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Gorr 05 YZ144 project is a success
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[QUOTE="Eric Gorr, post: 854372, member: 17225"] Hi guys, Thanks for the good words on the 144. Overall I like the new YZ125 engine. That thing is built tighter than a KX65! The extremely short intake enabled Yamaha to keep a straight path to the crankcase. It looks like they are trying to reduce the crankcase volume and the transition from the cases to the transfers is excellent, theres no opportunities to improve the flow with porting, so if some ambitious tuning company tells you that the cases need to be split on a new bike in order to port them, they're just looking to score more of your hard earned money. The cylinder allows for greater overbores because of the increased thickness, but hanging a big heavy piston on the end of the rod is just going to slow this bike down. The stock porting and head design are the most conservative since the 1998 model YZ125. This is the porting that I used for Ben's bike; the exhaust port opens 27.5mm ATDC and the transfers are staggered for more top end with a starting opening of 41.5mm ATDC. That's shifter kart timing! Are you guys at Max Power writing these specs down? Since you clowns seem to copy everything else I do including my web site, pricing, tech articles, services, and piston designs. You might as well steal this too! The stock head design seems to be adopted to reduce squish velocity and eliminate the chronic YZ problem of cylinder and head errosion due to o-ring leaks. I first saw this piston design 2 years ago when I bought out a batch of Yamaha of Troy's race team once they switched to YZFs. I think that Yamaha should've used a shallow conical crown design like my 144 piston, and pinned the head to the cylinder and widened the exhaust bridge if they were really serious about making the engine more reliable. The set-up for a cross-country ridden engine is much different than Ben's YZ. The port timing is more conservative than stock because when we bore a cylinder 4mm oversize the ports drop in the cylinder wall because of the roof angles. So that enables me to raise the ports to whatever timing works best for the application. Sometimes we'll Tig weld the exhaust bridge then stress relieve it to give the ring more support. Of course the exhaust port area is reduced but thats exactly what you need for an off-road engine that might peak at only 9,500 rpm. If I had more resources I'd make special pipes for 144s, but generally speaking a pipe with a larger diameter center section like a FMF Fatty is a good choice. The SST pipe might make the engine run hot because of the constricted convergence cone to stinger transition. When that pipe started to become popular I changed the design of my piston to position 50% of the mass in the piston crown to reduce the chance of melting a hole in the center from use with an SST pipe. For guys looking for even more displacement I'm stocking stroker cranks of 58.5mm for quick trade-ups. I'm working with TNR Machine in Dowling Michigan. They have the most precise method of locating the new pin holes on the crank. Unlike our competitors Max Power and RPM we don't need to weld the crank pin to the flyweights because TNR can hold precise tolerances on the new pin hole inside diameter and location. So our cranks can be rebuilt repeatedly using traditional technology, Welded cranks are pretty much set in stone. In order to rebuild them you have to mill-down the pin and flyweights past the weldment just to disassemble them. As far as the stock YZ125 is concerned, my current set-up for expert riders is to reconfigure the head for a flat top Wiseco piston (762MO5400) then raise the exhaust port and stagger the transfers. So far people are pretty happy with that set-up. Overall I think Yamaha has done a great job at investing in the 125 2-stroke class with a lightweight chassis. With the AMA banning 4-strokes from the schoolboy class and considering a separate 2 & 4 stroke class for the future, the 05YZ125 should be the bike of the class. I'm expecting the American aftermarket to step up to the plate and produce titanium bolt and axle kits for this bike to make it even lighter. Eric [/QUOTE]
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Gorr 05 YZ144 project is a success
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