# Brute Force 750 Piston Orientation



## MNBRUT750 (Jul 1, 2015)

Hi guys, I'm new to this site and I'm hoping someone can steer me in the right direction. 

I recently installed two new OEM pistons in my 06' 750 at the same time I fixed a spun rod bearing. The bike has 330 hours on it and everything else looks to be within good service limits. 

My service manual states that both pistons should be installed with the "F" facing the front of the motor. At first that seemed strange to me when the rear cylinder mounts the opposite direction to the front one. After inspecting the location and depth of the valve reliefs, I concluded that they were the same for intake and exhaust so I put them in as the book says. I set the valve clearance to the nominal numbers that the manual recommends. (.004" and .008" I believe) 

When I started the motor for the first time, it ran and idled smooth and quiet. (no noisy rockers) I let it run until the fan came on and made sure there were no oil or coolant leaks. Everything looked great. Then I went to rev the engine to higher RPM's and that's when my problem started. The rear piston hit the intake valves and made a LOUD clicking noise. (see attached picture of the piston top where valves hit) The engine would still ran nice at idle but had a power loss when I tried to rev it again. Now I'm not feeling so happy with my work. 

Upon tear down, I checked everything out with the timing chains and tensioners and all looked in good shape. Also, the cam timing was right on the money. That leads me to think the rear piston was installed backwards. I searched the internet high and low but cannot get an answer. I have new valves installed in the head now but am apprehensive to put it back together before I know what's going on. Any suggestions? I apologize for the long post but I wanted to make sure I had everything covered. Thanks for your help!


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## TEXASBAGMAN (Oct 13, 2012)

I don't think it possible for the valves to hit the piston running stock or low compression piston. 2ND THOuGHT maybe if the valve was sticking in the guide and not returning. rEMOVING THE COVERS WITH THE PISTON NOT IN TDC COMPRESSION STROKE YOU CAN BEND THE VALVES.


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