Leakdown Test Results

[jrdepew]

I performed a leakdown on my Ford 1920 today as I have a little smoke the whole time the tractor is running. It is either white or blue, very hard to tell exactly. This smoke doesn't go away when ran hard, just keeps on coming and increases with load. My compressor is suffering from a weak lung, so I could only test with 70psi of input pressure.

Cylinder 1 (closest to radiator) - 70 on inlet, 61 on outlet = 13% leakdown.
Cylinder 2 - 70 on inlet, 45 on outlet = 36" leakdown
Cylinder 3 - 70 on inlet, 60 on outlet = 14% leakdown.
Cylinder 4 - 70 on inlet, 45 on outlet = 36" leakdown

On cylinders 2 and 4 I noticed that I had excess air blowing out of the exhaust stack. I have adjusted the valves late last season, but it is smoking the same before and after. I am thinking I may pull the head this winter and check the condition of the valve seats. While I am in there I would obviously do a head gasket. Because I would have it all apart, I would send the injectors somewhere to get checked. I think this would cover all my bases except for weak rings...I don't intend to do a rebuild of the shortblock unless I see some bad scoring in the cylinder wall.

I used to be into racing and turbo buicks, so engines are nothing new to me...but diesels are. Is there anything else I should do while I'm in there? Any votes for another form of testing before I tear it down? Any other comments? Five angle valve job, bowl porting, teardrop the valve guides, back cut the valves? :laughing: just kidding...I am not hunting for every 1/100th of a second here.

Thanks in advance,
Joe

 

[jones6780]

If you do a wet compression test you can evaluate the ring condition.

 

[SSdoxie]

I second the vote for wet & dry compression test comparison. Engine air leakage, like hydraulics or water, takes the path of least resistance so if valves are in worse shape than the rings the leakage is more noticeable there. After valves are ground and reseated, the cylinder leakage would be more evident.

 

[jrdepew]

Sounds good, I will do a dry then wet compression test. One thing I was wondering about...is it possible to so a compression test on a diesel with the injectors still in? I have a fuel shut off in the supply line, but am thinking it isn't wise to let the injection pump spin without a good supply of fuel...or am I wrong? Right now I don't have much torn off the tractor, just the glow plugs.

I tried searching on the process to compression test a diesel and didn't find a ton of info on what to do and what not to do...any advice?

Thanks,
Joe

 

[Topher265]

Sounds good, I will do a dry then wet compression test. One thing I was wondering about...is it possible to so a compression test on a diesel with the injectors still in? I have a fuel shut off in the supply line, but am thinking it isn't wise to let the injection pump spin without a good supply of fuel...or am I wrong? Right now I don't have much torn off the tractor, just the glow plugs.

I tried searching on the process to compression test a diesel and didn't find a ton of info on what to do and what not to do...any advice?

Thanks,
Joe

There's no need to leave the injectors in while testing. There shouldn't be any IP damage from the compression test as it's very short and done at a slow speed. It's not really any different than getting air in the lines and cranking while bleeding...short bursts should cause no damage.

 

[jrdepew]

Just got the compression test done. From the front of the engine back,

350psi
325psi
370psi
360psi

Note that these are for a cold engine as I wasn't able to warm it up. Same with the leak down results above.

I then went to do a wet compression test and got a surprise....with a few squirts of oil the engine fired and the number went right to 600psi!!! Looks like the numbers I got before I pulled the injectors and fuel line off...Can you do a wet compression test on a diesel? Seems like it would fire as it is designed to do.

More notes: all injectors and glow plugs looked very similar to each other. Slight carbon buildup on tip of all injectors.

Let me know what you guys think.

Thanks,
Joe

 

[jrdepew]

Anyone? Was I doing something wrong with the wet compression check?

Thanks,
Joe

 

[jimmysisson]

The oil you put in helped seal the worn rings and raised the readings. Points to a ring job, or buy more oil, much cheaper and easier.
Jim

 

[MarentetteService]

You said you had air blowing past the exhaust valves in number 2 and 4. You found your problem. A leak down test is done with the valves CLOSED. Leakage past a closed valve is bad. Blue smoke = burning oil, black smoke = burning excess fuel, white smoke = burning water or running lean.

 

[Topher265]

Anyone? Was I doing something wrong with the wet compression check?

Thanks,
Joe

You didn't seem to do anything wrong. Diesels need only air, fuel and compression to run. You helped it's compression by using the oil, and since it seems to have enough air and fuel it started. As jimmysisson said, sounds like worn rings. Or it could be somewhat stuck rings. It might be worth using a specific cleaner to try and free any possibly stuck rings (I prefer GM Top Engine Cleaner).

Going back to your initial description, worn rings is indicated. The constant smoke could be oil pumping up the walls of the cylinder a bit and burning off. I'd also just buy more oil instead of doing a ring job.

 

[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