6066 (1960-1966) GMC Truck Club
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6066 (1960-1966) GMC Truck Club (https://6066gmcclub.com/index.php)
-   GMC V6 and V12 Engines (https://6066gmcclub.com/forumdisplay.php?f=9)
-   -   478M Loosening Rod Bolts (https://6066gmcclub.com/showthread.php?t=49859)

Mike Caldwell January 23rd, 2017 02:52 AM
Re: 478M Loosening Rod Bolts
 
You trying to make me drool? What kind of torque would that make???

1972RedNeck January 23rd, 2017 02:58 AM
Re: 478M Loosening Rod Bolts
 
Quote:
Originally Posted by Mike Caldwell (Post 66051)
You trying to make me drool? What kind of torque would that make???
A good bit. That is the eventual plan for the 478 going into my '72 K20. It is going to take a few years savings for the machine work, pistons, and porting though.

TJ's GMC January 23rd, 2017 06:04 PM
Re: 478M Loosening Rod Bolts
 
478's were known for crankshaft problems I believe...especially the early ones. Not to mention these v6's were horribly balanced to begin with. I'm betting that engine has been over revved most of its life.

James January 24th, 2017 12:05 AM
Re: 478M Loosening Rod Bolts
 
Quote:
Originally Posted by 1972RedNeck (Post 66039)
So I have a line on the front half of a '74 GMC 8500 with a 478M, five speed, and four speed OD brownie. The engine has had multiple fresh rebuilds. Apparently, after the first rebuild, one of the rod caps came loose. They pulled the pan, put a new bearing in it, and torqued it back to spec. It came loose again, and another time.

It was torn completely down and all new rods and pistons were put in. And it shortly thereafter developed a rod knock and was parked.

What do you all think could be the problem with it? The price is right, but I don't really need something that I can't fix either...
I wonder if they check the sizing of the new rods before they installed them. I would resized the rods to fit tighter on the bearings and maybe install a dowel pin in it to lock the bearing in place (like some of the racing engine mechanic do to their engine).

1972RedNeck January 24th, 2017 12:57 AM
Re: 478M Loosening Rod Bolts
 
Quote:
Originally Posted by James (Post 66070)
I wonder if they check the sizing of the new rods before they installed them. I would resized the rods to fit tighter on the bearings and maybe install a dowel pin in it to lock the bearing in place (like some of the racing engine mechanic do to their engine).
If any machine work gets done, the journals are getting turned down to fit BB Mopar rods...

TJ's GMC January 24th, 2017 03:55 AM
Re: 478M Loosening Rod Bolts
 
I wanna see a ton of pictures and a video of how it runs if that's the case. :thumbsup:

1972RedNeck January 24th, 2017 03:57 AM
Re: 478M Loosening Rod Bolts
 
Quote:
Originally Posted by TJ's GMC (Post 66074)
I wanna see a ton of pictures and a video of how it runs if that's the case. :thumbsup:
All in due time.

ilvracn January 25th, 2017 04:49 PM
Re: 478M Loosening Rod Bolts
 
are the mopar rods the same length?

bluestreak1854 January 29th, 2017 06:03 PM
Re: 478M Loosening Rod Bolts
 
Have you made sure you have the right flywheel and harmonic balancer? With the vibration loosening the rod nuts, it could be that the crank is not balanced as a result of having one of these incorrect.

bluestreak1854 January 29th, 2017 07:20 PM
Re: 478M Loosening Rod Bolts
 
the 401 and 478 have an externally balanced crankshaft-- that means that the flywheel and harmonic balancer have the counter weights on them-- if someone has the wrong flywheel or balancer on this engine it could be sending vibrations that are loosening the rod nuts-- but the vibration should be very noticeable


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