Craftsman 12hp smoking bad... HELP!


Old 05-06-10, 08:20 AM
Thread Starter
Join Date: Dec 2007
Location: Ottawa. Canada
Posts: 66
Question Craftsman 12hp smoking bad... HELP!

My Craftsman lawn tractor started doing some weird things the other day, here's what happened..

I was cutting the grass and when I hit long grass the tractor bogged down and then let out a huge plume of white smoke, then every few minutes it would happen again, running real rough!

Well when I checked the oil it was way over full, way too much (my fault) I was too much of a hurry the other day and probably checked and topped it when it was on a bad angle.

Anyway I took the top cover off the engine, all metal plates around the cylinder head, breather box and carb. All was soaked in oil.

Cleaned everything, gave the carb. a quick clean. Changed the oil, new spark plug and I made sure the oil level was perfect.

I could see with everything off that I was having oil leak indicators from those tubes that house the push rods and the main case gasket (sump I think it's called).

So I put all back together, put both screws at 1.5 turns on the carb. and she ran like a beauty, when engaged the blades she bogged again and I got a slight puff of smoke again but not near as bad as before. I adjusted the high speed on the bottom of the bowl slightly and it got alot smoother again.

Everything seems to be ok now but I still get the small puffs of smoke and slight coughing ever now and then when under load. Not near as much smoke as mentioned above but still seems to be happening.

I'm planning on doing the gaskets on this motor is there anything else I should be looking at hear. Can I adjust the valves on this engine? I did a compression test on it when it was cold in the morning and I got 125psi.

Any help you can offer is appreciated.

Thanks Wayne.

Sears Craftsman 944 605120 ser# 3456503779

12HP Craftsman 143 376012 ser 6342D Tecumseh 143.376010 OVXL125-20240 or TVM220-157106H
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Old 05-06-10, 10:41 AM
indypower1's Avatar
Join Date: May 2009
Location: Lake Winnipesaukee, New Hampshire
Posts: 634
You have an overhead valve engine. Yes, the valves can be adjusted and should be adjusted every year. You will be amazed at how much better the engine runs. that probably won't help the smoking any. Did you use SAE30 oil?
Old 05-07-10, 04:49 AM
Thread Starter
Join Date: Dec 2007
Location: Ottawa. Canada
Posts: 66
Hi yes I put SAE30 oil in it all the time. After watching videos on youtube about adjusting valves I think I'll have a go at it and adjust valves.
Old 05-07-10, 10:49 PM
cheese's Avatar
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Join Date: Jul 2001
Location: USA
Posts: 16,817
That engine is full of o-rings and seals. If it's just leaking a little, I would let it be. Is the gas still getting in the oil? The slight missing can probably be adjusted out with carb adjustments. Mainly with the screw on the bottom of the bowl.
Old 05-17-10, 05:40 AM
Thread Starter
Join Date: Dec 2007
Location: Ottawa. Canada
Posts: 66
Hi all thanks for the replies. I finally got some time to try it out again, been busy at work lately.

After changing the oil, making sure the level was correct, new spark plug and clean and adjust the carb. The wife cut the lawn yesterday and it ran good the whole time. No smoking what so ever, and no coughing from the carb.

All seems to be good except for a substantial oil leak from the engine case (sump ?) gasket. There's enough leaking that after a hour or so of use with the correct oil level it leaks down the side of the engine right under the head down onto the frame and dripping down to the ground.

I cleaned the engine really good and examined it closely. I can see oil coming from the crank case halves, no oil coming down from the head and very little from the lifter tubes (more like oil residue building up on the tubes).

So I plan on repairing the crank case gasket and I will do the shaft seal while I'm down there.

Do you guys recommend anything else I should do to this engine while I have it tore down.

I think I will buy the complete gasket set for this engine.

I have a second engine sitting on the bench in the basement. Hasn't ran in 15 years, looks like some piston sleeve damage. I have this engine tore down on the bench, I even made my own valve removal tool. So I have some experience with this engine.

Anything else you would recommend doing to get this engine back in top notch shape will be appreciated.

Thanks again.

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