Overheating K301 in a Cub 127

[yachtwork]

Hi all. Great info on this site.

I am in New Zealand with a Cub 127 and a Kohler K301 engine. It was a family heirloom so I threw it in the container when we shipped our belongings across. It always started very hard. A lot of turning over, and over while it slowly wound up till it started. Since it was a family gift I figured it was just old and tired. Then one day I noticed I could see right through the side of the head into the combustion and watch the blue flame inside the engine. Very strange that it still ran and even kept starting.

The other thing it was doing was overheating. I have plenty of airflow, but still, it would overheat. Of course, I never drove it less than full throttle as that was barely enough power to cut the lawn.

Anyway I just used it for a half hour or so and shut it down when it started sounding like a rod knock and piston slap was taking place, let it cool and it was good for another cut.

Then some guy down the road put up an ad for an old, old Cub. Turned out it was also a 127 like mine. What are the odds? The 127 was never imported into NZ and here in the next block in another. I figured the head might still be good so for 75 bucks I bought it and got a spare of most everything.

I pulled the head from the family tractor and found it was just a blown head gasket. I pulled the head from the old 127. The engine is very used up and I can see it has been rebuilt at least once with a noticeably larger piston. I put the old head gasket into the family Cub, started it up and it purrs. Just like that.

I found a new head gasket that is now on order. I went and cut the lawn and suddenly the engine has heaps of power and cut just great. Only after about 40min or so it again began to overheat. Same as before.

I am now trying to track down why I am overheating. I have heaps of airflow, the oil level is up. I have tried regular car 10-30, then tried oil for my little diesel engine, then I tried stationary engine oil 10-30 and it's all the same. 40min and it begins to overheat.

I am wondering if there is something internal that is loose so it slowly produces more heat than the engine can dissipate? But it sounds just fine till it overheats and then starts making all kinds of clanging noises. I shut it down, let it cool and its fine again.

I also have the engine from the second Cub. The guy told me it ran fine, but it was used to tow little trailers on the beach so the bolts are all stuck. I even broke a head bolt trying to take it apart. I am thinking of using that engine as a last resort if I can't fix the overheat but I keep thinking it must be something kind of simple?

Any ideas?

Thanks.

Scott in NZ