Cub Cadet 124 Runs Good, Knocks, Then DIES!

Well guys......I've been working on (3) Cub Cadets a guy brought by our place for me to get running for him. One of which was the CC 124. Since I'm doing this in my spare time (weekends), its taken a little while to get it done. I got the tractor running and operating about 2 weeks ago and was awaiting a new air filter before I tried it out and called the guy to pick it up. Mowed beautifully for about 3-4 passes in the front yard. This tractor had 115 psi compression when we got it going and puffed a little smoke only when you accelerated the throttle. Never smoked continuously or seemed to be of any concern. No knocks and ran beautifully. Well......made those 3-4 passes and in the last pass I put in in 3rd (was in 2nd), and decided to go across the yard to head back to the shed. Figured I'd leave the blades on since it was doing so good as I drove across the yard. As soon as I was going into a turn, I heard 3-4 knocks (pings) and all of a sudden it died. Towed it back to the shop, checked compression, 45 psi. UGGHHHHHH

I'm sure this is not an easy fixable problem. The engine sure was hot. I hate to call the guy and tell him none out of the 3 will be able to be used this season (one other one has 120 psi but smokes and knocks while running at all speeds, and the other tractor has 20 psi compression therefore we haven't fooled with it). I wonder what the specific problem is and what caused it?

That happened to me last week. Sorry I typed it all up and am just now submitting. I will be going back up tonight to check it out this weekend. Here is what we found out the other day (about 3 days after it happened).................

I talked to my grandfather this week, and he said that one of his helpers that cuts firewood for him jumped on it and moved it. Said it cranked right up and he was wondering why I had towed it to the shop. Now, how it ran or what it did, I don't know; but he said the guy cranked it right up and moved it.

The owner just called yesterday evening (Thursday) and left a message wanting to know if I was finished looking at it/fixing it, and I need to call him back. I really don't want to bring all of these issues up since the last time he had called I told him I just got it running and it ran good.

What do you guys think?? Just that the carb may need adjusting and it was just overheated? Also, what is a good way to test compression on those old Kohler engines to diagnose them?? I heard they have a compression release, but I don't know. We have been using a gauge like we use on the farmall tractors.

I have a 12hp Sears Suburban with Tecumseh engine that would run when cold, then knock a few times and die as it warmed up. Turned out to be a failing spark plug.

A common problem on K series when they get older is carbon buildup on valve stems causeing valves to stick when eng gets hot,possibly caused by worn valve guides/bushings.If valve sticks when eng hot,many times valve(s) will free up after eng cools.

What would be an effective easy fix to this? Adding some MMO to the gas ? I actually filled the tank with a half gallon of gas and put a quarter pint of MMO in the gas. That s what I have ran it on since I got it running.

(quoted from post at 05:16:41 05/25/13) A common problem on K series when they get older is carbon buildup on valve stems causeing valves to stick when eng gets hot,possibly caused by worn valve guides/bushings.If valve sticks when eng hot,many times valve(s) will free up after eng cools.

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Yes they do have an ACR (Automatic compression release) takes about 300 rpm to get a good reading .

Also did you check the timing ? on the left side of the engine shroud, should be a round hole kinda low right behind point cover.

When hot timing may have changed enough to make it Knock.

There is a mark on the flywheel you can mark with paint, and use timing light .

You change the timing by opening or closing the points

I've had carbon problem on valve stems on two eng(both tired & burning oil)I've also never had much luck with Marvel & other oil/gas additives when you have this condition as carbon buildup becomes quite hard & usually requires sandpaper/wire brush to remove,in addition there may also be rust on stems if eng sat for an extended time,easist/quickest cure I found was pull head & remove valve keeper/springs & remove valves and clean stems,depending on how much carbon/rust on stem this may have you talking to yourself & nasty to eng depending on how difficult it is to work valve back/forth thru guide till same can be removed from eng.

Probably has a broken piston ring. Same thing happened to
my K341. Could mow half the yard before it was blazing
hot and losing power and pinging. Hate to be the bearer of
bad news, but old equipment is usually pastured for a
reason.

I'm going to take a video of it tomorrow. I'll post the link once i get it uploaded, so you guys can see what it is doing. It actually cranked right up today like they said it did either day. All I did was crank it and shut it down, I didn't drive it. I'll do all that tomorrow for the video though.

Yep valve sticking open when hot.
I have an old K301 that I put synthetic oil in and the valve quit sticking.

Have new valves and guides... someday I will get around to changing them

Sorry. Was too busy today to fool with it. We ended up running across an international 300 utility at a yard sale and rescued it. Maybe I will get a chance to shoot a video of the cub cadet running. I did notice that when moving it it starts right up and runs great but after about 1.5 to 2 minutes it acts like it goes under load like when mowing. A few seconds after tht it acts like it is gonna die then I pull the choke out and let it catch up and push the choke in and all is well. I will try and get a video tomorrow. Too scared to try to mow with it again. Haha

IF you have to use choke from time to time to keep eng running this points to a fuel supply problem in addition to possible sticking valve(s) or a leaking head gasket.

Check out the fuel system,look for plugged/restricted filter,plugged restricted or bad hose between tank/pump,plugged outlet on tank,bad/plugged gas shutoff valve(if tractor has),plugged/bad vent cap on tank,weak/bad fuel pump,dirt/water in carb bowl & internal passages of carb body,sticking/bad float,sticking/worn float needle/seat,dirt in float needle seat hole,loose carb or bad mounting gasket for carb.

Sounds like dregs in the gas.
Fairly common with the gas we have now with ethanol in it.

I had soaked the carb for about 30 hours in carb dip, then cleaned it well, then reassembled with new kit paying close attention to passages and gasket surfaces. The tank was cleaned well and I added a good bit of MMO to the 1/2 gallon of fuel I put in the tank. I'm thinking its a sticking valve. SHould I put some MMO in the oil too?