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skwerlee

426 bore kits

9 posts in this topic

can't search...just wanted to know who makes a really good bore kit for a 2000 yz426f and where to buy and for how much? Also if properly installed would this type of a mod kill the reliability? thanks

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TT store, Luke's Racing.

Big bore kits add stress to the engine in two ways. First, anything that causes the engine to create more power puts more strain on everything that bears the load of that power. Second, a bigger piston weighs more, which is important every .003 seconds or so when the piston is told to reverse directions.

Still, the big YZF's are pretty tough, and unless you go hugely oversize and rev it hard all the time, they are pretty much up to it.

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TT store, Luke's Racing.

Big bore kits add stress to the engine in two ways. First, anything that causes the engine to create more power puts more strain on everything that bears the load of that power. Second, a bigger piston weighs more, which is important every .003 seconds or so when the piston is told to reverse directions.

Still, the big YZF's are pretty tough, and unless you go hugely oversize and rev it hard all the time, they are pretty much up to it.

thanks!

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I got the Lukes kit (Millenium Tech. does the machine work and they are good). Came with a 97mm Wiseco (either stock or 13.5:1), Cometic gasket kit and a the machine work for $350 shipped.

I did quite a few other mods (450 cam and exhaust ) at the same time, so I cant comment exactly how much the extra displacement helped. I can say that running 14/47 gearing felt like the 14/50 I was running before hand. I only did it cause my jug was damaged and this was cheaper than buying OEM , but I'm pleased with it.

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Hey Skwerlee,

I have the same questions. My '00 has never had a top end rebuild and I've been web searching big bore kits as well. I found a site (eric-gorr.com) that had big bore kits that sounded pretty reasonable. I tried to include a link but the site says it's undergoing reconstruction right now. I was looking at it two days ago and they had a deal where you sent them your engine and they would bore and replate your cylinder, redo your head with the kibblewhite valves (very durable from what I've read), and install Hot Cams (with auto decomp that you and I could both use), all for about 1200 bucks!

Has anyone had experience with Eric Gorr or have information about their work?

I don't think the increase bore will over stress the bottom end. I haven't seen anything over a 444 cc kit and that's still less than the modern 450's.

Jeff

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The valves in the 2000 are stainless and (nearly) indestructible. I cant even imagine how many hours I have on mine and the only head maintenence they've required was stem seals. In fact, they didn't even require it but I did it while the head was dissasembled for inspection. Save your money.

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Eric Gorr is a very reputable, respected, and experienced engine builder. I, however, would not use Kibblewhite valves.

For one thing, the reliablity of Yamaha OEM titanium is unassailable, and in the case of your 2000, the OEM valves are stainless steel, and are as near indestructible as machinery ever gets.

But, even if I wanted aftermarket stainless valves, I would go with Ferea. They have proven to be somewhat tougher in CRF's, and the company stands behind them better, IMO.

Send a PM to

RHC for info about how to buy them, if you're interested.

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Wow...I ride a '03 450..I realize the thread was about a 426..but I can't imagine the day when I need more power. I have been riding cr and yz 250's for ever and stepped up to the 450 about a year ago and I can only ride to about 25% of the bike's potiential.

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