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Hey i have a 2011 crf450, i just put it back together after having the cases split and tranny across my entire shop, cleaned everything, changed ALL bearings and seals in crankcase and top end. New piston, rings, head gasket, valves, everything. Put an entirely new water pump in it, have it all back together and still drains right out of the weep hole. So i took the cover off and had a honda dealer put an entirely new water pump in it, thinking maybe i broke the seal when i pressed it in. And still, without it running, radiator cap off, when i dump fluid in it drains right out. I tried riding it anyways, it doesnt leak while running, but as soon as i got back from a break in ride when i shut off the engine the radiator fluid empties through the weep hole! Any ideas GREATLY APPRECIATED! Thank you!

hopefully you replaced the shaft as well. also check the mechanical seal for damage and correct installation.

I am having the same problem on a 2010 crf250 that i put a new crank in. The first mechanical W/P seal i put in leaked out the weep hole soon as i dumped coolant into the radiator. Replaced the seal again and didnt leak this time until it was rode and then parked now it comes out the weep hole again.I am going to replace the shaft as i am thinking it might be scored causing the seal to get damaged.

on my 02 450r i am also having this probelm as well. I replaced all seals, the shaft, impeller, gasket and bearing and is still leaking out the weap whole any thoughts?

got mine solved and made my own special tool from damaging the seal when installed.you must take the side cover off. the service manual shows the special tools u need.

for those that replaced all seals, bearings, and shaft you have to look at the installation. make sure everything was installed correctly, seals and bearings correctly installed and seated fully.