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.