rebuilding 580cc Rotax

[Mudprop1]

Hi all

I am an experianced auto tech but have limited to no experiance with two stroke engines. I purchased a 93 Seadoo GTX with the knowledge that it was going to need engine work. I have removed the engine and inspected the engine for damage. I found that the needle bearings on the large end of the crank shaft had desintigrated and left metal in the crank case which also got up on top of the piston and damaged the combustion chamber and the top of the piston. I have ordered the new parts to put this engine back together. I bought a crank assembly and a top end kit along with a new rotary valve and a block off kit for the oil injection system. I have a hunch that the oil injection may have stopped working which caused the engine to fail. I do not mind running premix. I only plan on using this as a play toy at my camp.

Some of my concerns are.
1. Crank shaft lubrication. I understand that the internal parts get there oiling from the oil in the fuel but since i have completely disassembled this entire engine and there is no oil in it. Shouldn't there be some type of two stroke engine oil in the bottom of the crank case for splash oiling of the crank? If so what should i do to get the oil into the crank case? I have noticed two drain plugs in the bottom of the crank case. I removed these two drain plugs when cleaning the engine of the metal pieces. So this tells me that there is some sort of oil level in the crank case at all times. What is the correct oil level in the crank case? Since i plan on using the block off kit what should i do with the oil injection reservior? Discard it? leave it there and plug it off?

2. Rotary valve. When i disassembled the motor I did not like the condition of the rotary valve. I think that it may be warped a bit. I have noticed a very slight wear on the crank case side of the rotary valve. The wear line goes from one opening to the other. If i install a new rotary valve will this wear line affect the performace of the machine? The parts person where i am purchasing my parts recommended a carbon fiber replacement part. Are these units any better than the stock metal pieces?

Thanks for your time and all comments and opinions will be appreciated. Thank you all.

Gordon

[Technical Support]

Re: rebuilding 580cc Rotax

The score on the rotary valve surface needs to be machined flat. This can resultg in a future failure of the rotary valve or result in backfires. You should replace the valve if it is warped or damaged in any way. The regular metal valve is the best choice. The after market valves do not give you a performance gain and easily get destroyed if there is a backfire. The crank in 2-strokes gets its lubrication from the oil coming in with the gas or thru the intake. The oil and gas hit the bearings and then get sucked into the transfer ports and then on top of the pistons. There should not be a lot of oil in the crankcase. The two fittings need to stay hooked up even if you do an oil block-off because they provide lubrication to the gears that spin the rotary valve. The easiest way to do a block off isz to leave the lines connected and leave oil in the oil tank.