Scooterotica

David

give me some info m8 & ill do some calcs
also have u any pics of wear, I have seen this too?

need Bore, Stroke & Rod length.


Smiffy

you may both like to read up on" piston pin offset"...................
interesting stuff.

sean brady scooters wrote:you may both like to read up on" piston pin offset"...................
interesting stuff.

yep thats also has an effect

But well talk about that later a sean
I see another skicky for the tuning section

as far as i understand it.................on power stroke ,the ex side of piston is "major "thrust surface.............this is in effect pressed down (above gudgeon pin)..........and so inlet skirt side is pressed up (below gudgeon pin)...............this has the effect of scraping the oil off the bore in that area and so increases wear ...............

sean brady scooters wrote:as far as i understand it.................on power stroke ,the ex side of piston is "major "thrust surface.............this is in effect pressed down (above gudgeon pin)..........and so inlet skirt side is pressed up (below gudgeon pin)...............this has the effect of scraping the oil off the bore in that area and so increases wear ...............

so im not being totally thick then

presumimg im using a circa 4mm packing plate and a 74mm length piston with a suitable compression height piston ie TS250 with a 116 mm rod, where would you place the windows to leave maximun support from the skirt on the thrust face

sean brady scooters wrote:you may both like to read up on" piston pin offset"...................
interesting stuff.

not come across this yet, any references

the most important thing is to not widen inlet too much ,as this of course leaves less support either side for piston..............
piston holes can only be in line with this..........

sean brady scooters wrote:as far as i understand it.................on power stroke ,the ex side of piston is "major "thrust surface.............this is in effect pressed down (above gudgeon pin)..........and so inlet skirt side is pressed up (below gudgeon pin)...............this has the effect of scraping the oil off the bore in that area and so increases wear ...............

Yep Id go along with that sean

Can be reduced by extending rod length etc

ie Std ts1 stroke 58mm.... rod 107mm so Rod/stroke ratio 1.84
................stroke 58mm.... rod 110mm so Rod/stroke ratio 1.9
................stroke 58mm.... rod 116mm so Rod/stroke ratio 2.00
................stroke 60mm.... rod 107mm so Rod/stroke ratio 1.78
................stroke 60mm.... rod 110mm so Rod/stroke ratio 1.83
................stroke 60mm.... rod 116mm so Rod/stroke ratio 1.93

So what are we looking at here, well we are looking for as high a R/S ratio as possible
This is because the anglular motion is less & the Lower rod angles relates to less wear on the piston and lighter loads on the bearings and rod etc etc .

So what the best figure you ask ?well for tuned high performance engines 1.9 -2 is good
& you certainly dont want to go down below 1.7.

So be aware if you are stroking a crank with the standard 107mm rod IMO dont do it. I dont.
Min I use is 110mm

Smiffy

what bore size are you intending to use dave.............71/72.........?
put it this way...........even if inceasing bore to 72......i would be reluctant to widen inlet at all.........especially if reliability is a concern.........

sean brady scooters wrote:the most important thing is to not widen inlet too much ,as this of course leaves less support either side for piston..............
piston holes can only be in line with this..........

have seen pistons that have been cut as a reverse V instead of having windows, this will reduce the support the of the piston on the thrust face, but is the gain from having less obstruction for flow from the reed valve worthwhile

guess what i am asking how low should the holes go in the piston