03 big bore!

6 replies to this topic
  • tomk

Posted January 27, 2013 - 08:38 PM


So I recently lost the connecting rod in my 03, it ended up wreking the cylinder too, but the case survived with no damage. After a lot of thinking, researching, talking to buddies, and thinking some more, I decided to put a hot rods rod on the crank and bore the $h!t out of it, I decided to go with a steel sleeve fromLA sleeves and a wiseco 3mm over piston. I have a buddy that runs an engine machine shop so labor = beer, plus good deals on parts, total cost should be under 400$. Hopefully it will be back together by the weekend, anyone else done a big bore? What are some things to watch for? Any ideas on why the rod went? The bike has a snow conversion kit, so I figured I could used a little extra hp:) I will post pics as the engine goes back together, hopefully it goes back correct with minimal "extra" parts lol

  • tomk

Posted January 27, 2013 - 08:44 PM


Here are a few pics so far

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  • Kmiller2723

Posted January 27, 2013 - 09:02 PM


Wow man you definately got lucky that the rod didnt punch hole in your cases! Im looking forward to seeing the progress to come with the rebuild!

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  • MANIAC998

Posted January 28, 2013 - 04:46 AM


My guess is that the rod went from a somewhat lacking lubrication design built into our early year 450's. The newer 450's have an oil jet that squirts oil up underneath the piston to help cool/lubricate this area. Zibbit has an "Oil system Upgrade" that remedies this situation, do a search and it'll come right up. I've done the mod, and think it's highly worthwhile for our older Yamaha's, but you will have to see if you have clearance for it. I'm pretty sure that big bores are fine, but stroker cranks start getting very close to the oil jet.

  • Ukaszs2

Posted January 28, 2013 - 04:54 AM


How many hours on it?
Have you ever changed the piston or piston pin?
Did you look at valves for bend?

Year ago I lost gearbox in my 05. There was chance to inspect the engine. Only piston pin was out of spec and i replaced it. I think worn piston pin can cause rod failure. 2500 miles after i considering new crank but only OEM. I have read that oem crank last longer. I asked about valves because it is possible that they can be damaged due to rod failure or even cause it.

  • tomk

Posted February 06, 2013 - 09:11 AM


just an update, i know its been a while, finally started putting it back together last night, got the lower end back together last night still waiting in bb top end gaskets, put a wiseco conn rod on it. the rod is much thicker in both directions at the top, where my old rod broke. hopefully friday night I will get the top end all on and back in the bike!

  • tomk

Posted February 11, 2013 - 06:42 AM


Well the Wr ran awesome for 1hr, guess I should have gotten a valve job too, u can say told ya so if u want, any one interested in 03 Wr parts

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Edited by tomk, February 11, 2013 - 06:43 AM.


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