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'01 WR426 no compression

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#1
I have a 01 WR426 that I bought here about 7 years ago. I was planning to plate it but never did. It ran fine but has been sitting for about 5 years. My son wants to use it so I tried to start it, but the compression is low. I can kick it over without using the compression release. Could one of the valves be hung up in its guide? I thought about trying to pull start it behind a truck. Any suggestions?
 
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#2
It's really easy to pull the valve cover and check the valves and the auto-compression release function. Pulling it behind a truck is a really bad idea.
 
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#4
Especially then. The only acceptable tow vehicle would be an NSU 175,



or in a pinch a DKW 125, but only the leading link fork version of course.



 
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#5
Thanks for the replies, and the picture of one good looking bike. I pulled the valve cover, and there is reasonable clearance on all the valves. It's an '01 so it's manual compression release, and that looked ok. I did order an auto compression release camshaft since it's easy at this point. I need to get a 10mm tester hose so I can do a leakdown. My '03 CRF450 has been sitting just as long, and started and ran fine on old gas.
 
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#6
I did get a hose, and put the engine at TDC compression with compressed air. It leaks from both the intake and exhaust valves. I guess I'm at the point where I need to pull the head. Does an '01 have titanium valves, and can they be lapped or reground?
 
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#7
I did get a hose, and put the engine at TDC compression with compressed air. It leaks from both the intake and exhaust valves. I guess I'm at the point where I need to pull the head. Does an '01 have titanium valves, and can they be lapped or reground?
Yes it has Ti valves so you are looking at having the valve seats re-cut along with replacing the valves and springs. If you use OEM parts the cost is pretty reasonable. If you upgrade to Kibblewhite stainless valves it will cost a bit more but you are unlikely to ever have to replace a valve or spring again. They become pretty much bulletproof with the Kibblewhite setup.
 
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#8
Thanks Rich. The bike's pretty beat, so I'm not sure what to do. I was planning to set it up to ride the TWAT with my son. I may just get a proper dual purpose instead.
 
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#9
I've pulled and disassembled the head. It all looks to be in really good shape. The parting line is smooth and shiny on all the valves. It appears some grit was in the cylinder and was holding the valves open. I'd like to clean the valves and seats and reassemble the head. Is there a proper technique for cleaning the valves and seats? And is there a way to test the sealing of the valves before reassembly?
 
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#10
I've pulled and disassembled the head. It all looks to be in really good shape. The parting line is smooth and shiny on all the valves. It appears some grit was in the cylinder and was holding the valves open. I'd like to clean the valves and seats and reassemble the head. Is there a proper technique for cleaning the valves and seats? And is there a way to test the sealing of the valves before reassembly?
You can soak the valves and the head in acetone (or Mineral spirits) to clean/loosen the carbon, then wash with Hot soapy water and a stiff nylon brush to get the remaining carbon off.

At the very least change the springs while you have it apart. They are cheap to replace, and they will be worn if they are originals.

Once it's cleaned and reassembled you can fill the ports with a mix of acetone and food coloring to see if the valves leak. Machinist's dye (Dykem) added to acetone works as well but it can get a bit messy.
 
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