06 crank ...wr crank...which is more reliable

[SRH]

whats the diff, i know the wr crank is more....i was just going to get the 06 setup, also what compression ratio is the best i dont wanna run race and i see they offer 11.4 11.9 12.5

[jshtex]

Actually there is a big argument going on now on a couple of other yfz sites about the difference. Untill recently the prevailing wisdom was that the rod lengths were different. Now some are saying they are not. I am not sure that anyone has taken the two (WR, 06 YFZ) and actually measured the rods. The only thing that doesnt seem to be questioned is the fact that the 06 YFZ uses a larger wrist pin then the WR does. Now does that make it better ??? It might, obviously the folks at Yamaha could have just stuck the WR crank in it and let em fly, but they chose to go with a different crank with a larger pin.

Then there is the whole compression ratio issue. It sounds like a stock WR crank with a stock WR piston in an 04/05 will have a higher compression ratio than an 04 /05 with an 06 crank and a stock yfz piston. And there seem to be differences between using the 06 crank with an 04/05 piston vs using an 06 piston.

I am going to put one or the other in ours during our upcoming winter break, but I still don't know which one....

[muff]

I think the main factor for them not using the wr crank is because of the wrist pin diameter. Not because the bigger one has any advantages, but because the pistons that are out there already (GYTR, JE, whoever) will already work and wouldn't require a different piston for the '06 model.

[SRH]

is there any advantage reliability wise to run a crank with a smaller wrist pin

[jshtex]

Originally posted by SRH
is there any advantage reliability wise to run a crank with a smaller wrist pin

Well you would think that a larger pin would be better, but I have only heard of one WR pin failing (it might have happened a lot but thats all I have heard of).

It seems to me (and I am not an expert) like the only possible advantage to having a smaller pin "might" be that you should end up with a little more meat around the pin in the actuall piston itself. If you have two identical pistons and one has a smaller hole in it for the pin, wouldn't it be somewhat stronger (the piston I mean). I have heard of several pistons failing and I wonder if they fail at the pin, basically if the pin pulls out the bottom.

But ultimatly like I said before, wouldn't the enginers at yamaha put the better combination in the quad from the factory. They are the ones who will have to live with the results. And they certainly could have picked the existing WR crank over spending the money on a new design for a quad specific one.

[muff]

the smaller wrist pin will obviously be lighter, and a lighter rotating mass is better IMO

[SRH]

how come the pistons i see for the 04 -06 arent true 12:1...isnt it that stock suspposedly?