Scooterotica

rapido 250 with 62 stroke, i asume its been done before.

whats the pros and cons?

no cons i think. only a lot of pros in my opinion. think of the torque that you have !!

a very good road touring engine.


cheers mate

eden wrote:stupidly long transfer timing

so what is the end result ?is it powerful?greedy on fuel? or just poor?
have you done this conversion eden?
regards
joe

Are long transfer timings a no-no nowadays?

would a mugello 225 with a steel liner/ bigger spiggot taken to 72mm be a better start?

i had a go on train drivers rt255 and cant fault it but cant afford it. it kicks my ts1 240 in the ass on the road, if not on paper.

so im trying to simulate it with what i have.

eden wrote:all depends what you want from your engine, off the top of my head, rapido 250 have 130-135 degrees of transfer timing, now if you just bung in a 62mm stroke and just pack at the base the transfer timing will go up to around 143 degrees, which I think most people would agree was a tadge too long. to give it some perspective, standard gp200 has around 116 degrees of transfer timing.

What does longer transfer timing mean,
in simple English ?

Too much transfer timing means transfers are open for too long. One of the effects is similar to a tuned Vespa in that it won't pull fourth gear, whatever you do to the gearing.

The height of the transfer ports and the height of the exhaust port need to be in proportion. The exhaust port needs to be open for a period of time before the transfers open (this is known as the exhaust port lead - that's LEED, not LED). If there is not enough lead, then the engine does not have enough time to extract the spent gas from the cylinder before the transfers open and start to disrupt the process.

There are lots and lots of factors that can affect the above, such as the shape and direction of the port and the design of the expansion chamber/exhaust, so this is not a definitive explanation, only my best understanding of the situation.

I am happy to be corrected.

cezeta wrote:rapido 250 with 62 stroke, i asume its been done before.

whats the pros and cons?

I have not heard good reports about the Rapido 250 barrels. "Mark" on this site got through one in less than 4000 miles.

What about one of Harry Barlow's new barrels (well....re-made TS1 barrels). They have been designed for longer stroke cranks. There is loads on meat on the top and bottom of the barrel to accommodate top-and-tailing. Harry is proposing a 72mm piston and 61mm stroke to make a 248cc, but 62mm stroke would be easily accommodated.

Thanks Martin,
still running in so can't say many things yet.
Just hope for it,to last more than 4000 miles

The only fact at the momment is that it pulls very well the SX200 gearing.

Knowledge wrote:

cezeta wrote:rapido 250 with 62 stroke, i asume its been done before.

whats the pros and cons?

I have not heard good reports about the Rapido 250 barrels. "Mark" on this site got through one in less than 4000 miles.

What about one of Harry Barlow's new barrels (well....re-made TS1 barrels). They have been designed for longer stroke cranks. There is loads on meat on the top and bottom of the barrel to accommodate top-and-tailing. Harry is proposing a 72mm piston and 61mm stroke to make a 248cc, but 62mm stroke would be easily accommodated.

thats interesting, is there any info out yet?