100 psi compression on a D662, what's wrong and what's next

[Kaiten]

Howdy, folks.

I recently got a G1800 in pretty bad shape: dirty and not running. It was covered with dirty and dust, a thick layer and everywhere.

Power washed and started working on it. Cleared the fuel line, replaced the battery and cables, couple spliced wires, and replaced the starter.

Turn the key, the motor turned over, but no running. I checked the compression on all 3 cylinders. They are all around 100 psi. No wonder it does not start.

I noticed that the air intake on the engine block was very dirty with dust covered. Engine oil was black, and overfill.

What should be my next move? I have not done any engine rebuilt in my life, but not afraid to learn if that's the route. But just want to get the obvious other causes ruled out before do the big job.

Thank you.

 

[BruceP]

I noticed that the air intake on the engine block was very dirty with dust covered.

Lets hope that engine has not been "dusted"... allowing dust into engine can really mess things up. (cylinder walls, bearings.... EVERY sliding part)

You asked "Whats next?"... here are some suggestions:

• Squirt oil into cylinder and REtest compression (this tests ring-sealing)
• with piston at TDC compression, use compressed-air and listen for leaks thru intake/exhaust. (this tests valve sealing)
• Use borascope to 'look' into cylinders
  

 

[lugbolt]

dust in the air intake means the engine has been dusted. In other words, you're probably gonna have to rebuild it.

DO NOT put oil into the cylinder on a diesel engine and do a compression test. This is not a good thing to do unless you want more damage than you already have. I can't think of anyone who wants that. Besides even a few drops on these little tiny engines doesn't go into the cylinder right away, it goes into the prechamber. Then of course we automatically think "hey it must need more to seal up the rings"...then you get bent rods and/or the engine may try to start if the rings get sealed up enough to build 400 psi. I have done it and it's a good way to get a runaway diesel, which I have also done.

30 years of tech I ain't seen nor do I know everything but I learned a LOT....and much of it the hard way.

You already know your compression is low. Pull valve cover, check valve clearance. If they're tight, adjust them. Try a compression test after valve adjustment. Still low compression? You're going to have to go into the engine anyway so just pull it off the frame and get to it. At that point, if you know you have low compression and it's not the valves, there simply is no need to try to put any oil into the cylinder. You already know it's deeper than the head and you gotta take the motor apart anyway to find the problem.

 

[Kaiten]

dust in the air intake means the engine has been dusted. In other words, you're probably gonna have to rebuild it.

DO NOT put oil into the cylinder on a diesel engine and do a compression test. This is not a good thing to do unless you want more damage than you already have. I can't think of anyone who wants that. Besides even a few drops on these little tiny engines doesn't go into the cylinder right away, it goes into the prechamber. Then of course we automatically think "hey it must need more to seal up the rings"...then you get bent rods and/or the engine may try to start if the rings get sealed up enough to build 400 psi. I have done it and it's a good way to get a runaway diesel, which I have also done.

30 years of tech I ain't seen nor do I know everything but I learned a LOT....and much of it the hard way.

You already know your compression is low. Pull valve cover, check valve clearance. If they're tight, adjust them. Try a compression test after valve adjustment. Still low compression? You're going to have to go into the engine anyway so just pull it off the frame and get to it. At that point, if you know you have low compression and it's not the valves, there simply is no need to try to put any oil into the cylinder. You already know it's deeper than the head and you gotta take the motor apart anyway to find the problem.

Ok. I took the top block off. There are a lot of black soot inside the chamber. Here are some pictures. Would you please help me to understand what the next steps are. Thanks.

 

[Kaiten]

Is there any obvious issue that you can pick up from the pictures? The cylinders seem to be firm, not much give. One of the cylinder tops has some scorching.

 

[Pau7220]

Is there any obvious issue that you can pick up from the pictures? The cylinders seem to be firm, not much give. One of the cylinder tops has some scorching.

You already know your compression is low. Pull valve cover, check valve clearance. If they're tight, adjust them. Try a compression test after valve adjustment. Still low compression? You're going to have to go into the engine anyway so just pull it off the frame and get to it.

