YZ450F - 2003 - Crank Shaft Replacement

Hi all,

New to this site and find it really awesome.

Just purchased a YZ450F and the engine was a little noisier than the usual YZ450's I am used to being around. So I took it into a workshop where all my mates take there bikes and quads.

He opened the top end and today said to me that the noise is the Crank Bearing, the Piston and Rod can be rocked left and right a fair bit. Also the cam chain needs replacing, typical wear and tear.

My question is should there be any movement in the rod? I would have imagined that a little bit is OK, but this is really noticeable.

Also, just to be safe, I am getting the piston and rings replaced, whole crank kit (not just bearing) and valves adjusted\inspected.

I picked up the bike for AUD$2.5Kand these things fetch around AUD$4 o AUD$5.5K, so not fussed to spend a little on the bike so I can at aleast have the piece of mind.

Total cost for the rebuild is about AUD$1.6K.

What do you guys think?

The big end of the rod should have 0.15 ~ 0.45 mm (0.0059 ~ 0.0177 in) of side clearance. That is, the clearance between the side of the rod at the large end and the crank cheeks. 0.50 mm (0.02 in) is considered excessive.

To measure clearance between the bearing and crank pin, the big end of the rod is held to one side and the small end rocked left and right. The small end should move 0.4 ~ 1.0 mm (0.02 ~ 0.04 in). If it moves 2.0 mm (0.08 in) or more, it's excessively worn.

Download a manual:

http://www.yamaha-motor-europe.com/community/service/manuals.jsp

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