01 yz 426 leaking valve?

4 replies to this topic
  • honyam83

Posted December 30, 2008 - 05:00 PM


Hello I'm new to this site so forgive me if I wrong. I look in common threads for information on how to determine if I have a leaking valve but found nothing. I recently traded my yz250f for a yz426f that has been fitted with wr parts to make it street legal. It seemed to have a noisy valve train and coolant in the oil. So I have replaced the waterpump seals, bearing and impeller shaft I seemed to have fixed the contamination of the oil but upon start-up had a huge plume of blue smoke that clearer within about 45 seconds. I'm sure that this is a leaking valve, but would like conformation from you very knowledgeable folks. I was hopping that some one might say that they just need adjustment haha. thanks for your time.

  • grayracer513

Posted December 30, 2008 - 08:09 PM


"Blue" (white) smoke on the first cold start of the day would be an indication of leaking valve SEALS, not the valves themselves.

However, because you had contaminated oil, you need to determine whether what you are seeing is smoke or steam. Smoke drifts away and dissipates. Steam vanishes into the air as it cools. The water pump shaft seals you replaced cannot have been the source of your contamination because leaking coolant escapes through the passage provided by Yamaha for the purpose before it puts any pressure on the oil seal. A leaking head gasket is the more likely culprit.

Have a shop do a leak down check. Ask them to check for compression leaking into the cooling system in the process.

Visit the ThumperTalk Store for the lowest prices on motorcycle / ATV parts and accessories - Guaranteed
  • honyam83

Posted January 03, 2009 - 11:57 AM


Hello Gray thank you for your reply. I had the boys at fort collins motorsports do a leak down today. It had 11% leakage. They said it was through the rings. Sounds like a new top end for me. It does still smoke on start-up and I do believe that it is oil. So while I'm there I will need to replace valve seals as well. I just wanted to see if this sounds right to you since you seem to be the resident expert on these bikes. Is there any special tools I will need besides a valve spring compressor? Where can I find OEM gasket kits, or can I?

  • grayracer513

Posted January 03, 2009 - 01:22 PM


There are no OEM gasket kits. You need to buy the parts you need individually, or go to the aftermarket.

A spring compressor is all you need to service the valve seals. You can easily pluck the old ones out with needle nose pliers and install the new ones by hand. OEM valve springs are cheap, and cheap insurance. Might want to think about replacing them as well.

If the bike is an '01 or '02, it has titanium valves. You may want to inspect them while you have it apart, but be certain that all the valves and lifters get back into their original locations. This link will give you some idea what they should and should not look like.

No matter what you are told by anyone (including the service manual) NEVER lap a titanium valve. If they need resurfacing, replace them.

  • moto2000

Posted January 03, 2009 - 06:40 PM


I bought one of these off ebay...


Works great for the price. :thinking:

Related Content


Thinking about Yamaha 250... by Arctic Pride

Dirt Bike   Special Interest Forums   Pro Racing
  • Hot  491 replies

Michigan Motocross Tires by 288yz450

Dirt Bike   Dirt Bike Regional Discussion   North
  • 1 reply

2016 YZ450 by CaptainKnobby

Dirt Bike   Dirt Bike Technical Forums   Suspension
  • Hot  59 replies

Chubby dad, looking at bikes , First trip to the orange/black forum ! by Slow_ride

Dirt Bike   Make / Model Specific   KTM   250-530 EXC/MXC/SXC/XC-W/XCR-W (4-Strokes)
  • Hot  28 replies

Is it worth it? (Cam and High compression piston) by macgi77

Dirt Bike   Make / Model Specific   Honda   CRF 150/230 F/L
  • Hot  36 replies

Join Our Community!

Even if you don't want to post, registered members get access to tools that make finding & following the good stuff easier.

If you enjoyed reading about "" here in the ThumperTalk archive, you'll LOVE our community. Come join ThumperTalk today!

The views and opinions expressed on this page are strictly those of the author, and have not been reviewed or approved by ThumperTalk.