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General Category => General Discussion => Topic started by: steven c on April 04, 2023, 10:04:13 AM
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I think I need to replace the crank seals on my 74 Benelli 250 T2 2 stroke that I'm hoping to get back on the road. It's blowing ton's of smoke and spewing oil out the exhaust. This is the info I was given. "There are actually 2 seals and 2 'O' rings on the crank. On the alternator/magneto side the seal is
20mm(I.D.) x 47mm(O.D.) x10mm(Wide). On the primary drive side the seal is 27mm(I.D.) x 47mm(O.D.) x 10mm(Wide). Also on the primary side is machined sleeve/spacer, 27mm O.D. and 20mm I.D., on the crank mainshaft. The inner end of the sleeve/spacer is chamfered and an 'O' sits there next to the main bearing. It's 20mm I.D. x 1.75mm diameter cord. The second 'O' ring sits on the labyrinth seal in the middle of the crank and you can't access it unless you do a full engine strip. I would try to replace the outer seals and 'O' ring first and see if that cures the heavy smoking. Make sure you get the full 10mm Wide seals and not the more commonly available 7mm Wide versions. Also specify Viton material not the usual neoprene or Nitrile (NBR) seals. Viton is unaffected by ethanol in petrol which can affect NBR. Viton will cost about 30-50% more but it's well worth it."
So far I check Master Carr and Grainger and no luck. Any hints on who I can check? Thanks. He did say they can be had in the UK.
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Maybe? https://www.123bearing.com/seals-CC-20X47X10-FPM
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Or...bearingservice s.com they are in michigan, ships everywhere.
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First a question. Why do you think the seals are bad because of exhaust smoke and oil? Usually bad outside crank seals lead to hard starting. I would change those as a matter of course. The inner one is probably more trouble than it is worth. Old Mercury two cylinder outboards used a labyrinth "seal" between cylinders. It is a thick brass disc, for lack of better words, with grooves cut in it to disrupt flow between cylinders. Nothing touches the crank. They do tend to wear due to crank flex but probably mainly on very high rpm race motors. Good luck on finding what you need.
kk
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https://www.alliedmetrics.com/about/