Cadet 1250 WAS a stuck/burned valve!

[Matt Kirsch]

A few months ago, I posted here frustrated in my inability to fix the carburetor on a Cadet 1250 my neighbor gave me for dragging it out of his garage...

My neighbor found the missing side panel, so I called up the guy I sold the Cadet to.

He had torn the engine down and there was a burned valve that would stick when the engine warmed up a little...

Glad I got rid of it. That was absolutely something I did not need...

[SundaySailor]

Matt,

Thanks for follow up on this issue. This does indeed bear out what I've learned so far about these Quiet line tractors. In that once the muffler starts rattling around it causes a number of other problems including breaking the mounts and letting cold air hit the hot exhaust valve and causing further damage.

This is a great trouble shooting help to others.

Regards,

SS

[Rick Prentice]

Thanks Matt. Now I'm wondering if that's what's wrong with my 1250. I can go out and get it started and drive it around alittle. After it warms up it decides to quit and you might as well forget about starting it again.

Rick

[SundaySailor]

Thanks Matt. Now I'm wondering if that's what's wrong with my 1250. I can go out and get it started and drive it around alittle. After it warms up it decides to quit and you might as well forget about starting it again.

Rick

Rick,

That is the classic sign of the burned valve. No matter what you do about the carb adjustments will affect the running of the engine once it warms up. The valve heats up and no longer seats properly. My machinist found mine after I sent it in for a full rebuild. I'd already rebuilt the carb to Kohler's factory specs, and no dice.

Mine now runs sweet.

[Eugene]

In that once the muffler starts rattling around it causes a number of other problems including breaking the mounts and letting cold air hit the hot exhaust valve and causing further damage.

Ya all are gonna have to explain how cold air can enter a recently stopped, hot engine and damage the exhaust valve. Ain’t gonna happen.

Now I'm wondering if that's what's wrong with my 1250. I can go out and get it started and drive it around alittle. After it warms up it decides to quit and you might as well forget about starting it again.

Typical symptom of a faulty coil.

That is the classic sign of the burned valve.

Not.

[BigBill]

Stuck/sticky valve Rick for sure. If anyone has a picked up a cub cadet or any other tractor that has been sitting for a while, if it runs i would add seafoam to the crankcase and gas tank as to lube the valves/guides and free the stuck piston rings. Many years ago we would do this on the cars too. It was called Mobil upper lube(additive). My very first log splitter that i built lasted for well over 25 years because i added two stroke mix to the gas tank every so often to lube the valves/valve guides and lube the piston rings. It had the alumimum cylinder(briggs 8hp). I was told it wouldn't last a year when i purchased it. But i also changed the oil after every 8 hours of hard use too.

Food for thought(info on used cadets), facts;

It can also be your valve adjustment too. If the cam and lifters are worn to the point when the engine gets hot the valve stem will grow and the valve will leak hot gasses enough over time to actually burn away material on the seat and the valve face too. Checking your valve adjustment is important too.

On every used cadet thats been sitting i have found blown head gaskets on everyone of them so far. Only one had a stuck valve out of 10 cub cadets. I believe the stuck/sticky valves happen when the exhaust valves are open when the engine is shut off and stored for a many years. Rust forms between the valve and the valve guide so they will eventually dry out and stick. On my one cub cadet 104 its been sitting from when it was new, when the gas went bad. It sat for well over 30+ years in a shed and then it was left outside. I pulled the head when it had no compression and found the stuck valve. I sprayed the valve and valve guide with PB Blaster and after a few turn overs with me pushing down on the valve while it went up and down and a few more shots of PB Blaster it finally free'd up. I purchased a brand new(on the inside) 104 cub cadet. Its my one of my best running cub cadets. I believe kohler recommends removing the head and cleaning the carbon after ever season of mowing. I'm sure no one does this from the amount of blown headgaskets i'm seeing. I have also seen the exhaust valves / ports loaded up with carbon too. So decarbonizing is needed often too.

