Help I want to race tomorrow! YZ 426 cooling

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#1
My bike is shooting coolant out of the overflow. It does not matter if it is hot or cold, if i rev it up it will shoot coolant out of the overflow. Head gasket? The coolant is clean and it does not smoke. I even changed out the radiator cap. I want to race at the national hare scramble tomorrow, but I ant find the problem.:think
 
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#2
??

sorry cant help you with the overflow problem. i have heard to run a kx radiator cap as it has different pressure.

Make sure when you find the problem, to drain all the coolant and replace it with ENGINE ICE best stuff I have used so far.
 

Rich Rohrich

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#3
You can take it to any automotive shop that services Japanese cars and they can attach a cooling system pressure guage to the radiator. If you start at zero guage pressure and run the engine it should stay at zero pressure, if the guage pressure starts to rise then it's an indication that something internal is pressurizing the coolant which more often than not is due to combustion pressure leaking past the head gasket into the water jacket. With the engine cold recheck the head bolt torque and retest it.

Hope this helps.

FYI Engine Ice won't fix it. It's just marketing hype.
 
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#4
Hi Rich!
I will try the pressure test, but when I take the cap off it seems to be holding pressure. I will call Eric to see if he has a head gasket in stock. I missed the National Hare scramble today, but maybe I can get the bike right for next weekend.
Do you think The head will be warped? The bike is running perfect still, no smoke. When I got the motor back from ERIC the valve cover was cracked in shipping, I did not bother claiming it as I was preparing it to ride. I had it welded and orderd a new one. I looked for any other damage and could find none. I hope nothing is cracked? I have only taken that motor apart, I guess Jim put it together, any advice for putting the cams in? they were a little tricky to get out. Thanks for your time, Mike
 
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#5
This is a typical yzf problem. Go to a Kawasaki dealer and get the KX500 cap and it will stop completley. Take er easy.Jeff
 

Boit

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#6
My experience with my 426 is to fill the radiator to about an inch below the neck. I kept filling it to the top and it would spit it out as soon as it got to operating temperature. Once it spit out a little, it has kept the same level for over a year now. I suppose it needs a little room for thermal expansion since it has no overflow reservoir.
 
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#7
I am also having the same problem with my 96 cr 125 and my friend is also having the same problem with his 99 cr 250.If I got a kx radiator cap should i get the one for the 500 or for a 125?
 

Rich Rohrich

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#8
Originally posted by ssuperbike
Hi Rich!
I will try the pressure test, but when I take the cap off it seems to be holding pressure. I will call Eric to see if he has a head gasket in stock. I missed the National Hare scramble today, but maybe I can get the bike right for next weekend.
Do you think The head will be warped? , any advice for putting the cams in? they were a little tricky to get out. Thanks for your time, Mike
I've yet to see a warped head on one of these engines so I'd put that low on the probability list.

Have the cap tested at the same time you test for pressure in the system as the same unit can do both.

The cams are really easy to R&R just pay close attention to your timing marks and watch the C clips that locate the cam bearings in the head. When you pull the cams up these clips can fall out of their groove and into the engine. Stuff a rag in the cam chain tunnel and keep a pencil magnet in your hand as you pull the cams so the clip is attracted to the magent rather than the crank :)
 
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#9
Yeah man, that sounds like a cracked head or blown head gasket. I would do the pressure test and check the oil for any milk (water) . Oftern times with high comp motors (deisel) the pressure will go into the cooling system, but the water dose not get sucked into the motor. So sometimes presurizing the cooling system dose not show the leak. If the cooling system pressure test looks good, try a compression leak down test on the cylinder. This is where you will see the pressure leaking into the cooling system. good luck, hope its just a loose head or bad gasket.