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1995 4.0 OHV valve train odd issue question


HillbillyLes

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Question then a little history.

In trying to troubleshoot a miss in cylinder 1 I bought the truck with, I got to the point of pulling the valve cover thinking/hoping? to find a stuck valve or something obvious. The engine is as clean as any I seen on the inside. absolutely no gunk or varnish. I rotated the engine to check for loose clearances or maybe a sticking valve (bent?) however what I found was odd.

The exhaust valve in cylinder 1 (with the miss and compression of around 30 psi) when up all the way and the pushrod should be able to be rotated or spun with some resistance. It is still so tight on the pushrod that I cannot rotate it at all. All of the other pushrods can be rotated when the valves are up (intake and exhaust). Appears the valve is not closing due to lack of clearance however there are no adjustments in the valvetrain so what would have been an adjustment issue of being adjusted too tight is not possible with this engine. Is is possible in such a clean engine for the lifter to be hydrolocked in someway and not be doing its thing? I have worked on engines for years and do not recall ever coming across this on a non-adjustable valvetrain.

The truck is an extended cab 5-speed 4wd and was bought with 250K miles and supposedly has had a newer engine put in it at some point. Overall it looks like it has been well maintained except by the prior owner who did not do much maint. The fuel gauge did not work so I replaced the fuel pump/sending unit in the tank...the fuel pump which was working fine was the original Ford pump... No coolant in the oil, no oil leaks, no pressure in cooling system, no overheating, no issues with the engine other than the miss....the engine starts very quickly and purrs except for the miss which is always there in all loads and rpm ranges and thus power is way down. plug in cylinder (or any of the others) actually does not look bad. In any case as with all vehicles I buy I did a complete tune-up including oil change, air and fuel filters, plugs, etc. I have run cleaner thru the fuel. With no noises, leaks, smoke, coolant loss or coolant in oil (etc), it seems like it should be a simple fix but finding o clearance in the exhaust valve/pushrod has me stumped.

Is there a chance someone might have bent a pushrod and replaced it with a longer one? That or a locked hydraulic lifter (no noises) are the only things I can think of but thought before I sunk more time and money into driveway teardown, I'd run it by y'all in case someone might have run across this before. This is my first 4.0 so other than what I have read when researching this is about all I know about the engine/engine family.

Thank you-
Les
 


RonD

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It is possible to "tulip" a valve when it gets hot, although never read about that in a 4.0l, and it is usually an intake valve

I would remove the Rocker assembly and then use a straight edge across the valve stems, check the one rocker for debris and straightness.
Also pull a few push rods to check lengths and look at top of lifter for debris.

While not common a hydraulic lifter can jamb at or near full extension causing what you describe, opposite of collapsed lifter.
When you are removing rocker assembly have that exhaust valve in a closed position on cam, as you loosen the rocker assembly bolts you should see the lifter springs pushing up the push rods, not the valve stem rising.

When tightened the rocker assembling should push lifter springs down about 1/3 of their travel, the 1.5 turns you use on adjustable hydraulic lifter engines, so when loosened you will see that lifter spring return to full extension before push rod is no longer touching rocker.

With hydraulic lifters there really was no need of adjustment, the adjusters were hold overs from solid lifters, and for daily drivers caused more problems than they could solve, so were dropped.

Assuming other cylinders were above 140psi, then 30psi is an open valve, or hole in the piston(not likely), not rings, gasket or crack
 
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HillbillyLes

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absolutely no indication of hole in piston....oil is as clean as when I changed it 100 miles ago and I have been driving it to work and back (easy driving) about 15 miles each way 2x per week....something would have shown up contamination or blow-by wise or fluid loss but nothing...that is why I am going on the assumption of a valve not sealed. the engine is as clean as a 500 mile engine under the valve cover. Will pull the rocker assy tomorrow when I get off work.
 

HillbillyLes

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OK, so I pulled the rockers on the right bank and found all to be as expected with as many miles...some wear on the pushrod ends but not anywhare near something to cause issues. otherwise all looked pretty good except the exhaust valve spring height on cylinders 1 (one with the miss and 30 psi compression) and 2 are about 1/8 inch higher than the rest of the springs....I am stumped unless the 2 exhaust valves are tulipped??? Any other explanation as to why they would sit higher (spring base to top of retainer) than the others?

Also while tracing vacuum lines, I found injector number 5 unplugged. I plugged it in and did a hard reset on the computer and it runs MUCH better now except still has the obvious miss in cyl 1...the valve spring height is high enough, the rocker actually is holding that valve open just a hair when the cam is rotated to its base circle.....the exhaust valve spring on cylinder 2 apparently isn't quite as high (measured with ruler to get general measurement, not with caliper) because it does seem to be closing since no miss and good compression test there.

Obviously the future outlook is a set of new heads or more likely salvage engine since a set of heads ($385) and aftermarket rocker/hardened pushrods (~$200) if done "right" will cost about as much as pretty decent salvage engine for a daily driver (not toy and was not supposed to be a project :annoyed: ) and I won't be investing $600 in brand new top end to go onto a tired bottom end assuming it is the original 250,000 mile engine.

any ideas out there what might be going on with the exhaust valve spring height on the 2 cylinders? anyone ever tulipped or 'stretched' a valve on on 4.0?

Thanks-
 

RonD

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Cylinder has to get pretty hot to tulip a valve, no never ran across that with 4.0l OHV.
Exhaust valves are made of much harder steel than intake valves, maybe engine has been apart before and someone F*ed up and put in the wrong valve

You could get shorter push rod for #1 exhaust valve, but I might do a leak down on #1 just to make sure exhaust valve can seal
 
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enjr44

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I have seen a patch job where a valve had been sunk deeper into the head to get it to seal. Probably an 1/8 of an inch. But, that was 50 plus years ago and had solid lifters. It ran ok but you could tell something was wrong.
 

Andy D

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You have 2 burnt exhaust valves and as their outer diameters get thin , the valve recedes into the seat.which allows the valve stem to ride higher than normal. It should be throwing a code. I've burnt a few exhaust valves.So far not in the Rat. The 4.0 is the it's main virtue. :D.
 

HillbillyLes

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Thanks for all the input.

I'll check into all but still think ultimately putting a salvage engine is best for the money rather than investing in valvetrain or headwork, esp since I know nothing about if this is the original 250K mile engine or a "replacement".



Thanks again-
Les
 

tbunch

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I'm just finishing a rebuild on my 94 4.0, had a similar issue with sunken exhaust valves. In my case, the seats were more worn/sunken more than the valves being damaged. That being said, mine were only sunken by about 23 thousandths and even at that depth my machinist had concerns about blowing the valve out, I'm not surprised at 1/8th of an inch you would see misfires. these heads are also prone to cracking which could be another possibility, although I wouldn't jump to that conclusion right away. I would keep it in mind if you go with a salvage motor though, might end up doing headwork either way.
 

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