Valve Adjustment Question - Reason for it?

Henro

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I was reading another thread regarding valve adjusting and checking. This has been on my mind recently since I never did it on my tractors and they are 20 and 19 years old.

For some reason I had thought that Valve adjustment was important because if you neglected it, you could end up burning a valve, which would not be a great thing.

Granted I can see how a valve wearing in a bit would cause clearance in the system to decrease. So at some point when clearance reached zero, the valve would not close totally and a burned valve could result.

Am I seeing this correctly, and is this a real issue?

I certainly understand in theory it is a real issue. But in practice is it? There seems to be a fair number of Kubota tractors still in operation that are 40 or more years old...just wonder how many times they had their valve clearance checked. Not disputing that checking valve clearance is a good idea. Just wondering if there is a practical need.

Is it normal for valves to seat in enough to close the initial clearance to zero?

Just a question by someone who has no clue, but can understand the theory. I THINK I understand it anyway...
 

lynnmor

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B2601-1
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I was reading another thread regarding valve adjusting and checking. This has been on my mind recently since I never did it on my tractors and they are 20 and 19 years old.

For some reason I had thought that Valve adjustment was important because if you neglected it, you could end up burning a valve, which would not be a great thing.

Granted I can see how a valve wearing in a bit would cause clearance in the system to decrease. So at some point when clearance reached zero, the valve would not close totally and a burned valve could result.

Am I seeing this correctly, and is this a real issue?

I certainly understand in theory it is a real issue. But in practice is it? There seems to be a fair number of Kubota tractors still in operation that are 40 or more years old...just wonder how many times they had their valve clearance checked. Not disputing that checking valve clearance is a good idea. Just wondering if there is a practical need.

Is it normal for valves to seat in enough to close the initial clearance to zero?

Just a question by someone who has no clue, but can understand the theory. I THINK I understand it anyway...
You understand it quite well. Just because people neglect their possessions doesn't make the issue go away.
 

Henro

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You understand it quite well. Just because people neglect their possessions doesn't make the issue go away.
The question is more focused on the practical need, rather than absolutely following Kibota’s guidance, which could be right on, or not.

But remember! Kubota also says to remove rear tire ballast each time you attach your backhoe.
 
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GeoHorn

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Technically correct. As valves seat they can wear to the point that insufficient clearances can prevent full seating of valves and may lead to valve/valve-seat damage.

Valve clearance checks are usually pertaining to “solid” or mechanical lifter systems. Hydraulic lifter systems are not usually adjustable…. they hydraulic tappet takes up the clearance entirely opposed only by the valve springs.

Also, Mfr’s wish to protect their Warranty obligations… If they didn’t instruct owners to have valve clearances checked periodically …the Mfr’r would have little defense for burned valves due to insufficient clearances. (Isn’t it interesting the WSM only has them checked once in the entire lifetime of the engine…at 800 hrs…when the engine is most likely still within the warranty period?)

I seem to recall a certain banned former participant bragged he had his valve clearances checked frequently (annually?) by his dealer…yet never found any out of spec.

Henro, you have taken note of something interesting tho’… I wonder why so many diesel valve-clearances never receive any maintenance whatsoever yet operate thousands of hours…
…so the likelihood of finding anything untoward seems pretty remote heh?

Yes,..it’s taking a chance. Just not a big one. IMO

(One method to see if a valve is leaking without checking valve clearances is to use a differential compression test and listen for escaping air at intakes and exhaust ports, although if leaking is discovered damage has likely already occurred.)
 
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Mark_BX25D

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The question is more focused on the practical need, rather than absolutely following Kibota’s guidance, which could be right on, or not.

Whatever the industry, whether it's tractors or cars, manufacturer's maintenance guidance is intended to do four things:

  1. Meet government requirements. (EPA limits on total lifetime use of petroleum products, for example.)
  2. Protect them from lawsuits.
  3. Keep your equipment trouble-free past the warranty period.
  4. Protect their reputation by keeping your equipment in good enough operating condition long enough that you don't complain.

It's not Divinely Inspired, and it's not even the best advice the engineers can give you. #1 and #2 come far ahead of #s 3 & 4. For example, the trend towards extended oil change intervals and "sealed transmissions" (which have been an abject failure) are completely driven by #1.

Fanboys usually think it's Graven on Stone Tablets by the Engineering Gods and Cannot Be Questioned. This viewpoint makes it impossible to think rationally on the subject, so such people should be politely ignored.
 

lynnmor

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Fanboys usually think it's Graven on Stone Tablets by the Engineering Gods and Cannot Be Questioned. This viewpoint makes it impossible to think rationally on the subject, so such people should be politely ignored.
If one could think rationally they might know that mechanical things can wear and adjustment makes sense. Others can stick their heads in a dark place and continue abusing their equipment. Valve adjustment goes back to the dawn of internal combustion engines.
 
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fried1765

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If one could think rationally they might know that mechanical things can wear and adjustment makes sense. Others can stick their heads in a dark place and continue abusing their equipment. Valve adjustment goes back to the dawn of internal combustion engines.

