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Old 10-06-2007, 06:22 PM   #1
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Default Rossi interchangeability

Does anyone know if you can put a 9 port piston sleeve & rod into a seven port case.
I have a 721p that the piston and sleeve got damaged through my own stupidity (TOO LEAN) ,and I was wondering if you could put a 35 plus 21 race assembly in that crankcase?
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Old 10-07-2007, 01:14 AM   #2
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If the case is the same dimensions as far as sleeve fitement and height it will. and as far as the rod if its the same length. Also is the stroke the same as the 35+21?

If all that is yes then yes it will work, although some ports will be blocked and unmatched to the case also your powerband will change as i bet the port timings arent the same.
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Old 10-07-2007, 07:52 AM   #3
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It will probably cost you $300.00 or so for the P/S for the 35 plus 21. You could just buy another 721p.
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Old 10-07-2007, 09:38 AM   #4
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First of all, are the engines Rossi (Axel) or Novarossi?

Second, check the inside of the block and see if the venturi cuts match up with the cuts on the other sleve. If they don't, you will burn up a expensive motor rather quickly!
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Old 10-07-2007, 09:48 AM   #5
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Do not get fooled by the fact a 9-port sleeve is faster, it is all about the combination of the timing of the crankshaft and the poorts. The 721P is a nice engine but I think you can better buy 2 sets 721 for the same price as one 35-plus set.
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Old 10-07-2007, 02:37 PM   #6
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Quote:
Originally Posted by GHETTOTEACHER View Post
First of all, are the engines Rossi (Axel) or Novarossi?

Second, check the inside of the block and see if the venturi cuts match up with the cuts on the other sleve. If they don't, you will burn up a expensive motor rather quickly!
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Quote:
Originally Posted by Roelof View Post
Do not get fooled by the fact a 9-port sleeve is faster, it is all about the combination of the timing of the crankshaft and the poorts. The 721P is a nice engine but I think you can better buy 2 sets 721 for the same price as one 35-plus set.
VERY true! Almost everyone now goes by the mis conception that more ports=top end, and less ports=bottom end. The truth is the engine timings have everything to do with this. More ports just means more velocity.
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Old 10-07-2007, 06:43 PM   #7
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Thanks for the help.
I opened both motors up to see what the difference was and they are both very similiar except the 721 crankcase has some internal fins that are removed from the 35 plus, stroke & bore are the same, crank is different.
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Old 10-10-2007, 01:10 AM   #8
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rod length the same?
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