chance I’ll test for the cap with bolts just to see if it can be aligned correctly per the factory, I know it was line bored with the studs installed however one thing I noticed is that with the studs installed they do bind slightly on the cap so possibly opening up the cap holes to take side load off the studs will also help with end float somew
Marcohotrod
Well-Known Member
Is this a manual trans vehicle? then I agree that IF the cap is taking all the thrust lets do more fine tuning . is the cap offset to the front or the rear? if it is an automatic then the crank floats, unless u have ballooned the convert. and if your cap is directly aligned to the block the clearance = .018" = wide. so maybe Chrysler machined that block perfect to get the .002-.007" as in the service man. for 340
nm9stheham
Well-Known Member
Good thinking on the MT; that is a few hundred pounds force there.
I am not arguing here.... just thinking out loud. The problem is that seeing the cap and block aligned when torqued is not a 100% indication of where each thrust bearing shell's side load is being supported; it all depends on how the actual bearing shells nest up against the back sides of cap and block. It is almost as if you have to try to push the shells forward individually when torqued in place. With bearing crush, I am not sure how to do that.
moper
Well-Known Member
The position is set by the block side. The cap needs enough clearance to move and allow the halves to align then the crank is used to align them. Loosen the fit of the caps on the studs.
T56MaxTorq
Well-Known Member
Crash520, I have a very similar issue, with a 318 mag and arp studs. The top cap bearing thrust surface is tighter on one side than the other by .003 or so.
Goofy Thrust Bearing Gaps
I haven’t been able to correct it yet (time)
Also, a torque converter will thrust the crank foreward. More so if you’re putting a lot of power and pressure into it.
Goofy Thrust Bearing Gaps
I haven’t been able to correct it yet (time)
Also, a torque converter will thrust the crank foreward. More so if you’re putting a lot of power and pressure into it.
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