If one could think rationally they might know that mechanical things can wear and adjustment makes sense. Others can stick their heads in a dark place and continue abusing their equipment. Valve adjustment goes back to the dawn of internal combustion engines.
I checked the valve clearances on my 1989 Ford 1920 at 1,100 hours (17 years).
Replaced valve guide seals at the same time.
 

lugbolt

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I'm going to get long...so you've been warned.

First what is valve clearance? It is a engineered clearance between the tip of the valve and the rocker arm (in this discussion...there are other designs as well). That clearance is there for a reason. One, it allows for wear, among other things, and something else--that clearance gives you an idea of whether or not anything is wrong, when you check it.

Valve clearance will change with usage and wear. That is a given. It will also change with thermal expansion. The valves run hot and they will expand. The cast iron block has a different thermal expansion rate than the steel pushrods, valves, rockers, etc. it's all different. We are talking micro and milli inches when we are talking about expansion, but the stack-up is what we're looking at (the combined growth of all of the parts). Say you have .007" clearance at room temp, say 65 degrees. At 200 degrees that clearance usually closes up a couple thousandths. Many think it opens up, but IME, it actually decreases. I think the major reason is because of the valves; they run hotter than the rest of the engine, especially exhaust valves. Now you have .005" hot running clearance. Kubota would like to have a cushion; so that if you run it hotter than normal, or if you're working it hard, that clearance won't end up at zero. You don't want zero. Not on these engines (they are all mechanical tappets-NOT hydraulic; with the exception I think of the M7 or M8? tractor). If it goes to zero, the valve(s) get hung open slightly and allow gases to escape through them, which wears the face of the valve, and the valve seat. Also heat is more likely to build up since the valve cannot transfer heat from itself to the cylinder head; and on a diesel this is pretty important since there is no liquid fuel going across the valves, which helps to cool them. Air only.

You also don't want the clearance to be loose either. Loose valves act like a hammer on the tip of the valve, the rocker arms, the pushrods, tappets, and camshaft. Millions of cycles of hammering on them, something will usually break. Often the valve, or rocker arm. Sometimes the tappets will break and that is never pretty. But then again neither is a broken valve, usually destroys the engine and sometimes spectacularly.

Kubota (and every other manufacturer that uses "solid" tappets) asks you to check the clearance. The biggest reason here is to detect issues before they swarm. For instance if you are checking a V1505 and Cyl#1 Inlet valve clearance is .030 and all the rest were .009, you just found a problem. However, A couple thousandths either way of spec is normal wear. Secondly to account for wear. If they start getting loose, they hammer the seats out of the head among other things. If tight, high pressure gases will escape around the seat/face and wears them, and usually results in a cracked head, dropped/broken seat, worn seat, severely worn valve face, burned valve face, cracked valve, broken valve, etc. None of which are good. And yes I've seen it on Kubota. cracked valves especially-and cracked heads. Lots of cracked heads but usually due to overheating.

Most folks don't maintain them, they never check valves. I think 800hr is the interval on a lot of them. Normally they're still pretty close. Run them twice that without checking, and they're usually starting to get loose or tight depending on how much wear there is. "Well it runs fine and ain't noisy so I ain't worried about it". Right. Can't hear the noisy looseness over the normal clattering of the diesel engine. By time you hear it, it's too late. Or when they tighten up, you never hear that either. Just starts getting harder and harder to start, keep spraying the starting fluid to it, next thing ya know its running on 1 less cylinder until warmed up (clearance opens up a little), then you think it's fine. Then one day you're cutting grass with the shredder on back at full load and rpm, wham bang clank, engine stops, and death fluids begin leaking out of the engine...broke a valve off, destroyed the entire engine (nothing salvageable in most cases, maybe the intake manifold and maybe the valve cover), all because ya didn't have time or was too lazy (that's usually my excuse) to check the valves. It really does need to be done. if you don't have time at 800.0 hours, write it down on your to-do list. If it goes over big deal. But it still needs to be done asap.

on a lot of modern gas engines with overhead and dual overhead cams, there are no rocker arms. The valves are actuated by the camshaft alone. The clearance is the gap between the cam and the "bucket". There is a metal cup that fits down kinda tight into a cylinder in the head, over the outside the valve spring(s), and the bucket usually has either a little shim between the tip of the valve and the bucket, or the bucket itself is made in such a way that it can be had in different thicknesses, to adjust the clearance between the bucket and the cam. IIRC the Sidekick 850 Kubota has this design. That is the only reason I mentioned it. They're a little more involved to adjust the clearance than a rocker arm style valvetrain but they also don't need adjustment nearly as often, as there are less moving parts and also a lot more stable valvetrain, which means higher RPM potential which means more HP.
 
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The Evil Twin

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Typically it is the seat that wears and closes the gap. Valves usually "get tight" as the hours pile on.
While not the exact same design, my motorcycles valves usually have to be adjusted once. Maybe twice for a random cylinder. Once they wear in there is little change. Likely the same on any mechanical lifter (one of my cars as well). After 24000 race miles at over 10000 rpm I never needed to adjust them.
I'll check the 'Bota when it's time. If there is no need to adjust then I may never do it again.
 
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