Any old Honda 125cc experts out there?
I am currently enhancing a stock TL125 in stages. I'm starting off my enhancement with a 185cc cylinder (63mm bore) and a 59.4mm stroke (185cc, 9:1cr) using a stock ATC185 piston and cylinder, standard bore. While I'm in there to bore out the case spigot to accept a larger cylinder, I'll machine the cases to accept the larger 65.5mm sleeve, and I'll weld up all the opened oil passages and use an external bypass (I may even add a high tech billet aluminum oil cooler as long as I'm routing pressurized oil outside the cases).
I'll give the 63mm bore/9:1CR a try for a while, but I also have a 65.5mm sleeve and 10.25:1CR Wiseco forged piston that I can install later if I choose. I'm hoping to keep the bike running really cool for Texas summer trials use (2-4 hours straight in 100+ temperatures), so I'm hoping the standard ATC185 cylinder/piston and a crank stroke will prove adequate. The TL's smaller combustion chamber will up the ATCs compression from 8:1 to above 9:1, and the lower compression will also help low end performance.
Anyhow, in order to adequately move all that additional air, I have decided to stick bigger valves in my one piece head. I'm going to use the 25mm/30mm valves from the two piece S head instead of my 21mm/27mm valves in the one piece head. I'll use Neway cutters to open up the valve seats, and I'll do a proper valve guide restoration. Porting and polishing of the head as well.
Because I am going with larger valves, I hope to get by with the TL125 camshaft which has a profile tailored for trials riding. So, rather than getting a new Megacycle needle bearing camshaft with a less trials oriented profile, I hope to convert my existing cam/head to use needle bearings. The problem is that the only person I have heard that was doing that conversion somewhat recently is no longer around (Hoyt McKagen at Best Motorcycle Repair), so I may have to do the work in-house.
I can do all of the work myself (I have a moderate machine shop at home), I am merely hoping to not re-invent the wheel, and instead use existing conversions to model my conversion after. I would love to know details about the conversion: what bearings were used? How is the mounting plate modified? Dimensions, ... That sort of stuff. Or, if there are any other companies doing the needle bearing camshaft conversion on Honda XL125s and similar bikes with one piece heads.
I could possibly just get the Megacycle cam and have it reground to facilitate more bottom end performance, but that would be very expensive ($500 total).