Are these valves shot?


7 replies to this topic
  • youthenrage

Posted November 05, 2009 - 09:43 PM

#1

Just pulled the head on my 98 WR400, I bought this bike for $800, threw a jet kit in it and got it running pretty good. I'm tearing it completely down over the winter, just got the head off. The exhaust valves were one feeler gauge size too tight (i wrote the #s down, but left them in my garage..) then I checked out the combustion chamber. Lots of carbon build up, and when I cleaned up the exhaust valves, they're showing some scoring. Are they still good or do I need to replace them?

Before cleaning (I brightened this pic up so you could see a little better)
Posted Image

close up of the pitting. Upper valve is an intake, lower is the exhaust...
Posted Image

  • klossWR450

Posted November 06, 2009 - 06:32 AM

#2

I'm no expert but these are normal combustion deposits, can't see anything unusual

  • tribalbc

Posted November 06, 2009 - 06:57 AM

#3

Wow what did you use to clean the carbon off so well ?
Spray some brake cleaner in both the intake and exhaust ports to see if anything leaks past the valves. If not I'd say your good.

  • rkwfxd1

Posted November 06, 2009 - 07:19 AM

#4

I too am no expert and those look OK to me....

However...

I have been down this road before and if it were me, I would go ahead and replace them while I had it torn down. The bike is old and probably has a lot of hours on it. I just feel more comfortable riding across the desert in a vehicle that is either new or completely re-built.

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  • Yamaha8519B

Posted November 06, 2009 - 07:31 AM

#5

Considering how old the bike is that doesn't look bad. Even though the valve lash measurment was tight there was still some clearance, its when there is no clearance you have a real problem.

The valves should be taken out so you can inspect them and the valve seats. If they are worn have the seats recut and put in new valves and guides so you don't have to worry about it. A good machine shop will only charge about $100 to install guides and touch up the seats.

  • GCannon

Posted November 06, 2009 - 10:30 AM

#6

You need to take the valves out of the head and inspect them where the valve and seat interface.

Before you do you could fill the combustion chamber with fluid and see if any leaks into the ports. quick but effective test. even if they don't leak you still need to inspect the sealing area on the valve and the seat.

  • rufusz

Posted November 10, 2009 - 04:57 AM

#7

Valves look great from the photos. If they are not stretched too much, don't change them, unless you have money for such insurances...

  • mkporn

Posted November 10, 2009 - 06:40 AM

#8

These are stainless valves in that year of bike. Chances are they are perfect, but to be sure, pull them and make sure the faces and seats are in good shape. As for replacing them, those valves can actually be refaced and the seats recut. Unless they are completely trashed and the stems are not within spec, you can pull the valves and have the faces ground, the seats cut and thro new guides in it.

They do not need to be replaced unless the stems are bad or the faces are so bad that they can not be refaced. Unlike the 426 and 450 from 2001 up, the valevs in the 98-2000 are stainless and do not wear the same way as the Ti units. also, they are 100% stainless and are not hard faced like the Ti units so they can be reground.

A good auto shop can resurface the faces and trim the length on a souix valve machine, then it is a matter of ned guides and cutting the seats. Guides are cheap and surfacing the seats is about 5 bucks a valve seat. You can rebuild that entire head for $150 including labor if the valve stems are withing tolerance......so, grind the valves, cut the seats, replace guides and new valve seals and you are good as new.....




 
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