Subject:RE: RE: making progress 61 hummer super 10 Date:Wed Aug 10 09:44:53 2016
Response to:21442
Dave, I have replaced both crank seals on atleast 3 different
bikes, without tearing the motor down. Ya only need to remove
the gen/mag and it's seal and the primary chain and sprocket.
If anyone is interested in the procedure, email me.

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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