GP100/125 question

[Tristan.]

My GP100 has 123 stamped on the barrell, but the bore is 50mm (or pretty close, lost my verniers so measured with a tape measure) The GP125s bore is 56 mm, can anyone shed any light? My theory is the whole engines are shared, then the 125s barrell is machined out to 56mm and the 100s to 50, so theyre cast from identicle moulds.

Presumably if this is the case I could make it a 125 with just a rebore and piston and gasket set.

EDIT ignore that last bit, that wouild obviously just remove my cylinder liner

[P.]

We had a 100 and a 125 GP, the 100 has 100 stamped on it and the 125 indeed had 123 stamped and a label on the headstock with 9kW printed.

Not sure if that helps you, but im pretty sure thats the 125 setup.

[Tristan.]

It helps, but it throws my theory out of the window. I'm so confused

[cb1rocket]

my gp125 engine also has 123cc on it, its just the way it is i suppose and classed as the 125.

The gp100 (i think at the mo) also has 99 or 98cc stamped on it.

So wether its a 400, 600 of any engine size its not quite exactly dead on the 400cc etc figures

[Tristan.]

You misread. I have a 100 with 123 stamped on it

[cb1rocket]

sorry got a bit tired there

If its def a 50 bore then it could be that someone has put a linear in it maybe to bring it back to the 100cc size as the previous owner couldnt find another 100 barrel.

Still sounds odd thou, cheaper to reline the existing barrell and/ore rebore to suit.

werid