LM7 rebuild into C1500 help
Thread Starter
Teching In
Joined: Jan 2022
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LM7 rebuild into C1500 help Hello there! I'm looking for help with rebuilding my Gen 3 LM7 5.3L I got with mentioned 125K KM on it. I was looking to get 400HP NA reliably, with a motor that will also be able to accept boost. I've been researching and researching but nothing sticks, so I figured I'd come to the forums to get some help and have all my information in one place.
I was wanting to change the pushrods, rocker arms and trunnions, valve springs, roller rockers and camshaft with APR bolts (Don't know all of which to get) while doing a full rebuild and re-gasket on the long block.
Keeping the main bearings and crank stock and untouched if they look good. It has 706 heads and I'm not looking to do machine work as it'll cost too much for where I live.
I'm mainly looking for help with what parts to pick off of summit racing, possibly? (Only place I know to get parts for Manitoba) and specifically what to really pay attention to for re-gasketing. As well as where to find tolerance's, torque spec's, and basic engine assembly information. How far the valves can stretch before hitting stock dished pistons?
It's going into my 1991 C1500 pickup paired with a 700r4 / 4L60 that has been rebuilt for 800HP. What kind of steps would it take to get it in there? I know I'm going to need a harness and computer along with motor mount adapting plates. But is there anything else? Is there anything I'm missing for engine parts?
I'm trying to keep things as cheap as I can while also building up something reliable for street/strip.
Thanks for any input and help on this build! It's much appreciated.
I was wanting to change the pushrods, rocker arms and trunnions, valve springs, roller rockers and camshaft with APR bolts (Don't know all of which to get) while doing a full rebuild and re-gasket on the long block.
Keeping the main bearings and crank stock and untouched if they look good. It has 706 heads and I'm not looking to do machine work as it'll cost too much for where I live.
I'm mainly looking for help with what parts to pick off of summit racing, possibly? (Only place I know to get parts for Manitoba) and specifically what to really pay attention to for re-gasketing. As well as where to find tolerance's, torque spec's, and basic engine assembly information. How far the valves can stretch before hitting stock dished pistons?
It's going into my 1991 C1500 pickup paired with a 700r4 / 4L60 that has been rebuilt for 800HP. What kind of steps would it take to get it in there? I know I'm going to need a harness and computer along with motor mount adapting plates. But is there anything else? Is there anything I'm missing for engine parts?
I'm trying to keep things as cheap as I can while also building up something reliable for street/strip.
Thanks for any input and help on this build! It's much appreciated.
Last edited by ChiefBuddhaBaby; Apr 5, 2022 at 08:14 PM.
TECH Senior Member
Joined: Jun 2016
Posts: 22,298
Likes: 3,619
From: Central Cal.
WHY are you rebuilding? These engines see 300-400k MILES on the regular.
Is yours making funny noises or using/leaking too much oil? Then OK.
BTW, the gaskets in these are light years ahead of the old cork junk in older engines. Many are reusable.
Is yours making funny noises or using/leaking too much oil? Then OK.
BTW, the gaskets in these are light years ahead of the old cork junk in older engines. Many are reusable.
Thread Starter
Teching In
Joined: Jan 2022
Posts: 5
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I have the engine sitting on an engine stand and figured I wanted to get it as close to new as I could so it's a fresh rebuild ready for install so I dont have to worry about having a gasket blow out or interally leaking oil presssure
Never heard or seen it run because it got ripped from a bush truck that was used as payment to a cousin.
Never heard or seen it run because it got ripped from a bush truck that was used as payment to a cousin.
TECH Fanatic
Joined: Jan 2018
Posts: 1,250
Likes: 239
From: Dade City, Fl.
Hey Chief...sorry to say it but is this post for real? I never heard of someone thinking a LS engine with 78,000 miles needs a rebuild. Throw a camshaft and compatible valve springs do the trunnion upgrade if you want. The rpm and valve springs will determine if a pushrod investment is worth it. Change the seals if you don't plan on ever taking the engine out again. As for the 700r4 trans, doesn't it require a TV cable?
On The Tree
Joined: Sep 2010
Posts: 145
Likes: 5
From: Lima oh
Rebuild not nessecary as others have stated. Does it run? Does it smoke or knock ?
