GS Polini longstroke

[Juan]

On learning of the DRT eccentric crank pin it got me thinking it could be of use to the GS piston on a Polini or DR barrel.

My understanding of the GS piston is that it requires 1mm machined fron the top or the barrel and a 1mm packer placed under it to raise it back up to suit the standard crank.Now,if I'm correct then the barrel wouldn't require shortening with a 53mm stroke if the packer was used.

I appreciate the ports would still require work and this may not be the ideal configuration,perhaps shortening the barrel 1mm and using a 2mm packer may work better?

I look forward to hearing your thoughts on this.

[knoker]

i don't understand very well what you write but i try to explain you what i have undestood....
for mounting 53 stroke you had to use 1mm gasket.
if you use it at the bottom of the cylinder you have an increase of port timing.
if you use the gasket at the top you have a decrease of port timing.
if you want the same port timing that you have now, you have to use 0,5mm gasket at the bottom and 0,5mm gasket at the top...
you have also to consider paper gasket.

if you don't understand what i have wrote, please ask again....

[Juan]

I understand this fine.

However,the Grand Sport replacement pistons require the barrel to be modified to work with the Polini or DR(at least on the standard stroke),the question here is really to clarify which way will produce the best results.

I would be more intrested in a good,strong touring motor than an out and out sporting item.

[knoker]

from sip:
Compression height original cylinders 125cc = 36.5 mm.
Compression height with GRAND SPORT conversion pistons for Polini/Dr/Malossi cylinders = 30.5 mm.
so, if you use 51 stroke, you have to mill the bottom of cylinder of 6mm, and you have original Polini port timing
if you use 53 stroke and if you want original port time, you have to mill the bottom of 5,5mm and use a 0,5mm gasket at the top of cilinder
if you use 53 stroke you have to mill the bottom of cylinder of 5mm and you have also an increase of port timing, i think it is the better solution but in this way you open the boost port (transfer in front of exhaust)

[hank]

sounds complicated.......but enhancing the mighty DR sounds promising......... ;D

what advantages are you getting with a GS piston anyway? is it just a longer lasting better quality piston, or is there also a performance gain?

[Juan]

Okay,thanks Knoker.That's cleared it up a little.Suppose I should really read the bumf available. ;D

6mm on standard stroke?Thats loads. :oI'm a liitle confused about the compression height though,shouldn't the differance be halved?


I'll look into this a little further after I've spoke to Denis about the pin.

[Juan]

More better quality which lends it's self to the quest for power and maximum abuse. ;D

[jonnysnatchsniffer]

could you not fit a t5 conrod and use a jap piston fromm a crosser and get even more abuse out of it