Re: [Amc-list] Frankenstein 390 problem

[Dan Curtis <d.curtis@xxxxxxx>]

>From a cost and streetability perspective,  I would suggest finding a used 360 instaead of rebuilding the 390.  Between the bad crank shaft and the incorrecgt harmonic balancer and flywheel, you are looking at a signficant cost for just the correct parts let alone the machine work to correct the damage from the 360 parts on the 390 motor.  More importantly, the 304 heads will continue to strangle the 390 so overall you have a mismatched hodgepodge of AMC parts that someone patchworked together which seriously suboptimizes that 390.  

With regards to head compatibility, you can interchange most any year heads with an early motor with a set of 4 head bolt dowels for the 7/16 studs to properly align later model heads on the early motors.  All 360 and 390/401 motors from 1970 forward use 1/2 head bolts (which I suspect is also the case for the smaller V-8 as well although I have no first hand experience with the smaller motors to say for sure), thus the need for the dowels on the early motor 7/16 head bolts.  

In one of my post earlier this week, I offered a very good, lightly used 360 shortblock with new bearings, freezeplugs, cam and lifters with the factory harmonic balancer. You could use your flywheel and clutch along with your intake and timing cover and be ready to go.  Either way, I strongly suggest that you change the heads to the big valve 360/390-401 large valve heads, preferably the later model heads if you rebuild the 390 or the 291C dogleg heads if you use something like my '75 360 to achieve a nice streetable compression ratio on either type of motor.

Feel free to contact me if you would like to discuss further. I would be interested in a trade of my lightly used 360 shortblock for the damaged 390.

Regards, 
Dan Curtis


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