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Discussion Starter · #1 ·
It's been a while since I've posted. Nice to be back. A while ago I swapped a doner 3.4L of unknown milage and it's been great so far but the motor is getting tired. The compression is about 150 in 4 cylinders and about 114 in 2. So, it's about time to do something with it. The tranny etc. seem fine.
I have 3 options:
1. Buy a crate with a tow package for about $1500. Since I've already done all the swap stuff I'd only have to drill the starter mount.
2. Replace the heads (leaky intake valves seem to be causing the low compression), cam and lifters for about $700
3. Get rid of the Trooper . . . it has about 400,000 miles on it.

I'd like to save as much $ as possible, but I'm worried that if I just replace the heads and cam without rebuilding the lower end I may be just buying myself a little bit of time before the rod and crank bearings go out. Right now the lower end seems fine - there's no noise and the oil pressure is about 27psi at warm idle and 65psi at warm 3500rpm, but I'm worried that the increased pressure from the new heads and cam could put too much stress on the old parts.

So, what kind of luck have you had putting new heads on an older block? Should I just bite the bullet and buy the crate engine?

Any sage advise is greatly appreciated. Jim
 

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Have you done a leak down test? This will determine where the loss of compression is.

But a crate is the best option. It has a much better cam than the Camaro 3.4L did so it will make more power.
 

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If your dealing with chevy why don't you up grade to a 4.3 they are a much better motor and i beleive the same bolt patterns as the 3.4,s
 

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Discussion Starter · #4 ·
I did a leak down and it indicated bad intake valves in the back two cylinders on the passenger side. But I'm thinking it may be a leaky head gasket. I'm losing coolant without any sign of a leak and it's hard to start after sitting for a while. One of the 4 good cylinders is down a bit but not as bad as the other 2.

At a minimum I'm going to upgrade the cam to a 252 with the whole kit (springs, rockers, etc.). Since I'm going to have the top end apart anyway I figure I might as well refresh the valves too.

The 4.3L swap is much more complicated than the 3.4L. For starters you can't use the stock Trooper tranny, since the 4.3 is not a 60 degree V6. They used to make an adapter plate but not any more. Then you have to cut and wield new motor and tranny mounts. I've been told that the Trooper CPU is not a good match to the 4.3 so it might have to be replaced. The stock 3.4 puts out about the same HP and torque as the 4.3 although the 4.3L can put out more with mods. All in all, the 3.4L is pretty much a straight bolt in swap, the 4.3L is not.
 

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Need to check the bottom end. If you are low on compression, only couple of places where it seals mechanically. Heads and cylinder bores.
 

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Discussion Starter · #6 ·
All I'm really trying to get some feedback on is - what's the most cost effective thing to do? Fix the compression problem only or replace the motor with a crate?

I figure once I pull the heads I will be able to see if I have a blown head gasket or bad valves, even if I have to do a bench test. Figuring that out is not too difficult.

But I'm afraid that if I just fix the compression and put in the new 252 cam package I may have some bottom end problems soon because of the increased compression unless I rebuild or replace the whole motor. I don't want to throw good money after bad.
I don't know what the milage is on the motor, but the oil pressure, measured with a mechanical gauge, is about 27psi at warm idle, and about 67psi at warm 3000rpm. Given there is no bottom end noise or any other obvious sign of bottom end trouble, should I risk doing just the head work and saving some bucks by not replacing or rebuilding the whole motor? Or have people on this forum had trouble with the bottom giving out because of the increased compression from the new heads?
 

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Ask yourself a few questions.

If you do a crate or full rebuild, are you willing to put another 50k-100k miles on it?

Do you have $1,500-$2,000 avail, or do you have a few hundred?

Do you want to rebuild a motor, or even just the top end?

Can you sell it for enough to put you into a reliable replacement? (sale + savings)

The honest & unfiltered/undebated answers to these should help.

Personally: Provided the frame/cab are in good shape, I would refurbish the suspension & steering (after 400k they need it, unless it's been done recently), & start hunting for a screaming deal on another 3.4L. If you find one in good shape swap them & rebuild the tired one. If you find another tired one, rebuild it before this one croaks.

~psguardian
 

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Discussion Starter · #8 ·
I'm just going to address the top end and maybe replace the cam with a 252.

I think the bottom end is ok and hopefully it can handle the increased compression. I don't think I want to put an additional $1500 into the car, I don't think I'll be keeping it long enough to justify that expense.
 

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Why not do the whole thing? If theres no spun bearings or damage to the bottom end then just strip the block, have it honed and reassemble it with new seals/gaskets, bearings, and piston rings. Its a few hundred bucks to know your bottom end is fresh and ready to go for another 150,000 miles
 

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Where can you get a 3.4L crate motor for $1,500?
 

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Discussion Starter · #11 ·
littlegray said:
Where can you get a 3.4L crate motor for $1,500?
This place has a crate long block '93-95 3.4 V6 rwd iron heads for under $1300. That's with stock cam. I didn't double check the application but I believe it's the correct 3.4L. Even if that particular block isn't the correct one, I assume that the right one is about the same price.
http://www.cmengines.com/se/search.aspx

Realistically, I only plan to keep this car for another year maybe less. If I put a new crate in it I will not be able to sale it and re-coupe my outlay. The body is just too beatup. and at 400g miles, I'd be lucky to get $1000. So, if I put a new crate in it, the only way it makes economic sense is if I keep the car for 100 - 150,000 miles and get my money back in use. On the other hand, if I put half that money into it and fix the top end so it runs strong for another 50,000 (or one year, yeah I drive a lot), then I get my use out of it and I can sell it for whatever I can get at the end of the year.
But that's only true if the motor will last for 50,000 miles without touching the bottom end. If I put $600 into the top end and 2 months later I spin a bearing then I've basically wasted the $600. That's why I'm trying to get some feedback on whether I'm putting too much stress on the old bottom end by only fixing the top end.
 
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