I'm getting ready to rebuild some kohler engines and i'm thinking of going with new valves/valve guides along with new crankshafts and connecting rods. I can do all the boring/honing and work myself and i want a brand new engine when i'm done. If the used parts aren't within spec's i'll replace them with new parts. I want it perfect and i don't do things twice.

[SundaySailor]

In that once the muffler starts rattling around it causes a number of other problems including breaking the mounts and letting cold air hit the hot exhaust valve and causing further damage.

Ya all are gonna have to explain how cold air can enter a recently stopped, hot engine and damage the exhaust valve. Ain’t gonna happen.

Now I'm wondering if that's what's wrong with my 1250. I can go out and get it started and drive it around alittle. After it warms up it decides to quit and you might as well forget about starting it again.

Typical symptom of a faulty coil.

That is the classic sign of the burned valve.

Not.

Eugene, with all due respect, etc., you are not quite right this time. If I can, I will try to dig up my burned valve and take a photo of it. It was definitely burned on the side.

Also, I'm still running on the same coil that this engine was having problems with, and I've run this engine solid for 2 hours moving mulch. If it was the coil, then why did the engine rebuild (which included new valves) cure the problem, and I'm still running on the same coil?

BTW, I did change out the coil in my original troubleshooting and found that wasn't the problem.

Here's what happens with the Quietline engines: There is an elbow coming out from the exhaust port. It isn't all that hefty to start with. Then, it passes through a cast aluminum duct of which there is a very heavy muffler attached to both the duct work and also to the elbow. As I remember correctly, those are the only two attachment places for that heavy muffler.

This series of engines doesn't have the balance gears and also has the ISO rubber mounts. Those mounts wear along with all that other vibration and the muffler loosens up and starts vibrating. The vibration gets worse to the point the entry point on the muffler cracks and in my case it also broke the elbow. This allowed cooler air to enter the hot exhaust area, and little by little caused the valve to burn. At least this is what my machinist said happened.

I've also had plenty of contact with other people who have the Quietline series of Cub Cadet, and they've confirmed they had the same problems - loose muffler, runs for a while, shuts down, no start condition. No amount of carb adjustment would do anything. Pulled the head off, and viola - burned valve.

Now mind you, this all takes place over a long period of time. You also have to keep in mind this line of Cub Cadets has been around since the mid 1970's and the prior owners for the most part just drove them into the ground with little regard to proper maintenance.

Geez, sounds familiar - like with the Farmall Cubs doesn't it?

Anyway, I will try to see if I still have that valve. If so, I'll sure as heck post a photo. It cost me a good penny to get this thing back and running, but I truly enjoy this machine.

[Eugene]

I think Bill explained the sticky/stuck valve. Uncontained exhaust gasses burn valves.

Faulty coil is typical of engine (coil) running until hot then no start until cooled down.

Exhaust valves do get burned but not from cold air. Physics class - heat moves to cold until temps equalize. More than sufficient thermal mass surrounding the exhaust valve/valve stem to prevent a sudden drop in it's temperature.

Nother thought. Exhaust valve - engine at below zero temperature. Engine start up. The exhaust valve head will go from cold engine temperature to over 1000 degrees F in seconds with no damage. They will hold up to an engine cool down.

[Eugene]

After it warms up it decides to quit and you might as well forget about starting it again.

Also check the valve tappet clearance.

[dhermesc]

I agree with Eugene, the isn't much chance that a leaky muffler is going to cause a rapid cool down of cylinder head - and even if it did it isn't going to do much. But a leaky rattling muffle is a sign of neglect. If they haven't been doing the baiscs I doubt they've been checking the tappet clearence either.

Given the small cost involved I always pull the head and have the valves checked (and ground if needed) on these old cubs when I buy them. The newest ones are 30 years old and its just a basic maintenance item that's usually neglected - even on the decen running units.

[Paul B]

A stuck or sticking exhaust is a known problem with the K series Kohler engine, whether the valve is burnt or not, carbon will build up on the valve stem under the valve head, and if not cleaned off, will cause the engine to run rough and or quit running after it gets hot. The carbon causes the valve to sitck in the valve guide. Let it cool down and it will start and run another 20-30 minutes, and quit again.

