Boring a 360 Challenger out to 83mm

[Ian]

I'm looking to bore a 360 Challenger out to 83mm - has anyone here done this before?

Chris Goodfellow commented about this once... "you turn a 360 into a 380 by sticking a bigger piston in , the works 360were at varous times 390 & 400 using a 83mm & 84mm piston"

Can I get away with boring a 360 barrel (80mm) out to 83mm?

What piston could I use? A 380 Griffon +0.040?


Any ideas or advice appreciated.

[Phil Hyde]

I guess that boring the cylinder is the easy bit.

Getting the squish correct to accommodate the extra diameter will need some trial and error

[teamferret]

Be careful on the lining thickness too, I bored my challenger barrel out to 68,5 and as it bored Ok I thought it would work fine, but it kept on seizing ( in trials not MX) and the top reboring guru reckons that this is due to the liner being too thin. This is made worse by the holding down method which 'crushes' the barrel (his words not mine)

[Ian]

I think I should be able to turn it in a lathe on a mandrel and carefully widen the squish band. Might be tricky as the 360 head is quite an irregular shape, compared to say a 9E one.

Regarding the liner thickness, that's my biggest concern but I'm yet to look into it properly. It's worth noting though that the 360 barrel is bolted directly to the crankcases - it isn't squeezed down by sleeve bolts like a 250 Challenger top-end on a trials bike (I have a 250 Challenger barrel on a TFS).