Exhaust Valve Sticking (updated with photos)?
 

My 73 starts easy and runs well for the most part. However, when I am cutting grass after about 30-40 minutes the RPMs will dramatically drop until I either clutch the tractor, or disengage the deck blades. Then the RPMs will pick up again. If I attempt to cut grass again, it will do the same thing. A friend said he thought the exhaust valve might be sticking when it heats up. Could this be right? If so, is there something I can do to repair it, or am I looking at replacing the exhaust valve? If I do need to repair or replace it, are there any special tools that would be needed? Tractor runs fine unless it has the deck running. Thanks,
Jason

Try the following..

1: CLEAN the engine and make sure that there are no obstructions in the cooling path. You can use high pressure air and blow out all the dirt, mud dauber's nests, etc, that may have been blocking the flow of cool air from the flywheel, across the head and engine cooling fins.

2; Make sure the engine is in good tune, points adjusted to spec, carb set, etc. Avoid running lean, it will cause overheating.

3: Try running a little Marvel Mystery oil in your gas. I know, snake oil.... but it actually helps out in the Kohlers.

If all else fails, you may need to decarbonize the piston , head, and valves, and in extreme cases dismantle the valvetrain and run the correct reamer thru a tight guide. Clearance is recommended to be at 4 thousandths.

truckntran,

Try running a little Marvel Mystery oil in your gas.

About how much is that per gallon?:bigthink:

I'll have to ask my Economy owning neighbor..but I beleive he adds a few ounces per gallon. None of mine have needed the MMO treatment.

Thanks Truckntran. I'll look into that when i get an opportunity. I should also note that one time when this occured, it was smoking pretty good from the engine until it cooled down. hasn't done that again. It does seem like it's running pretty hot when I use it. After half an hour the hood is pretty hot to the touch. Jason

Pull the head to see what is going on, It's not a bad job, it may need something as simple as a head gasket, when it gets hot it may leak. You can then inspect the valves, if you have a local shop you could get them ground cheap that would be great if they are in good shape, if not I think new valves are not to expensive. I also agree check the guides.

It may also be the head gunked up with carbon, if it has never been cleaned this would be a good thing to do while checking the valve, I would check the common tune-up items before doing all of this, however cleaning the head, valves etc with a new head gasket is really part of a complete tune-up

Clint

Ok, so I got brave and pulled the head today (never did anything in an engine before) and took some pictures. It isn't as bad as I was expecting, but you guys would know better than me. By the looks of it, could this be causing my above stated problems of losing power and smoking after about 40 minutes of mowing? Thanks,
Jason


http://photos.cubfest.com/albums/use...8Medium%29.jpg

http://photos.cubfest.com/albums/use...8Medium%29.jpg

http://photos.cubfest.com/albums/use...8Medium%29.jpg

http://photos.cubfest.com/albums/use...8Medium%29.jpg

http://photos.cubfest.com/albums/use...8Medium%29.jpg

Ok, so I got brave and pulled the head today (never did anything in an engine before)

Jason thanks for the inspiration!!! I have never done anything like that either BUT my 127 could use a knew head gasket. If that's the head gasket in the fourth or fifth picture, I think that I can do that and change it.:beerchug:

jfinney,
You bet. See the dark places where the head gasket sits? That is where the gasket was leaking. Get a piece of glass about a quarter inch thick and around 14-18 inches square. Tape some emery cloth or 220 sand paper to it and make a figure 8 motion with the head on the paper. When the surface is shiny everywhere the gasket sits, it's flat. Replace the head after cleaning it with some oven cleaner. The type that works cold.

You should check the adjustment of your valves while you are at it. And even better lap them then adjust. If you do everything by the book that repair will last you a very long time ( about 500 hrs).

Ok, here comes a novice question...how do you lap the valves? Thanks for your input Rpalmer.
Jason

I run a lead additive in my model 70 and under heavy loads like plow day or mowing, I have never lost power or had issues with a sticking exhaust valve. I tend to see that problem more on the larger HP Kohlers over the smaller 7 and 8 horse models. These old Kohlers dont seem to like this new gas we have. Once I treat it with the lead additive, I notice it run smoother and seem to do its work easier under a load. Some guys run MMO, I never have. Clean up the head and seating surface, you will find the warpage if any will be mainly on the head and not the block. But check both. Keep the piston at the top of the bore when doing your work, keeps the crud out of the bore. A putty knife will clean the top of the piston, as well a wire brush on a cordless drill. Also double check your points with your feeler gauge, make sure they are set to spec, might as well get a new set and a new condenser while your in there. Give the old girl a fresh ignition turn up.

You have to remove the keepers. They are what "keep" the valve spring compressed. You put a little grinding compound on ...enough to thinly coat the surface of the valve, and then you use a twisting motion like you see starting a fire with a stick with a tool about 15 bucks or you can use a kids suction cup dart from his dart gun. What you want to accomplish is to get the two surfaces mated. They need to both seat without pitting or restriction. Just like your head surface. They will then have a positive seal and once again last for many hours without being an issue. That is not to say though that they will never need their adjustment checked/adjusted.

This might sound like a lot but it isn't. Actually pulling the head is the most work. And you have that done. Take your time, don't rush and when you are finished you will not only be rightfuly proud, you will have a great running engine. ... I promise.

Thanks again for the encouragement and helpful advice. I'll be diving in head first tomorrow morning. I checked the head with a straight edge and all seemed well. Should I still use the glass and sandpaper? Jason

Page 1.5 in a Kohler service manual recomends to use clean, fresh unleaded fuel. The lead additive leaves deposits on the piston and valves.

