Junkyard engine- lower compression on one cylinder

[PDHSB]

I just got a junkyard engine, compression tested it out of the car. Results are 180psi on all cylinders but #4, sitting at about 150. Is it fine to just bolt on my heads to this short block or should I just rebuild this one?

 

[nickyb]

Let's see,it's out , it needs some help, yes I vote yes rebuild her. We can rebuild her better then before,she'll run better,faster , longer.
Parts list, new pistons( yourchoice), rings, rod bolts, rod,main,cam bearings, oil pump( standard press.) , cam,lifters,gasket kit.Oh a good machine shop.
This is my very own opinion , I'm sure you'll get more. Happy motoring.

 

[7991LXnSHO]

On another thread I was outvoted about someone running a wet compression test and doing a leak down test with similar numbers. It was running fine in the car, but the owner was just testing for due diligence.
I still say finish the tests to see why the compression is down (is it leaking out the valves, past the rings, or past a gasket?), then also tell us your intended use, how long you want it to run and your budget.

 

[PDHSB]

On another thread I was outvoted about someone running a wet compression test and doing a leak down test with similar numbers. It was running fine in the car, but the owner was just testing for due diligence.
I still say finish the tests to see why the compression is down (is it leaking out the valves, past the rings, or past a gasket?), then also tell us your intended use, how long you want it to run and your budget.

I intend to run it like this just for the Summer, I should have enough saved for a forged rotating assembly by then so it's inevitably coming back apart.

I dropped maybe 1.5 teaspoons of oil in the cylinder, compression went up to 185ish. So in thinking rings. I just don't want to spend an extra month without my car, I'm anxious to finally bolt on my ported heads and enjoy it for once. If it's bad enough I'll rebuild it, but if it'll get me through the summer I'm fine as long as it'll let me get over that 300hp I've been aiming for.

 

[7991LXnSHO]

I intend to run it like this just for the Summer, I should have enough saved for a forged rotating assembly by then so it's inevitably coming back apart.

I dropped maybe 1.5 teaspoons of oil in the cylinder, compression went up to 185ish. So in thinking rings. I just don't want to spend an extra month without my car, I'm anxious to finally bolt on my ported heads and enjoy it for once. If it's bad enough I'll rebuild it, but if it'll get me through the summer I'm fine as long as it'll let me get over that 300hp I've been aiming for.

Run it for now - if it has oil pressure.

 

[PDHSB]

Run it for now - if it has oil pressure.

Everything but the shortblock is getting torn down to be replaced with my ported heads and cams, so that won't be too big a concern.

 

[7991LXnSHO]

Everything but the shortblock is getting torn down to be replaced with my ported heads and cams, so that won't be too big a concern.

That leaves your rod and main bearings, and they are inspectable before you make the final decision.

 

[stormsedge]

Or, as an alternative short term "fix" (since you intend a full rebuild shortly): while the engine is out, pull the pan and re-ring #4. You can take a look at the rod bearing at the same time just to see what you have. That way, you may gain some longevity if the rebuild is pushed to the right. Cheers.

 

[PDHSB]

Or, as an alternative short term "fix" (since you intend a full rebuild shortly): while the engine is out, pull the pan and re-ring #4. You can take a look at the rod bearing at the same time just to see what you have. That way, you may gain some longevity if the rebuild is pushed to the right. Cheers.

Will the rings seat right if the cylinder is worn though? I was told this thing was at 130k when pulled. I might re ring it if it'll give me a good temporary increase.

 

[7991LXnSHO]

Will the rings seat right if the cylinder is worn though? I was told this thing was at 130k when pulled. I might re ring it if it'll give me a good temporary increase.

If the crosshatch pattern is still there and there is no ridge at the top of the bore, it should work. Search “Flex Hone cylinder ball hone” for the right tool to deglaze the cylinder walls. That’s the right way to do a redneck rebuild that your rings will seat in. I’ve done it with small engines, and know others who do it with car engines.
In the first episode of Roadkill, they do this in a Cleveland for a Cougar, and although they show the process briefly, it is not like their ensuing level of Hackery.

Ball Hones for Cylinder Wall Deglazing and Engine Rebuilds

Flexible honing tools from Brush Research Manufacturing (BRM) have a few nicknames. Although we market our surface finishing solutio...

www.flexhoneblog.com

 

[HemiRick]

@ 130K I wouldn't touch it, its probably fine.....

 

[stormsedge]

If the crosshatch pattern is still there and there is no ridge at the top of the bore, it should work. Search “Flex Hone cylinder ball hone” for the right tool to deglaze the cylinder walls. That’s the right way to do a redneck rebuild that your rings will seat in. I’ve done it with small engines, and know others who do it with car engines.
In the first episode of Roadkill, they do this in a Cleveland for a Cougar, and although they show the process briefly, it is not like their ensuing level of Hackery.

Ball Hones for Cylinder Wall Deglazing and Engine Rebuilds

Flexible honing tools from Brush Research Manufacturing (BRM) have a few nicknames. Although we market our surface finishing solutio...

www.flexhoneblog.com

^this^...and maybe--it depends on the wear. It just seems counterintuitive to slap your nice hot rod heads and cams on a used short block that is not up to snuff. Hope it does what you want.