when to service piston/rings

[erion929]

As a few of you that have responded in the past know my son picked up a new 450f. He was told to start checking piston and rings every 13 hrs and replace as necessary (primarily rides on track for practice and races weekends) Currently has 16 hrs. and would like to finish a 5 race series before checking.) Is this realistic or what is the minimum he should do?

Thanks 

[numroe]

For motor wear, hours alone don't tell the whole story. It's a function of time, throttle opening and revs. I'd say wear goes up exponentially with RPMs, and is proportional to time and throttle opening.

 

The rings don't wear much as far as I know, so you just replace them when doing a piston. When worn you'd lose a little power, but no risk of a motor blow up.  Your forged piston is tough and will rattle around a little before breaking. When you have the cylinder removed, it's easy to inspect the cylinder bore and measure piston bore clearance. Then you'll start to learn how fast your boy wears out the top end.  The timing chain is the critical part to replace. Inexpensive and also pretty easy to replace. I've never tried it, but maybe there is a way to measure and track the change in the auto-chain tensioner position.

 

If your boy is real fast, and gets the job done with a lot of revs, then after 20 hrs the piston and timing chain would be due for replacement. 

 

You should tell him to keep the revs down anyway, because the bike handles better. In interviews I've heard Villopoto, Reed and others say this. I've even heard of Roczen laughing about how long it took Barcia to learn to ride a 450 faster by using less motor RPMs.

 

If your boy is opening the throttle in very short bursts, like just about every rider on a 450 on most types of tracks, and he keeps the revs down, then the piston, timing chain and valves could easily last 100 hours, or a lot more.

Edit: Always assuming you change the oil and filter at least every 6 hours.

Edited April 29, 2014 by numroe

[kx450f63]

In my experience with these four strokes, my top ends last twice as long as my bottom ends and I replace my bottom end every 50 hours.  I do the top end at the same time and valves every other time.  The piston, and cylinder just don't seem to wear very fast due to the additional lubrication of the four stroke.