Suzuki GP125 nearly dead - need advise

[MrClifford]

So here is goes, my suzuki gp125 has been fouling apark plugs since i got it, then piston slap, then no compression - simples! Rebore and new piston/ring or not. It has already been bored to 58mm and is now at 58.48mm hence the low/no compression they dont make any bigger pistons so here is a solution i have that could work but need advise.

1. Rebore to 59mm and make a new piston - but as the piston wont be forged it will be weak

2. Rebore to 59mm try and find a similar piston and turn it down to make it smaller

Problem is the cylinder lining will then only be around 2.5mm - not too thick eh!

Or 3. If anyone has one to sell

Just wondering on your advise guys as i cant afford a new engine and could scrape enough for a lump of alumium or a piston!

Or if is a new engine time does anyone know what a good fit to the gp frame is?

Cheers peeps!

[Pete.]

Doubtful the new piston will be forged anyhow - it'll be cast most likely. No reason why you shouldn't make a new one but where will you find rings for it? You'd have to source those first and cut the ring grooves to suit, but 2.5mm cylinder wall is no problem.
It's possible you might fit a piston from another bike even a piston-port engine but you'll have to find one with the pins in the correct place to keep the rings out of the exhaust port, the right gudgeon pin diameter and pretty close pin to crown distance and of course the skirt length for the transfer ports. I bet there's one out there but it'll be hassle trying to research it.

Couple of other choices are find another barrel or re-line the one you have, then you can use a stock oversize piston and have three or four overbore chances.

Personally, I don't think half a mm of wear on the barrel is a lot, I'd be thinking about new rings and crank bearings and seals. I bet it's burning gearbox oil that's fouling the plugs. It'll at least keep you on the road until you source another barrel.
____________________
a.k.a 'Geri'

132.9mph off and walked away. Gear is good, gear is good, gear is very very good