From:Dave Hennessey
Subject:RE: making progress 61 hummer super 10 Date:Tue Aug 9 23:54:37 2016
Response to:21439
Yes, a stuck ring could give you low compression. I think 110 psig might be a little high, 80 or 90 is probably more like it. Easy enough to pull the cylinder and see what the rings look like. If they're OK, you have a bigger problem.

BTW, what kind of compression readings are you getting?

A common problem for low compression / low power in two-stroke engines is worn oil seals in the crankcase. Several people have mentioned this. To understand this, you have to understand some fundamentals of two-stroke engine design.

The air-gas-oil mixture is sucked in through the carburator INTO THE CRANKCASE where the oil in the gas lubricates the flywheel bearings. The air-gas-oil mixture is then sucked from the crankcase into the combustion chamber, where the spark plug ignites it, etc. The animated image below (hope it shows up OK) illustrates this.

For this strange process to work, the crankcase has to be totally sealed. If the "oil seals" are worn, air will be sucked in from the sprocket shaft, generator/magneto shaft, transmission shaft instead of the carburator.

Four-stroke engines are totally different. Their crankcases are purposely vented to the atmosphere to remove any combustion by-products which pass by the rings.

So, if your rings aren't stuck, you're in for a complete teardown of the engine to replace the oil seals. If that's the case, I'd recommend having Mutt do the work.

BTW, the oil in the gas in a two-stroke lubricates everything in the engine, so it's very important to have the correct mixture, which is 25:1 I put a gallon of gas in a red platic gas can, add 5-1/2 ounces of two-stroke oil, shake a little, and pour into the gas tank. If you can find ethanol-free gas in your area, use it.

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