What is the noise? RMZ 450 Rebuild!!

DG252
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DG252
I just rebuilt my motor top and bottom ends. It had 48.5 hours on it when my piston cracked in half, luckily it did not grenade though. I put in a new crank, main bearings, Wiseco high compression piston, had cylinder replated and matched to piston, and put a new cam chain in. I got everything put back together, valves are in spec and timing is dead on but it makes this knocking noise when I start it up. The only thing I can think is that the valves are hitting the piston since the high compression piston is the only change during this rebuild. I took it back apart and there are no marks or scratches on the new piston. I should note that i do have Yoshimura stage 2 cams in it.

Can anyone give me some other ideas of what might be hitting inside causing the knock. I will add a video once I figure out how.

https://www.facebook.com/darren.grangroth/videos/10155581475279178/
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Acidreamer
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Acidreamer 9/7/2017 2:12am
9/7/2017 2:12am Edited Date/Time 9/7/2017 2:13am
Would love to help but video doesnt work :/

Since you have aftermarket cams and a high comp piston, make sure youre running race gas or you will have a knock.

Also if your spark plug gap is off it can cause noise.
Bruce372
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Bruce372 9/7/2017 6:26pm
9/7/2017 6:26pm
Does the noise change when actuating the clutch?
omalley
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omalley 9/7/2017 7:31pm
9/7/2017 7:31pm
if you still have it apart, take some modeling clay and put a small amount on/ around each valve relief. Install your head and cylinder and torque to spec (using your old compressed gaskets so you don't ruin new ones). Manually, slowly move the engine through both intake and exhaust cycles and disassemble. Cut across the squashed part of the clay and carefully peel away one side. Measure the thinnest part of the portion still on the piston with some calipers or a steel ruler. You may not see marks, but it would be peace of mind for clearances. Any time you change cams and/or go to higher compression pistons it is a good idea. It's also not unheard of for a mfr to goof on lobe lift, shape and/or timing, giving you something you didn't plan for on clearances.

There is a minimum clearance on intake and exhaust valves. I'm guessing you could get it from a service manual, or one of the hop up shops (or maybe wiseco).

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