.004" Thrust Clearance... Run it or tear it back down?

[loudandproud]

As the title says. This is only my 4th SBC shortblock, all the other motors were just top end builds.

I set the thrust bearing with all of the caps torqued down to spec, minus the rear cap. Pryed it back, pryed it forward.

When the crank is pressed back and then forward, the dial indicator settles on .004". If i pry alittle bit (just a tug) the crank will reach .006".

Did I set the thrust wrong? Crank turns silky smooth with no tight spots. Whats with the .002" give?... should be solid shouldnt it?

[TMSJoe]

So you are saying you have .006 of movement? Sounds good to me. Most SBC blocks have a pin pressed in the block that locates the rear cap. Other then sanding the flange to make it thinner, you can't adjust the thrust. I wouldn't worry if it were me.

[raynorshine]

sounds good to me as well..

spec is .006 to .010" i'm guessing...

any other issues?

[Strange Magic]

To properly set the thrust:

You should torque all caps in place with the exception of the 5th cap in your case. Then just seat the 5th cap. Draw that 5th cap down to seat it and moderately snug teh fasteners, then back off the fasteners until loose. Then slightly re snug the fasteners down. I don't know how to emphasis slightly, but maybe with about 5-7 pds, similiar to the slight snug you would put on a valve cover bolt or nut and thats it. Then with a heavy rubber mallet or dead blow, take a swing at the back of the crank like your hitting a grand slam out of the park, then another very hard shot on the snout. This process will center that thrust. If that engine stand doesn't move after that swing, then you didn't hit it hard enough. After that process torque to 25 and check that thrust end play. Then torque to the desired spec.

Why torque light and then torque to spec? This process will show you if something is wrong if you have two different results with slight torque vs. the final torque. The 25 ft pds should yield the same as the final torque for end play.

I am explaining what I do, although I am sure you will get other opinions as well.

P.S. I shoot for .007-.009 and have ran up as much as .014 with no issues at all.

[TMSJoe]

sounds good to me as well..

spec is .006 to .010" i'm guessing...

any other issues?

My old boss had the 5 5 and 5 rule. .005 thrust, .005 back lash on timing gears, and I don't remember the other 5

[PWMAX]

Run it, its fine. Whats happening with the .002 change when you use some leverage, is just that, by hand, the oil or assembly lube that seeps in that area, can decieve the reading a bit. When you use a some leverage, with a big screw driver or pry it with some sort of prying tool, it will show the actual clearance. Run it, your good

Frank

[Barry_R]

Sometimes a north and south smack with a dead blow hammer on the ends of the crank will square the flanges of the bearing up and give clearer readings. Thrust is one of those things where a little tight can be good - think "slide hammer"...

[Strange Magic]

You can have two senerios and yet have the same clerance whereas one senerio might run the risk of thrust failure where the other does not.

Lets take two engines both with .004 for example. If the thrust is seated correctly in engine A and seated correctly means those two bearing shell parting lines meet together perfectly, then both halfs of the bearing the bearing thrust surface will see equal amounts of residual oil. If in the case where engine B still nets the same .004 yet leaves one upper shell, or lower for that matter, hanging over (mis-aligned) than one bearing side, per side, will actually be used as a scraper and remove that oil film clear off and you run the risk of damage from mis-alignment even though you have your so called desired thrust clearance.

[Transman]

Short answer: run it.

[Belgian1979]

You can have two senerios and yet have the same clerance whereas one senerio might run the risk of thrust failure where the other does not.

Lets take two engines both with .004 for example. If the thrust is seated correctly in engine A and seated correctly means those two bearing shell parting lines meet together perfectly, then both halfs of the bearing the bearing thrust surface will see equal amounts of residual oil. If in the case where engine B still nets the same .004 yet leaves one upper shell, or lower for that matter, hanging over (mis-aligned) than one bearing side, per side, will actually be used as a scraper and remove that oil film clear off and you run the risk of damage from mis-alignment even though you have your so called desired thrust clearance.

Hitting the back side of the crank while on the stand ?

You hit the crank to seat the bearings. I don't see how those shells could move ?

[robert1]

1. Remove the rear cap.

2. Check the end play with no cap. You'll then know if the upper bearing is corect.

3. Set the lower bearing back on the crank, no cap, measure the gap between bearing and flange with a feeler gage. You'll then know what the lower clearance is.

4. If you have correct clearance with the upper then you know you only need to work on the cap bearing. If you do not have enough with the upper lap the front side until you get the right amount.

5. If everything checks out say you have enough with the upper and you can get a feeler gage in then there is an alignment problem. You could remove the dowel pin if it's keeping the cap from locating correctly. If the cap has been cut and the face is not square to the bore then lap accordingly. Again I would lap only on the front side if possible. You can verify this by installing the rear cap and measuring with your feeler gage. If after checking all of the above and you can not get the feeler gage in one side or the other then there is your trouble spot. lap that part.

6. I did see an aftermarket block once that had no chamfer on the front side, there should be a large chamfer on the front and back of the bearing bore. The bearing was hitting this area. The guy building it couldn't figure out why it had no thrust.

[prostreetL-78]

I agree with Strange magic. Whack the crank and you will probably see a solid .006" or more. The bearing shells are probably not aligned and will act as a wiper. I would follow his instructions.

[DaveMcLain]

I've seen a flanged thrust bearing get spread out a little during shipping and or installation and this can give a springy feel to the thrust by a few thou even if they halves of the bearing are aligned correctly. Generally it doesn't hurt anything.

[Belgian1979]

Good info. thx

[loudandproud]

Wow guys thanks for all the input. Im gonna go out and use a good whack and see if the .002" comes out of. If it does... great... if it doesnt... I wont lose sleep.