SX/SXi/SXi Pro big pin bottom end and small pin top end compatability???

[ksarge91]

Alright, helping a friend out with his 1992 sx750 with a busted crank (nosecone broke off, long story) anyway, bendix is trashed, flywheels trashed, and time is a bit of an issue, so I decided it would be cheaper and faster to simply find a complete bottom end, and install his old cylinder, pistons, head and carbs.

We found a complete big pin bottom end with a crank, cases, flywheel, bendix already together for a couple hundred bucks that I'm thinking should work. From my understanding, this bottom end/top end combination would be better than before power wise, and the cylinders will match right up.

Question #1: Can we use the existing pistons without trimming the skirts or anything? I'm going to do rings and a hone, but would like to re-use the pistons since they aren't too bad and trying to save some money.

Question #2: Will his single carb manifold match up to the big pins case?

Question #3: If we have a complete motor with a bad crank, bendix, and flywheel, and we buy a motor, like say, this one,

http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&item=180540981319&viewitem=

What other parts will we be needing?

Sorry for the long saga

Thanks,

Kevin

 

[madscientist]

do it, just bolt and go on that pakage. great bottom end.

 

[ksarge91]

do it, just bolt and go on that pakage. great bottom end.

Alright cool. So the single carb manifold will work on the big pin cases? No problems with the skirting? I'd really like to avoid buying new pistons.

 

[madscientist]

all good, should have no issues. might i ask what single carb?

 

[ksarge91]

Think it's a Keihin 40. Not sure though. Whatever the stock carb is on a 92 750. I don't have the ski right now to check

 

[madscientist]

it will work, but i suggest a manifold and larger single or a set of stock duals.

 

[ksarge91]

it will work, but i suggest a manifold and larger single or a set of stock duals.

Alright cool. As long as it will work for now I just wanna get it running again first. He's still learning how to really ride the ski and it has a factory pipe, with the fresh hone and rings, and maybe some head work this will be more than enough power for him for another season or so.

What carbs would be best? Dual 38's? I have a keihin 42 I will rebuild and put on if it will make a big difference.

 

[madscientist]

run the 42 if you have it, take your time and dial the jetting in. the stock sxr dual mikunis are a great budget duals.

 

[ksarge91]

run the 42 if you have it, take your time and dial the jetting in. the stock sxr dual mikunis are a great budget duals.

Alright cool. I leave for college in a couple weeks so I'm probably just gonna leave the 40 on there for now to make the tuning process easier. But for next year would you recommend dual 38's or a bigger single like a 46 or 48?

If the 42 does end up on there can I'm assuming I can just match the stock manifold with a grinder?

 

[madscientist]

46-48 if you have the coin

 

[kevbo]

Small pin pistons will not fit a big pin crank.

 

[madscientist]

doh!!! i overlooked that one. thanks kevbo.