Engine Build
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Joined: Jul 2021
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From: Pennsylvania
Engine Build
So I want to build up my magnum 5.9l just a little bit. I want to run the Comp Cam 20-745-9 with their 901-16 valve springs. From what I read those are computer friendly and use the stock push rods.I want to do it as cheaply, yet reliable as possible.
The thing that I am contemplating is if I should just build my current engine with 200k miles that I know runs smooth as new. No misfires. Claims to have great oil pressure. It does have a tick that I think is either a lifter or exhaust leak but I would be replacing those anyway. I would also have the heads gone through if no cracks are found.
Or should I buy a used motor that I don't know the condition of and build that. That worries me because I wouldn't be able to be sure it runs fine, but it would be quicker because I would have an engine ready to go in as soon as I pull mine. I would also have the expense of having to buy the used motor. Any opinions? What would yall do?
The thing that I am contemplating is if I should just build my current engine with 200k miles that I know runs smooth as new. No misfires. Claims to have great oil pressure. It does have a tick that I think is either a lifter or exhaust leak but I would be replacing those anyway. I would also have the heads gone through if no cracks are found.
Or should I buy a used motor that I don't know the condition of and build that. That worries me because I wouldn't be able to be sure it runs fine, but it would be quicker because I would have an engine ready to go in as soon as I pull mine. I would also have the expense of having to buy the used motor. Any opinions? What would yall do?
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Joined: Apr 2010
Posts: 87,379
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From: Clayton MI
If you have something else to drive while the truck is down, that makes the decision easier.... Also depends on where you live... Winter is soon to be upon us..... (much as I hate to say that..... 
) so, which would you rather be driving in the ugly stuff?
That said, you can pick up 'core' motors around here pretty cheap, my choice would be pick one up, go completely through it, and then just swap. You can either sell the original motor, stash it in the garage somewhere, or scrap it.... (the last option ain't the best for a motor that runs good.)
I would also simply replace the heads. With 200K on yours, it is highly likely they are going to be cracked. They were notorious for that.
What year is your truck, and how much power would you like to get out of it?
) so, which would you rather be driving in the ugly stuff?That said, you can pick up 'core' motors around here pretty cheap, my choice would be pick one up, go completely through it, and then just swap. You can either sell the original motor, stash it in the garage somewhere, or scrap it.... (the last option ain't the best for a motor that runs good.)
I would also simply replace the heads. With 200K on yours, it is highly likely they are going to be cracked. They were notorious for that.
What year is your truck, and how much power would you like to get out of it?
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Professional
Joined: Jul 2021
Posts: 198
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From: Pennsylvania
[QUOTE=HeyYou;3525598]If you have something else to drive while the truck is down, that makes the decision easier.... Also depends on where you live... Winter is soon to be upon us..... (much as I hate to say that..... ) so, which would you rather be driving in the ugly stuff?
That said, you can pick up 'core' motors around here pretty cheap, my choice would be pick one up, go completely through it, and then just swap. You can either sell the original motor, stash it in the garage somewhere, or scrap it.... (the last option ain't the best for a motor that runs good.)
I would also simply replace the heads. With 200K on yours, it is highly likely they are going to be cracked. They were notorious for that.
What year is your truck, and how much power would you like to get out of
If I had another vehicle it would be a no brainer to me. But I don't unfortunately. I feel like if I buy a used motor the heads would also be cracked. If I could buy a used one and know the heads are fine, then I would do that. Mine runs so smooth that it makes me want to believe mine may not be cracked. Don't they misfire a bit if they crack? I really don't want to touch the bottom end of the engine at all if possible. Just the top end. From what I've heard the bottom ends are pretty bulletproof. Also this would be during next summer when the weather isn't about to be crap. Maybe if I just used my motor I could use the money I saved by doing that and buy new heads if needed... idk. Can't decide as usual. How hard is a cam swap in the truck? Doable if I take off the radiator and stuff?
) so, which would you rather be driving in the ugly stuff?That said, you can pick up 'core' motors around here pretty cheap, my choice would be pick one up, go completely through it, and then just swap. You can either sell the original motor, stash it in the garage somewhere, or scrap it.... (the last option ain't the best for a motor that runs good.)
I would also simply replace the heads. With 200K on yours, it is highly likely they are going to be cracked. They were notorious for that.
What year is your truck, and how much power would you like to get out of
If I had another vehicle it would be a no brainer to me. But I don't unfortunately. I feel like if I buy a used motor the heads would also be cracked. If I could buy a used one and know the heads are fine, then I would do that. Mine runs so smooth that it makes me want to believe mine may not be cracked. Don't they misfire a bit if they crack? I really don't want to touch the bottom end of the engine at all if possible. Just the top end. From what I've heard the bottom ends are pretty bulletproof. Also this would be during next summer when the weather isn't about to be crap. Maybe if I just used my motor I could use the money I saved by doing that and buy new heads if needed... idk. Can't decide as usual. How hard is a cam swap in the truck? Doable if I take off the radiator and stuff?
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Professional
Joined: Jul 2021
Posts: 198
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From: Pennsylvania
If you have something else to drive while the truck is down, that makes the decision easier.... Also depends on where you live... Winter is soon to be upon us..... (much as I hate to say that..... ) so, which would you rather be driving in the ugly stuff?
That said, you can pick up 'core' motors around here pretty cheap, my choice would be pick one up, go completely through it, and then just swap. You can either sell the original motor, stash it in the garage somewhere, or scrap it.... (the last option ain't the best for a motor that runs good.)
I would also simply replace the heads. With 200K on yours, it is highly likely they are going to be cracked. They were notorious for that.
What year is your truck, and how much power would you like to get out of it?
) so, which would you rather be driving in the ugly stuff?That said, you can pick up 'core' motors around here pretty cheap, my choice would be pick one up, go completely through it, and then just swap. You can either sell the original motor, stash it in the garage somewhere, or scrap it.... (the last option ain't the best for a motor that runs good.)
I would also simply replace the heads. With 200K on yours, it is highly likely they are going to be cracked. They were notorious for that.
What year is your truck, and how much power would you like to get out of it?
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Joined: Apr 2010
Posts: 87,379
Likes: 4,210
From: Clayton MI
The thing with cracks is, they don't get better, they get worse. What usually happens is, the heads will crack around the valve seats, as the cracks open up, they will allow hot gases to escape when the cylinder fires, and that accelerates expansion of the cracks, until eventually, you get popping thru the intake, and eventually, misfires. Of course, you have gone 200K miles without any of that, so, could they go another 100K? More? It's a crap shoot. 
If it runs good at the moment though, why not just drive it as is, save some more money up, and go from there? I am a firm believer in "If it ain't broke, don't fix it." Doing headers, better exhaust, maybe even 1.7 roller rockers, would bump you up a few ponies, and you wouldn't need to open up the engine at all. Could do most of it in a weekend. (I don't know what your capabilities are as far as exhaust goes.)
What year is your truck? It makes a difference.
If it runs good at the moment though, why not just drive it as is, save some more money up, and go from there? I am a firm believer in "If it ain't broke, don't fix it." Doing headers, better exhaust, maybe even 1.7 roller rockers, would bump you up a few ponies, and you wouldn't need to open up the engine at all. Could do most of it in a weekend. (I don't know what your capabilities are as far as exhaust goes.)
What year is your truck? It makes a difference.