Hi All, (especially Chris kenny or Druid !! - or anybody who knows about 2 stroke porting)
Am having some challenges tuning my 250 Griffon - which had to have a new cylinder liner - reworked head and new piston ( a new forged one from Simon but to original griffon spec). I am aiming to end up with a 12:1 compression ratio but optimise squish band clearance.
My basic problem is that to get the compression any where near spec - I will need to take off some of the top of the liner. In addition the piston edge is slightly proud (above the bottom of the transfer port) when at BDC - so adjusting base gasket isn't an option as this would raise the piston edge even further at BDC.
How critical and accurate does the piston edge need to be to the bottom of the transfer port at BDC (assume it MUST not be below it)?
Do we have any factory drawings of barrel /port dimensions so I can check against? - e.g At BDC - what should the effective height of the transfer ports - an the height form port to cylinder top edge?
So my assumption is i need to do the following.
1. Adjust base gaskets till the piston edge is flush with the bottom of the transfer port @BDC
2. Check compression ratio
3. machine off top of cylinder liner - to reduce piston edge to top of cylinder gap to raise compression ratio
In all the above - assume I will maintain a minimum squish of 1.5mm (does anybody have any data on optimum squish?)
Many thanks for any assistance
Kim
Am having some challenges tuning my 250 Griffon - which had to have a new cylinder liner - reworked head and new piston ( a new forged one from Simon but to original griffon spec). I am aiming to end up with a 12:1 compression ratio but optimise squish band clearance.
My basic problem is that to get the compression any where near spec - I will need to take off some of the top of the liner. In addition the piston edge is slightly proud (above the bottom of the transfer port) when at BDC - so adjusting base gasket isn't an option as this would raise the piston edge even further at BDC.
How critical and accurate does the piston edge need to be to the bottom of the transfer port at BDC (assume it MUST not be below it)?
Do we have any factory drawings of barrel /port dimensions so I can check against? - e.g At BDC - what should the effective height of the transfer ports - an the height form port to cylinder top edge?
So my assumption is i need to do the following.
1. Adjust base gaskets till the piston edge is flush with the bottom of the transfer port @BDC
2. Check compression ratio
3. machine off top of cylinder liner - to reduce piston edge to top of cylinder gap to raise compression ratio
In all the above - assume I will maintain a minimum squish of 1.5mm (does anybody have any data on optimum squish?)
Many thanks for any assistance
Kim
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