Re: [Amc-list] 390 vs. 401 crank casting numbers ....

[Frank Swygert <farna@xxxxxxx>]

390/401 has larger main bearings, but the forged crank mains can be turned down to fit 304/360 blocks. Might be able to line bore the block for the bigger journals too. The bottom of the 304/360 cylinders have to be notched a little to clear the longer throw of the 390/401 crank. Once the crank is fitted and rods mounted rotate the assembly and note where the clearance needs to be ground. That can be done with a die grinder since it's not rotating mass (doesn't affect balance). There needs to be at minimum of 0.020" clearance between the rod bolts and the block, a little more wouldn't hurt a thing! 

The 304 and 360 use the same crank. Balance is worked out with the counterweight on the flywheel/flexplate and harmonic balancer. Gee, I'm not sure the balancers are different on the 304/390, might be the same! I think the 390/401 balancer is different from the 304/360 -- would have to look that up too. 

------------------
Date: Tue, 11 Nov 2008 14:57:27 +0000
From: Wrambler242@xxxxxxxxxxx

You're correct in everything except the stroke on the 390-401 crank being the same.
If it was Greg would not be gaining 10cu.in. by using a 401crank over the 390 crank.

Not, 100% sure the 304 and 360 cranks are 100% the same, IIRC they are balanced different from the factory for the larger 360 pistons?  

-- 
Frank Swygert
Publisher, "American Motors Cars" 
Magazine (AMC)
For all AMC enthusiasts
http://farna.home.att.net/AMC.html
(free download available!)

_______________________________________________
Amc-list mailing list
Amc-list@xxxxxxxxxxxx
http://splatter.wps.com/cgi-bin/mailman/listinfo/amc-list