Q: Rough vibrations from 500cc big bore w/ stroker crank on 07 YZ450F

[Victorr]

Good morning TT,

 

I owned a 07 Yz450f and bought the 500cc Cylinder Works Big Bore Kit with Hot Rods Stroker Crankshaft, and had it installed professionally by an independent motorbike shop owner. I ride my bike 50/50 on the roads and in farmland, I have a license plate, so I was hoping to get more good usable power on the road.

 

However to my surprise, the bike vibrated so bad my butt and hands hurt and you could see it shaking, and the power was definitely more torqy but overall seemed to NOT be better for high RPM cruising, it almost seemed HARDER for it to cruise at high RPMs? Like it was working harder and revving higher. Is this normal or is it the stroker crank, do I absolutely need that stroker crank if I get this kit installed in the future? Any ideas appreciated.

 

So I'm getting a new 2010 yz450f OR a 2010 kx450f because their on CL and I lost that 07 in a house fire, and I'm wondering if the installation was bad, or if its just the stroker crankshaft that maybe isn't good for what I want (sustainable high RPM cruising)? Idk, the powerband seemed more responsive but more flattened out and just crazy reckless not as steady and overall efficient for my situation. So yeah, should I just not do this if I get a new bike or should I do something differently? I just thought the extra CC and HP would help with being on the road rather than hinder, I already had the sprockets maxed out to cruise better too so idk, THANK YOU for your input,

 

-V

[grayracer513]

The first problem is that you didn't have the crank assembly balanced.  The crank was probably built with the stock bore in mind, so the heavier piston threw things off.

 

Secondly, no, a stroker crank is not a better choice for high RPM cruising, although it may have worked out if it had been balanced.

[camman]

Make sure the counter balancer is timed correctly. The Hot Rods crank is balanced for a standard bore piston. However, the Vertex big bore piston is not terribly heavier than stock so overall it shouldn't shake a lot more. It will shake more but not significantly. Also, when using a big bore typically one removes a tooth or two of the rear sprocket and uses the increased torque.