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426WROhio

426 Cam chain jumped time?

8 posts in this topic

My 01 426 decided she didn't want to start on her own anymore. Might have sat too ling between rides, but oil was changed and air filter cleaned frequnetly. Either way, with a pull start or "poppin'" the clutch down hill, she fired right up and ran fine. I took it into the shop for carb cleaning and valve adjustment. They think the cam chain jumped time or the valves clearance was too tight, because I have bent intake valves. (leak test shows 60% leakage... and i was riding it like that?! I am no mechanic, butI do question that...)

My delima is this: If they are gonna rebuilt the top end, what would YOU do to increase performance while you were in there? I can probably afford an extra $300 or so for upgrades vs. stock. They gave me a ballpark of $1000 to $1500 for the topend rebuild. Right now, they are looking at the bottom end. (Which should be fine!) The bike is stock, and I trail ride and hillclimb.

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I really don't know that there's anything you can do - for any price. Once that stuff's in good shape, the bike is all about jetting. The motor is really hard to improve on at that level. I think you'd really have to be exceptional to notice any differences.

Good luck :thumbsup:

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Get a Wiseco 13.5:1 piston. Its one of the best things I've done with my 426. It will give it alot harder pull from idle to about 9500 rpms.

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Thanks for the reply! I was told I could get it ported and polished, but the cost wasn't clear. Jetting, huh? Since I'll owe the local Yamaha shop my next born child, maybe I can have them check that out.

Thanks! I can't wait until the weather breaks!

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Thanks for the reply. If they question the condition of my piston, I'll definitley be looking at your suggestion. Is that a stock size, or did you have yours bored out? if not, what kept you from a big bore kit?

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With the high comp piston you will most likely have to run very expensive race fuel. I would go with the port and polish. My dad had it done on his 450 and it was definitly worth it. You may lose one hp on the bottom but gain 3 on top. With the high comp it will also make it harder to start. I would go with stock piston or at least stock compression and go with port and polish. It already has plenty high enough compression.

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Thanks for the reply. If they question the condition of my piston, I'll definitley be looking at your suggestion. Is that a stock size, or did you have yours bored out? if not, what kept you from a big bore kit?

My cylinder was in perfect shape, so I couldn't justify the bigger bore.

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With the high comp piston you will most likely have to run very expensive race fuel. I would go with the port and polish. My dad had it done on his 450 and it was definitly worth it. You may lose one hp on the bottom but gain 3 on top. With the high comp it will also make it harder to start. I would go with stock piston or at least stock compression and go with port and polish. It already has plenty high enough compression.

You can still run pump gas, as long as it doesn't ping. Harder to start? The extra punch is well worth the slightly harder kick.

Yamaster, don't take this the wrong way, but, you need to ride a stock bike and then a bike like mine before you post a recommendation on the internet. I bought my bike brand new and have done every modification myself and seen first hand what works and what doesn't.

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