CRF450R - Big Valve Adjustment

[cthowards]

I recently rebuilt the top end on my CRF450R including piston, rings, Kibblewhite valves and springs, etc. I sent the head to a local shop and they installed the valves. The motor has 1.9 hours on it since the rebuild and the last time I rode it ran rough and had popping on decel at the end of the day - seemed to happen suddenly. I checked it over and found that my header bolts were loose allowing the pipe to move around and I thought that was the reason. Winter hit and I have not done anything to the bike since then.

Anyways, I am going riding this weekend down in Maryland and expect to put alot of hours on the bike so I decided to check the valves. The left intake valve was .005in when I did the rebuild and now it measures .002in. I did the calculations and determined that I need to remove the 190 shim currently in there and replace it with a 180 shim. The right intake valve and both exhaust valves were right on spec. Can anybody offer explanations as to why I would have such a big adjustment so soon? Should I be concerned and remove the head or simply shim the valve and move on?

Thanks for your help.

 

[Rich Rohrich]

It's common for there to be a bit of settling on a new valve job and new valves. Shim it, and check it again after you put some hours on it. If it closes up again you probably have an issue, but what you are describing is pretty normal.

 

[cthowards]

Thanks for the quick reply Rich...I get really nervous about this stuff.

Just so I understand, what are the consequences of leaving a valve with that tight of a clearance? Would you run the risk of floating a valve more easily (by the valve getting pushed farther open than normal which requires the spring to work that much quicker to close it before the piston makes contact)?

Thanks again.

 

[Rich Rohrich]

The only risk is if the clearance gets too small at some point, the intake valve will never close completely. If that were to happen the valve would never cool properly and the heat of combustion would destroy the valve in short order.

 

[02yz426f]

What causes the popping on decel if the exhaust header is tight and there are no holes in the pipe? Is it something to do with jetting?

 

[Matt90GT]

try cleaning out your pilot jet