1977 k20 build

[squarebodyn8tion]

Hows it going everyone,

Picked up a project a few weeks back. its a 1977 single cab long bed. 8" lift 36.5" swampers, pretty solid besides a small part in the firewall, inside cab corners tucked back, and the drivers side door corner. i received the engine in 100000 pieces, with an assortment of new parts to install. after getting everything put together, timed, etc. im almost positive the cam was not broken in properly from the last owner and is trashed. shows all symptoms ( backfire out carb, upper end noise, almost a thud like sound every so often, and a wanting to stall occasionally under load. while taking it for the test drive it was also SCREAMING high rpm at 42mph. for a 350trans and 350 engine, is there anyway the gearing in it is just insanely high? i cant imagine even with say 5.13 gears it would be that bad. i understand the turbo 350 is a 3 speed (which it shifts into all 3) but i dont think there should be any issue hitting 65mph even with 35" tires. Am i wrong? looking forward to hearing what everyones got to say as i now tear back apart the motor i just assembled to swap out the broken (i think) cam for a new one to then properly break it in.

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[Mr Clean]

Sounds like the cam is a good place to start. Have you checked the rods? Bearings? Wrist pins? Wrong rocker arms. To long push rods. Could be bad lifters... anyone of them can cause problems like you listed.

 

[78C10BigTen]

Thats a great truck! I like it!!

 

[squarebodyn8tion]

Sounds like the cam is a good place to start. Have you checked the rods? Bearings? Wrist pins? Wrong rocker arms. To long push rods. Could be bad lifters... anyone of them can cause problems like you listed.

everything seemed fine when I assembled it, one wrist pin was a bit tighter than the rest but wasn't horrible. what more of a pain in the ass. pulling the entire motor or yanking everything off the front end to get to the cam

 

[Shorty81]

Welcome fellow Buckeye

 

[Mr Clean]

I'd pull the motor. Much easier then getting everything back in alignment. I'm sure you know if you are going to run a 3 speed, I'd replace the TH350, with a TH400.

If you are just doing the cam, you can pull the radiator, and A/C condesor that should give you enough room to pull the cam.

One other thing, are you sure the trans is shifting all 3 gears? I had a TH350 in a 85 short bed, and it didn't want to shift into third. It made the motor do some of the things you described. I changed out the shift module and it fixed a few of the problems I had with the truck.

 

[Mr Clean]

Oh by the way

 

[squarebodyn8tion]

Welcome fellow Buckeye

OH

 

[squarebodyn8tion]

I'd pull the motor. Much easier then getting everything back in alignment. I'm sure you know if you are going to run a 3 speed, I'd replace the TH350, with a TH400.

If you are just doing the cam, you can pull the radiator, and A/C condesor that should give you enough room to pull the cam.

One other thing, are you sure the trans is shifting all 3 gears? I had a TH350 in a 85 short bed, and it didn't want to shift into third. It made the motor do some of the things you described. I changed out the shift module and it fixed a few of the problems I had with the truck.

I counted the gears and im pretty positive its shifting into all 3 but 2-3 was a short gap. the issues happen at idle as well so I don't think the trans is the issue there.

 

[Mr Clean]

Transfercase is in 2 high? The high RPMs just sounds like transmission, or tranfercase is in the wrong gear...

 

[ChanPerry]

Nice truck dude super cool!

 

[squarebodyn8tion]

Transfercase is in 2 high? The high RPMs just sounds like transmission, or tranfercase is in the wrong gear...

yea its in 2h. spun the rear wheel loading it on the trailer

 

[Mr Clean]

Kinda got me on this one. Go with your first thoughts, and recam it.

 

[Mr Clean]

There are some good guys here. They might have some better insight.

 

[Craig Nedrow]

Go Here: post#7 front end is very easy to remove.

https://www.gmsquarebody.com/threads/1973-k20-350-to-454-swap.29840

If the cam is bad, in my experience, all the fines have gone throughout the motor reeking havoc on every bearing. Don't want to bum you out, but if it were me, I would pull the engine and check everything out. At least drain the oil get it in the sun and look for silver filings. If there their, the oil is telling you what you should do.