Here is s link to a kohler Service Manual:
http://www.onlycubcadets.net/forum/showthread.php?t=38

My old Kohlers don't have any problems on todays gas....as long as it is fresh. I haven't had any fuel related problems since I went to a 30 day gas rule. It is an easy rule to follow. I try to buy enough gas for all ( 2 and 4 cycle) my small motors to last only a month. I will add a fuel stablizer to my gas before I fill my gas container(s) up. Two good fuel stablizers are the one made for Briggs and Stratton and Sta-Bil. I use Sta-Bil because it is cheaper in my area. Any gas (2 and 4 cycle) that is over 30 days old is dump into one of my autos...usually my Suburban or my Monte Carlo.

How you store your fuel containers is important too. The container(s) should be sealed. Watch closely the next time you fill you gas on your Cub. You should see vapors coming out of fuel tank when you fill it. The vapors is the additive package that the gas company puts in the gas. You need all the additive package so your Cub will run at it's best performace. I store my fuel containers in a cool dry place in my shop. All my fuel containers sit on a board. I feel that storing fuel containers on a cool garage/shop floor-ground can attract moisture easier-quicker than placing a fuel container on a piece of wood.

This works on straight gas and ethanol blended gas. The ethanol in the ethanol blended gas will help clean deposits in the combustion chamber (top of piston-valves). I haven't had any problems with ethanol. The key to ethanol blends fuel is how you store it.

Kohler has a FAQ section:
http://review.engines2008.kohler.com...ance/faqs.htm#
There is a question and answer about fuel additives.

Can I use any oil or fuel additive in my KOHLER engine?

Kohler's answer
Kohler does not recommend using additives or cleaners in the oil or fuel system. Air-cooled engines operate at higher temperatures than liquid-cooled automotive engines, and additives developed for automotive use may not perform properly at higher temperatures. Oil additives can prematurely break down, altering the properties of the oil and leading to extensive internal damage or failure. Fuel system cleaning additives have a tendency to separate and turn acidic, causing damage to fuel system components. However, a fuel stabilizer is recommended in the fuel during periods of non-use (one month or more) to retard fuel deterioration.

If you are happy with it, fly it. :biggrin2.gif:

I would go ahead and use the glass and sandpaper, even if just enough to clean the head mating surface. It's hard to check a head with a straight edge, a couple minutes work and you KNOW it's good.

Dale, I dont think unleaded fuel was avaible when the 70 or the 73 for that matter was new was it?? I think that manual is updated for more current times, I bet a vintage maunal from 1964, the vintage of a model 70 doesnt say that.

The job is over and done with!!!!! Well, the worst part of it was figuring out how to get the keepers out. Having never seen them before, and the service manual having a poor picture, I didn't know what I was looking for. I poked around and pulled on the Retainer (don't know what it's really called, but it sits over the keepers) for about 45 minutes before I realized the keepers were under the retainer thingy. Then, the next valve came out in about 1 minute. I lapped the valves, checked the clearances, replaced the weird filter thingy, cleaned up the cylinder head surface and put all new gaskets back on. Put everything back together and...turned the key. Success!!!! My worst nightmare was that it wouldn't start and I would have screwed something up. I drove the tractor around for a few minutes and, it could have just been my imagination, but it seemed much more peppy. I started out pretty easily in third gear on a flat surface with it running just slightly over idle. It also went up hill in third better and with less laboring than previously. I then did a dry compression check and got just around 120 psi, give or take a few psi. The true test will be when I have to cut the grass, as that was when I was really noticing difficulties. I will run it a bit longer and then retoque the head bolts. Sorry for the really long post, but I just wanted to thank everyone for their help, it motivated me to try something I had never done before. To everyone who's been putting this off, or any other repairs you've never tried before, give it a shot, you'll be really happy you did. Did it take me WAY longer to do this than someone with experience...absolutely...but, I learned a lot, had fun, and feel a great deal of satisfaction in taking on a new task and giving my old tractor some new life. Again, thanks to all for their advice, helpful tips, and inspiration/motivation.
Jason

Congrats!! Awesome story. :beerchug:

Way to go Jason! :beer2:

Jeff (teet)

Great job, Jason! :beerchug:

Good job! I always figger if humans built it humans can fix it. Sometimes I feel barely human, that's why I barely get some stuff fixed...lol. :ThumbsUp:

I'm not sure when unleaded gas made it arrival at the local gas station. I think unleaded gas was here before leaded gas was. The lead was added because some motors were having valve problems. Most if not all K series Kohlers have a harden valve and seat that will work with unleaded fuel.

A vintage manual may state the fuel requirements as being leaded gas. The infomation I posted is the latest infomation from Kohler. Running a lead additive will leave deposits in the combustion chamber which can lead to a sticking valve and the need to decarbon the head sooner.

My current shop manual is at least 10 years old. It has the same fuel requirements as my post states. Fuel techonology has change since the 70 and 73 came out. I've owned my 149 the longest. That motor was in boxes when it came home 8-9 years ago. Only fuel that my 149 had in it was unleaded fuel. I've never had a fuel related problem with it.

If I have my choice between a old manual and tha latest recomendations from the manufacture that made the motor on which fuel to use.....My choice is the latest recomendations. All small manufactures have to be testing their motors with current fuel(s).

jfinney,

Way to go.:ThumbsUp: Next time... on a different Cub, those valves will just pop out.:biggrin2.gif:

Great Job:

Nothing like the pride in doing it yourself. Enjoy the fruits of your labors.



Chris