250

Yes.

Blaz1 said:

Damn lik how often would you say?

Click to expand...

Numerical experiments are performed for elliptic and parabolic frequencies. The comparisons between an iterative solver (PCG) and a direct solver (unifrontal/multifrontal) show that the direct solver is more efficient. Moreover, its performance is not correlated with the system matrix conditioning. It appears that the new formulation requires significantly less rebuild time for elliptic PDEs and is competitive for parabolic PDEs. The new formulation remains also accurate enough even in nearly singular situations.


conclusion:with regular use, you would need to rebuild an mx bike at regular intervals. :cool:

Your question is a little too vague: what bike are we talking about? How experienced is the rider? Trail riding or MX track?

Many of the "off road" bikes have low performance engines: lower compression, heavier, stout. These engines can run a long time between rebuilds. Race bikes are going to have high performance engines: High compression, light weight, high revving with very little margin. These engines need to be rebuilt frequently. The harder you push the engine, the more often (and more critical) the rebuilds. To that end, a 250ccc four stroke race engine might need to be rebuilt in 20 hours compared to 25 hours for a 450.

Now, my question to you: how hard do you push your bike?

There are conditions that can tip the balance one way or another. At a recent race I was in there was a 5 mile run down a sand wash. If you could handle the whoops you could leave the throttle wide open for 5 miles. That stretch of the course was the demise of quite a number of bikes, especially the smaller displacement bikes.

For general trail riding, however, it is really hard to push a bike that hard. In just a few seconds you will be going pretty fast, even on a 250. Once you are at speed a 250 isn't really being pushed any harder than a 450.

Let me ask you this: how often do you have to replace your brake pads? If you are not wearing your brake pads out, then you probably are not pushing your engine that hard.

Buy the bike that makes sense for you based on how your ride and how much performance you need. Don't buy it based on the rebuild schedule.

Rod

All depends on how you ride it - and that applies to any bike. Generally speaking, a fast “A” rider will need to do it A LOT more than a slow “C” rider.

My buddy - who is a “C” rider - bought a new KX250f and rode/raced it for 3 years without doing anything to the motor. The valves stayed in spec and he never had a problem with pistons/rings or anything else. He was probably racing 15 times per year and play/practice riding 2-5 hours per week (that’s total time at the track, not hours with the motor running).

Not saying I’m recommending my buddy’s maintenance schedule, just telling you a true story - and his bike was a 2005 KX250f - which, as I recall had a notoriously unreliable motor.

A top 20 pro from Columbus, Ohio rebuilds his every 2 nationals.

If you’re on the rev limiter constantly, you’re going to need to rebuild it a lot. If you ride like me (maybe 2 hours per week of actual time on the motor from April to October - and not very “hard” time at that), I’m suspecting that once a year will likely be sufficient.

You might want to specify if you are talking 250 4T or 2T, it looks like the assumption is a 4T.