71 GMC 3500 "Longhorn" engine build

[hilandr452]

Hi guys,

It's been awhile since I've posted here, but some bad decisions when I last switched motors in my truck have led me to need to change or rebuild motors in my truck. I have some choices to make.

My pickup is a 1971 GMC "longhorn" which came with a turbo 400 and a 402 big block.

Here's the story. A few years ago, I removed the stock 402 Big Block from my truck and dropped a 454 from an 83 dually I had laying around. The PO of the dually told me that a rebuild was performed about 10000 miles before I purchased the truck. I had added a few thousand miles to the truck myself. I cleaned up the motor, painted it, and changed the oil pan, valve cover, and intake manifold gaskets. I also removed the stock intake and carb and added a new edelbrock performer 2-0 intake with a 750 cfm edelbrock 1407 performer series carb.

This build ran excellent but had a vibration i could not fix. I asked you guys and found out that a 402 BB was internally balanced and a 454 is externally balanced, so the flex plate I installed did not have a counter balance and this caused the vibration. After I had this information, I failed to change the flex plate, thinking "I'll get to it." This truck was used to move my family about 35 miles, using a horse trailer. Maybe about 20 trips. I estimate the total miles through the years to be about 3000. This truck is used to haul hay and perform farm errands only. I drive a POS subaru to work 70 miles a day.

Recently, valve noise began becoming an issue and I was periodically adjusting the rockers to compensate. This turned into a more serious issue until I started hearing a distinctive knock.

I removed the engine and put it on a stand. There is little wear in the cylinders and no ridge ring. There is little wear on connecting rod bearings. Valves and pushrods are all in good shape and not bent. The problem is the camshaft. Several lobes are worn nearly round. When I removed the timing cover, the chain was single roller and very loose. I removed the cam gear and there is NO cam retainer plate. WTH?

Has anyone seen this before, can this cause the lobes to wear like this or was it the vibration? It ran fine for a few years, then suddenly this problem occurred.

I also took apart the 402, and it has a groove down one cylinder, so will need to be bored if I decide to rebuild it. It is otherwise a good block.

My third option would be to take the motor out of my 73 motorhome with 75000 miles on it and swap it out until I rebuild one of the other motors.

What do you guys think? Should I re-ring the 454 and add a cam, rebuild the 402, or swap until I get to another rebuild?

I hate having the old girl down for any stretch of time even though I don't drive her much.

Thanks for your input!

Dan

[1972RedNeck]

I am a power junkie motor head. Bigger cubes = better.

[kwmech]

I'd freshen up the 454

[The Camaro Guy]

X2 454

[hilandr452]

I am leaning toward the 454 also.