B8200HST Decompression Lever Stuck

murky

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Mar 30, 2012
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Vancouver, WA
I got a 1987 B8200HST a few weeks ago. So far I'm very happy with it. I've been going through trying to see what needs fixing and how it is supposed to work.

One thing that doesn't appear to be as it should is the decompression knob. If I pull on it nothing happens. If I follow the cable under the hood to the lever it I can see tha the lever is stuck.

There is a spring that appears is supposed to pull the lever back into position when the knob is released, but the lever is way too stuck for that spring to do anything.

With significant force I was able to pull the lever open a little bit. The amount of force it took scared me. It was difficult to push it back closed. Not knowing exactly what it does (somehow holds exhaust valve open or somesuch?) I was afraid that failing to close it all the way could cause a problem.

So what is likely to be wrong and what can I do to fix this? Is this a safety concern in case for some reason the engine shutoff doesn't work? Am I missing anything other than improved starting in cold weather or with weak battery?
 

Stumpy

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L175
Dec 1, 2011
848
3
0
NE Ohio
Yeah you don't want that to get partially stuck open. What that's doing is turning a cam that pushes on the top of the rockers for the exhaust valves holding them open. If it's pushing on them only enough to keep the valves off their seats but it still runs the valves will melt.

Aside from the cold starting benefits it gives you a more positive way to shut the engine off. It's rare and happens more on diesels with oil cooled turbos but if engine oil gets mixed into the intake air the engine will keep run on it's own without fuel injection til it over speeds or you can lower the compression ratio enough to stall it. You can do the same thing by blocking off the intake with something. It's called a run away diesel.

Not sure why it froze up other than lack of use but it's completely contained in the valve cover so you can get it off and work on it fairly easily.
 

murky

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Mar 30, 2012
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Vancouver, WA
Thanks for the fast reply Stumply. I don't have a lot of experience on tractors, or car engines for that matter.

Are you saying that I need to take off the valve cover in order to get to the journal, or bearing, or whatever this pivoting lever is riding in and somehow clean it out and get it freed up?

I'm assuming I don't want to leave penetrating oil and solvents and such behind. Do you, or anybody, have a suggestion for a specific set of actions to take? Sorry for being dense. I'm a little green.

I've changed brake rotors and pads and bled brakes, swapped out alternators and belts and that sort of thing on a car. Haven't messed with engines yet and haven't built up a lot of practical experience.

I mostly learn about these things via the internet.
 

Stumpy

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L175
Dec 1, 2011
848
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NE Ohio
No worries dude, we all started there at one point. Heck a good portion of overhauling my tractor has been researching how to do this stuff.

Yes to get to the decompression shaft you need to remove the valve cover. On yours you'll need to remove the decomp cable, breather tube, and then the two or three big nuts to remove the valve cover. It's a bit of work but not hard just time consuming. Your shaft appears to be sealed by a single oring where the shaft comes out of the cover (the grove might be in the cover). That oring is probably broken or something has rusted, make sure it's not just the cable before you goto all this trouble. The cams are actually screws going through the shaft retained by nuts and they'll have to be removed to slide the shaft out. You may need to remove the 3 access plates in the cover (two bolts each) to get to the nuts and since they need to come off anyway pop em off and clean the mating surfaces. Once the shaft is out clean it and the end journal (scotch brite works wonders) and replace the oring. You can just match up at the hardware store.

You don't have to be too careful about solvents getting in the crankcase, it's dirt and dust you need to watch, but be careful around rubber seals. Surgical cleanliness isn't necessary but do what you can to clean any dust and dirt you generate out of the inside of the valve cover. Brake clean can be useful but again keep it away from rubber.

