Scored cylinder

9 replies to this topic
  • xjruss

Posted March 27, 2006 - 09:08 AM


I can post pictures later if needed... I'm in the process of fixing my transmission on my 426 (4th gear blew up) and noticed the cylinder wall and piston skirt are scored. What is required to repair this? Do I have to bore the cylinder and use a larger piston? I can't feel the score marks with my fingernail so it doesn't appear to be severe damage.

~ Russ

  • NYMXer

Posted March 27, 2006 - 09:27 AM


If you can't feel it with your fingernail then it isn't scored and probably OK. Take a good look at the piston inder a light. Feel the bump if you can and file it down. If you can't feel that either then forget about it, put it togethre and ride! :thumbsup:

  • xjruss

Posted March 27, 2006 - 09:41 AM


Maybe my definition of "scored" is incorrect... but there are visible vertical lines on the piston skirt and the cylinder wall... maybe I can get away with just honing the cylinder.

  • Pincushion

Posted March 27, 2006 - 09:50 AM


If boring is required check out the packages at Lukes Racing. I had my 426 jug bored 2mm/renakasiled plus a Wiseco piston and Cometic gasket kit for $350 shipped. Workmanship was excellent and haven't had any problems.

  • NYMXer

Posted March 27, 2006 - 01:58 PM


Put it back together and ride it hard. :thumbsup:

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

Posted March 28, 2006 - 08:23 AM


Here's a couple pics:

Posted Image

Posted Image

  • Pincushion

Posted March 28, 2006 - 08:29 AM


Looks like it was loose in the bore and you're getting some side slop. How's the large and small end bearings feel?

  • xjruss

Posted March 28, 2006 - 08:39 AM


Looks like it was loose in the bore and you're getting some side slop. How's the large and small end bearings feel?

Bearings felt ok to me... there's a tiny bit of side-to-side movement on the crank end which I thought that was normal but no up-down movement.

  • Pincushion

Posted March 28, 2006 - 08:59 AM


Minimal side to side play is normal. Looks like the piston got too big for the bore.... has the bike been overheated much?
It looks heat damage to me and I think a bore job may be in your future.

Here's what happens to a 426 when the oil pump goes AWOL and what the heat does to the cylinder adn piston. Check that oil pump while you get it tore down!!!!
http://photobucket.c...or damage pics/

  • grayracer513

Posted March 28, 2006 - 09:02 AM


The vertical marks in the cylinder don't look like much. Actually, the "shadow" of the second ring at the top of the cylinder is a bigger deal if it's deep enough. Run a bottle brush hone through the cylinder and see how it looks after 5-6 quick passes. If it cleans up that easily, it's probably OK. The piston looks as if it should be replaced, though.

Related Content

WR Camshaft Swap Info - last post by jamesm113

WR Camshaft Swap Info

  • 0 replies

First Hare scramble tips by dhend8

Dirt Bike   General Dirt Bike Forums   General Dirt Bike Discussion
  • Hot  33 replies

Snake pit oct 30th by The Anvil

Dirt Bike   Dirt Bike Regional Discussion   California
  • Hot  293 replies

Thinking about Yamaha 250... by Arctic Pride

Dirt Bike   Special Interest Forums   Pro Racing
  • Hot  491 replies

Megabomb Fitment by 288yz450

Dirt Bike   Make / Model Specific   Yamaha   YZ 400/426/450
  • 1 reply

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.