John Deere B engine issue

[Aaron Juhl]

This week I have had trouble with my 1941 B and am wondering if anyone has any troubleshooting ideas.
It was restored about a year and a half ago, and the engine has seemed to run fine until now.

Now it is intermittently pushing air back through the carburetor (and air cleaner stack) when it runs. Thinking that maybe an
intake valve was open too soon or too late, I have taken off the valve cover and it appears as though the valves are working
correctly.

Any thoughts about what else I should check?
Thanks for any help you might have!
Aaron

 

[[email protected]]

Ehat was the valve clearance? Should be. 020 cold.

 

[old]

An intake valve can and will some times stick due to carbon built up or lack of lube and if ti sticks open just a little bit it will do just as your having a problem with. Try running ti with say 1qt of ATF in 3 gal of gas and see if it clears it up. The ATF will clean up and lube the valves and the cylinders also

 

[ET]

Try a fresh set of plugs.

 

[Lee B]

Check that both exhaust valves are getting adequate oil dripped onto their rockers while running with the valve cover off.

To me it sounds like an intake valve sticking due to lack of lubrication, but only occasionally. That means that the exhaust valve next to it is not getting enough oil dripped onto the rocker from the distribution pipe which may be partially plugged with gunk. Air pressure fed into that tube can blow the obstruction out of it for a quick fix, but do not add holes for the intake rockers or you will wind up with blue smoke in your exhaust and it will use a lot of oil at that point. The intakes get their oil from the exhaust valves by splash alone and it's more than enough provided the exhausts are getting enough to start with. The rocker tube gets it's oil supply from inside the crankcase via copper tubing connected to the block, probably the better place to inject shop air into the rocker arm oiling tube as it could be blocked just about anywhere. This oil feed typically goes thru a hole in the oil pump drive shaft to effect a momentary pulse of oil sent to the rockers as a means to limit oil going to the rockers - if this is where the obstruction is you'll have to roll it around some until the holes line up and figure a way to blow it clear in reverse flow mode. You won't really see what I'm talking about here until you get inside the crankcase.

Still no joy, drop the oil pump entirely with an oil change and get that hole in the oil pump drive shaft cleared the old school way (looking thru it with your eyeballs).

You can check your valve timing with the LH exh timing mark on the flywheel if you would like to. When that mark is horizontal at 3 o'clock position and lined up with the mark on the transmission cover AND on the proper stroke, the exhaust valve for #1 cylinder will be seen to be just starting to lift off it's seat. That's why that mark is there. Be sure to roll the flywheel around 360 degress if it doesn't appear to match the above description because it will fail if it's on the wrong stroke. It only lines up correctly to the mark once in every two revolutions of the flywheel.

 

[BushogPapa]

Every year, Once a year, Dad would use a large oil can of used oil and squirt in (with the tractor idling at half throttle) all the engine could take, into the carb, until the oilcan was MT...(just to avoid sticking valves)..

Please do this OUTSIDE...!!!!

Ours burnt valves badly until the original mufflers rusted off...about 1954..

Since, (with straight Pipes), there have been no more burnt valves..

FWIW...!!

Ron..

 

[Kent Petersen]

Frist thing i would check is valve setting should be .022 cold next check compression if low on one cyl you have a bad valve

 

[Aaron Juhl]

Thanks everyone for all of your suggestions!
Tomorrow I plan to
-re-check valve clearance
-re-check the timing mark on flywheel against the valve action
-try running with ATF in the gas in hopes of cleaning things up internally
-try a new set of plugs as I have a spare set
When I had the valve cover off yesterday, I did notice that the rocker oilers were providing good lubrication, so I think we're OK there.
Fingers crossed that the solution doesn't involve tearing the whole engine apart!
I appreciate your willingness to share your knowledge in these forums.
Aaron

 

[Aaron Juhl]

Thanks for the advice! Just double checking, if it is a valve problem, it won't do any further damage to run the engine long enough to burn those three gallons of gas + 1 quart ATF?
Really hoping that does the trick! Tractor is all repainted and would much rather not tear it all apart again!
Thanks again,
Aaron

 

[old]

Not likely to hurt any thing in that short of a time. Ya if you ran it with say 300gal and it kept doing that it could burn a valve but 3 gal is only maybe 3 hours run time

 

[Lee B]

You are quite welcome, that's what most of us are doing here in the first place, trying to help when we can. AND learning a great deal from other contributors.

A year and half ago when it was restored is there a chance this head got new valve guides and new valves, done by the previous owner? When this is done by the common man as it were, it's not very typical that he would know that you absolutely should always run a proper sized reamer thru those new installed guides to ensure proper clearance and when that is NOT done, you wind up with this exact situation - to a Tee. Ask me how I know this - it was my second ever engine build and thankfully my own so nobody else was on the hook for it. Even with adequate lube, it just can't get in there and they can start sticking like this willy, nilly when ever it suits them. Now with added information from your follow up post, I'm suspicious myself that it was put together without a proper reaming. And it really still needs that done.

I wouldn't trust that a jigger of oil in the gas will cure anything longer than the tank of gas lasts. Unless you want to do this forever more, you might start thinking about pulling the head and reaming the guides with a borrowed reamer. Cost you a head gasket and some labor. No real harm in waiting to see how it works out either, you can do this to fit your schedule.

 

[Aaron Juhl]

I wanted to take a moment to thank everyone for their advice and provide an update. Putting ATF in the gas and letting it run did the trick at least for now. I have run it for about an hour now with just straight gas and the problem has not come back. I may still open it up and take a look at the valves as suggested at some point, but at least now I can wait until it is convenient.
Also put in a new set of plugs which worked wonders for easy starting.
Thanks again,
Aaron