A few questions about pistons and tuning?

[look no hands]

Hi all,

I'm thinking of doing some piston tinkering, now a few questions to the tuners amongst us

If you can get a decent mirror polished saddle/area on the rear of the piston, is it really worth buttoning the piston for smoothness?

Is it actually worth buttoning the piston, does it really make that much difference?

What is the best weight for a piston?

What is the best way of lightning a heavy piston, machine off a bit of the girth in the middle or drill holes?

As for seal sizing, what's the best way and what's the sliding fit supposed to be like, should it glide down under it's own weight or a gentle push from your finger?

Thanks for any advice.

Pete

[TonyL]

Hi all,

I'm thinking of doing some piston tinkering, now a few questions to the tuners amongst us

If you can get a decent mirror polished saddle/area on the rear of the piston, is it really worth buttoning the piston for smoothness?

Is it actually worth buttoning the piston, does it really make that much difference?

What is the best weight for a piston?

What is the best way of lightning a heavy piston, machine off a bit of the girth in the middle or drill holes?

As for seal sizing, what's the best way and what's the sliding fit supposed to be like, should it glide down under it's own weight or a gentle push from your finger?

Thanks for any advice.

Pete

Hello Beesa Pete.

Buttoning (or Delrin ring):- Would always have to be seen as a good idea to reduce metal to metal contact. However, on reassembly, I always grease the rear of the skirt. Then, once the piston is pushed fully forwards I always smear some more moly grease on the inside circumference of the cylinder, behind the piston. Recommended by Steve Pope in his fitting kit instructions so it has to be good advice and it's always worked for me. Using synthetic bearings would reduce the amount of lubrication required in this vital area.

Best weight for the piston? Blimey, that's a BIG question and the answer very much depends on the individual gun, bore and stroke dimensions, transfer port size, preload, spring force and even the pellet used.

In terms of seal fit, I'd prefer to go for a "push fit" rather than the piston dropping under its own weight thinking, but it does seem to be down to personal preference.

Sorry it's all sounding a little of a cop-out, but like so many aspects of springer tuning, much of it is down to the individual.

[look no hands]

Hello Beesa Pete.

Buttoning (or Delrin ring):- Would always have to be seen as a good idea to reduce metal to metal contact. However, on reassembly, I always grease the rear of the skirt. Then, once the piston is pushed fully forwards I always smear some more moly grease on the inside circumference of the cylinder, behind the piston. Recommended by Steve Pope in his fitting kit instructions so it has to be good advice and it's always worked for me. Using synthetic bearings would reduce the amount of lubrication required in this vital area.

Best weight for the piston? Blimey, that's a BIG question and the answer very much depends on the individual gun, bore and stroke dimensions, transfer port size, preload, spring force and even the pellet used.

In terms of seal fit, I'd prefer to go for a "push fit" rather than the piston dropping under its own weight thinking, but it does seem to be down to personal preference.

Sorry it's all sounding a little of a cop-out, but like so many aspects of springer tuning, much of it is down to the individual.

Hi Tone,

Hope you had a good weekend boingering yourself stupid

I know most tunes are down to personal preference and as for all the difference figures, I wasn't sure if there was a 'starting point' so to say or an idealish sort of figure to head for and then do your fine adjustments from there, I understand it's a complicated science which only a few have mastered over the years.

I often read springer tuning threads and people get replies like "your pistons too heavy" and other such answers, I know the piston in project 'cock is a bit on the light side (according to JB at the time of us chatting about it) but I'll have to weigh the Supersport piston when it's out and see what would be best.

Thanks for your input yet again Tone

Pete

[Shed tuner]

assuming the supersport is 29mm and longish stroked, you cant go too light on the piston, so 250-300 g range ? buttoning good if rear of piston loose in the bore. if tight, less advantage.
hth JB

[look no hands]

assuming the supersport is 29mm and longish stroked, you cant go too light on the piston, so 250-300 g range ? buttoning good if rear of piston loose in the bore. if tight, less advantage.
hth JB

Thanks for that Jon, just what I needed to know, the piston in my Airsporter RB2 and the Brocock Indy have nicely finished/machined and mirror polished rear skirt/saddle and fit pretty well in the cylinder, all I want to do is take the 'spit and polish' tune up a stage after the usual kit fitting and spring end polishing etc, I may have a go at transfer port sizing as I have access to a lathe now but that's something I'll have to pester you and others about at a later date, as soon as my seals arrive and my spare piston, I'll do a measure up and so what figures I have.

Many thanks for your advice yet again Jon

Pete

[robs5230]

never messed with piston weights as I don't have a lathe.

Rear piston bearings I don't mirror polish. I just use finish emery that still shows sanding marks. The marks will retain lube and I use moly paste on the rear bearing.

Seal, sized so it can be gently pushed down with one finger for me. Again, moly paste rubbed in the sides but wiped off. The sanding marks retain enough lube.