kubota 800 hour engine valve adj maintenance=worth it?

Freakingstang · Apr 26, 2012

There are a couple mis- conceptions in this thread. You thought because it started then the glow pugs should be operating?! Not necessarily true. One could be working and that is why it fires, but runs rough for a few seconds until the air heats up. Remember a diesel engine just runs off of compression ignition. There is no spark to ignite the fuel/air mix. So if it is cold, cold air is much denser and also has a higher dew point (moisture content).

Both my Kubota g1900 (three cylinder) and my 2cyl Mitsubishi do the same thing. Starts, and puffs a little until you get some heat in it. Takes Longer to warm up the colder it is...

Now, for the valve adjustment. At work(generator rental company) we have Kubota 15kw generators. We do an overhead valve adjustment every 2000 hours along with testing the injectors. The whole purpose of adjusting the valves isnt because they are "loose". Think about the valve slamming back into the seat, four times per revolution. Now think about how many times the valve has slammed back to the seat in the last 900 hours.....

As the valve and seat wear, the valve tip becomes raised. So your valve clearance will tighten up over time causing both the intake valve and exhaust valve not to fully open. This means the engine won't take in as much air, and can't expell the burnt gases as efficiently. The engine will still run just fine, but it will start to loose peak power. We are not talking much in terms of clearance... Just a couple thousandths. But on the other hand, it is very possible too that the rocker has loosened up. This is normally due to someone not tightening something to torque more than from just coming loose on it's own.

BeezFun · Apr 26, 2012

namesray said:
don't really understand. starts hard. not rough running. only sputters for around 5 seconds immediately after start. i attribute that to starting hard.

Sorry for confusion, I interpreted your original post "since last fall it has started starting rough" to mean that it ran rough after it started. I understand you mean that it's difficult to start, and that could sure be a problem with the plugs.

kuboman · Apr 26, 2012

I too would check the glow plugs. It sounds like you have one that is just a bit weak. Glow plugs are often neglected and miss diagnosed. At close to 900 hrs it would not hurt to replace them all with new. :thumbsup:

EE_Bota · Apr 26, 2012

Freakingstang said:
There are a couple mis- conceptions in this thread. You thought because it started then the glow pugs should be operating?! Not necessarily true. One could be working and that is why it fires, but runs rough for a few seconds until the air heats up. Remember a diesel engine just runs off of compression ignition. There is no spark to ignite the fuel/air mix. So if it is cold, cold air is much denser and also has a higher dew point (moisture content).

Both my Kubota g1900 (three cylinder) and my 2cyl Mitsubishi do the same thing. Starts, and puffs a little until you get some heat in it. Takes Longer to warm up the colder it is...

Now, for the valve adjustment. At work(generator rental company) we have Kubota 15kw generators. We do an overhead valve adjustment every 2000 hours along with testing the injectors. The whole purpose of adjusting the valves isnt because they are "loose". Think about the valve slamming back into the seat, four times per revolution. Now think about how many times the valve has slammed back to the seat in the last 900 hours.....

As the valve and seat wear, the valve tip becomes raised. So your valve clearance will tighten up over time causing both the intake valve and exhaust valve not to fully open. This means the engine won't take in as much air, and can't expell the burnt gases as efficiently. The engine will still run just fine, but it will start to loose peak power. We are not talking much in terms of clearance... Just a couple thousandths. But on the other hand, it is very possible too that the rocker has loosened up. This is normally due to someone not tightening something to torque more than from just coming loose on it's own.

I didn't see the earlier misconceptions. I did like what you wrote, however.

I think the last paragraph is a bit confusing. If the banging into the head causes the tip to rise, and the tappet clearance gets too tight, it is not failing to open all the way, rather it is risking not closing all the way*. Failure to close all the way leads to a chance of "burning" the valve, particularly an exhaust valve.

*Too much clearance=>failure to open as far as possible.
Too little clearance=>risk of not closing fully, therefore not cooling adequately, while also getting increased heat from hot gases leaking through the not fully closed valve.

namesray · Apr 26, 2012

EE_Bota said:
Reread my post above, it explains that you can CHECK them and the consequences of neglecting them. Remember, I don't know the difference between what you don't want to do, don't know how to do, or feel uncomfortable doing, so I don't let me push you in any way. But above you seem to be interested in both how the tractor works, and learning more about how to take care of it.

I doubt your valves are causing this...and as far as problems go, your problem seems very minor. Your tractor starts fine, balks for about 5 seconds, and then works fine the rest of the time. Were it me, I'd lower my level of concern about that, and instead get a service manual and start reading. I'd CHECK my own valves, and if I felt confident and comfortable (I do) I'd adjust them if needed.

In a car...sometimes it is best to just "turn up the radio." On a tractor, maybe you yell at it for 5 secs when you first start it "Ha! Ha! Get UP! Ha!" I'm joking..but less than you may think. I have to manage myself with I interact with equipment..any little noise, any little difference, I'm on it. But I can justify that..I'm an engineer for a maintenance department...always trying to learn, especially how to diagnose.

very well put. you read me well. i am very interested in how it works and do want to learn this stuff, hence why i am here at tbn. my grandpa when he was alive was an excellent mechanic and if he were still alive today, he would love to help me fix this stuff and teach me. when i had the chance to learn when he would work on his farm equipment, i was too young and stupid to take the time to learn with him. probably the biggest regret in my life. i do tend to pick up on mechanical things fairly good, scored with in the top 99% on the military asvab test in the mechanical comprehension section. (that's another story for a different time.) problem is i am so cautious, i get worried that i will not do something quite right and make the problem 10 times worse. like trying to adjust the valves and thinking i get it good and start it up and bamb, there goes the engine at 2300rpm. that could cause a lot of damage and since i lack tools and experience, i usually just leave it to mechanics. their work is also backed by warrenty=peace of mind.

