Causes of low compression

[Tractorboy88]

Ford 3000 diesel.
Owner bought it used several years ago. Has had to use ether since day 1 to start it.

Fuel system checked out, has visible white smoke (unburnt fuel) coming through exhaust, fresh fuel, new filter, and the valve is open.

Checked compression with all injectors removed. All cylinders 225-250 psi. Spec is 420-510 with 50 psi variation between cylinders.

In addition to low compression, I hear air escaping through exhaust and blow by.

A valve and ring job later, I'm back to square one.

Tried a spare set of injectors with no change.

Removed injectors and checked compression.
275 psi.

Measured bore is 4.2.
Measured stroke is 4.2.
Piston crown to deck is within spec at .012.

What am I missing here? Could timing gear alignment be off causing low compression?
What other possibilities for low compression are there? I'm pulling my hair out.

 

[davesl708]

Timing could cause a valve to be open when in compression.

 

[Egon]

Rings may not help for worn cylinder bores.

 

[Tractorboy88]

Rings may not help for worn cylinder bores.

Surprisingly the bores were in decent shape. Within taper and out of round spec.

 

[Tractorboy88]

My manual does not list an intake/exhaust lift measurement, only event timing.

Does anyone have a manual that gives a lift spec? If so does .310" sound close for intake lift?

 

[Tractorboy88]

Timing could cause a valve to be open when in compression.

That's what I'm thinking. Have to pull front axle to remove crank pulley and timing cover to check. That will have to wait till tomorrow.

 

[KYErik]

When the rings were replaced, were the cylinders honed to break the glaze? If so, it may just take some time for them to wear in.

As was mentioned, if the valve timing jumped, it would affect compression.

 

[Qapla]

How many rings are on each piston? Did they get "lined up" when they were installed so that the gap where each ring comes together creates a passage for compression to escape? (I have seen this done before) They should be offset so that the seal is complete.

When the valves and rings were done, was the head planed or trued? Were any valve guides replaced?

 

[Tractorboy88]

When the rings were replaced, were the cylinders honed to break the glaze? If so, it may just take some time for them to wear in.

As was mentioned, if the valve timing jumped, it would affect compression.

All 3 cylinders were honed as well.

 

[KYErik]

Are valves adjusted with the correct lash? A valve with no lash would leak compression- especially as the engine warmed up.