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Greekcj5 01-22-2013 12:52 AM

Rebuilt AMC 304 crank won't turn manually
Hey ladies and gents. Here's the jist. I have a 72 AMC 304 that I just had honed, had the crank turned to .020 and installing new main and rod bearings. I got the .020 bearings and installed them with a ton of assembly lube. The problem is when I torque the 1,2,3,4 rod end caps and try to turn the crank to torque 5,6,7,8 it won't budge:brickwall. If I loosen 3 of 4 caps it turns easily. I'm positive the pistons are in the right cylinders and facing the right way. Is this normal or should I be worried about something else? Thanks

roboto65 01-22-2013 06:34 AM

Need to get some plastigauge and check your clearances just because the bearing says one thing does not mean it is so it is best to check before assembly. I bet one of the bearings is binding down and that in turn locks the crank down it happens. When I do engines I always check the clearances not knocking the machine shop but we are human.

Matt1981CJ7 01-22-2013 06:40 AM

Have you checked the connecting rod side-to-side endplay?

Did you check the bearing tolerances with plasti-gauge?


timgr 01-22-2013 06:49 AM

Yes, measure everything you can - don't assume that the shop did everything right.

Did you assemble the crank in the block without the rods? That assembly should turn freely, and you can Plastigage the mains. Then assemble the pistons and rods one by one and Plastigage.

Matt1981CJ7 01-22-2013 06:57 AM

When properly installed, the entire assembly should turn smoothly with moderate effort using a 3/4" wrench, or socket on the crank's end bolt.


Greekcj5 01-22-2013 07:37 AM

I didn't measure end gaps because I'm reinstalling the same crank and rods. I'll get some plasti-gage and measure them. Is it possible the crank is just a bit bigger than the rod guides and it just needs to be worn in?

Matt1981CJ7 01-22-2013 07:49 AM

Not likely. If it's binding at all, there is a problem, and it will likely cause fire-up problems, or worse. I learned that lesson the hard way....

My heads had residual glass bead dust in them, that wasn't cleaned out properly before reassembly. This caused to much friction between the pistons and the cylinder walls. Although my crank assembly would turn manually, it took a considerable amount of force to do it. My first fire-up attempt, at the dyno shop, was a complete bust due to this condition. The engine wouldn't spin fast enough to fire. It cost me another $800 to have the dyno shop diagnose and correct the problem.

Hope this helps,


Greekcj5 01-22-2013 08:13 AM

Ok so plasti-gauge the rod ends for side to side gaps. Should i worry about the crank end gap? I already rtv'd and installed the timing cover and water pump.

CSP 01-22-2013 08:17 AM

Plasti-gauge isn't for side to side gaps. It's for the clearance between the bearing and the journals, both main and piston.

And yes, you should worry about the end play of the crank.

This makes me wonder what else you've missed in the assembly.

Greekcj5 01-22-2013 08:17 AM


Originally Posted by timgr (Post 14831530)
Did you assemble the crank in the block without the rods?

Yes. I got as much done on the engine as i could while i was waiting for the new piston rings.

Greekcj5 01-22-2013 08:23 AM

The only reason i didn't check end play out rod end gap is cause that's the word i got from the machinist who honed the block and turned the crank. It's my first rebuild and everything else has been done according to specs. Ring gap, timing, timing chain play allowance etc. i just started with the pistons last night so plasti-gauging the rod ends can still be done. What if the gaps are too small?

Matt1981CJ7 01-22-2013 08:26 AM

1 Attachment(s)
As CSP stated, you use plasti-gauge to check bearing clearances. A feeler gauge is used to check endplay.

Please tell me you are using a manual, of some sort, to do this overhaul.


82JeepCJ7 01-22-2013 08:27 AM

Just a thought.... bearing caps mixed up, installed backwards?

Greekcj5 01-22-2013 08:48 AM


Originally Posted by Matt1981CJ7 (Post 14832025)

Please tell me you are using a manual, of some sort, to do this overhaul.


Yeah. I'm using a Chilton manual. I'm mechanically inclined but mostly on helicopters.. I do all our auto maintenance, I've just never been this deep. Its fun so far, i just wanna do it right. Thank u all so far.

Greekcj5 01-22-2013 08:55 AM


Originally Posted by 82JeepCJ7 (Post 14832028)
Just a thought.... bearing caps mixed up, installed backwards?

I wish it was as simple as that. I double and triple checked them all.

The time now is 06:04 PM.

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