Technical Crank end play issue

New bearings after polishing SBC 350 crank. Using Clevite .001 undersized mains.
Have proper clearance just under .003. Torque the caps down 15/20 ft/lbs crank rotates fine just pushing it over on the throws.
Measure end play. Almost nil.
Wet/dry with MM oil on the thrust, take .003 off the front of the bearings.
Back in, tq to 20 ft/lbs and get no end play. Back all the caps off, have .005. Snug all caps but the thrust cap and still have .005.
Snug the thrust down 20 ft/lbs and near zero again.
My thought is maybe the thrust bearings were/are made a bit too “proud” ? And doing a mild distortion on them when tightening down.
Your thoughts and advice appreciated.
Thanks

 

what happens when you torque the caps all the way? I would not expect the bearing bores to be round until the bolts are properly torqued.

 

I haven’t tried that, but easy enough to do and will report back in a few.
Thanks, makes sense too.

 

Well, crank actually rotates without effort at all now, but still no end play.
I hate to mess with the crush of the bearing, thoughts on taking more off the thrust? (Crank/cap side)
I mean I can push the crank over with a finger with little effort.

 

One thing to note. I haven’t bolted the oil pump on yet. Could that be working against me?

 

In case you aren't familiar with the procedure, here's a good article explaining how to "seat" the thrust bearing and properly check crankshaft end-play.

https://www.enginelabs.com/engine-t...hrust-bearing-and-setting-crankshaft-endplay/

 

You’re supposed to whack the crank front and back to help seat the flange against the bulkhead .
Sometimes the flanges can be slightly bowed out when new .
A rubber hammer usually will seat it just fine .

Tommy

 

Ahhh, I missed a step I think. But wonder what would keep the bearing shells in place if that procedure was followed I put in 1 and 5 tap and measure, then pull the crack and put in 2 3 and 4? My feeble thought is all caps and bearing in place, tap the crank back, measure, if good torque down.
Thing is my way seems to produce almost no end play. Lol

 

I’d heard that about BBC’s but never a SBC. Worth a try!

 

You should do it on any engine with a thrust bearing.

 

Yes I some cases you can have for and aft movement of the cap. I always see the cap and just snug the bolts and lightly pry the crank to the rear and then to the front as to have both the flanges flat as possible being the major of the thrust load is in that direction. Then torque the bolts fully. The oil pump should not change the any of the dimension.

 

Well, gave it some good whacks with the caps at 15/20 ft-lbs, still no love.
Must now sit and think a bit.
I used a set of calipers to align the bearing shells as I clamped them together before some sanding.
Since I have good end play without the bottom cap snugged down, I’m thinking my alignment was not perfect.
So going to look at the bottom bearing and take a bit off and recheck things. Worst case I buy another set of mains.

Funny is this isn’t the first SBC I’ve screwed together and haven’t come across this before. But in the past I’d have the shop who did the machine work supply the parts to put things together. Maybe I didn’t cut that fat hog in the *** and using my parts after Machine shop is the issue.
Thanks all!

 

I built 2 SBCs recently. One came into the right endplay without messing with anything besides the whack it back and forth. The other I had to dress the thrust down quite a bit to get correct endplay.

 

I’m at that point I think. I did both at the same time, but going to try the bottom thrust now.
Lord give me a steady hand!

 

Okay. Seems it was my issue when sanding down the bearings at the same time. Just took .003 off the bottom bearing and now have .003 end play.
So when I get to .005 I think I’ll crank the mains down and grab a beer…or three