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honyam83

01 yz 426 leaking valve?

5 posts in this topic

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.

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"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.

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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?

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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.

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