catd69u

Also I should add, I shook the rocker arms on both valves, and they are loose, which should mean the valves are closed, right? When the air was going in, the engine didn't offer to move at first. But just for kicks, I decided to turn it a little while I had it pressurized, and when I moved it, it turned on it's own and took the wrench away from me and mashed a couple of fingers. After I thought about it, wouldn't that mean there's some compression in there someplace? I'm really lost here............................................

AlpineRAM

Now you've seen the difference between compression and a pressure loss (leakdown) test, for the price of smashed fingers.

While the engine turns slowly, the air has time to escape. At a higher speed the leak (imagine it as a hole with a fixed diameter) simply can not flow enough to actually stop the engine from running.
What still makes me curious- if you had that much blowby or leakage around the piston and down into the crankcase - you should have a veritable storm from the crankcase vent and a lot of oil fumes and smoke coming from there.
Your assessment of the rockers having play and the valves being closed is correct.
But you should not check for leakdown or compression on an engine that hasn't run for a while. Actually the engine oil in the ring grooves seals it, but it goes away if not replenished due to the engine running.
Maybe you could repeat the test (without the finger smash part) with the crankcase vent plugged and the oil filler open- this should net a definitive result.

catd69u

Thanks for the input, I'll try this in a few days and let you know what happens....

catd69u

I finally got around to tearing this thing apart. So far I haven't seen anything that looks bad to me. It seems to have about 10 to 12 thousandths of an inch wear in the cylinders, and the top ring on #1 has about 25 thousandths end gap. I was wondering what the max allowable wear would be on the cylinders, that new rings would take care of. The cylinder walls look good, no scuffs or pits, and I can still see the factory hone marks in them. I've also checked the valves for leakage, and so far haven't found any.................

AlpineRAM

About the measurements- get a factory service manual, they are less than 50$ on CD.

A leakdown that massive and no traces on the cylinder walls is strange. But maybe you still see the hone marks, but they don't hold oil any longer, I'd definitely go over it with a ball hone.
New rings need a fresh hone to seat correctly anyways.
You should also measure the vertical play of the rings in the grooves.

texasprd

Downloadable '95 FSM

catd69u

Well, I finally got it back together with new rings, rod bearings, and valve grind. We had to push it with the backhoe to get it started. Still has the same problem that it had before, won't start on its own. Just cranks and cranks................could bad injectors cause this?

AlpineRAM

Bad injectors might be the cause- but the russian test method for this goes as follows:

Remove injectors and injector lines from engine- install injector lines turned 180 degrees, attach injectors to injector lines. (They'll hang in the air around the driver's side fender.

Install leak line on injectors, connect as stock.

Bleed system.

Watch the diesel spray while cranking (Catch the fuel in 6 mason jars, no need to douse your truck with diesel. )

But first check that the shutdown solenoid actually turns the shutdown shaft on the pump...

catd69u

I changed out all 6 injectors today, I put 6 known good ones in that I took out of another engine. Still won't start on it's own. I'm now pushing the truck to start it, as I don't want to use ether....had to push about a hundred feet before it finally started. Truck runs great after it finally starts.I took the lines loose where they attach to the unit in the fuel tank, and I got a lot of air from the smaller one. I don't know which one is pressure and which is return, but I rigged them up in a 5 gallon bucket of fuel. Bled the system, putting out fuel at injectors. Still won't start. Just cranks.................

AlpineRAM

Did you do this?

catd69u

Yes, as a matter of fact I don't even have the fss on it, and I'm operating the shutdown lever by hand..............

AlpineRAM

While you crank it- does it emit white smoke from the exhaust?

If you crack an injector line while running does it squirt the same as while cranking?

Since everything is rebuilt... maybe verify timing again. Offset timing can cause very hard starts.

catd69u

Update: I checked the timing and it's good. I finally decided to replace the lift pump, because all of a sudden the hand primer didn't seem to be putting out enough. I also done away with the prefilter/ fuel heater while I was at it. After doing this the truck would finally start on it's own after lots of cranking and priming. I took the afc housing off, and found the throttle plate was slid almost all the way towards the rear. I slid the plate all the way forward, and slid the afc housing forward also. Now if I pump the pedal while it cranks, it will start right up. If I don't touch the pedal, it will crank and crank, but not start. It seems that I have to rapidly pump the pedal. If I just hold down it don't start as quick, sometimes not at all. But if I rapidly pump while it's cranking, it starts instantly. So, I've still got a problem, but at least it will start now.

AlpineRAM

Interesting.. pumping the throttle is a game of chance. I think that you are hitting the spot where it starts by chance if you "pump" the "throttle" ( both not applicable to diesels.
And again- did you verify that the shaft is turned- not the lever, I had a lot of loose bolts and worn shutdown levers and shafts where the lever was moved but the shaft was not..

catd69u

I know it doesn't make any sense about pumping the throttle, but that's what it takes to start it.............. From everything I've seen and found, I'm beginning to think somebody else has had this apart, and they've got something out of kelter. The smoke screw was opened all the way, but the plate was slid all the way back. Sliding the plate forward helped, but didn't cure the starting problem. I'll check the shutdown mechanism again, a little closer. Thanks for the help.