Cycle Forums: Motorcycle and Sportbikes Forum banner

1 - 13 of 13 Posts

·
SoCal Racer #13
Joined
·
263 Posts
Discussion Starter #1
What parts are needed to convert an RSR 7.5 A/C to a 4.2. Do I have to buy a whole new engine and exhaust? By looking at the part numbers; the 7.5 is a series II and the 4.2 is a series I. Is this the reason a whole new engine is needed? The cost for a new one with exhaust is pushing $900, yikes. I was hoping I can just swap engine parts and exhaust.
 

·
CF Steward - TSMMR,
Joined
·
1,378 Posts
If you need to switch from series II to series I, I believe its possible to just purchase a series I engine casing, reed block and manifold as opposed to a whole new engine. I think everything else ought to fit.
DISCLAIMER: This is something I've not done personally, so you might want a
second opinion if you decide to go this route.
 

·
SoCal Racer #13
Joined
·
263 Posts
Discussion Starter #3
Thank you! I hope I get more people replies, I might not sell my air-cooled if I can do this econimically.
 

·
Registered
Joined
·
84 Posts
Well, first things first. You need to box up your complete motor and exhaust and send them to "ME". Then, buy a complete 4.2 motor and exhaust to put back in there. Just kidding, would be a great motor to have. You might send an email to Mid-South Minimoto, they will know exactly what you need to do.
 

·
SoCal Racer #13
Joined
·
263 Posts
Discussion Starter #5
lol, I emailed MSM for tech questions.

If it's just the case and manifold/reed block I'll keep my RSR.
 

·
Crash
Joined
·
29 Posts
it is my impression that to create a 4.2 a/c motor you need a series I case, standard crank, single stage reed w/ 14mm carb and stock polini exaust. I have an extra series I case w/ standard crank collecting dust if you would like to trade for your series II case w/ race crank. I am looking to build a proddy motor for my GP. I would even be willing to pay the shipping if you like.
 

·
Registered
Joined
·
1,209 Posts
Flip, i was just about to post that you need to find a guy like this. Imho, this would be the best way to do it.


whiteknight said:
it is my impression that to create a 4.2 a/c motor you need a series I case, standard crank, single stage reed w/ 14mm carb and stock polini exaust. I have an extra series I case w/ standard crank collecting dust if you would like to trade for your series II case w/ race crank. I am looking to build a proddy motor for my GP. I would even be willing to pay the shipping if you like.
 

·
SoCal Racer #13
Joined
·
263 Posts
Discussion Starter #8
Please check your PM

whiteknight said:
it is my impression that to create a 4.2 a/c motor you need a series I case, standard crank, single stage reed w/ 14mm carb and stock polini exaust. I have an extra series I case w/ standard crank collecting dust if you would like to trade for your series II case w/ race crank. I am looking to build a proddy motor for my GP. I would even be willing to pay the shipping if you like.
 

·
Registered
Joined
·
379 Posts
Ya your best bet would be to get the hole bottom end of a series I motor that already has the crank in it. Its a real pain sometimes to swap just cases but it certainly can be done. with the proper tools. you should already have the 14 mm carb form your other set up and the exhaust you have may be allowed depending on what it is. 7.5 as far as i know does not have a race axhaust on it. the super proddy as they are called 10 hp usually has the race exhaust. Is your pipe stamped or does it look like a bunch of pieces welded to gether? if its stamped it should be cool.My 4,2 came with a good size pipe on it i think it may be the polini race pipe wich is stamped not sure though if its the race one actually i think its the standard series II pipe which is slightly bigger than series I exhaust. otherwards if its welded then its most likely a biezata pipe which you cant use .
 

·
Registered
Joined
·
1,236 Posts
FYI guys, the cranks are the same on the 4.2, Proddy and Super Proddy bikes. Race cranks appear to come standard in 40 cc and 50 cc engines only.
 

·
SoCal Racer #13
Joined
·
263 Posts
Discussion Starter #11
Thanks for all your replies. I think I'll hold off on doing anything until the announcement is made for our next year's rules and regs (SCMiniGP). If it's anything like AZPRA (and I think USMGP & SMRRC) I'll probably just get a restictor and race in production class (it's the cheapest way to go).

I'm sure I'll re-visit this subject again later, after the announcement is made.
 

·
Moderator, , Dorkus Maximus
Joined
·
2,749 Posts
elo could probably give more accurate info, and im not speaking/representing for either club, but i believe that SCMGP will be working closely with AZPRA to have as much homogeneity in their respective rules as is possible.

i was told this a few weeks back by an SCMGP rep, and that it was to encourage racing between both clubs....

sounded good to me!

vince
:D
 

·
Registered
Joined
·
1,236 Posts
That's the goal. While each individual club is setting classes up that work best for their racer population, we're trying to make it so that anyone can go to another club and race without having to do any work to their bikes. SMRRC may not have a Production and a Standard 4.2 class but every SMRRC 4.2 will have a class to race in out here and vice versa. We're ironing out the details with SCminiGP as well. :) There's no reason why we shouldn't be able to feel at home on other people's tracks. ;)
 
1 - 13 of 13 Posts
Top