If it moves freely now reinstall the shaft (don't forget the oring) and the screws (height doesn't matter just yet), clean out any dirt/dust and then reinstall the valve cover on the engine and reattach the cable. Now it's time to readjust the decompression bolts so they're at the right height. You need to rotate the engine so the exhaust valve on the cylinder you're adjusting is fully closed. Rotate until the rocker is in the top most position and hasn't moved for dozen degrees of crank rotation or so. It's probably easiest to turn the engine using something hooked to the fan belt just make sure the fuel cut off is pulled, don't want thing thing starting on you! Once the rocker is in the top most position pull the release cable and turn the screw so it's just touching the rocker and then go in another 1-1/2 turns and tighten the nut. Rinse and repeat for each cylinder. Once everything looks good apply a light film of instant gasket or RTV to each access plate, bolt them back down and reattach the breather tube.
 

murky

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Mar 30, 2012
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Vancouver, WA
Thank you for what sounds like a very good explanation. It sounds like if I'm going to do this I might as well do a valve adjustment at the same time.

I'm not yet ready to do this for something that isn't a necessity. I'll keep this post ready for when that comes. Higher on my list is to replace my radiator hoses and coolant, fan belt, and install a new oil pressure switch and gauge and hour meter/tach drive. All of those things sound easier.

Well, the fan belt seems like it should be the easiest but have to move the radiator around apparently. I thought a tractor would be easier to work on because everything would be in the open and bolted on. But there is a lot more removing things to get to other things than I expected.

Thanks again.
 

Stumpy

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Equipment
L175
Dec 1, 2011
848
3
0
NE Ohio
No problem. In general things are easier but every machine has it's quirks. Anyway yeah valve lash should probably be done at the same time, it's similar in principle except you use feeler gauges for better accuracy.
 

kubotasam

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Alfred Maine
I am certainly not saying that you should not fix this. However the decompression cable has been stuck on my b7100 since I have owned it. I have never felt the need to fix it. My tractor starts and runs great without it. I actually just bought a second B7100 and the cable on this one is stuck also. People don't need then/use then so the stick.
 

sparky66

New member

Equipment
B8200
Nov 6, 2011
3
0
0
Hinckley, OH
I have a B8200 that doesn't even have the cable anymore. I have never needed to use it. It starts fine even in the winter(Northern Ohio),
 

Lil Foot

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I have seen a B7100 that had similar symptoms, but it turned out that the decompression mechanism was free, but the cable was almost immovable. We lubed the cable & worked it free, & that fixed the problem. Good idea to check valve lash while you are in there, mine were all sloppy loose, & the tractor runs noticeably smoother & quieter now.
 

murky

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Mar 30, 2012
107
0
16
Vancouver, WA
Hmm, I'll have to take a look at it again, but I don't think in my case it is just the cable. I pulled on the lever the cable is attached to and it was difficult to move. I don't think that was just fighting the cable. It was difficult to move in both directions.

I'm sure the previous owners never touched it. They also seemed to have never touched the seatbelt. It was completely rusted shut. That was the first thing I replaced on the tractor.
 

murky

Member
Mar 30, 2012
107
0
16
Vancouver, WA
No worries dude, we all started there at one point. Heck a good portion of overhauling my tractor has been researching how to do this stuff.

Yes to get to the decompression shaft you need to remove the valve cover. On yours you'll need to remove the decomp cable, breather tube, and then the two or three big nuts to remove the valve cover. It's a bit of work but not hard just time consuming. Your shaft appears to be sealed by a single oring where the shaft comes out of the cover (the grove might be in the cover). That oring is probably broken or something has rusted, make sure it's not just the cable before you goto all this trouble. The cams are actually screws going through the shaft retained by nuts and they'll have to be removed to slide the shaft out. You may need to remove the 3 access plates in the cover (two bolts each) to get to the nuts and since they need to come off anyway pop em off and clean the mating surfaces. Once the shaft is out clean it and the end journal (scotch brite works wonders) and replace the oring. You can just match up at the hardware store.

You don't have to be too careful about solvents getting in the crankcase, it's dirt and dust you need to watch, but be careful around rubber seals. Surgical cleanliness isn't necessary but do what you can to clean any dust and dirt you generate out of the inside of the valve cover. Brake clean can be useful but again keep it away from rubber.

