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[stinkwheel]

I just went to prep the cases on my 350 bullet to bake the main bearings out (just been given a garage oven) and spotted something odd.




















I should also point out, I've owned this bike for over 10 years, it had 300 miles on the clock when I bought it and was absoloutely stock-standard. I seriously doubt the 80 year old bloke it belonged to before me removed the timing pinnion in the 300 miles he had it and I most certainly haven't. So this is almost certainly how it came from the factory.



If you haven't spotted it yet... The timing side crank seal is in backwards. This bike has ALWAYS burned a shedload of oil, it's also puffed smoke on the overrun, breathed heavily and had a horrendous problem with mayo formation in the oil. I always thought there was something fundamentally wrong with it but eventually blamed the breather system. Well... Shit...

[stinkwheel]

Humm. Is this a mistake? Is it supposed to be in that way round? I'd have always put a bearing seal in with the spring facing the bearing...

[Adrian]

Have a look here:



http://accessories.hitchcocksmotorcycle ... dian/37777



The purpose of this oil seal is to keep the timing chest oil from seeping into the crankcase, NOT the other way round. If all is well with the crankcase breather and whatever duckbill/non-return valve is used, I gather the pressure in the crankcase is reduced when the engine is running, so the greater pressure in the timing chest is forcing the lip of the seal onto the little bit of crankshaft behind the timing pinion.



If the 30x20x7 seal isn't sitting on the crankshaft properly try a 30x20x5 which will move the seal lip in a bit.



Other things like oil scraper rings, bore (glazed?) and valve guides are all things to check, though a good breather is essential, as you suggest.



A.

[ChrisD]

Hi all. I always thought seals like that went in with the spring side where the oil is and the plain side where the oil shouldn’t be. ChrisD

[Andy C]

I agree with Chris D - spring side should be facing the oil that you are trying to keep out, so is fitted the right way round.

[stinkwheel]

And yet you would always have the crankseal spring facing the bearing, even on the "wet" side of a 2-stroke. This is what's thrown me.



It does also make me wonder why we don't use bearings with a built-in seal in this kind of application. Perhaps a rubber seal can't cope with the heat? But then the separate oil seal does. I've done it before with output shaft bearings on Japanese bikes. Ordered up a 2RS version of the bearing and pried the inside seal out so the bearing is open on the "wet" side and sealed on the outside. I also fitted the separate oil seal but worried less about it.



In any case, this has given me the opportunity to block up the hole between the oil tank and crankcase so it breathes in a more conventional manner rather than with a massive through-draught as it currently does. With the crankcase breather below the barrel re-instated and the hole still present between the oil tank and the crankcase, it sucks air in through the oil tank and blows it out through the crankcase breather at around 10litres/min!