Piston life - trail riding?

[nots0much]

Can these top ends last 200hrs?

[mlatour]

While I wouldn't expect a Kawasaki to be as long term durable as a Honda or Yamaha,

it's no doubt possible if you start off with brand new components and,

unlike constantly accelerating hard from corner to corner on an MX track

mostly limit the average rpms to 1/2 throttle in a recreational trail/off-roading usage.

 

Pending you also keep up regular maintenance like oil changes and especially the air filter.

Also avoiding to overheat the engine in slower technical stop-and-go situations as well.

 

The valve train will likely wear to the point of being problematic (hard to start) way before the piston and rings.

 

Edited February 21, 2020 by mlatour

[nots0much]

Do you think using the white coupler (lower performance tune) will have an effect on the top end's lifespan?

[mlatour]

Nope.

From infos read in past discussions, green seems to be the standard coupler, white the more aggressive and, black the mellower output ones.

If anything, running the 'harder hitting' white coupler with it's generally leaner settings, the engine may run hotter and risk overheating a bit more.

 

Considering it's an MX race engine designed for maximum performance & light weight, not maximum longevity in mind,

moderate rpms & good maintenance will give it a better chance but still no guarantee it will last the expected interval.

 

Edited February 22, 2020 by mlatour

[nots0much]

So "hard track," per the manual, is lower power and "soft track" is more power?

Edited February 22, 2020 by nots0much

[shrubitup]

On 2/21/2020 at 1:13 AM, nots0much said:

Can these top ends last 200hrs?

As said, valves will let go before 200 hours so budget for that. Find out what fast heads says abt the valve train....

[nots0much]

I've just shimmed them. The bike has about 50hrs. What's the lifespan of the valvetrain on these bikes?

[450Ruf]

On 2/21/2020 at 3:13 AM, nots0much said:

Can these top ends last 200hrs?

Yes. With proper maintenance, not a problem. 

[shrubitup]

5 hours ago, nots0much said:

I've just shimmed them. The bike has about 50hrs. What's the lifespan of the valvetrain on these bikes?

According to fast heads.... not very long. My 16 motor Blew up around 60 hours. 
 

 

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$699

GHS plus CrN PVD plated Titanium Del West valves, new OE Springs and Viton guide seals. OE valves can be substituted for the same price but is definitely a downgrade.

Note: KX250F models, mostly EFI units, have a problem with the intake seats crumbling which can cause major engine damage. We eliminate the problem by installing Beryllium Copper A25 intake seats an extra $178 when done with any service. They also have a problem with the intake lifter buckets cracking and offer hardened thicker wall units for $60 each.

[mlatour]

6 hours ago, nots0much said:

I've just shimmed them. The bike has about 50hrs. What's the lifespan of the valvetrain on these bikes?

Are you the original owner since day one?  (meaning it's only seen your specific trail usage and not MX ridden or raced by a past owner)

 

Say the bike has 50 hours and you are the original owner, 

if the valves required re-shimming at 50 with your current usage, figure it will require it again at 100 or a bit sooner.

(that's also pending that a previous owner didn't re-shim them before you)

 

Generally, by the 2nd time you re-shim valves it means they've started going downhill and will continue to do so exponentially (wear progressively faster)

meaning you might not reach 150 hours before they require to be shimmed a 3rd time.

The more you 'shim' valves to get more usage out of them, the thinner they'll wear (contact faces) and the more you risk of one failing (grenading your engine)

 

In the world of 250F's which in reality are all 'disposable' MX race bikes (after a certain time they cost more to fix properly than they're worth)

if you follow the discussions in the various TT sub forums (Honda, Yamaha, Suzuki etc.)

versus the other bikes, the KX250F engine does not seem to have an enviable track record in terms of long term durability.

 

Edited February 22, 2020 by mlatour

[nots0much]

Thanks for the feedback! It's my only MX bike, so it won't see much use. Only trails around here, and I have 3 other bikes for that. Previous owner was a beginner, who spent more time admiring it than riding. He was too noob to do anything besides oil changes and graphics kit. But at low hours, it wasn't a concern for me. Just spent 3 days doing valves, fork oil, linkage bearings, headset, wheel bearings, spokes, cables, air filter (crusty old filter fused to the airbox), plus some new bits and protection. It's nice to have a bike that can take some jumps without bottoming out. But that MX clutch and tranny is something else... 

Edited February 23, 2020 by nots0much