1.6 Head question

[bc]

So I have 300 plus lbs. compression on two of the four cylinders. The other two have 0 lbs. registering on the gauge. As if the cylinder is not building pressure at all. The block is freshly rebuilt with new rings. The head is questionable from an unknown source. Does this sound like the head is toast, considering the new piston rings?

[vwtyp133]

Toast? Could be... or not. It could be any of a number of things giving those zero readings (with no knowledge of who did the re-ring & assembly: no offense intended, please)... valve shims wrong, bent valves, frozen valve followers, broken cam (mine was a 3-piece unit!), head or block surface warpage, excessive thread friction causing improper headbolt torque readings & leaking head gasket, gasket installed backwards (oh,yes), improper ring orientation (it's been done before!), cylinders too far out of round for new rings to seal...all come to mind, as well as any of the truly terminal head maladies such as major cracks cam tower breakage, etc.

Pull the rocker cover & let the investigation begin on top by observing valve follower actions at each cylinder as the crank is slowly rotated clockwise with a wrench through a few revolutions of the crank. Hope it's a quick & easy fix.

[82vdub]

If you're getting zero compression, my first area would be to look at the valves for that cylinder. Even bad rings, a cracked head or other things will register some compression. Zero means to me that the valves aren't closing properly. If you have bent valves and you rotate the engine with a wrench on the crank, you should be able to feel the valves hitting the pistons, if the valves are bent from hitting pistons. Otherwise, I would guess that the valve(s) isn't fully closing. I actually bought a rebuilt head, had it installed (back before I wrenched on OHC engines), and the car ran horribly. Come to find out that the valves weren't shimmed correctly, leaving 3 of 8 valves hanging open.

[greg lousy]

so this was a cold compression test I would assume?
In any case, I'd test the tester first if I had absolute zero... the adaptor parts, threads, etc. maybe retest the cylinders with compression, just in case its all a bad dream

[bc]

Yes, a bad dream Greg Lousy. lol. This is a fresh rebuild of the lower end. So I'm just trying to get it started. I'm going to pull the head and look closer at the valves. I don't think it's the tester because the other two cylinders registered over 300 psi.

[bc]

Any advice on rebuilding these heads?

[Fatmobile]

If they aren't warped it's pretty straight forward.
Valves guides and seal can be had for under $100 on the mechanical heads.

[bc]

I've heard the valve guides are kind of a nightmare. How do I tell if they are closing all the way? When the cam loves are up, the valves look like they're in there nice and tight.

[vwtyp133]

I've heard the valve guides are kind of a nightmare. How do I tell if they are closing all the way? When the cam loves are up, the valves look like they're in there nice and tight.

Shadetree method: With the cam removed (all valves should return to closed positions), and the head propped upside down with the combustion faces level, you can drop some light oil (ATF?) around the valve heads. If they leak the oil into their intake or exhaust ports, the valves aren't sealing properly.

[bc]

I'll have to try that out vwtyp133.

[bc]

So, I gave up on the head in question and swapped over another used one. Now I'm getting around 100 psi in two cylinders and 300 psi in the other two. So, my question is, shouldn't it still run even with low compression in two cylinders? Remember my other head had zero psi in the same two cylinders. So the head I'm using now has slightly better compression.

[Fatmobile]

300 is about as low as it gets and still starts,.. if I remember right.
So 100 is way too low,.. that's gasser compression.
Try turning it over by hand, with a socket on the crank bolt and see how it feels.

[Prairieview]

Was any attempt made to check the surface of the engine deck for flat and the same for the face of the heads?
Guides don't close. You are referring to the seats. And, seats heat pit and need to be cut and valves generally need to be replaced because these engines beat the valve margins (esp. on exhaust) to nothing. Hand lapping does virtually nothing to rectify the problem.

These engines are very hard on their guides as well as they are subjected to very sharp carbon and rather high heat.

[bc]

Turning the engine by hand is no problem. It just won't fire. Just crank over and over till the battery dies. I was hoping it would try to run even with a couple low compression cylinders.
Would you recommend a full head rebuild and machining? Prairieview?
None of the things you mentioned have been checked out.

[Prairieview]

Head rebuilds are very important to these engines. I have only found one head which did not need guides on all 8. And, that head had been rebuilt like 125,000 miles earlier. Again, these engines are very hard on their seats....esp. the exhaust.

You need to work with someone who knows these old diesel heads quite well. Osvat valves (made in Italy) are very good for a standard engine and they are quite cheap as well. Sealed Power valves are very good as well.

It is best to have your new valves with you when you take the head to a machinist. And, it is best to only have then cut the seats as little as possible to allow you the longest possible life out of the head. The oil galley in the head needs to be thoroughly flushed after the work is complete.

The new guides have to be reamed to a specific diameter and NOT larger. The oldest Bentley manuals used to list the value of clearance for reaming guides. For some reason, they quite listing it in their publications. The old red Bentleys had the info.

If you have ever taken the valves out of a high-mileage head, you will see that the margin is so narrow and sharp that you could almost use it to skin a deer! I always laugh when some guy sez his machinist "ground" his old valves. Ground them into what? Powder? That was real good back when we all ran old two-cylinder John Deere tractors. Things have changed.