Don’t mess with it, put it in the truck. get the truck drivable with your trans and rear end.
after you get the bugs worked out- then mess with the cam / valve springs etc
I’m not sure if it’s be possible to swap the wiring harness from a similar model year truck as your current motor;
and have your brakes still work.
Don’t mess with it, put it in the truck. get the truck drivable with your trans and rear end.
after you get the bugs worked out- then mess with the cam / valve springs etc
I’m not sure if it’s be possible to swap the wiring harness from a similar model year truck as your current motor;
and have your brakes still work.
TECH Addict
Joined: Aug 2005
Posts: 2,305
Likes: 126
From: Monroe,NY
You will not be able to make that power on a budget. You will need some good heads and up that compression and a big cam. I have an Lm7 with tsp 5.3 heads and a 222/226 cam .600 lift and it runs great. Not sure on power since i never had it on a dyno but goes pretty good. 92 c1500 5 speed.
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TECH Addict
Joined: Oct 2016
Posts: 2,513
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From: PDX-OR-USA
Pick up a cheap bore-scope.. pull the plugs, check the cylinders, drain oil, peek in there look for cruft in the pan.
plugs back in tape up all the holes paint it and install. (the LS is not known for leaking. )
You could just do a cam upgrade, don't even touch the bottom end if the cylinders and pistons look decent.
The truck manifold will get you nicely up to a fun power level. Site sponsors have a cam just for your needs.
If you just have the long block, cheapest way to go is find a wrecking yard that has a bad engine ,
you buy that as a core and ask for it as a drop out with all the harnesses ecu etc, all the front mounting stuff.
Piecing it all together is $$ and a pain in rear. I paid 400 for a complete pullout from a Van.
I wanted the manifold, oil pan front end stuff I did a terminator to run the engine.
There is a guy near me in Vancouver Washington that has a decent deal on lightly prepped used engines and harnesses ready to run, about $3500.
plugs back in tape up all the holes paint it and install. (the LS is not known for leaking. )
You could just do a cam upgrade, don't even touch the bottom end if the cylinders and pistons look decent.
The truck manifold will get you nicely up to a fun power level. Site sponsors have a cam just for your needs.
If you just have the long block, cheapest way to go is find a wrecking yard that has a bad engine ,
you buy that as a core and ask for it as a drop out with all the harnesses ecu etc, all the front mounting stuff.
Piecing it all together is $$ and a pain in rear. I paid 400 for a complete pullout from a Van.
I wanted the manifold, oil pan front end stuff I did a terminator to run the engine.
There is a guy near me in Vancouver Washington that has a decent deal on lightly prepped used engines and harnesses ready to run, about $3500.
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Teching In
Joined: Jun 2019
Posts: 12
Likes: 3
Pick up a cheap bore-scope.. pull the plugs, check the cylinders, drain oil, peek in there look for cruft in the pan.
plugs back in tape up all the holes paint it and install. (the LS is not known for leaking. )
You could just do a cam upgrade, don't even touch the bottom end if the cylinders and pistons look decent.
The truck manifold will get you nicely up to a fun power level. Site sponsors have a cam just for your needs.
If you just have the long block, cheapest way to go is find a wrecking yard that has a bad engine ,
you buy that as a core and ask for it as a drop out with all the harnesses ecu etc, all the front mounting stuff.
Piecing it all together is $$ and a pain in rear. I paid 400 for a complete pullout from a Van.
I wanted the manifold, oil pan front end stuff I did a terminator to run the engine.
There is a guy near me in Vancouver Washington that has a decent deal on lightly prepped used engines and harnesses ready to run, about $3500.
plugs back in tape up all the holes paint it and install. (the LS is not known for leaking. )
You could just do a cam upgrade, don't even touch the bottom end if the cylinders and pistons look decent.
The truck manifold will get you nicely up to a fun power level. Site sponsors have a cam just for your needs.
If you just have the long block, cheapest way to go is find a wrecking yard that has a bad engine ,
you buy that as a core and ask for it as a drop out with all the harnesses ecu etc, all the front mounting stuff.
Piecing it all together is $$ and a pain in rear. I paid 400 for a complete pullout from a Van.
I wanted the manifold, oil pan front end stuff I did a terminator to run the engine.
There is a guy near me in Vancouver Washington that has a decent deal on lightly prepped used engines and harnesses ready to run, about $3500.