D905 low compression after sevice

[MrShawn305]

So I have a D905 on a generator that got a bunch of water in the fuel system. I pulled the injectors and pump, had them all rebuilt by a reputable shop here in town. While I was waiting for that, I had the unit at a friend's shop (Heavy duty diesel mechanic), and we did some checking on it and found one of the exhaust valves was leaky.

We pulled the head, inspected the cylinders (which looked beautiful), I cleaned off all of the carbon, lapped the valves and replaced the valve guide seals. Put it back on with new gaskets and torqued to spec.

After that, it was very hard to start. Takes alot of cranking before it will start spitting and sputtering for a few seconds with some white smoke and then running like a top after that. If I let it run for a minute or two and shut it off, it will start right back up again. I pulled the pump and injectors and had them rechecked, everything checks out good there. We did a compression test and found the compression to be well below spec. All 3 cylinders were within 3-5 PSI of each other. We did a leakdown test on it and that passed with flying colors. When I had the head off, I noticed the cylinders still had a faint crosshatch on them. I shimmed the pump out some and that seemed to help it start easier with less smoke, but now that the temp is starting to drop outside, it's getting almost impossible to start it.

Before the thing tried to run on water, it ran beautifully. Cranked up right away and ran great. I'm beating my head against the wall trying to figure out what went wrong. I get the funny feeling that when I cleaned the head I may have messed it up somehow as I used a wire wheel to clean it. Should I pull the head again and see about having it machined?

Sorry for the long post, and thanks in advance for any ideas you all might have.

 

[Tooljunkie]

You never mentioned actual psi from compression test. Also valve lash needs to be adjusted after you warmed it up. Glow plugs test good?

 

[85Hokie]

You never mentioned actual psi from compression test. Also valve lash needs to be adjusted after you warmed it up. Glow plugs test good?

I agree with TJ - WHAT was the psi, and are you sure the glow plugs are working???? It sounds as if you are not getting any pre-heat.

The thickness of the new head gasket vs old?

 

[CountryBumkin]

Your mechanic probably did not connect the glow plug wire back up after the rebuild.

 

[D2Cat]

You say, "I shimmed the pump out some and that seemed to help..."

Unless you had material removed from the head during shop work, you do not change the shims. When you change the shim you change the timing.

My guess would be fuel system has air in it. Do the same process you did when you thought you had it ready to start, just do it a few more cycles. Be sure pure fuel is coming out at the top of the injectors before tightening the nut.

Don't get in a hurry and overheat the starter.

 

[CountryBumkin]

After that, it was very hard to start. Takes alot of cranking before it will start spitting and sputtering for a few seconds with some white smoke and then running like a top after that. If I let it run for a minute or two and shut it off, it will start right back up again. I pulled the pump and injectors and had them rechecked, everything checks out good there. We did a compression test and found the compression to be well below spec. All 3 cylinders were within 3-5 PSI of each other. We did a leakdown test on it and that passed with flying colors.

Another thing that has me thinking - you said compression was "well below spec". But cylinder cross hatch pattern still visible (meaning little cylinder wear) and it passed the cyl leak down test (so rings and valves are good).

Could you have installed a head gasket that is too thick (the wrong gasket)?
I'm not sure about Tractors, but with high perf-auto builds you can get head gaskets in a lot of different thicknesses, and just a small change like .050" in thickness can make a big difference in compression. The bigger the change, the larger the cylinder bore.

 

[North Idaho Wolfman]

#1 answer needed, what is the compression #'s!

 

[MrShawn305]

Wow! Not even 24 hours and a ton of replies, you guys rock. I'll do my best to get caught up and answer all questions:

Tooljunkie: I don't remember the actual numbers, this was about a year ago. My buddy had to fabricate an adapter to thread in the the injector hole for the test. I remember that it was about 1/3 below spec minimum. I was able to read it without maxing my tester, as I couldn't believe the numbers and mine maxes at 300 psi. Glow plugs are good, we actually realized they weren't hooked up before we started working on it. Valves were adjusted but I think they were checked cold. That's something I can check hot this weekend at home. I have a good set of feeler gauges.

85Hokie: They weren't even hooked up before we started messing with it and it always started like the awesome machine it is (was). As far as the head gasket, that was my first thought. But we used a genuine Kubota gasket and I verified with the vendor it was the correct part number. It might be worth it to go to a different vendor and see if they come up with the same part number.

CountryBumpkin: I made sure to hook it up. Glow plugs should be working fine as they passed an ohm meter test.

D2Cat: No material was removed from the head or the deck. I changed the shims as sort of a "lets see if this helps" sort of thing. By that time we were both stumped as to what could cause these issues. Fuel system doesn't have air in it. I generally let the lift pump run for a minute before I crank it to ensure it has flow. I can hear it dripping back into the tank from the return.

CountryBumpkin: As for your head gasket question, I will do some research and make sure the one I got is the only one Kubota made. I got a genuine Kubota gasket from a retailer here locally, they said it was the only one, but it may have been the only one they stocked. I'll talk to a Kubota dealer and see what they have to say. That was one thing I suspected heavily.

Northern Idaho Wolfman: I wish I could remember those numbers, I want to say they were like 250ish. It was about a year ago we took them and my friend had to make an adapter to make it happen. I'll see if I can find the specs again and if he still has that adapter. I seem to remember them being about 1/3 below spec minimum and being like "what the actual hell" haha.

Again, thanks for ALL of your responses. These are all great things to consider and I will get all of the information I can. I will have to wait until Monday to call the deal in regards to the head gaskets, as I believe they are closed weekends. It just sucks, I've put so much work into this thing getting it to the point where it's complete and makes power, but I feel like I can't rely on it and it's a terrible feeling.

 

[lugbolt]

If you checked compression with a 300 psi gauge, and it didn't PEG or BURY the needle, it's low. Should be 450-550 psi. Below about 400 and they'll get hard to start; and since the little engine is so small, it doesn't take much to make compression pressure low. A piece of dirt stuck on a valve seat. A couple cc's of water/fuel/oil in the cylinder will bend rods-and this is not uncommon. Neither is bent rods and/or broken pistons from using starting fluid.

 

[Tooljunkie]

After replacing head gasket and running engine, valves need to be re-adjusted. That was my understanding when i did one on a grasshopper with a kubota engine. Believe it was adjusted cold both times. Unless manual shows a spec for hot setting. It was 3 years ago, I cant remember what i had for breakfast this morning.....

And a side note, sometimes a made up adapter may not necessarily give a good compression reading,yet your results were consistent.

 

[MrShawn305]

Lugbolt: I'm hoping it's not bent rods, the only way that could have happened I'm guessing is from water in the fuel. I was near it when it sucked up the water, it just quit running. Like it was starving for fuel, nothing more dramatic than that. As for starting fluid, I hate the stuff. I'll never use it in any engine for this reason.

Tooljunkie: I'll check the valves this weekend and see where they're at. As for the adapter, he's pretty competent. So I trust him on it. Also we used it for the leakdown test as well, which passed with flying colors.