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Intake valves losing clearance on Kubota ZB600

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blue_tractor_man

Member
I have three (3) Kubota ZB600 two cylinder 12 HP diesel water cooled engines driving agricultural spray pumps. It seems that once or twice each season the engines get hard to start and begin puffing a little white smoke. The compression drops. It is always the valve clearance and it seems to only affect the intake valves. We open the valve clearance back up and the problem goes away.

What would cause these little engines to lose valve clearance? Could it be the ULS diesel? Do you think these engines have hardened valve seats? They stopped making them about 4 years ago.

Thanks
 
More than likely the valve seats are wearing. Common problem withn the older engines using the ULSD.
I've had several older Deeres in the shop with more or less the same problem.Not losing all the clearance,but cold starting problems.Seats hammered in,and deteriorated. Have the head rebuilt with hardened seats and the proper valve standout,and no more problem
 
I can't imagine why the ULSD would make any difference.
You've either got valve recession due to seat wear or the adjustment screws are moving...

Rod
 
basically the only thing that would decease valve lash clearance is the seats and valve face wearing. cam shaft wear and rocker wear, including bushings and valve stem wear increases clearance. thats including proper adjustment of valves.
 
I'm pretty sure the valves are receding into the seats. I just don't know why.

It would seem that if there was wear anywhere except the valve seats the clearance would increase.
 
possibly the valves were not properly hardened and are tuliping had this problem on early 4.3 liter chevy engines
 
Sounds like you run them enough this may be a good time to try some additives and do a test. Try nothing in one and something different in each of the other 2. Adding some motor oil into one may be a good idea to try as many posting here have tried it.
 
Had an old air cooled VW did the same thing, valve seat recession in the aluminum head. I think you were to adjust VW's valves every oil change.
 
NO big diesel expert here BUT I do not see how the low sulfur diesel would be affecting the intake valve. I would guess valve seat/valve face erosion or the valves are stretching. If it is the valve stretching, one of these days you are going to drop a valve and ruin a engine. It might be worth your money to pull the head from one engine and have a look at the valves and their seat. You should be able to determine if it is valve face/seat erosion or valve stretch. Might save you big money.

Kent
 
All diesel engines do that to some extent or another.If you use them a lot then you have to adjust the valves.On Cummins engines I worked on that were in the 1980s you were supposed to set the valves at about 80,000 miles.Thats about every 6 to 8 months on a big rig.Newer valves seem to go a lot further before they need adjusting.I know they use real hard metal nowdays and probably have better stuff in the seats too,but the valves wear a groove in the face.Then they loose clearance.Other parts wear too.After a while the other parts need to be rebuilt too.They had bushings that could be replaced in the rockers and cam followers.Another thing is a few times I saw a cam wear a lobe off.
 
Might pay to inspect your air cleaner and plumbing real close. wipe the inside of the air intake pipes between the air cleaner and engine with a white rag to see if they are dirty.
I have seen severe intake seat and valve face wear on gas and diesel engines from dirt getting in with the air.
 
I am not familiar with Kubota engines but I have had more problems since the low sulfur fuels came out. It seems that the older motors are having more valve trouble with it. Some claim that the sulfur lubed the valve surfaces. I don"t know if this is true or not.
 
I am not familiar with Kubota engines but I have had more problems since the low sulfur fuels came out. It seems that the older motors are having more valve trouble with it. Some claim that the sulfur lubed the valve surfaces. I don"t know if this is true or not.
 
I was having a similar problem and ended up being the overlap of the cam was wearing to a point that the valves didn't seat long enough to cool and basically allowed them to forge the valve face and seat. I re-ground cam, rebuilt heads using sodium filled titanium valves and new seats. I ported the cooling jackets, used synthetic oil and increased the size of the air cleaner.

Dat's what I did.... 6 years ago!
 
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