01 426 Top End question


6 replies to this topic
  • 426_Pilot

Posted August 11, 2005 - 07:15 PM

#1

Just rec'd a new piston and gasket kit for the 01. I've never done a 4 stroke top end before, but have no doubt that I can. My engine is stock and has all the original parts in it with the exception of new clutch plates. I'm the original owner.

Can I just pull the old piston out and install the new one, or do I need to do any honing? I certainly wouldn't do any honing or boring myself unless it was really easy. Any tips/pointers would be greatly appreciated.

BTW, I've never had a lick of problem with this bullet proof machine. Thanks in advance.

  • Slowmotion426

Posted August 11, 2005 - 07:42 PM

#2

I just finished piston, rings, cam chain etc last monday on my 01' 426. I measured the cylinder bore to make sure it was still in spec. I measured my old piston to see if it had any deformities. It didn't. The cylinder was well within the tolerances shown in the manual. I took a 220 grit scotchbrite pad and lightly rubbed the cylinder to break the glaze. I could have re-used the original piston but since I had already ordered a new one I put it in with new rings. Just check your cylinder with a bore gauge and micrometers. If it's in tolerance you can just scuff it up with the scotchbrite pad. Just make sure you have a fine grade and barely take the glazing off. Make sure you apply oil to the piston, and the cylinder before putting it back together. Make sure you orient all the ring ends according to the manual. The oil ring is in three pieces and can be a challenge for a first timer. Just take your time. And you're right, these bikes are bulletproof. I still have all my original valves too. And they're all in spec ( I pulled them out and measured them for trueness and measured the lip tolerances). Good luck.

  • grayracer513

Posted August 11, 2005 - 08:06 PM

#3

The absolute best way to refinish a cylinder, or for that matter, to finish one that's been bored, is with a ball, or bottle brush hone. Get one about a half to 3/4" larger than the cylinder diameter, and use it with a low rpm drill, like a 1/2", about 500-600 rpm. spray the hone and cylinder down with WD-40 or shop solvent and run the hone up and down the cylinder as it turns to establish the "cross-hatch" pattern. Make three to four passes up and down, then pull it clear of the cylinder while still turning. It shouldn't take much more than that to break the glaze off, but if there are "shadows", spots the hone hasn't cleaned, repeat the process once more. Rinse it thoroughly with soap and hot water, dry it immediately, and wipe it down with ATF. There isn't a piston ring made that won't seat in that cylinder in the first two hours or less.

In checking the cylinder, look for vertical scoring or a slight ledge at the top, where the piston ring stops at TDC. If these are present, run the hone through only twice up and down quickly. If the defects are significant enough to be of concern, they will still be there. If they are mostly gone that quickly, you are probably OK.

Most people don't own an inside mike, or a set of snap gauges, and even experienced techs have trouble using them well. But, you can very accurately measure the cylinder for being straight by using a compression ring and a feeler gauge. Put the ring near the bottom of the cylinder and push the piston upside down into the bore against the ring to square it up with the bore. Measure the gap. Then, using the piston again, push the ring into an area you suspect of being worn, and measure the gap again. If you measure a difference, divide the difference you measured by 3.14, and that's the taper of the cylinder.

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  • tp3dxf

Posted August 11, 2005 - 09:23 PM

#4

What prompted the re-build? Was there any loss of compression or was it just a matter of hours? I know that a top end failure can be very costly so proper maintenance is a good thing. I guess my question is did you see any loss of performance or was this just a good idea piece of mind thing. How was the bike running before the rebuild? How did the valves and springs look. Did you replace them?

My WR has 200+ hrs on it. I have been thinking about having it torn down and checked out as well. But the damm thing runs better then ever. Even with the 3700 miles and many races. These things are rock solid. I think that may lead to it's total destruction. It may just run till it blows. With no real signs of touble. Any thoughts?

  • biznet1

Posted August 12, 2005 - 02:16 AM

#5

What Gray said. When he speaks I listens. :D

  • 426_Pilot

Posted August 12, 2005 - 02:14 PM

#6

I guess the best answer is an ounce of prevention is worth a pound of cure. This thing is 4 years old and has the original piston and rings. I can't afford a massive failure and I'd be banging my head against the wall if I didn't have anything to ride. :D You wouldn't let your oil go until the engine blew so I'm not going to do it with the piston either.

  • 642MX

Posted August 13, 2005 - 03:43 PM

#7

What prompted the re-build? Was there any loss of compression or was it just a matter of hours? I know that a top end failure can be very costly so proper maintenance is a good thing. I guess my question is did you see any loss of performance or was this just a good idea piece of mind thing. How was the bike running before the rebuild? How did the valves and springs look. Did you replace them?

My WR has 200+ hrs on it. I have been thinking about having it torn down and checked out as well. But the damm thing runs better then ever. Even with the 3700 miles and many races. These things are rock solid. I think that may lead to it's total destruction. It may just run till it blows. With no real signs of touble. Any thoughts?




I would only replace the top end if its using oil. I would recommend replacing the timing chain every year, and of course, check the valves twice a year. Remember YZF and WR's are blue, not red. :D





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