I don't know about a broken exhaust elbow/muffler causing a burnt valve, but I was always taught by my father ( an engine mechanic from the 20's to the 50's) not to run an engine with out an exhaust manifold or short header pipe (don't run it right out of the head/block) because it could suck in cooler air and could cause damage to the exhaust valve in the form of warped valve head and or stem. If you run a Kohler "K" with a broken exhaust elbow, you are basically running it right out of the block without any manifold or pipe. The Kohler engine manual tells you to "Clean Cylinder Head and the Combustion Chamber" every 500 hours, or sooner under some operating condition. When the valve is stuck open because of the carbon on the stem, that stem is then basically in a continuation of the combustion chamber. Keep the carbon cleaned out and you will solve most of the "quit running when hot" problem. I said most, because a coil can cause a similar problem, but the engine usually acts a bit different before it quits with a coil problem than it does with a sticking valve.

[Jim Becker]

The story about no/short exhaust pipes causing burned exhaust valve has been around about since engines were invented. I don't know whether there is any substance to it or not. However, there shoud be no question that a sticking exhaust valve can burn pretty quickly. If it doesn't close completely, it has no opportunity for heat to transfer to the cooler valve seat.

[SundaySailor]

FWIW, when I had tested this engine's no start condition when hot and found it wasn't the coil, here's what we found in the tear down:

Exhaust elbow was cracked enough that when I removed the muffler, what was left was a sheared part of the exhaust elbow left in the engine block. We had to use a Dremel tool and a couple of bits along with an ice pick of some sort to get the remaining part of the elbow out of the block. Muffler was badly cracked at the entrance for the exhaust elbow. The cast aluminum muffler duct which the muffler attached to was broken at the muffler mount. Had to replace that part too.

Engine rebuild consisted of new valves & I think maybe seats - don't hold me to that part, boring block to .010, polish crank and went back with std rod. New governor gear - old plastic seemed brittle to machinist. Rings, gasket set, etc.

Engine runs very well now with original coil. Yes, I do agree in some cases the coil would probably be suspect, but not in this case.

So, take it as it is. With the job my machinist did on my Farmall Cub engine's rebuild and how well it runs, I'm sure he did what he thought was right for this engine too.

[BigBill]

The story about no/short exhaust pipes causing burned exhaust valve has been around about since engines were invented. I don't know whether there is any substance to it or not. However, there shoud be no question that a sticking exhaust valve can burn pretty quickly. If it doesn't close completely, it has no opportunity for heat to transfer to the cooler valve seat.

Your right with the exhaust valve material they use which is a rock hard stelite should never burn, will never burn unless something else is wrong like the valve adjustment being too tight so when the valve stem expands from the heat the valve can be open and not fully closed. Or the carbon build up or sticky valve stem can be another problem. My point is the valve won't just burn by itself. Something has to cause it to burn.

I just picked up a 12hp short block that had a score line in the cylinder. After instecting the crank and rod fit its fine only the cylinder was huffing oil from the score mark in it. The cause was a dirty air cleaner which may have had a hole in it which allowed dirt to enter the cylinder. Its lack of maintenance and neglect that causes these problems. Some don't worry until it won't start or it blows smoke. These engines aren't cheap when there purchased brand new, new short blocks or even rebuilding them if we do it. Lets see a $5 air cleaner or rebuild it? Silly isn't it? How often do you pull the dip stick to see were the oil level is? Grease it or check the tranny oil?

I taught my son about this on the dirtbikes too. When a piston blows apart something else caused it rather than fatigue. It had to go lean to score the piston and cylinder. Most of the time its crank seals and loose crank bearings. I see so many just put in a new piston and rings only to blow it up again. I've also seen the cylinder base gasket get sucked in also. They forget to retorque the cylinder base nuts. Which they should be checking them often anyway. Again my point is we need to find the cause of the problem before we try to repair it.