The Home Machinist!

Greetings All,
This is my first post here so please bear with me if I make any gaffs. I have been thinking about converting an air cooled small engine to liquid cooling for some time now. Harold sent me pictures of a side valve engine that he converted. This was several years ago and I now have a similar engine that is waiting to be converted. But for more immediate use I would like to convert a 4 stroke weed eater motor. The main reason is so that it will run quieter. It will not be running a weed eater anymore either. With the engine mounted with the cylinder vertical the fins will be horizontal. What I would like advice on is how to direct the water flow. I could machine grooves through the cooling fins so the water flows up the cylinder, or machine away most of the fins and just let the water go where it wants. I am afraid that if there are any fins left they will keep the water from nooks and crannies and the engine won't be cooled evenly. Any thoughts ?
Thanks,
Eric

I don't know much of anything about converting to water cooling but I do know that water cooled engine designers take care to not have blind pockets where air or steam can collect and prevent cooling in that area. Auto engines often have small bleed holes between the block and heads just to prevent that. The small holes do not allow any significant water flow but they do allow gases to escape into the main flow passages. So be sure your design is self-bleeding for air.

dly31 wrote:I don't know much of anything about converting to water cooling but I do know that water cooled engine designers take care to not have blind pockets where air or steam can collect and prevent cooling in that area. Auto engines often have small bleed holes between the block and heads just to prevent that. The small holes do not allow any significant water flow but they do allow gases to escape into the main flow passages. So be sure your design is self-bleeding for air.

To avoid that when I converted the 8 horse Kohler engine to water cooled, I did two things. One of them was to eliminate all but the top and bottom fins, to which I attached the water jacket, plus the discharge for the water was the highest point of the engine, to ensure that there was always a presence of water.

The engine ran extremely well, and didn't appear to run hot anywhere (including the water cooled exhaust).

Harold

Greetings Harold and Don,
Thanks for the replies. I am worried about steam pockets and was discussing this issue with my son yesterday. I also wondered if removing all the fins would weaken the cylinder. From your reply Harold it looks like it won't hurt the engine. So I'm gonna start hackin' and a hewin'. It will certainly be a lot easier to attach the cooling jacket with all but the top and bottom fins gone.
Cheers,
Eric

If the cooling system uses a water pump, you need to restrict the water outlet from the head slightly in order to maintain a positive differential pressure in the head to keep steam pockets from forming.

Etpm wrote:Greetings Harold and Don,
Thanks for the replies. I am worried about steam pockets and was discussing this issue with my son yesterday. I also wondered if removing all the fins would weaken the cylinder. From your reply Harold it looks like it won't hurt the engine. So I'm gonna start hackin' and a hewin'. It will certainly be a lot easier to attach the cooling jacket with all but the top and bottom fins gone.
Cheers,
Eric

When I mentioned eliminating the fins, I should have been somewhat more descriptive. They were reduced in size, but not totally eliminated. I expected that they were a part of the integrity of the cylinder, so they were not removed to the base, just well reduced in size.

I agree with Glenn's comment about restriction, but make sure you discharge from the top, not the bottom of the cooling system, so gravity doesn't encourage a discharge rate faster than the pump can provide water. Barring something quite unusual, the cooling system should remain full. That seemed to work quite well in my setup.

Harold

FWIW, why remove the fins? The engineers went some effort to put them where the cooling fluid flow would be most efficient. Water is just a more viscous cooling fluid. Watch how the air is pumped over the fins and arrange the water flow to duplicate it.

The most difficult to arrange is sealing around the spark plug. Get that right and all else is cake

jack vines

This is a very interesting topic and many good points. Harold didn't remove all fins as not to "remove the integrity" of the Kohler engine's cylinder. The head also needs cooling in relation to that. I suppose "sealing around the spark plug" was because of the cooling lines. A separate heat exchanger unless a tall radiator and adjustable.