B6100 compression test not so favorable

[AaronH]

All,

I bought a B6100 about a month or two ago. I've been working on it because it starts hard and smokes quite a bit. Almost as much as those hand held propane bug foggers (not quite that bad, but close). The smoke is mostly light grey with a hint of blue. I tried cracking the injector lines loose and found that the injectors weren't tight in the head. Someone in the past has really goobered up the injector line tube nuts and the injectors themselves with either a pair of channel locks or a pipe wrench. Once I got them out I took them to a diesel injector service shop and had them checked out. He said they were good. They cleaned them up, installed new washers and gave them back. I also bought new injector lines from Kubota.

Today, since I already had the injectors out I checked the glow plugs. I found that number 3 wasn't working (cylinder towards the rear of the tractor). So, I bought a new one from Napa and installed it. I also checked the compression this afternoon. Doesn't look good. The results are as follows:

After about 8 cranks:
Cylinder #1 - 220 psi
Cylinder #2 - 200 psi
Cylinder #3 - 320 psi

Then I rechecked 1 and 2:
Cylinder #1 - 240 psi
Cylinder #2 - 220 psi

I'm really hoping it's not rings. Since two adjacent cylinders are low I suppose it could be something with the head (head gasket, valves, or cracked head). I did notice that 1 and 2 had a fair amount of carbon buildup. There was what I would call creosote in the injector threads that I had to clean out with a dental pick. The end of the injectors had some carbon deposits and I could see some looking down in the injector port. #3 cylinder had some oil buildup on the injector threads, but not too bad.

I figured I would post here before I go much further. What do you guys think?

Thanks,
Aaron

 

[Stumpy]

It's possible it's just leaking valve stems and carbon buildup on the valves but I'd wager on the rings if not both.

My tractor had similar symptoms. It started a little funny and smoked a bit but ran ok. I took the exhaust manifold off and found a bunch of wet carbon deposits in the runners. Condensing a long story I found the exhaust guides had loosened in the head and one of the cylinder liners had shifted down in the block.

These engines use a thermosiphon cooling system instead of a water pump and are sensitive to a dirty radiator. Combine that with a lack of temp gauge and it's easy to overheat without knowing it. It's just a guess but those symptoms sound unfortunately similar.

 

[B7100]

If you did not repeat the test with a spoonful of oil in each cylinder then try that and post back the results.
Do you have access to a leak down tester,it will give a clearer idea of what is wrong.


N

 

[AaronH]

Matt,

Thanks for the info. That gives me a few things to think about and look at when the time comes.

N,

I haven't done the wet test yet, but I will. I also don't have a leak down tester (yet). I didn't have a diesel compression tester until just last Saturday either.... There's always one more tool isn't there?

I should also point out a couple things just in case it matters. I added a can of Seafoam to the fuel tank. I've only run the tractor 15 minutes or so since. Also, when I did the compression test I had the injectors out of the cylinders that weren't being tested.

Part of me wants to put it back together now that I have replaced the bad glow plug on 3# and fixed the loose injectors, but the other part of me says, "you'll just have to tear it back down to fix the low compression issue."

Thanks guys,
Aaron

 

[B7100]

The extra info you posted should not make any difference to your test, it has reduced the possibility of a leak between cylinders with identical readings but not completely eliminated it.
There is so little work involved in taking injectors in and out I would whack them back in and see if it runs ok, that way you won't be wondering if you could have got away with it had you not tried before fixing the low compression issue

 

[motorhead]

Check your valve clearance for tight valves.

 

[Stumpy]

Mine seemed to run ok despite the issues but you're certainly not doing it any favors running it with an oil leak like that nor are you making much power. You can do a good enough leak down test without a kit. Check your hose threads on the compression tester. It's probably standard NPT pipe thread. You want to hook a male air compressor fitting up to the compression test fitting that screws into the injector ports. Remove the shrader valve from the end of the compression tester fitting and then blow compressed air into the cylinder when it's at TDC on the compression stroke. Listen to the air escaping through the exhaust, intake, and dip stick and see which is louder. You'll identify your leak quickly. Make sure you've got all your injectors out and tools and limbs are away from the crank if you try this, 120psi on a piston is enough to break things.

 

[AaronH]

All,

I did the wet test. I poured a generous cap full (probably too much) of 15W-40 that I had near by into each cylinder. I then rolled the engine over with the starter a bit to disperse the oil in each cylinder and also allow any extra to come out. Then I checked each cylinder. #1 and #2 came up to 300/320psi and #3 came up to 420psi or maybe just a bit more. So, rings certainly seem to be the likely cause. Checking valve clearance would be easy enough, and I could pull the head, but rings are probably going to have to wait till Spring. I'd like to get it done and checked off the list but I have a lot of other irons in the fire right now. I'll likely just put it back together for now and wait until I have time to tear it apart. We'll see how ambitious I get.

Aaron