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Old 09-12-2010, 12:11 PM
Kevbo Kevbo is offline
Join Date: Mar 2005
Location: Albuquerque
Posts: 64
Default Sump Cooling Blower

The main cooling fan for the engine is located behind the recoil starter and blows air over the alternator, cylinder, head, and exhaust. There is a second cooling fan on the other end of the crankshaft. This sucks air over the finned oil sump and fins on that end of the crankcase.

The blower wheel is a nice aluminum casting, not plastic! It will have to come off if you need to split the case, or just replace the oil seal on the shaft. I mistakenly thought that was the source of my leak.

You do not need to remove the wheel to get to the oil level float switch. There is a sliding hatch on the bottom of the engine to get at that.

If you really DO need to remove that blower wheel, you will remove the 14mm nut, and find it has no tapped holes for a puller, the housing is too tight to get a gear puller on it, and if you could, it is so thin you would likely bend and/or break it trying.

The trick is to heat the blower wheel with a propane torch. Now would be a good time to go back and read post #3, even if you didn't skip it the first time. Move the fuel tank any other fuel containers far from your work area. Clean up any rags or papers you were using to soak up spilled oil or fuel. Spend a couple minutes thinking what could go wrong, and make sure those things don't happen. Don't set your torch down while it is still lit...too easy to knock it over and start a fire. The new trigger/piezo operated torches are a great safety advance and handier than a shirt pocket. Wish I had bought one years ago.

Take care not to melt the plastic cooling shrouds. There is some foam between the cooling shrouds that can hold spilled oil or gas. Aim the flame paralell to the shaft, and keep the flame in the cupped center of the blower wheel. Keep the flame moving, and don't over heat it. Just too hot to touch is about right. 150-200F or so. If it won't pop loose, cool it with a wet rag and then try again, repeat several times if you need to. Each time you heat cycle the aluminum wheel, it will "walk" a smidgen off the shaft. Better to take your time and not damage the shaft seal with too much heat, or bend the wheel trying to force it off.

If you need to run the engine with the blower wheel off to make sure the shaft seal isn't leaking, be sure to knock the woodruff key out first, so it doesn't get flung into your eye or otherwise lost. Mine was a very tight fit, but still better safe than sorry.

Last edited by Kevbo; 09-12-2010 at 12:55 PM.
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