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Message: [QUOTE="DualSportr, post: 142498, member: 19592"] Okay, let me apologize in advance - this will be a long one, but I wanted to answer a few different points brought up here. Yes, or do the 415cc kit. I'm going to stick my neck out here - but here goes -- XR's Only has always relied on derivative technology - they don't design most of their products, but purchase them from other sources. Because they're not actually designing the product, they don't really know its limitations as well as the company that initially produced the kit. They are very nice people. I like them very much. They are able mechanics, but I don't think I'd put them in the same class as a technician who designs and tests this stuff. If you want to, ask them what the sleeve wall thickness is at the bottom of the sleeve after the 430cc kit is installed. If they can't answer this question quickly, then they have no way of knowing whether the sleeve thickness will be a problem or not. A stock engine will do the same thing - it's not really the heat that does them in - but the motion of the valve travelling up and down. Higher lift cams will cause this to happen much more quickly, and those will cause head temps to drop. I do agree the high comp is not good for most applications. Especially trail riding. Yes, the seals are made of a rubbery plastic material, with a metal retaining spring. If the engine only smokes at startup, it's definitely the seals. If you want your seals to last, use brown ones, or green ones. If you purchased a gasket kit which includes stem seals, if they're black, throw them away and purchase the seals separately (they'll come brown or green that way). The black ones don't work at all. BTW, for those of you who are used to doing valve jobs on automotive stuff, you might not know this; On ALL Japanese motorcycle engines, the valves are stellite coated, and can't be ground! Even lapping them in more than a few strokes will cut thru the hard coating and you're back where you started. We've seen brand-new engines with cupped valves because they were over-lapped at the factory. Cut the seats & grind the seats only. Of course, the solution to this problem is Stainless Steel valves! It depends on your weight - if you're under 200 lbs, I'd go for the 415cc kit. If you have the extra cash laying around ($1,500), do a cam, hardfaced rockers, valve springs, an FCR carb and a 3 angle valve grind. This is really a pretty neat setup for motocross (but still not a YZF beater :( ). The 440 produces more torque than the 415, but the 415 realizes the power much more quickly. [/QUOTE]

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