Boring 200 to 225?

[Davidsquaredson]

Hi, friend has a GP200. Asked me about going to 225 but is on a tight budget. I see steel lined ALU 225 barrels for sale. Wondering having the stock barrel bored out to 225. Is there enough meat for that? What about cooling, is the iron and fins sufficient?

If the way to go is ALU, I won’t buy the crap on eBay, so does any particular shop have a quality product in thus budget option?

Thx in advance.
David

[HxPaul]

I have an RT 225 kit for sale,brand new in the box.£350.

[warts]

I had my SX bored to 70mm by A Francis in Watford in 1967. Hopefully pistons are a lot better these days. OK once sorted.

[nick b]

i had mine done by ray kemp at af watford about 1980 had a series of heat seizures took it out to 230cc by dave webster with a bultaco piston so i think that is probably the maximum

[Warkton Tornado No.1]

I wouldn't hesitate to bore a 200 OEM cylinder to 70 mm but with the following criteria:

Utilise a good piston, my preference being a TS250 with adjustments being made for different compression height , cylinder head profile, squish & wrist pin diameter. Squish has a maximum as well as minimum value!

Ensure honed bore to correct clearance. Needless (I hope!) to say port edges should be de-blurred....

Understand the significance of engine speed & cooling.

Realise the relevance of air/fuel ratio & that ADDING EXTRA OIL effectively weakens the carburation.

[nick b]

gp crank at minimum to add to your spec

[cgt75b]

Hi

I have a cast cylinder bored at 71 mil and a forged Wossner piston with no issues.

Hope this helps

Ps the most expensive bit was the piston.

Cgt75b.

[Adam_Winstone]

I'd rather bore an original 200 barrel out to 225, rather than buy one of the iron lined alloy ones, which often prove soft and wear out as quickly as they are run in!

Adam