Leakdown Test Results

[jrdepew]

I just realized that I used a regular valve core from a tire when I did my compression test. When I first went to do the compression test I still had the injectors in and even though the fuel was off there must have been enough for a combustion event, as it ruined the spring in the original valve core. I just popped one in from a spare valve stem and moved on...

Upon further research, and that I have been burned by this before, I should have known better. The opening pressure on standard valve cores is much higher than a compression tester valve core, and I am sure lowered my readings. I am tracking down a set of white-banded valve cores for compression testers now, but I am thinking my rings are doing pretty well. Ford factory manual says that they should be around 430 +-50psi, with less than 50psi spread between cylinders.

I am thinking I have a valve seating issue like MarentetteService said, as that is where the leakdown showed leakage. Even if I do have tired rings, I think this needs to be fixed. The question is, do I tear it down now, or do I try some sort of upper engine cleaner like suggested above first? Also battling with the fact that I have it halfway torn down now, so do I just continue or put it back together and probably have to tear it back down again...

For the gaskets, is it best to just go ahead and buy the gasket set from NH? I found them online for about ~250...not too bad.

Thanks,
Joe

 

[MarentetteService]

Pull the valve cover and remove the rocker arms, keep them in order on your bench, then redo the leak down test. If you still have leakage past the valves, pull the head and bring it to a machine shop. If not put the rockers back on and adjust your valves again. Does your manual say to adjust them hot or cold?

 

[jrdepew]

Pull the valve cover and remove the rocker arms, keep them in order on your bench, then redo the leak down test. If you still have leakage past the valves, pull the head and bring it to a machine shop. If not put the rockers back on and adjust your valves again. Does your manual say to adjust them hot or cold?

Good idea. I will do this sometime this week. The manual says to adjust to 0.008" clearance cold.

Joe

 

[jrdepew]

Just got the head off. I started working on it at about 10pm and decided to redo the compression test on the lowest cylinder with the new valve core. It shot up to 380 which is much better. This is one of the cylinders that leaked down to the exhaust as well...

Next I took the valve cover off and removed the cast piece that holds the rockers so the valves would be closed for sure. Went with the leak down test and still had air coming out of the exhaust. If I held my hand over the stack it would whistle out the joints in the exhaust system.

Started taking it apart and keeping everything organized. Got the head off and to my surprise the bores look very good. No visible scoring and no ridge at the top of the cylinders that I can feel with my fingernail.

I must say, I am very impressed with how this engine is build compare to the gas engines I have pulled apart. It is more than likely due to the high compression, but fine thread head bolts and lots of them, studs to hold down the rockers instead of press ins or bolts, exhaust manifold and intake came off almost too easily. Only thing that was a pain in the *** was the injector hard lines as the nuts at the pump are **** near touching.

I called the machine shop earlier today and they said they should be able to turn the head around in less than two weeks assuming it just needs the seats and valves touched up.

Should be back and running before the really cold weather hits with less smoke and more knowledge about what makes these engines tick.

Thanks for all the help and I will keep everyone updated as I get it back together.

One question....is it worth cleaning the nozzles on the injectors at this point or because it ran so smooth should I just leave it alone?

Joe

 

[jrdepew]

One thing I forgot to add...I can't believe how little spring pressure these valves have. I can push them open very far by hand...wasn't expecting that.

Also, there seems to be a good carbon caking on the valve seats. Maybe I could have gotten away with just a top engine cleaner, but it will be interesting to hear what the machine shop has to say when they get it cleaned up.

Joe

 

[JimRB]

Usually a head shop will either knurl and ream the guides or replace the guides when doing a valve job. Some engines are more prone to wear guides than others.

Here is an interesting web site about valve seat grinding. Brooks Elliott Cylinder Heads

 

[Topher265]

One thing I forgot to add...I can't believe how little spring pressure these valves have. I can push them open very far by hand...wasn't expecting that.

Also, there seems to be a good carbon caking on the valve seats. Maybe I could have gotten away with just a top engine cleaner, but it will be interesting to hear what the machine shop has to say when they get it cleaned up.

Joe

Well that's interesting. Good valve springs are needed to break up / keep carbon build up off the seats/faces. If you have springs so weak you can compress them, I'd look up the spec and think about replacing them. At least measure them and compare to stock. Seeing a lot of carbon on the seats could be the whole cause of the lack of sealing in the first place.

 

[brain55]

One thing I forgot to add...I can't believe how little spring pressure these valves have. I can push them open very far by hand...wasn't expecting that.

Also, there seems to be a good carbon caking on the valve seats. Maybe I could have gotten away with just a top engine cleaner, but it will be interesting to hear what the machine shop has to say when they get it cleaned up.

Joe

Remember these diesel engines run at 1/2 to 1/3 of the rpm that automotive gasoline engines do. They also typically have smaller and lighter valves so they need much less spring to control them.

Brian

 

[jrdepew]

Remember these diesel engines run at 1/2 to 1/3 of the rpm that automotive gasoline engines do. They also typically have smaller and lighter valves so they need much less spring to control them.

Brian

Good point. My reference is springs spec-d for use with aggressive camshafts with very fast lobe ramps, which takes a lot more spring to control...

I will have the machine shop measure them just to be safe though.

 

[brain55]

Good point. My reference is springs spec-d for use with aggressive camshafts with very fast lobe ramps, which takes a lot more spring to control...

I will have the machine shop measure them just to be safe though.

Yeah, they're a far cry from the 230 lb seat pressure we ran on the 8500+ rpm big block with .700" lift on my buddy's front motor dragster.

Brian