YZF 426 maintenance tips?

4 replies to this topic
  • brasso

Posted August 07, 2010 - 06:23 AM


Just got a 01 426, with a 450 thumper big bore kit. Never really owned a four stroke, so can anyone tell me what I should check, maintain, change out, etc. on this bike? I really need info guys

  • grayracer513

Posted August 07, 2010 - 10:08 AM



Oil change:

Air filters are critical.

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  • mike_dean

Posted August 08, 2010 - 03:04 PM


Disassemble and lube rear linkage, and steering head bearings. Check the wheel bearings and sprocket bolts. Flush out the brake fluid, fork oil. The usual valve check, oil change, spokes, tire pressures and tighten bolts. The engines are very tough.

  • brasso

Posted August 09, 2010 - 04:34 AM


I dont understand the valve checks..? I mean what am I looking for, and what do I do if they need to be reshimed or changed?

  • elcubeo

Posted August 09, 2010 - 05:00 AM


I dont understand the valve checks..? I mean what am I looking for, and what do I do if they need to be reshimed or changed?

Basically as any engine runs it experiences some wear. These engines are a little more special since they regularly see 5-digit rpm. If you have the model with steel valves, they stretch a little, but mostly just beat themselves into the valve seats. If you have a model with Ti valves, they stretch a decent amount so that adds to the effect. The buckets and cam wear minimally if at all, so basically over time your lifter bucket to cam clearance will decrease.

So you want to maintain your clearances (.005"-.006" int, .007"-.008" exh.) otherwise it can lead to valves not closing properly, loss of static compression, or worse, burning valve seats. Watching these clearances will tell you if there is a problem, if you start noticing more stretch in one time interval, its probably time for new valves, since you are getting closer to the breaking point.

To maintain clearances you just change the shim between the tip of the valve and the underside of the lifter bucket. Roll the engine so that the lobes on the cam you are checking point directly away from the valves. Measure the clearance you have, and add or subtract to your existing shim number to figure out the shim you need. Using a metric feeler gauge really helps ease some confusion. A stock Yamaha shim may have 186 lazer etched on it meaning 1.86mm thick. Say we need .06 mm more clearance, you would install a .06 mm thinner shim marked 180. They are cheap, you can get a set of every possible size from Hotcams for about 80 bucks, or if your local dealer is awesome they might let you snag a few of the size you need for a few bucks.

!!Fun tip!!, wire up your chain so it stops falling into the motor, and stuff a clean rag in the timing chain passage in the head so you cant drop stuff down there when your fingers get fumbly. Keep a telescoping magnet (as i fondly refer to as the "Yamaha Tool") in your shirt pocket, you will need it every 5 minutes lol. Actually I find a magnet helps tremendously when trying to pull the oily lifter buckets out of their bores.

If you need to change one or all of the valves, you will need a valve spring compressor among a few other special tools. It's going to involve pulling and re-torquing the head, so grab a new gasket. Depending on the race hours:ride:, a new piston and rings and timing chain :banana: might be cheap insurance too. Just glue yourself to the manual and take your time. Its not too tough to do.

Edited by elcubeo, August 09, 2010 - 05:15 AM.

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