Scooterotica

for those of you that already understand the basics here regarding such matters....my appologies for going over old ground.
This is just for those that as yet still do not quite fully understand the importance of a good quality piston assembly......
what ever your tuning/performance requirements are....above a std ,that is....whether a torquey touring tune OR a rev monster...SO much depends on the piston assembly that you intend to use...
basically better pistons that use thin rings (and deeper in section)....can handle safely wider ports and higher revs...
so if you are trying to achieve a real torquey tune these will allow you to use a much wider exhaust port.
and if extra revs are required ,these will also cope safely.
just an example.....std indian 200 piston (3 ring,1.99mm)....max ex port width....say 40/42mm
thinner better rings allow 46mm at least...

Hi Sean,
I understand what you're saying, but how dose that relate with the exhaust port width being a percentage of the bore size?

Your making me feel guilty now Sean... ..I might just order a mahle. do you fancy keeping it there and doing the neccesary changes..

piston rings are usually thought of as quite a simple piece of kit, but actually, can involved up to 40 machining operations to the end product! wire rings , are just that, flat wire that is coiled into a "slinky" spring, just like the ones you had as a kid, but about 4 foot long! then slit, surface ground, the outside edge is machined (this is done in banks of rings) and hard chromed, then the chrome is machined to the required profile, then the gap "let in" (this can be done up to 3 times) more surface grinding /polishing, an anti sieze coating (granolite or similar) , laser marking for the size and fitting spec (TOP, +.4 etc) scotchbrighting of OD, two inspections, light tight testing, final inspection, packaging. and thats a simple steel ring! some can be .5 of a mil thick! cast iron rings can be very tough, if OD chromed, and made from spheroidal graphite iron, or similar. the cheap thick rings on most indian pistons, are just plain cast iron, with the minimum of machining ops for cheapness. SG iron , moly inlaid rings are very tough, but you will struggle to find them these days. a thick ring can be tough, it"s the contact area on the bore that you should look for, i.e barrel ground. a 2.5 mm ring can have a contact area of 1mm or less. piston rings will be a thing of the past soon on modern engines, japanese company TAIKOKU PISTONS, has been developing a ringless piston, with a pressurised air in the crankcase system, to force air under extreme pressure around the outside of the piston, to remove the blowpast, and keep optimum performance in the engine. less power needed, and better fuel economy and decreased engine wear.

goldeneye wrote:piston rings Etc,Etc,Etc and there`s quite a bit of info there

Absolutely spot on.
But all we need to know is that if you ain`t running a near standard engine you should be looking at a high silicon (Jap) piston and wire rings to allow for good tuning. That is wide ports rather than big timings.

There is still a bit to be said for standard engines , low maintenance, good economy, etc.,etc.,etc.
But honestly I always liked a well tuned engine, big carb, wide ports, nice expanie, and a helmet wth plenty of padding to protect my ears

Has anyone tried wosner pistons? I`d be greatfull for any info

tthe dactek bikes run wossner pistons , they are top quality and teflon coated as well .

http://cgi.ebay.co.uk/KTM-Piston-Kit-EX ... 27acc5c6bc
Like this one Mark
PS £78 For a TS1 (YZ250)

red ghost wrote:Hi Sean,
I understand what you're saying, but how dose that relate with the exhaust port width being a percentage of the bore size?

on a 200/66mm bore ,a 42mm wide exhaust is roughly 65% of bore...
.66 x 65 =42.9mm

70% would be .66 x 70 = 46.2mm

Which piston ring profile (in wire) is best suited to a high reving cast iron barrel. And which is best for a low reving cast lammy barrel??? Anyone know.

J1MS wrote:Which piston ring profile (in wire) is best suited to a high reving cast iron barrel. And which is best for a low reving cast lammy barrel??? Anyone know.

Hopefully asso for high revs cause that what I will be sending to Sean to replace my soon to be ornament standard piston.