If it moves freely now reinstall the shaft (don't forget the oring) and the screws (height doesn't matter just yet), clean out any dirt/dust and then reinstall the valve cover on the engine and reattach the cable. Now it's time to readjust the decompression bolts so they're at the right height. You need to rotate the engine so the exhaust valve on the cylinder you're adjusting is fully closed. Rotate until the rocker is in the top most position and hasn't moved for dozen degrees of crank rotation or so. It's probably easiest to turn the engine using something hooked to the fan belt just make sure the fuel cut off is pulled, don't want thing thing starting on you! Once the rocker is in the top most position pull the release cable and turn the screw so it's just touching the rocker and then go in another 1-1/2 turns and tighten the nut. Rinse and repeat for each cylinder. Once everything looks good apply a light film of instant gasket or RTV to each access plate, bolt them back down and reattach the breather tube.
Thanks again for your great instructions. I'm reading them again now that I've done the other work that was a higher priority for me.

With the benefit of the parts diagram in front of me, this seems much less daunting. There are 3 areas that I'm not quite yet confident about:

1. I assume I need a new gasket for the cylinder head cover and I probably need to torque the two cap nuts to a specific torque. Do I need to oil or otherwise treat the gasket before installing it? I think my WSM omits the engine for some reason so I don't know if it specs the torque.

2. I'm not quite following the part about hooking something to fan belt to rotate the engine. I suppose you are saying to grab it somehow but I'm not sure what you mean by hooking it, and not sure how much force it is going to take.

3. Your instructions sound pretty clear about how to adjust the screws to reach the rocker plus 1.5 turns, but I want to make sure I understand what this is accomplishing. Basically, is what I'm doing setting how much I push the rocker when the cable is pulled? Cable released the valve closes, cable pulled the valve will be open whatever amount corresponds to pressing down on the rocker by the length of 1.5 x the screw pitch minus any play or slop? So the decompress pull just barely cracks open the exhaust valves?

In operation, I need to pull the release hard enough to overcome the valve springs, and when I push back in the release the valve springs will re-close the exhaust valves? The spring on the decompress shaft is just to help it fully return to its rest position and seat the decompress pull handle?
 

phildac

Member

Equipment
1984 B8200E, L260F
Jul 29, 2009
203
1
16
Wentzville, MO
Murky,

Definitely get another valve cover gasket. They are pretty small and flimsy.
A little trick, use some grease to help the gasket stick to the valve cover when you're reinstalling.
 

Stumpy

New member

Equipment
L175
Dec 1, 2011
848
3
0
NE Ohio
The valve cover gasket doesn't need to be oiled, the orings on the shaft do. There really isn't a torque for the valve cover nuts, I do em by feel. Get the nuts on finger tight and then start turning with a wrench or ratchet. What you're feeling for is how much force it takes to break the nut loose and get it turning each time you start pushing on the wrench again. The tricky part deciding what's enough force that it won't rattle loose before you've gone to far and stripped the threads. It's easier than it sounds but you've got to strip some threads before you get good at it. Valve cover nuts are pretty forgiving thanks to the light loading and all that rubber. Just check those nuts for a while after you get it running again to make sure they're not rattling loose.

For rotating the engine I was referring to putting a wrench on the nut of one of the accessories driven by the fan belt (alternator, cooling fan) and turning that to rotate the crankshaft to the required position. It's possible it'll require enough force that the nut would back off before the crank moves but I doubt it. I would remove your glow plugs before doing this to make completely sure it can't start and so you don't have to push it through compression.

Everything you said from #3 on down is exactly right. That 1 1\2 turns is straight from my WSM. Again the trick is to open the valves just far enough to decompress the engine (it's doesn't need much) when the cable is pulled but not so far that valves don't get held open when the decomp cable is released during normal running.
 
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Stubbyie

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Jul 1, 2010
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Midcontinent
Make certain the cable is completely free before diving into the valve cover. If not used the cables tend to rust up tight.

Before breaking out the wrenches try soaking the entire mechanism at the lever end with Kroil or similar top-notch high-quality penetrating oil. You've got a good shot at it all coming loose. If later you think the oil has contributed to deterioration of any O-rings you can still pull it apart. Chances are if you can get it loose it'll work fine for as long as you're interested in using it.

