No compression in all cylinders

[JagWarXCIII]

My engine overheated some months ago and I'm just now getting around to rebuilding it. I took the heads in to a shop to be resurfaced and have the valves reseated with new stem seals. I installed the heads with all new gaskets, new lifters, push rods, and rocker arms.

We did a leak down test prior to installing the engine, and it showed 80% leakage in cylinders 2,4,5, and 6, and about 50% in 1 and 3. One side was leaking air through the intake ports and the other through the exhaust. We installed the engine anyway and assumed that starting it would cycle oil though them to get "wet" seal and perhaps stop the leaking. However, the engine will not start. It turns over but that's it. We checked spark and fuel, and have both. However with a gauge attached, there's no compression reading as the engine turns over. The heads were taken to the shop and were tested and they have a 5% leakage, so I'm not sure what's going on. Any and all help is appreciated, thank you.

 

[alwaysFlOoReD]

Cooked the rings...
Do a leak down test to find where the compression is going.

EDIT
You did a leakdown test and found 80% leakage! Thru the intake and exhaust ports? That means the valves are not sealing.... The head job was not done correctly or you have something wrong in the geometry of the valve train. Perhaps new pushrods that are too long?

 

[Dirtman]

Rings are gone, or timing jumped way off.

 

[Snoranger]

If you’re leaking compression through the intake and exhaust it’s valve train related. I suspect an issue with the timing chain and/or gears not installed correctly... at least that’s where I’d start checking.

 

[rusty ol ranger]

If you have 0 compression on 6 cylinders you got a timing chain thats jumped like a SOB.

Even with fried rings you should have *some* compression on attleaat a couple cylinders.

 

[JagWarXCIII]

I read through a lot of threads, and I came to the same suspicion about the timing. I'll take it apart again and see if that fixes the problem. Also, could the camshaft synchronizer be a part of the problem? I read that it has to be placed in a certain manner.

 

[JagWarXCIII]

Cooked the rings...
Do a leak down test to find where the compression is going.

EDIT
You did a leakdown test and found 80% leakage! Thru the intake and exhaust ports? That means the valves are not sealing.... The head job was not done correctly or you have something wrong in the geometry of the valve train. Perhaps new pushrods that are too long?

I took the heads back to the shop and they did a bench test and they were fine only leaking 5%. As for push rods, I got what Rock Auto had as standard and they matched my original ones in length.

 

[Elutheros]

This may not be it at all, but on a 1991 4.0 a couple years ago the key on the camshaft gear sheared off and left the camshaft in a position where there was no compression on any cylinder. We had to replace the gear and all was well.

 

[Snoranger]

This may not be it at all, but on a 1991 4.0 a couple years ago the key on the camshaft gear sheared off and left the camshaft in a position where there was no compression on any cylinder. We had to replace the gear and all was well.

That’s how I got my 95 Explorer for $250. The guy “tried everything” to get it to run. The cam gear had jumped on the cam.

 

[rusty ol ranger]

Just something that occured to me though....

Wouldnt there of been bent valves? Or is the 4.0 non interference?

 

[Dirtman]

They are non interference.

 

[RonD]

4.0l OHV(1990-2000) is non-interference engine
4.0l SOHC(1997-2011) is an interference engine

 

[RonD]

My engine overheated some months ago and I'm just now getting around to rebuilding it. I took the heads in to a shop to be resurfaced and have the valves reseated with new stem seals. I installed the heads with all new gaskets, new lifters, push rods, and rocker arms.

We did a leak down test prior to installing the engine, and it showed 80% leakage in cylinders 2,4,5, and 6, and about 50% in 1 and 3. One side was leaking air through the intake ports and the other through the exhaust. We installed the engine anyway and assumed that starting it would cycle oil though them to get "wet" seal and perhaps stop the leaking. However, the engine will not start. It turns over but that's it. We checked spark and fuel, and have both. However with a gauge attached, there's no compression reading as the engine turns over. The heads were taken to the shop and were tested and they have a 5% leakage, so I'm not sure what's going on. Any and all help is appreciated, thank you.

You have a 4.0l OHV engine in a 1993 Ranger

Did you do the leak down tests with valve covers OFF so you could see that you were on TDC compression stoke for the cylinder being tested, i.e. both valves closed all the way

0psi compression wouldn't just be bad rings, a valve would have to be open a bit on compression stroke, which would mean valve crank timing is off, but not 100% diagnoses

Valve crank timing issue would not be caused by overheating, but I guess next step would be to pull a valve cover and check cam crank timing visually, #1 or #5 cylinder share the TDC marks on crank pulley


More likely scenario
You could have gotten incorrect push rods, they come in different lengths, so could be letting valve stay open too long, or not fully seat when closed
When a valve cover is off loosen the 3 bolts holding the rocker arm assembly on, just loosen, so valves still work
Then retest compression on that bank of the engine
Should be 150+ PSI
This would mean wrong lifters or pushrod length which is fixable without disassembly, just need shorter pushrods

When a cylinder is at TDC compression stroke you should be able to spin both its pushrods with your fingers, so almost 0 pressure, just lifter spring holding it, not valve spring