i agree with you it is probably not the valves and the problem is probably minor. sometimes i am a overly cautious person. i know something off in an engine that revolves so fast and so much, little things let go can turn into BIG problems and cost big $$$$. me lacking experience and knowlege does make me too cautious most of the time. a reason i try to learn here at tbn from more experienced people with knowlege and tricks of the trade.

i like the idea of turning up the radio to drown out the noise.:laughing: i remember my grandpa telling me a story of a guy who did that. i should start yelling at the tractor when it is sputtering.:laughing: might relieve some stress. hopefully i get it fixed soon and the warmer weather comming, the problem won't be as noticeable. i should get a kubota service manuel. check with my dealer to get one. anyplace else i could get one if dealer doesn't have them?

thanks for the suggestions so far. i talked to dealer today and he doesn't think it is the glow plugs but he will check them if i take it in. he keeps saying fuel or maybe fuel injector. i don't get it as i think fuel would cause the problem all the time, injector too. like i say though, i lack knowlege and experience. i will try to get the tools to check the glow plugs in the mean time. i think i could at least handle that.:laughing::thumbsup:

kuboman · Apr 26, 2012

i talked to dealer today and he doesn't think it is the glow plugs but he will check them if i take it in. he keeps saying fuel or maybe fuel injector. i don't get it as i think fuel would cause the problem all the time, injector too. like i say though, i lack knowlege and experience. i will try to get the tools to check the glow plugs in the mean time. i think i could at least handle that.:laughing::thumbsup:[/QUOTE]

It may not be but I do know a weak GP will cause sputtering on a cold start. I had a GM V6 diesel in an old Celebrity and it liked to eat GP's. With 6 fresh plugs it would start right up with no smoke or sputtering. Quite impressive really, but after a while one plug would get a bit weak and you would get just a hint of sputtering. After 2 got weak starting got to be more difficult, so I would not be surprised if you had one plug just a bit weak. JMHO

Freakingstang · Apr 26, 2012

EE_Bota said:
I didn't see the earlier misconceptions. I did like what you wrote, however.

I think the last paragraph is a bit confusing. If the banging into the head causes the tip to rise, and the tappet clearance gets too tight, it is not failing to open all the way, rather it is risking not closing all the way*. Failure to close all the way leads to a chance of "burning" the valve, particularly an exhaust valve.

*Too much clearance=>failure to open as far as possible.
Too little clearance=>risk of not closing fully, therefore not cooling adequately, while also getting increased heat from hot gases leaking through the not fully closed valve.

let me try to explain this again. As the valve and the seat beat against each other 4 times per engine revolution, they wear over time. As they wear, the valve will sit higher. if the clearance on the rocker hasn't been adjusted, the valve stem is raised (from the seat and valve angle wear). The clearance between the valve tip and rocker is less and less with each hammering on the seat. So after time, if the exh clearance is factory set at .030. after 800 hours the clearance will be less. these are what if scenario numbers. So after 800-1000 hours, the valve stem to rocker clearance is now .020. The valve will still fully close, and it will cause undue stress on the springs, retainers, rockers etc. IT will NOTt be fully opened as there is .010 difference.

I do this everyday. Granted our generators will run at a continuous 1800 rpm, but 2K hours is 2K hours. .015-.020 tightened lash will affect performance. you'll probably never notice it in a tractor, but the idea is the same across the board.

EE_Bota · Apr 27, 2012

Freakingstang said:
let me try to explain this again. As the valve and the seat beat against each other 4 times per engine revolution, they wear over time. As they wear, the valve will sit higher. if the clearance on the rocker hasn't been adjusted, the valve stem is raised (from the seat and valve angle wear). The clearance between the valve tip and rocker is less and less with each hammering on the seat. So after time, if the exh clearance is factory set at .030. after 800 hours the clearance will be less. these are what if scenario numbers. So after 800-1000 hours, the valve stem to rocker clearance is now .020. The valve will still fully close, and it will cause undue stress on the springs, retainers, rockers etc. IT will NOTt be fully opened as there is .010 difference.

I do this everyday. Granted our generators will run at a continuous 1800 rpm, but 2K hours is 2K hours. .015-.020 tightened lash will affect performance. you'll probably never notice it in a tractor, but the idea is the same across the board.

I don't care if you do it everyday. What I do care about is whether something is right or not. I give advice to mechanics everyday too. That doesn't mean I'm not full of false information and wrong most of the time. I do my best though.

I believe what I said is correct. I believe what you are saying is incorrect. Neither of those gives me any particular pleasure. I don't really care to get into a spat about it either. I wish you great success in your field of endeavor.

Freakingstang · Apr 27, 2012

EE_Bota said:
I believe what I said is correct. I believe what you are saying is incorrect.

That's fine. I don't care what you think is right or wrong. Read a service manual, google it. Whatever. Don't come on here and tell me I'm wrong when you don't have a clue what you are talking about. I'm sorry this isn't your sisters uncle's cousins kid sisters 77 chevy caprice.

EE_Bota · Apr 27, 2012

Freakingstang said:
That's fine. I don't care what you think is right or wrong. Read a service manual, google it. Whatever. Don't come on here and tell me I'm wrong when you don't have a clue what you are talking about. I'm sorry this isn't your sisters uncle's cousins kid sisters 77 chevy caprice.