In industrial settings runaway diesels occasionally happen. Had one go off once in the oilfield sucking natural gas on worksite. Sort of exciting for a few minutes. In such situations turning the key off accomplishes nothing--she just keeps running, faster and faster depending on fuel available mixed with air. In that case killed it with a large CO2 fire extinguisher shot into the intake. Note CO2 not drychem. Years later saw on an oilfield truck somebody had installed an aftermarket push-pull gate valve on the air intake stack.

We crank ours year-round by pulling the decompression lever, spinning it with starter, and then pushing lever in. Takes longer to write than to do it. Seems easier on engine and starter and gets a squirt of oil moving internally. Also ensures that if needed it's--the decomp--ready.
 

murky

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Mar 30, 2012
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Vancouver, WA
Okay, its only 2 years later and I'm almost ready. I have new gaskets, new glow plugs and a cheap diesel compression tester on hand. Oh, and a couple of the O-rings for the decompression shaft.

I even bought a used D950 manual (different suffix, assume that doesn't affect torques and such) but of course I can't find it any more.

Now I just need a few hours with just me and my garage and I'll let you know how it went.

Thanks again for the advice guys.
 

murky

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Mar 30, 2012
107
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16
Vancouver, WA
I found a Kubota 70mm Stroke (includes D950-B) service manual PDF for $10, on my computer I won't lose it.

After seeing the gasket and the advice I wasn't too worried, but FWIW it says about 6 lb-ft for the head cover nuts, so not much.

And here is the procedure for setting the valve clearance:

 

murky

Member
Mar 30, 2012
107
0
16
Vancouver, WA
Bad news :(

I fixed the sticking decompression lever. It turns out that there is a bolt (#19 on the diagram) that tightens down into a groove in the decompression shaft to prevent axial thrust (hold it in place front to back). I think the last person to open things up had the shaft out of position axially so that this bolt missed the groove and acted as a set screw clamping the rod in place.



That was the good news. Its very smooth now and the o-ring was fine but I replaced it anyway.

Bad news is, I took the glow plugs out (after removing intake manifold) since I have new ones and to make it easier to position the cams for valve adjustment.

When I rotate the engine periodically about a half teaspoon of green liquid (presumably coolant) forcefully squirts out of the empty glowplug hole of the middle cylinder.

I have another thread about the tractor blowing white smoke out the exhaust especially when cold.

Does this mean a new head gasket, or worse?
 
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North Idaho Wolfman

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Bad news :(
When I rotate the engine periodically about a half teaspoon of green liquid (presumably coolant) forcefully squirts out of the empty glowplug hole of the middle cylinder.

I have another thread about the tractor blowing white smoke out the exhaust especially when cold.

Does this mean a new head gasket, or worse?
Sadly, yes that's exactly what that means, Fingers crossed it's just a blown gasket, take the head off and remove it carefully and look for signs of a rusted out or blown gasket in a water area.
 

murky

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Mar 30, 2012
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Vancouver, WA
Thank you Wolfman. I guess that means I'll have to remove the injectors, and other stuff I wasn't planning.

I guess this should teach me to be more organized and methodical. I hadn't been arranging the bolts or taking pictures of assembly because I figured I could keep track just changing the glow plugs and fixing the decompression lever and valve lash.

I need to make some more space and now wish I'd cleaned things much better before I started.

Wish the damned workshop manual had the motor included.

Thanks again for your helpfulness.
 

amthatiam

New member
Apr 14, 2013
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PA
I hope for you it is the head gasket, while you have the head off look very closely around the area between the center cylinder intake exhaust valves and injector prechamber for cracks, it is common for this to happen on these engines when over heated.

Mine was cracked in this way, I tried to have it repaired but that did not work had to buy a new head. I also had sleeve damage in the center cylinder so rebuilt the engine while I was in there, not suggesting you need to do that, just look real close for cracks and better yet have the head pressure tested before reinstalling to save yourself the aggravation of installing the new head gasket than finding out the head was cracked and having to do the job over again.

Good luck
Dan
 
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