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Discussion Starter · #1 ·
Ok, so here's the deal...

I bought three YFZ's this weekend... All of them non runners. Busy stripping the motors and deciding what to do and how to do it.

Chassis :

First chassis is a black and red '07 Limited edition chassis in very good condition. Hauser steering stem, aftermarket nerf bars, lone star axle, wheelie bar, bumper and exhaust. This is the bike I'm gonna build up for myself.

Second chassis is apparently an '06. Not much extras except for pro circuit pipe and red bull sticker kit. Gonna build this one up and sell off.

Third chassis is a bare frame with front suspension and PEP rear shock. Do have a set of plastics. Also has a Lonestar swing arm and axle. Will either sell off as spares or try and build a hybrid/std bike.

Motors :

First chassis' motor is disassembled and doesn't look like there's much wrong with it. Has a hotrods conrod and ported head, and a gold coloured GYTR clutch.

Second chassis' motor we took appart yesterday. To my dismay it dropped 2 valved, broke the piston, bent the rod and obviosly stuffed the crank. Oh and tore through the barrel...

Third chassis' motor is totally stripped and in boxes.

Fourth motor... Well I got half a fourth motor in between all the spares :) As well as an extra crank, conrod and about 3 pistons. One is a WISECO one is standadrd and the other seems to have a higher compression than standard.

So, I don't know much about these bikes and I hope I could pick your brains over the coming week or two.

The goal : To build a reliable and powerfull engine for Chassis 1.

1. Mainly (for now) I need to know if there is any play allowed on a crank/conrod (assembled). Three of the cranks I have, have sideways play on the conrod but no up & down play. Maybe about 1mm or so.

2. Regarding the heads, is flowed heads with bigger valves an option or is a standard head fine?

3. I read somewhere about the WR's crank that could fit. Is there any other parts from other motors that will fit the YFZ?

4. So after '06 the upgraded the motors with the oil squirter. Is there a how to on this? Or is it machine shop only?

Thnaks in advance guys!! :clap
 

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I would probably stick with the OEM 06+ cranks, just because you don't have to worry about remembering whether or not you need a piston with an 18mm pin or not. I'd also probably use the Wiseco crank in the one that you sell. Just preference. I've seen some of the Wiseco cranks break at the tapered area for the stator. Not sure how common it is on the 4-strokes, but it's fairly common on the 2-stroke stuff. There has to be a little side play on the crank. I'm not positive what the tolerances are, though. As for the oil mod, I would try a PM to J&T here on the forum. They're the cheapest place that I know of to get the mod done. The heads from '06+ are good when cleaned up. Bigger valves and port work will help, of course, depending on how radical you plan on getting. Your best bet for that is to look at other people's builds and decide whether or not it's right for you. Or, just call an engine builder and see what they recommend. Good luck.
 

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Discussion Starter · #3 ·
I would probably stick with the OEM 06+ cranks, just because you don't have to worry about remembering whether or not you need a piston with an 18mm pin or not. I'd also probably use the Wiseco crank in the one that you sell. Just preference. I've seen some of the Wiseco cranks break at the tapered area for the stator. Not sure how common it is on the 4-strokes, but it's fairly common on the 2-stroke stuff. There has to be a little side play on the crank. I'm not positive what the tolerances are, though. As for the oil mod, I would try a PM to J&T here on the forum. They're the cheapest place that I know of to get the mod done. The heads from '06+ are good when cleaned up. Bigger valves and port work will help, of course, depending on how radical you plan on getting. Your best bet for that is to look at other people's builds and decide whether or not it's right for you. Or, just call an engine builder and see what they recommend. Good luck.
Thanks bud.

BTW, the Wiseco item is a piston not a crank 8)
 

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Wr cams will work, along with rod and piston. If you use the wr piston, you must use the wr rod. Cams can be used with yfz internals. As far as the play on the cranks, a little side motion is acceptable, especially 1mm. So long as there is no up and down play, you should be fine. I wouldn't use hotrods' crank in anything.... OEM or just about anything else.
 
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