B6000 Decompression Valves

[richie]

Hi everyone. One of my decompression valves is broken on my B6000. I never did use the decompression lever before to start the tractor, but I would like to know everyones opinion on wether I should replace the valve or just plug the holes? Is it really hard on the tractors to start without using decompression? Any comments would be appreciated.

I read that the lever opens up the exhaust valves just a bit ti relive compression, but how would a diesel start without compression?

Also, while I had the head off I noticed that the two end valves had a small gap between them and the rocker arm. Is this OK? I hope it is!

 

[Russell King]

I read that the lever opens up the exhaust valves just a bit ti relive compression, but how would a diesel start without compression?

The lever opens a valve and allows no compression - you are correct.

Engine does not start in that position. You pull the lever, spin engine up to speed (easier on starter, easier start in cold) then release lever, compression starts, inertia helps starter, engine starts.

I can't speak to the rest of your questions.

 

[Stumpy]

What do you mean by decompression valve? All the decompression system is is a rod that runs through the valve cover with round tip set screws through it. When that the decomp cable is pulled the rod rotates and those set screws push on the top of the exhaust valve rockers holding them slightly open. What's broken?

Russel's right with how to use it. It's easier on the starter than having to push through compression from 0 rpm. Not everyone uses it, no real harm in starting it normally but it's handy in the winter with a cold battery. Also makes a nice emergency shutoff.

The gap between the rocker and valve stem is called the valve clearance and proper clearance is somewhat critical. If it's too tight the valve can get held open slightly and burn up (valves dissipate most of their heat by contact with the valve seat). Too loose and the rocker and valves slam into each other and wear faster. A little looser is better than too tight but it's best to have them set correctly. The correct gap varies with the engine but is in the neighborhood of 0.010 inches and is set with a feeler gauge. A clearance that small normally can't be seen easily but you can feel it but moving the rocker with you fingers.

 

[birddogger]

Also, while I had the head off I noticed that the two end valves had a small gap between them and the rocker arm. Is this OK? I hope it is!

That really depends on the crankshaft position when you observed the gap.
Adjusting valves is done when the piston associated with the valves you are adjusting is at the top dead center of its' stroke. Marked on the flywheel and observed through an inspection port in the bell housing. When turning the flywheel slowly you will find, 1|TC, 2|TC, 3|TC; each for adjusting valves on cylinders 1, 2, and 3 respectively. You only have 2 cylinders but the methods are the same. If you are at the mark and valves are compressed, bring it around 360 degrees to the TC mark again.

Oh, a slight gap is better than no gap; correct gap is best.

 

[richie]

THanks everyone for your responses. I have decided that I am just going to plug the holes where the decomp screws are. After years of broken use by previous owner, it has worn some grooves in the valve cover on one of them causing it to be very sloppy. I never used them before so I see no harm in doing away with them. As for the valve clearance, I have a motor friend who will adjust them for me, as the gap is way too wide. The manual says the clearance should be 0.0098 in. so i will just set it at ten thousandths. Thanks again everyone!

richie

 

[ChrisMacon]

I have a 1977 B6000E and the decompression bar is missing. I can't stop the tractor from running without standing on the brakes at low RPM and stall the motor. It's been many years, but isn't the compression rlease also used to "Stop" the motor? When the head was re-worked, the tech removed the bar.

We just obtained the tractor from my mothers estate after her passing. I haven't used the tractor for 20 years.

Thanks

 

[freewheel3]

No, the decomp is not designed to stop the engine although it will in an emergency. The engine on B6000's is shut off by pushing the throttle lever all the way forward. If that does not stop the engine, there is an adjustment on the throttle linkage rod that needs to be made.

 

[yyri]

Old thread, sorry!
I don't know if I'm stupid but I cannot figure out how the B6000 decompression system would be adjusted. My tractor has all parts for the linkage but it is very loose. Decomp linkage for cylinder nearest to driver is slopping around with over 5mm vertical play so it won't catch the "half moon" indent of the rod going through valve cover and the lever is then not doing anything.
There is no "window" to see the decomp system pressing on the rockers, just the valve cover bolts+washers? The B6000 user- or workshop manual just says that assemble the parts properly lol.
Tried looking on B6100/7100 WSM. but it seems very different than that.

I guess I should check the valve clearances at the same time while messing with the decomp system, as I got the tractor this summer. I guess they cannot be totally wrong, as it runs pretty ok. Just have to source valve cover gasket somewhere in Finland.

 

[North Idaho Wolfman]

Do you see the ends of the stems coming out of the valve cover for the decompression levers have a slot, that's how you adjust them.
Loosen the nut, then turn the stem to get them into adjustment.

Go to kubotabooks.com and download the service manual if you haven't already to tell you how to adjust them.

 

[JerryMT]

Hi everyone. One of my decompression valves is broken on my B6000. I never did use the decompression lever before to start the tractor, but I would like to know everyones opinion on wether I should replace the valve or just plug the holes? Is it really hard on the tractors to start without using decompression? Any comments would be appreciated.

I read that the lever opens up the exhaust valves just a bit ti relive compression, but how would a diesel start without compression?

Also, while I had the head off I noticed that the two end valves had a small gap between them and the rocker arm. Is this OK? I hope it is!

I have an M4500 and I rarely use the decompression system but when I do, it kicks off by itself. It only allows a faster spin up on the engine for starting. Igntion of the fuel occurs with the decompression system is closed. As an aside, my operators manual never even mentions it! I found it my accident.

 

[yyri]

Do you see the ends of the stems coming out of the valve cover for the decompression levers have a slot, that's how you adjust them.
Loosen the nut, then turn the stem to get them into adjustment.

Go to kubotabooks.com and download the service manual if you haven't already to tell you how to adjust them.

Thanks, so adjusting by the stem and locking of setting by the jam nut.
Problem is to know when the setting is correct, as there is no access port on valve cover to input feelergauge between rocker and the decomp system.
The B6000 service manual is really unhelpful with this, as this is only reference to the system I found:

 

[trevoroni]

I followed the instructions from the B5100/6100/7100 service manual that Lil foot posted and it worked for my B6000.

With the lever pulled and the cylinder at TDC tighten until the screw contacts the rocker and then an additional 1 1/2 turns.

From my B5100/6100/7100 service manual:
(for what it is worth)
View attachment 95173 View attachment 95174