Should I replce the con rod bearing!?!?!?!?

11 replies to this topic
  • Pincushion

Posted June 29, 2005 - 10:39 AM


I've bought a new jug, piston, all lower end bearings, circlips, gaskets and about 5 gears due to my oil pump taking a dump. The rod feels tight and the small end looked good too, but I have this nagging feeling about reusing it with $1k+ of new parts relying on it.

Do I trust it or not?
Assuming not..... Do I just have it pressed apart and the bearing changed or would it be better to get a new crank assy? New is about $260 from JT motorsports.

  • grayracer513

Posted June 29, 2005 - 10:53 AM


If you can get new Genuine Yamaha for $260, I'd ask how much it costs to put a new big end in the unit. But I would think about doing something wiith it if you had that kind of damage.

What went down with your oil pump?

  • Pincushion

Posted June 29, 2005 - 11:09 AM


What went down with your oil pump?

Not exactly sure..... it grenaded!
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I'll call around and see how much labor would be (parts are about $100 for rod, bearing & pin). I'm sure I'd only be saving less than $100 going the rebuild route.

I guess what I should've asked is: What determines if my crank/rod assy can be reused?

  • fowler175

Posted June 30, 2005 - 04:28 AM


When I got the crank rebuilt for the wife's WR250 (new rod, bearing, pin, and labour), I ended up saving a whopping $15 canadian compared to a new one. Next time I'll definately go with a new crank.

  • Pincushion

Posted June 30, 2005 - 06:06 AM


$185 +tax to replace the rod & bearing or $260 w/ no tax brand new.

  • Vibeguy

Posted June 30, 2005 - 06:58 AM


Murphy's Law states that if you don't replace the bearing it will be the next thing that fails.

Think about it, you replaced everything else due to a failed oil pump, don't take the chance that the con-rod bearing was not affected as well.

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  • grayracer513

Posted June 30, 2005 - 07:03 AM


At those prices, I'd get it rebuilt IF I was confident in the machine shop doing the work. There is an additional critical aspect of rebuilding these cranks in the fact that the pin has to be correctly indexed in the right crank axle so the oil feed to the rod and left main bearing lines up. Otherwise, it's the usual question of getting the thing trued up.

I guess what I should've asked is: What determines if my crank/rod assy can be reused?

The problem is that you can't inspect it, and if you take it apart, you can't reuse it. The rod bearing, like all other rolling element bearings, usually fails before any detectable wear shows up, or at the same time as the wear event. If you could look, you would check for dents and scoring in the surfaces of the rollers and races that would lead to chunks of the surfaces breaking out. Once this happens, it's like a pothole in the road; it gets bigger faster the bigger it gets. Lack of looseness unfortunately doesn't tell you everything you need to know.

  • Pincushion

Posted June 30, 2005 - 01:45 PM


Would an 2001 crank drop in my 2000 motor?
Are the rods the same or would I need to trade in my new piston?


  • grayracer513

Posted June 30, 2005 - 04:43 PM


I believe it will. That will also get rid of the key that drives the balancer gear and the problems it causes. You'll have to get the newer style, splined balancer gear, but it's a worthwhile upgrade if you're changing cranks.

  • Dirty_Sanchez

Posted June 30, 2005 - 04:54 PM


Whoa yeah replace that puppy.

You change your oil when you change the filter don't you.

I always replace all bearings even if they are still in spec. on every engine I rebuild. Think of it as cheap insurance when your 40 miles from nowhere.

Fix it right the first time.


  • s3706

Posted July 01, 2005 - 06:50 AM


I just finish rebuilding the bottom end of my 00 426 and I replaced the crank assembly with an 01 model assembly and it fits perfect. The only thing extra you will have to order is a new drive gear to fit the 01 crank assembly. The old drive gear from your 00 crank will not fit the 01 crank. I paid $290 for my new crank assembly through I also got a new cylinder from them for $150 and i got my piston from for $89 and that was the cheapest I found. There was a new crank assembly listed on ebay for I think 229. I hope this helps if you need any other info just pm me. :)

  • Pincushion

Posted July 01, 2005 - 06:59 AM


Appreciate the info :)

I got my big bore cylinder/piston through Luke's Racing. Good people!!

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