crankshaft split (Big end bearing)

9 replies to this topic
  • kikk0

Posted July 11, 2008 - 11:17 AM


I ordere a rebuilt wiseco crank from lukesracing for my 03 wr450. When I should put on the starter clutch I discovered that the shaft is 22mm on the crank and my 03 should have 20mm. I checked with luke and wiseco was not aware of this issue. he checked out hotrods etc, and noone have crankshaft for my 03.

So the questions are:
How do I split the crank for abig end bearing change?
How do I get the crank back together so the two sides are aligned?

Tanks for response

  • matt4x4

Posted July 11, 2008 - 11:49 AM


The crank has to be done by a machine shop for the big end bearing

  • WR450FGreg

Posted July 11, 2008 - 01:30 PM



The crank has to be done by a machine shop for the big end bearing


matt4x4 is right, it's generally beyond most home mechanics to rebuild a crank.

While I haven't had a look at a WR crank physically, pictures of them indicate it's the usual pressed interference fit style unit.
If so then it can be done at home if you have:

The knowledge of how to do it
A bearing press
Jigs made up to hold the components as required
Accurate V-blocks
A dial guage
Vernier calipers
Feeler guages
Magnetic dial guage stand
Surface plate (or the bed of a lathe)
A copper headed hammer
A cold chisel
A ball-pene hammer

But you really need to know what you are doing before attempting it. :thumbsup:


  • WR450FGreg

Posted July 11, 2008 - 01:57 PM


Here's a few links discussing various aspects of crank rebuilding/aligning from a few years back if you are interested.
They relate to old Yamaha two stroke twins (RDs, TZs etc.) but the principals are still the same for any pressed crank.

(.....BTW, I'm the "tzeggy14" making posts in the discussions!)

http://www.yamaha-rd...t=crank rebuild

http://www.yamaha-rd...t=crank rebuild

http://www.yamaha-rd...t=crank rebuild


  • William1

Posted July 11, 2008 - 05:01 PM


'Building a crank is not hard, but experience is key. The first few I did, I was watch and tutored by an old pro. How to press, where to rap is key. The guy I learned from could almost press them perfect, a few raps and he was done. Used to take less than a hlaf hour for him. Me was more like an hour. Without his help, it would of been all day.

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  • WR450FGreg

Posted July 11, 2008 - 06:45 PM



Me was more like an hour. Without his help, it would of been all day.

Right on William!
I found it exactly the same for me.... I remember panicking that the Loctite I put on the webs would harden before I got the thing trued up!
(The use of Loctite on webs is a topic for debate. Some say yes, some say no.)

Definately an experience thing with the "whacking" isn't it ? :thumbsup:
You think it needs a decent hit, so you give it one and then check the runout and find you've gone past where you wanted it to be, so you whack it back and go back past in the other direction.....again.... and again.... and again !! :thumbsup: :thumbsup: :thumbsup:

A very frustrating process when you first try it.


  • 02WR426Cali

Posted July 11, 2008 - 06:52 PM


I worked at a shop and I used to rebuild cranks all the time. They were all 2 stroke cranks but they are the same except for the 4 strokes having a gear for the cam chain that usualy needs to be taken off first, and also the pin is bigger on 4 strokes but that does not matter. My shop had a jig that made it very easy and accurate to press back together. First you press the old pin out. Inspect and clean the 2 crank journals. Then put the 2 journals and the new pin and thrust washers in the jig and press it back together. The jig was so accurate that all you had to do was check the side to side clearance. It was very easy with the proper tools. The old school way without a jig is much more time consuming and harder, requiring more patience.

  • kikk0

Posted July 13, 2008 - 09:17 AM


Thanks for all the reply.
I'm thinking about making a jig for this operation.
The workshop is charging me about 400$ for the job + the price of the bearing that costs 2-3 times more than what you pay in america:confused:

Do I have to think about both axial alignment and the side clearance? I should use a seekblade or whatever they call it, and a feeler guage to measure the axial runout?

I'm just thinking about how to create the jig. so I'm happy for suggestions

  • William1

Posted July 13, 2008 - 01:00 PM


The jig is only needed to speed the process. Doing a single crank, it will take longer to make a accurate jig then to do it without.

You press the crank together, put it in a parallel stand and using a dial indicator with a roller tip, rotate the crank, aiming for zero runout. Also, you use feeler gages to set the big end side to side and a large micrometer to check for total width. You use different size shims on the big end to set the total thickness.

  • WR450FGreg

Posted July 13, 2008 - 01:11 PM


Do I have to think about both axial alignment and the side clearance? I should use a seekblade or whatever they call it, and a feeler guage to measure the axial runout?

Axial alignment is the most critical. To measure that you'll need the surface plate, V-blocks, dial-guage and stand.

Use feeler guages to measure side clearance.
Speaking from roadracing two-stroke experience: side clearance is less of and issue. The bigger the gap the better because more oil can get to your big-end bearing that way. As long as it still spins in the crankcases it's fine.
But mind you, this may be different with these oil-pumped four strokes, maybe a bigger gap will effect oil pressure elsewhere .... (any suggestions here guys?)

I took a series of photos of a crank rebuild I did 4 or 5 years ago. I can't find them at the moment unfortunately. :thumbsup:



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