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Crankshaft Clearances

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JGRANTAMX View Drop Down
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    Posted: Apr/05/2021 at 8:00pm
 I have assembled my 401 short block and found some crank clearance issues I don't know if there is much I can do but ask those who know. The machine shop told me the crank as received end play was on the high limit .008", when the crank is all in except for #3 main cap the end play is .008" when #3 cap is put in and torqued the end play drops to .003". I have worked the crank forward and back making sure the thrust bearing is seated .003" is all I can get, the main caps are aftermarket 4 bolt caps so it seems there is an offset of .005". My concern is any material that might wear off during break in and the possibility of ending up with .013" end play? I don't know if I am going to run an automatic or standard trans yet I had a new flywheel and flex plate balanced for this engine. Second issue the side clearance between the connecting rods is between .018 and .022" they are new Molnar rods the TSM lists .009" - .015" will the extra clearance be an issue?


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Post Options Post Options   Thanks (0) Thanks(0)   Quote Trader Quote  Post ReplyReply Direct Link To This Post Posted: Apr/05/2021 at 8:33pm
The connecting rod side clearance I would not worry about. Loose there is fine.
I don't understand the thrust bearing information. 
#3 is the thrust bearing and clearance is measured when it is torqued down. Are you stating they measure 0.008" before they put on #3 bearing cap? And 0.003" after #3 bearing cap is installed?
If this is the case, have them mike the thrust bearings themselves as you may have a miss matched set of bearing halves. This would mean returning the bearings for another set.
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JGRANTAMX View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote JGRANTAMX Quote  Post ReplyReply Direct Link To This Post Posted: Apr/05/2021 at 9:20pm
 That's correct end play changes from .008 to .003 when #3 main/thrust bearing cap is torqued in place, I supplied the bearings I do have two more sets of that size main bearings I will measure them and check fit. I don't think the machine shop checked the crank fit in the block they measured the width of the thrust surfaces on the crank only.

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Post Options Post Options   Thanks (0) Thanks(0)   Quote Trader Quote  Post ReplyReply Direct Link To This Post Posted: Apr/06/2021 at 7:08am
Did this machine shop also install the 4 bolt caps?
The cap may have been installed wrong.
You can measure this with a dial indicator the the #3 bearing removed. Measure end play with cap off/cap on. They may have mistakenly flipped it 180 degrees.
The 4 bolt caps will be the same width as the block, this can be measured also.
I'd be finding out why the offset and then fixing the end play.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote jcisworthy Quote  Post ReplyReply Direct Link To This Post Posted: Apr/06/2021 at 7:38am
Loosen up the thrust cap. Just snug it up enough to keep it seated then gently pry the crank forward getting between a crank throw and the main webbing somewhere away from the thrust. If that adds to the clearance, torque the cap and see if it holds. 

if it does not you can sand the front face, the side that will face the front of the block when installed, of the bearing to make more clearance. 

I always register the thrust forward to allow for forces at the rear of the engine exerting forward. 
Specializing in engine building and cylinder head porting

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Post Options Post Options   Thanks (0) Thanks(0)   Quote 6PakBee Quote  Post ReplyReply Direct Link To This Post Posted: Apr/06/2021 at 9:04am
I ran into one situation similar to yours.  Measuring the distance between the flanges on the thrust bearing showed that the flanges were spread a bit and reducing the crank end play.  A little careful massaging and measuring corrected the problem.  I guess a new bearing would have worked too but when you are in the middle of assembly, you hate to quit if you can solve the problem. 
Roger Gazur
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"Shotgunning works great for pheasants, not so great for electrical problems"

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JGRANTAMX View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote JGRANTAMX Quote  Post ReplyReply Direct Link To This Post Posted: Apr/06/2021 at 11:10am
 I fit the new main caps they are in the same orientation as factory caps going by the bearing tabs the machine shop align bored it from there. Later today I will seat the thrust bearing/cap forward by leaning on the crank then tighten it down. I will try to get a feeler gauge measurement to find what half upper or lower is further back towards the rear of the block then remove material from it so that it's in same plane as the mating half keeping the rear side of the two halves in the same plane, if it needs more adjustment from there I will work the front side that is further forward. 

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Post Options Post Options   Thanks (0) Thanks(0)   Quote jcisworthy Quote  Post ReplyReply Direct Link To This Post Posted: Apr/06/2021 at 3:44pm
Set up a dial indicator on the crank shout and measure end play without the cap then with it installed and you will find out what is what. I though you already did that. 

Make sure the thrust bearing does not have a burr on the inside edges near the parting lines also. i find one or more edges always has one. Use a light file to chamfer it if you run into it and check it again. 
Specializing in engine building and cylinder head porting

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JGRANTAMX View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote JGRANTAMX Quote  Post ReplyReply Direct Link To This Post Posted: Apr/06/2021 at 7:02pm
 Yes I have a dial indicator on the crank, last night when I checked end play the first time I had 0 so I removed #3 main cap then checked and had .008". I put #3 back on hand tight and worked the crank forward and back a few times then tightened it down with some light pressure holding it forward when the cap was torqued down I had about .003. Tonight I removed #3 cap measured it all around it's good. I put the lower half thrust bearing on the crank and measured end play with it loose it moves .008", I assembled it and torqued it down and now have .004". The only micro thing I did find was one area of the #3 main bearing cap bore on one side had a minimum amount of chamfer so I increased it, no burrs, dings, or abnormal marks theses are King bearings, I will say I have Clevite rod bearings and they are crappiest looking bearings I have ever used only reason I have them is nothing else seems to be available.

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Post Options Post Options   Thanks (0) Thanks(0)   Quote Trader Quote  Post ReplyReply Direct Link To This Post Posted: Apr/06/2021 at 8:31pm
Try putting some Toolmakers blue on the flange side of the thrust bearing and rotate the crankshaft to see the contact points. Thinking you have heavy bearing crush and distorting the seam.
As JC states, the crankshaft flange side is important for load carrying and if this is the case and all else is well, scrape or use a fine file to get a good contact pattern on the thrust side.
I don't like using any kind of grit on bearings to size them as you may imbed a hard piece of grit in the softer bearing.
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