Coolant Leak - need help asap

Click this link and look at numbers 5,7,12, & 14.

http://fiche.ronayers.com/Index.cfm/Module/Main/TypeID/26/Type/Motorcycle/MakeID/4/Make/Yamaha/YearID/41/Year/2000/ModelID/7781/Model/WR_400F/GroupID/369856/Group/RADIATOR_HOSE_

I am buttoning up a bike I bought that was disassembled. All has been relatively straightforward with the occasional snag. After a month or so of rebuilding it's finally ready to be started.

I proceeded to fill it with coolant and it is running out these two steel tubes where they are inserted into the head and case. I thought the o-rings may be too small, though they came with my gasket kit. I bought new slightly larger o-rings and squeezed them in. These are the largest that will still fit in the orifice. Refilled with water just to test. Better but still leaking. What am I doing wrong!? I have the Chilton's and the factory manual and neither says anything about the o-rings - just says "install pipe #1, #2" etc.

The season here in Maine is rapidly coming to an end and I am losing precious riding time. Anyone have ANY suggestions? Thanx in advance...

Did you put any lube on the O-rings? Sometimes I have had leaks from putting lube on parts, it makes them to slippery and won't seal. Try fitting them up dry (if you did) and see if that fixes it. I have never replaced your specific part, so I'm not sure if it will fix your problem.

Tried it dry and lubed. Nothing works. I've tried the correct sized o-rings, fatter (tighter) o-rings, I see nothing cracked, etc. No matter what I do I get a steady stream of fluid between the pipe and motor. This is very frustrating. I've been working on this bike every night for a month, waiting for parts to show up (Yamaha is the WORST when it comes to parts delivery!), etc etc. I just want to ride the stupid thing.

Have you tried making sure it's tightened down to the right torque?

Sounds like you're leaving it too loose....

I got something for you.....You said this was a basket case right? Well, some times if these are able to sit for some time, the actual port that the tube slides into will get a little corrosion. Take a piece of still wool or very fine sand paper and make sure the inside sealing surface of the port is clean, also do the same for the tubes (clean them well). A o-ring will seal under a lot of conditions but they don't like it when there is corrosion. I have seen o-rings in hydraulic valving hold up under 2000psi and only be finger tight. Then agian I have seen o-rings fail und 70psi water pressure due to calcium deposits.....

Point is, make sure the sealing surfaces are clean and use a little lube...

Thanx for the suggestions. There was no corrosion and I'm still not sure why it wouldn't seal. I ended up using more than one o-ring and added Ultra Gray RTV. I know it sounds mickey mouse but it worked!

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