Scooterotica

help needed please
doing a suzuki conversion ,had barell board to suit 64mm piston ,had 5mm off bottom of barell and 2.5mm off top
the question is that once barell is tightened down and piston bottom dead centre the bottom of transfers are about 1.5 mm higher than top of piston,
i havant got a tool to grind tranfers ,will this be ok or will it affect perfomance
thanks john

Don't be tempted to do it as it will ruin the gas flow and actually make the bike slower. I learnt from experience years ago and I seem to remember reading about not doing them recently on MB's Tech site.

Yeah, definitely best to leave them alone. They will end up like that on those conversions, but trying to do anything with them is almost certain to hurt rather than help.

Twinny wrote:help needed please
doing a suzuki conversion ,had barell board to suit 64mm piston ,had 5mm off bottom of barell and 2.5mm off top
the question is that once barell is tightened down and piston bottom dead centre the bottom of transfers are about 1.5 mm higher than top of piston,
i havant got a tool to grind tranfers ,will this be ok or will it affect perfomance
thanks john

if both the ex port and transfers are sat too high then ur timings may be too high with only little port area, would another 1.5mm off base get u level,and check inlet duration isnt too high ,and not leave u with a problem at the head /squish end to sort
without grinding or lowering the cylinder it will still work but a calculated approach would be superior which includes the transfer ports sat level or slightly below piston crown at b.d.c. ,the transfer flow across the crown has a very important cooling effect especially on aircooled motors

Twinny wrote:help needed please
doing a suzuki conversion ,had barell board to suit 64mm piston ,had 5mm off bottom of barell and 2.5mm off top
the question is that once barell is tightened down and piston bottom dead centre the bottom of transfers are about 1.5 mm higher than top of piston,
i havant got a tool to grind tranfers ,will this be ok or will it affect perfomance
thanks john

Whats your deck height at now? any room to play? wheres the bottom of your ex port at? Your really want the bottom of your ports to be bang on or slightly lower. Looks like you got your sums fooked up Obviously if you still have a positive deck height then you could resolve by taking more out of the bottom of the cylinder. Are you using gaskets? have you tried setting things up with a gasket or a thinner gasket?

Darrell Taylor wrote:the transfer flow across the crown has a very important cooling effect especially on aircooled motors

wot I wus thinkin

Nah, he's alright. It comes from trying to put a piston of much lower compression height in too high of a barrel. The intake and exhaust ports (transfers too) all end up too far away from each other compared to the stroke. It turns into a compromise between too much intake timing or too much transfer timing. When you do these, you have to lower the stock exhaust height to match the piston at BDC during porting, not raise it a bunch. You lower the base to give you reasonable transfer timing, and still end up with like 160 deg of intake before you've even touched the barrel.

Darrell Taylor wrote:the transfer flow across the crown has a very important cooling effect especially on aircooled motors

Perhaps why they can be prone to overheating

Wayne Miller wrote:

Twinny wrote:help needed please
doing a suzuki conversion ,had barell board to suit 64mm piston ,had 5mm off bottom of barell and 2.5mm off top
the question is that once barell is tightened down and piston bottom dead centre the bottom of transfers are about 1.5 mm higher than top of piston,
i havant got a tool to grind tranfers ,will this be ok or will it affect perfomance
thanks john

Whats your deck height at now? any room to play? wheres the bottom of your ex port at? Your really want the bottom of your ports to be bang on or slightly lower. Looks like you got your sums fooked up Obviously if you still have a positive deck height then you could resolve by taking more out of the bottom of the cylinder. Are you using gaskets? have you tried setting things up with a gasket or a thinner gasket?

re bolted on with no gasket i f i take 1mm off bottom the transferes line up with piston ,measurments i have at mo are from top of barell
exhaust38.62 and 18.27 deep
inlet 72.52 and 16.55 deep

Twinny wrote:re bolted on with no gasket i f i take 1mm off bottom the transferes line up with piston ,measurments i have at mo are from top of barell
exhaust38.62 and 18.27 deep
inlet 72.52 and 16.55 deep

Sorry Mate I dont under stand?

Are you saying that if you take out a 1mm gasket then your trans line up with your piston crown @ bdc?
or are you saying that without a gasket your trans are still 1mm above the piston crown @ bdc?

either way @ tdc where does your piston crown now sit? +1mm 0mm -1mm

Also I guess the other measurements are in mm from the top of the cylinder, they dont mean a thing without the stroke and conrod length and deck height. If you can get those details then we can visualise how things are looking