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Discussion Starter #1
I recently installed a tb108cc stroker crank on my crf50.



It has a tb race head, piston, and cylinder along with hv oil pump.



My problem is when I start the bike up it knocks very loud it kind of sounded like the piston was making contact with something so I took the head off and piston and valves show no signs of contact at all.



Anyone have any ideas it seems to be getting worse and I can't figure it out.
 

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Adjust your valves. Mine always seem to come loose over time and they will start knocking when there loose.



Intake valve set it at .003



exhaust valve set at .004
 

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Discussion Starter #3
Adjusted them both more times than I can remember. I even kicked it over without the rockers with the valves sitting closed all the time and it still did it.
 

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Discussion Starter #6
Tried a second base gasket still knocks.



Its kind of a slow knock and I can only hear it at idle.
 

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Discussion Starter #12
XRshfifty said:
forget a bearing when installing the stroker crank?


I don't have any extra parts laying around that I am aware of.



Branyers said:
What clutch are you running? Are you sure the noise is coming from your top end?


100% positive its coming from the cylinder/head of the engine.



The most confusing part is the knock literally goes away as rpm's increase. It is really loud at idle but if I turn the idle screw to raise the idle it nearly goes away.
 

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Is the flywheel tight? Do you hear it if you turn the crank by hand? I just built a tb108 with no problems, but I have left the flywheel nut loose before and makes a noise as you describe. HTH



Derek
 

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its a head gasket just had mine do it took it apart and head gasket was torn put a new one on and ran like a champ!
 

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Nick-G said:
I recently installed a tb108cc stroker crank on my crf50.



It has a tb race head, piston, and cylinder along with hv oil pump.



My problem is when I start the bike up it knocks very loud it kind of sounded like the piston was making contact with something so I took the head off and piston and valves show no signs of contact at all.



Anyone have any ideas it seems to be getting worse and I can't figure it out.


Your crank could be hitting the oil pump drive shaft. Or you could have a bad rod bearing right from the factory.
 
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