advice needed

[dave wheeler]

my TV 175 has just had a new piston (62.8, last oversize), .3mm clearance, rich jetting and 17"btdc, and at very mild revs its seized after 15 miles, a 3 point seize, that though mild and the scoot restarted almost immediately, a strip down reveiled a trapped top ring which naturally couldn`t be got out without snapping.The piston is an S.R diamond 2 ring piston, not expensive
my question is why did it seize? is it cos the expansion rate of the piston was greater than standard and a hone to a wider clearance and new rings and everything will be ok, if so, how much should the clearance be.
on a related topic is an SR alloy barrel a straight swop for a standard TV barrel, and if i used a suzuki TS185 piston with a 116 con rod, how would that work regarding top and tailing?
cheers

[dave wheeler]

sorry thats 3 thou piston/barrel clearance

[bristolmod]

probably the coefficient of expansion on the cheap Diamond pistom is way out of kilter with the barrel- hence the seize.

Try a Mahle from Scooter Restos- not expensive and good IMO.

Chris

[dave wheeler]

out of stock, i wouldnt have used one of these pistons had i any other options but there were no other 62.8 pistons available

[shocky]

Hi dave I think 3thou is to little clearance om a budget piston 4thou is the mark maybe your piston could be cleaned up and reused with new rings and a light hone to remove any scuffing on the cylinder have a look at the beedspeed page for costing to top and tail how ever it seems a shame to do that to a tv cylinder

[dave wheeler]

thanks for the reply guys, i spoke to paul at scooter restorations and he said " oh these definately need 4 thou", well given that a piston is only going to be used for one thing would it not make sense to let the customer know?? Anyway theyre sending a new set of rings and barrel honed out to 5 thou, as im on the last oversize i cant take a risk with another seize, given how well it ran last year with only 1 ring sealing i cant believe the clearance is so critical that it warents such tight tollerences

[shocky]

Who said 5 thou seems loose to me piston slap CAN cause the piston skirt to break off just be carefull

[shocky]

I just looked and there are other bigger oversizes who said you were on the last for your cylinder , I dont know what series your cylinder is but the series 3 tv can be taken to 66mm 65 mm being an old school "200" conversion

[eden]

4 thou all day

[dave wheeler]

well its done now so will see, cant believe 5 thou is over the top when 3.5 and it nipped up when it was so rich it was barely rideable?
anyway what about the sr barrel? is it a straight swap? and id like to know where all these pistons are, i know theres an ancilloti conversion piston on ebay just now but what else, i have very little faith in this piston but there were NO alternatives, what work would a suzuki 185 conversion need as surely some of the machining is unnessesary with a 116 con rod, btw i cant imagine the skirt is at risk, you wanna see it, its built like a tank!