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Rebuilt k241 (oil ring stuck). now runs hot and valves will not keep their clearance. Replaced rings, gaskets, cleaned everything. ran about 30 min.
then the problem started. Right after. cut grass till engine got hot then loss
of power. let cool, checked clearance and it was to wide. Reset ran again
same thing. yesterday took head off, had carbon, cleaned, lapped valves,
reset clearance. ran it and the same thing happened.

Flywheel key sheared, camshaft not properly times to crankshaft, points not set correctly, and in some cases reuse of head bolts can all be possible issues.

Flywheel key not sheared. Camshaft is in line with crankshaft mark. Points are set correct. If all of this was wrong, why would the valve clearance be changing.

These K241s are not as critical about loose valve clearances as the newer OHV rocker style engines. Being that it has had repeat overheating, the valve seats could be slipping in their machine fit grooves of the block (rare).

The overheating issue is likely due to a lean fuel mixture. Dirty main carburetor jet? Intake sucking a little air where it mounts to the head? Main throttle shaft has too much play from many years of use?

Or the exhaust is carbon choked from age and the previous oiling issue.

Are all of the sheet metal covers installed? They must be in place so the flywheel cooling fins can circulate proper airflow while the engine is running.

I serviced many of these engines when they were new back in the early 80's.

Cleaned both valves, no carbon build up. Lapped them in again. How do you know if the seats have moved. Is there anywhere to take a measurement from to check this? Are the after market carbs worth while or rebuild the OEM?

Hello spankyscamp,

Are your center adjuster bolts on the lifter turning to easy like the threads might be worn?

Here is a video that may help:


Aftermarket carburetors are a crapshoot, but they are improving.

Personally, I prefer to rebuild the original if the parts can be had. Usually, not all of the parts will come in a kit, but most do.

Thanks Doc. The adjuster bolts turn hard, so I assume they should not be turning. I have not had any trouble rebuilding the k241. I have two k241's. One is on a 108 and this one on a 1000. This is the only one I am having the trouble with. I have all the engine covers on but not the side covers on the body. Where I had machine work done before, it was suggested to leave them off to get more air around the engine.

The adjuster screws have what is known as interference fit threads. It takes 2 wrenched as shown in the video I sent you. One holds the lift tappet, and the other is used to adjust the center screw.

The top of the center adjust screw head often gets a valve tip "wear saddle" with age and that could also affect how the feeler gauge is fitting each different time it has been checked after running.

This is why setting the valve clearance on a solid tappet engine is not exact as some people like to think it is. Get the adjustment within specification cold initially and then leave them alone. Never make them too tight at the minimum allowance of the specification.

As for cooling the engine properly:

Unless you are moving 30 above MPH, those covers must be in place.

There are many people who do not understand the importance of those covers. They are not there for looks, they direct airflow. The machinists do not typically work on the running engines; they make sure everything fits correctly so the engine can be assembled.

Opinions often get skewed a little in this industry, but the Physics of the situation is real.

Why? Look at the standing vanes on the flywheel and study the direction that the flywheel turns.

The flywheel turns in a way for the standing vanes draw air from the top cover middle opening down into the upper flywheel cover and then it is distributed inside the covers around the cylinder(s) and engine block. It is known as "cross flow" air cooling. It is how a majority of small, air-cooled engine survive.

I think some of the confusion also comes with the old airplane radial engine designs, because they often had exposed cylinders/ cooling fins. but they also had a giant propeller blowing lots of air across them when on the ground and once in the air, the speed and cold altitudes are what kept the cylinders cooled even better.

Doc. I set the valves at mid range of spec.. The engine covers are on on like you say, for proper cooling. I meant the side covers on the tractor to allow for more air to move around the engine. All fins are all open for air flow. Starts up quick runs OK till it gets hot, then the power drops off.

Did you check the ring end gaps prior to assembly? I made that mistake many years ago when I spent hours sleeve honing one of these engines to install an oversize piston and rings. (My first) Being young and "green" at the time, I knew very little about metal components expanding as they got hot.

I eventually learned that the ring gaps were too tight and corrected them.

That is just an experience of my part, yours may be ignition related due to a wrong heat range plug or a coil that is failing.

How long does it run before it starts losing power? Is it a gradual loss like fuel starvation or cutting out and stalls like ignition or some other electrical problem.

Is the key switch overheating?

Does it only happen under load with the deck engaged or all of the time regardless of load?

Are the points and condenser new or has it been converted to electronic ignition?

I checked ring gap, they in spec spacing. It is not stopping, it just looses power all of a sudden. The last time it ran about 15 mins. then started loosing power. Not like running out of gas. Not cutting out. I am cutting grass checking it out. I have a 108 with the same engine, I rebuilt maybe 10-15 years ago still running (starting to smoke a little), I bought this one new in 1974. The 1000 I bought used not running.

From the sound of it, the tank may have a blockage starting at the fuel nipple or the fuel filter is choking up. Gradual loss of power is fuel issues.

That will also contribute to the heating up, because the fuel mix is getting too lean. A rich mixture will not cause an overheat.

Verify the fuel lines do not have anything in them like a dirt-dobber (bee) nest. I have had to blow through all of my fuel lines, both new and old before if they were left open even overnight.

Checked fuel lines. All open. I run an inline fuel filter (clear) so you can see what is going on.

spankyscamp said:

Thanks Doc. The adjuster bolts turn hard, so I assume they should not be turning. I have not had any trouble rebuilding the k241. I have two k241's. One is on a 108 and this one on a 1000. This is the only one I am having the trouble with. I have all the engine covers on but not the side covers on the body. Where I had machine work done before, it was suggested to leave them off to get more air around the engine.

Click to expand...

ALL COVERS in PLACE as per manufacturer/assy specifications...they are on there for a reason!
Goodluck with your project

All covers are on the engine.