atb

The manual provides for crank end play from 0.110mm - 0.312mm (.0043"-.0123")



Based upon my measurement wackiness with this motor to date, I'm measuring each tolerance two different ways from here on out. With both the dial gauge at the snout of the crank, and with feeler gauges at the Thrust bearing, I'm getting about .0039" clearance. This is tighter than the factory minimum.

Old school says the tape the bearings together in the same orientation as they sit in the crank case, fab a holder to keep the one side of the thrust surfaces flat (on the same plane), oil up some emery on a sheet of glass and have at it with the exposed thrust surfaces.

Is this an accetable method to spec in the thrust bearing, or is it totally nuts?

We're talking less than half a thousandth here.

IcemanG17

Adam
When Bill & I mearsure sharky....we use a large screwdrvier to pry the flywheel to its max-min positions...once its at min (forward) we setup the dial indicator and pull it back to get a #......okay I can't find the write up I did.......odd

SharkSkin

Adam, aren't the bearings plated copper? If so I'd be reluctant to take anything off the bearing. My inclination would be to just put it together as-is since you're only talking about a 10% reduction in clearance, but I would want to get some input from an expert like Greg Brown before going ahead.

dr bob

Adam-- Freshly-ground crankshaft? Sometimes lack of endplay is a sign that the shoulders on the crank journal are not radiused correctly.

Sometimes the split bearings are not perfectly matched, causing the endplay to be reduced. The Good News is that your normal engine assembly starts with fitting the crank into the bottom, installing the girdle loose, and verifying that all clearances are good and there are no rubs as you torque the girdle. You should be able to loosen the girdle, tap the crank end lightly to make sure the bearings are squared and true to each other and the crank while in the girdle, then slowly/gradually/progresssively add tension to the bolts.

I'm not sure I'd get excited about half a thou', since that can be attributed easily to measurement error. Might not get 'excited', but I would for sure be 'interested'.

For grins, you may want to plastigage the thrust mains on the normal surfaces to make sure the bearing shells are in fact fully seated in the saddles. A tiny bit of crud behind a shell will show up as a low bearing clearance on one side. I've also used a little blueing to identify places where you have metal contacting metal. If that's not even and cosistent contact all across the thrust face of the bearing, it's time to figure out why.

docmirror

Bob has the same words I do. If the crank was ground, the grinder didn't fit the radius of the thrust journal right. Happily, this will scuff off soon after startup by heating the bearing to the point where the material will be removed. It would be best to remove material from the journal corner. Less good is to remove material from the corner edge of the thrust bearing. Worse case is to leave it as is, and let the running engine grind that area down on start-up.

If you're at the point of having the girdle tight, but no rods. I'd fix it. If the rods/pistons are all in, I'd prolly leave it.

dr bob

Should be checking assembly plays and clearances before any rods are fitted. One of the joys of performance engine assembly is fitting each attached part, verifying clearances where you can measure them, then 'testing' the breakaway torque required at each step to verify you don't have something hidden causing unexpected binding or friction.

I got an interesting call from a friend a few decades back. The SB Chevy he was 'blueprinting' was locked up on the stand. What did you last attach to the crank? "Everything" Disassemble and re-attach "everything" in sequence to find the problem. At least it was still on the stand.

docmirror

Yes, that's the way I did it. Since I was using a used crank, my endplay was fine. I rolled the crank around after each rod set was inserted.

GregBBRD

With new bearings and a standard crank, the endplay is almost always .15mm-.16mm, when we assemble a stone stock engine. If anything was machined...block or crank...you will need to check things, as dr bob suggests. Make sure that the dowel that locates the cradle onto the block (it's on the rear main bearing on the non oil pump side) is present and not damaged. This dowel locates things pretty securely, in terms of fore and aft movement, between the two pieces.

Really need more information about the history of the crank and block, to help much more than this. Is this an early engine or late? Are you using the proper thrust bearing for the engine (there are wide and narrow flanged bearings)? One of the infamous California engine builders loved using the narrow flange bearings (944) on the wide flange crank, so that he could save money on the main bearings. Crooked bastard!

blown 87

Instead of scattered on the pavement.

Lizard928

this is for a stroker engine.

I am pretty sure its a Scat 6CW unit. but Adam will hopefully correct if wrong.

I would not touch the thrust surfaces with anything.

atb

Thanks for the input everyone.
The crank is a 6cwt Scat stroker like Colin mentioned.
The main bearing set was bought for an S4, but the block is an '85.
Greg may have the answer with the shuttle pin around rear main stud. I don't have that fully seated yet, since all of the studs and pins were removed for nikasiling, and I haven't permanently loaded in the main studs yet.
I have the spec now for the stud height, so I can loctite them in and fully seat the shuttle pin, and then take another measurement to see where I'm at.
Interesting point: Not all the main studs are the same length. The one in the rear with the shuttle pin around it is longer than the rest.
Thanks again everyone.

docmirror

I'm sorry but I disagree. The shuttle pin is not going to change the thrust end play if the crank is machined right. You should have all crank journals tightened before checking end play. If the last journal is out, your measurement is invalid.

The issue is going to be the radius of the thrust plate area. You'll see.

Lizard928

has anyone else who has a scat 6 cwt crank had to have this area modified to obtain correct clearence?

SharkSkin

Why not? It makes perfect sense. If the girdle is shifted along the crank axis, half of the thrust bearing moves with it. So your thrust bearing clearance is whatever it is, less the amount the girdle is shifted.

docmirror

Ok.