As one of our most respected techs, you need to take lugbolts advice. Pictures aren't perfectly clear but I can see vertical scratches on the cylinder walls which means dirt got in where it shouldn't have and the pistons and rings did the scratching. So from this point... 1, turn the engine over by hand to make sure all pistons come up to the top of the deck equally to check for bent rods. 2, disassemble and have a pro measure the cylinders for taper and wear. 3, if you're lucky you may get away with honing and a re-ring. From the sound of the way the PO maintained it you could be in for a major overhaul.

 

[GeoHorn]

Did you follow the sequence offered by lugbolt..?? by first checking valve clearances prior to disassembly? Did you perform a differential compression-test (with compressed-air to determine if valves, or rings were leaking?)
(The visual inspection of the cylinders do not reveal anything out of the ordinary, IMO. Checking for full cylinder travel is a good idea (to check for bent rods) but that would also be only cursory, not definitive without removing the lower sump and pulling them out.)

 

[whitetiger]

First thing, you should check the accuracy of your compression test gauge. Especially after looking at the pictures, I would be very surprised if you only had 100 PSI compression plus the fact that you get 100PSI on all 3 cylinders throws up a huge red flag.
The allowable limit on the 68mm Stroke Kubota engines is 327PSI with less than 10% differential.
Factory production compression is 412PSI to 469PSI.

 

[Kaiten]

First thing, you should check the accuracy of your compression test gauge. Especially after looking at the pictures, I would be very surprised if you only had 100 PSI compression plus the fact that you get 100PSI on all 3 cylinders throws up a huge red flag.
The allowable limit on the 68mm Stroke Kubota engines is 327PSI with less than 10% differential.
Factory production compression is 412PSI to 469PSI.

The gauge should be relatively accurate. I was working on a D782 recently and I got 360psi for all 3 cylinders.

I took the top bock off, and found that there is lot of soot/dirt buildup on the rings. Hope this is the reason that I have low compression.

Now all the rings are cleaned. I'm waiting for the head gasket to arrive.

Will update on the outcome.

Thanks for all the advise.

 

[Pau7220]

The visual inspection of the cylinders do not reveal anything out of the ordinary

Like these vertical scratches?!?!

I'll make the popcorn

 

[lugbolt]

yes I see evidence of engine dusting. It is obvious.

I'd question your gauge. 360 psi is low on SOME D782's. Some of them are spec'd over 600 psi. I had a gauge like that one (Matco) that was way off. Cost me a ton of time, and a lot of money. Had a BX with a 782, smoky when running but seemed to run ok. Compression showed 425 on all 3. Threw me for a loop. Finally I gave in and pulled the head. #2 piston was about 1/4" down in the cylinder at TDC, the other 2 were a few thousandths down. They outta be out of the cylinder a little. Found bent rods. Ether caused it, was run out of fuel so they gave it a little spritz and bent #2 rod. Then found bent #3 rod. And finally more inspection revealed bent #1 rod. All 3 were bent. Starting fluid will cause this and a lot of other issues as well.

While you have the head off rotate the engine so that the front piston is as far up as it will go. You can use your finger to judge where TDC is. In other words, feel the piston as it is rising. When you feel it start to go back down, stop and reverse direction and when the piston just barely starts to go back down again, stop. Split the difference--that will be very close to TDC. At TDC how far down is the piston into it's cylinder? Repeat for all 3 cylinders. There is a spec for them as to how far OUT of the cylinder they are supposed to be, but I don't have that information handy--WSM is on the other computer in the shop. If you find them way down in the cylinder, you may have bent connecting rods. If they're all in spec, you're gonna have to pull the engine off of the frame and get the pan off, remove all 3 rods and pistons noting which one is which cylinder and which direction they all face (they are directional), inspect and see what's causing your low compression issue. If rods aren't bent look closely at the rings and the areas where the rings are in the pistons. I've seen quite a few with broken ring lands, again, due to starting fluid. If those are ok and you don't see bent rods, pull a ring off of one piston (carefully-the rings break pretty easily) and then push it down into a cylinder. Turn the rod/piston upside down and push the ring into the cylinder to square it up. Eyeball the gap between the ends of the ring. If it's much more than, say, 1/16", you have worn rings worn cylinders and probably worn pistons-all of which will equal a rebuild. But the good thing is, once properly rebuilt with bored/honed cylinders and oversize pistons/rings, it should run like a brand new engine and last many hours--which is exactly what we want.

 

[BAP]

Listen very carefully to what Lugbolt and Whitetiger have to say. They are both very experienced mechanics and know these Kubota’s well.