Malossi MHR TEAM BB 77cc
- Thread starter trueOverrev
- Start date
47lamy
Well-Known Member
Big NRG knows that 52 is the bore, I think he is mocking the poster above, 52 would be near impossible on a 50cc casings, they will use the normal 44stroke, but.. will they run a larger small end bearing for this 52mm piston? you think they are using an Asso pistons for this kit as well?
tiba_karotsu
OVERREV TUNING
52mm bore kit would fit the 50cc carters with a lot of machining, Jog90 carter almost the same as Jog50 carter in external dimensions, we overbore Jog90 cylinders to 54mm & it still uses 12mm pin.
same with 47,6mm BWS100 crank, it can fit the Jog50 carters only with lots of machining & welding which is no longer practical.
however i do not find the 84cc S6 kit with the 52 x 39,2/39,3mm very promising, the oversquare engine layout doesn't suit the 2stroke engine for the lack of port area vs displacement ratio, 2stroke engine with a square engine layout tend to make more power bcoz it had more port area for a given displacement.
i just think S6 is jumping into the big bore bandwagon to get a share of action the 2Fast & TCR kits enjoy.
same with 47,6mm BWS100 crank, it can fit the Jog50 carters only with lots of machining & welding which is no longer practical.
however i do not find the 84cc S6 kit with the 52 x 39,2/39,3mm very promising, the oversquare engine layout doesn't suit the 2stroke engine for the lack of port area vs displacement ratio, 2stroke engine with a square engine layout tend to make more power bcoz it had more port area for a given displacement.
i just think S6 is jumping into the big bore bandwagon to get a share of action the 2Fast & TCR kits enjoy.
Im kinda with you on that one there
If you look at any performance two stroke then you will find that they go for a square engine
I would liketo see some one do this well
i guess its gets to the point of not being practical to actually do it in the end and you have to go to overbore
if you could run a 47mm crank on a 47mm cylinder that would be the ticket
81.5cc
If you look at any performance two stroke then you will find that they go for a square engine
I would liketo see some one do this well
i guess its gets to the point of not being practical to actually do it in the end and you have to go to overbore
if you could run a 47mm crank on a 47mm cylinder that would be the ticket
81.5cc
Tom.#86
TKT!
But you can't with a 50cc crankcase.
trueOverrev
Well-Known Member
Fabrizi FHT did release their share of that idea.
47.6mm Bore with 47mm Crank, however dont see any positive feedbacks anywhere.
Minarelli 50cc engine can accept 54 and 55 mm bore cylinders without any serious problem. I've also used 55mm size pistons. They need the same cylinder skirt size like a Team cylinder (~57 mm). But you can even bore up more and use a thicker sleeve.
The Minarelli crankcase wall is thick enough for huge crankcase diameters and still stiff enough, it's a pitty the top of the wall is very thin. So only the sealing is the problem. You can rebore the case up to 77 mm and you still have more than 2 mm wide sealing surface (2mm is the minimum for proper sealing).
Because of the sealing problem Fabrizi uses that ~4mm thick crank spacer. So you have to shave of the thin part of the wall on left and right cases and use the wide spacer.
Jog50 and Minarelli copy engines doesn't have that thin top wall, so you can rebore them more than 79 mm. (so you can insert the 78 mm diameter crankshaft).
The Minarelli crankcase wall is thick enough for huge crankcase diameters and still stiff enough, it's a pitty the top of the wall is very thin. So only the sealing is the problem. You can rebore the case up to 77 mm and you still have more than 2 mm wide sealing surface (2mm is the minimum for proper sealing).
Because of the sealing problem Fabrizi uses that ~4mm thick crank spacer. So you have to shave of the thin part of the wall on left and right cases and use the wide spacer.
Jog50 and Minarelli copy engines doesn't have that thin top wall, so you can rebore them more than 79 mm. (so you can insert the 78 mm diameter crankshaft).
Does some one have a link to a picture of there cylinder
Its a shame it wasnt successful
It will be interesting to see what 2fast come out with
I am going to wait and see before i build my race engine
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Its a shame none of the copy ones have a disc brake rear end
that would be the one to have
I guess you could always weld the brackets on for the caliper and make it work
Tom.#86
TKT!
Not, if you want to use a proper size big-end pin or don't want to weld on the casing
Yes, they all use drum brakes.
If you want to convert a drum brake engine to a disc brake, you don't need to hurt the crankcase. You can use outer disc brake. (this is an Aprilia Sonic that uses Jog engine).
rear disc conversion
Sure you can use the original place of the exhaust. This scooter is for iceracing, that's why the exhaust moved and the cover protected.
Once again you are wrong. Read my upper post. Don't need welding And you can use 18 mm pin.
Wow thats an interesting way of fixing an issue
47lamy
Well-Known Member
Going back to the engine arrangements, I’m remain more upbeat tiba, My MHR setups work very well and that’s not exactly square i.e. 39.3 x 50mm-77, Ok not as square as (2fast 44x47.5mm) but it works, ok your theory might be correct but very limiting for development on original 50 carters. I think this S6 will still be awesome using 44x52mm-93, new 5 stud design is ideal, as i personally would avoid any welding to carters as they are fragile (especially on circuit racing) so its a good work around. The 44 crank is a good fit so generally it seems like the way forward in terms of development for me. I think probably too much for many on a tight twisty track. Also if i was lucky enough to be involved with producing cylinders like s6 I wouldn’t want to be left behind in terms of production/development.. As you know these new MHR cylinders were flying off the shelf since launch. S6 haven’t rushed this, one original concept was filmed in march 08.
tiba_karotsu
OVERREV TUNING
if the carters are the limiting factor then why not build an improved version, a thicker & bigger crank well along with thicker walls on the transfer tunnels will solve this problem, the carters need to catch up to these new 80cc to 90cc cylinders & we will soon find out the limits of the stock carter dimensions. i had to slap on a lot of epoxy when i tuned our 2Fast 80cc engine, the size of the transfer tunnels alone made the walls on the carters very thin which necessitated adding epoxy externally to support the fragile wall.
