G503 Military Vehicle Message Forums

I am not personalty knowledgeable on the correct procedure for adjusting the valves on the 160AX engine. However with a hyd. lifter if the valves are adjusted or set to tight the valves will not seal when the lifter pumps up "period". This should be sorted out prior to going any further in my opinion.

Roger

The compression is at the top of the specs-as good as any engine would ever get, so that is not the problem. I would suspect that when the valve job was done, the shop sank the valves into the block too far. This would remove the valve lash if they didn't shorten the valve stems to account for the deeper seating. The other possibility mentioned earlier is that the lifters are "pumping up" which means that when the engine is running, the engine oil pressure is causing the lifters to apply too much force to the valves and lifts them off their seats. There is a check valve that can stick and not let the pressure in the lifter bleed down so it holds the valve open. Since the shop rebuilt the lifters, there could be a problem with the rebuild.

Thanks guys for all the feed back just have to do one more test then he can drag himself up here and fix it

your engine is cam time,spark time or or firing order is not right.check your distributor rotation first.Valve lash will not make a engine not run unless you are holding a valve open or not opening a valve.valve lash is for heat expansion and lubrication only.Adusted to tight will not let a valve seat proper,to loose will damage valve stem ,possibly break valve and be noisey.your compression test seems to show all is fine.On all straight sixes the firing order is 1 5 3 6 2 4. To check your crank and cam timing, 1 and 6 are at the same crankshaft position,2 and 5 are at the same crankshaft position and 3 and 4 are at the same crankshaft position.That means when #1 is on tdc # 6 is also at full as high in cylinder as possible.When rotating the engine in the proper direction both valves on # 1 will remain closed (power stroke) ,however #6 will open its intake valve ,and intake will remain open until #6 hits bdc.

Here is what the first three cylinders look like

And the last three that are not firing

Last cylinder got chopped off but it looks clean like 4and5

If the engine were 1 tooth off, would it even run?

This is a interesting problem. I sure would love to have this one within my reach to see everything first hand.
Gary

If you've wrung out the spark, ignition timing, valve lash, valve timing and compression, all that's left is fuel. Could it be that 4,5 and 6 are firing but there's nothing to ignite? Are these a dual-plane intake manifold? If they are and the manifold is clear, could the carburetor be the problem?

I thought that too at first pulled the manifolds off nothing blocking. That side of the carb isn't feeding as good as the other side but it goes back to why do I have crappy compression on those cylinder after it's running.

I guess I lost track of the compression - I thought the numbers were all good. If the numbers are bad after the engine is warm, a leak-down tester would help you to know where it's leaking so you can zero in on the cause. On the low cylinders, listen to intake, exhaust and breather.

A running compression test is great for testing valve seating problems ' the test should be ran with the check valve removed from the compression gauge . The readings will not be near as high as a cranking compression test and should not vary by more than several PSI . At my auto repair shop we have had vehicles with good cranking compression but a cylinder with running compression that was as little as 4 PSI lower and when torn down for inspection found valve seating problems . Warren Duchesne

Any new news? Wondering how the trouble shooting is going?

Took a back seat for a bit.im leaning toward that set of valves. Engine builder said he would work on it but would need to go back to his shop.would have to rig a gantry outside the garage to pull it. Steep driveway. Will keep you guys updated

I would not pull that engine with that good of cranking compression.More test needed , possible lifter problems . The valves on the missing cylinders may be pumping up and holding the valves off the seat . Warren Duchesne

I'm pretty sure it's the valve/ lifters. Don't think he ground enoug off of the valve stem.

Thought I'd bump this back up. Have you had any luck with the problem? It is an interesting problem and I was curious if you got it fixed.