Modern four stokes?

[brp]

Whats the maintenance side of things like - time ? cost ?

Heard they high maintenance, what got me miffed as brother inlaw been on loads of trail rides
and to my knowledge never had the top off his 2005 YZF250F (be 300 plus hours easy) then others on trademe doing top end rebuilds as low as 70 hours

What gives ?

How many hours before a top end rebuild on your 250 or 450

How ofthen adjusting valves ?

Be looking at 2009 plus CRF450F if get one

[Boo]

It depends how there ridden, a trail rider may not have it bouncing of the rev limiter. Its just when they need a rebuild it costs more than the bike is worth.
09 CRF450 have a few problems which can be fixed with a after market parts.
They went to a 4 spring clutch. They really need an after market 6 clutch. They have an stink bug factor[ass up] they tell me a longer swing arm linkage improves it. It stalls at low speeds as the EFI is unable to monitor low RPM.
The clutch or ass up didn't improve in the later years, 2010-2012, don't know if they solved the EFI problem.

[motor_mayhem]

It depends how there ridden, a trail rider may not have it bouncing of the rev limiter. Its just when they need a rebuild it costs more than the bike is worth.
09 CRF450 have a few problems which can be fixed with a after market parts.
They went to a 4 spring clutch. They really need an after market 6 clutch. They have an stink bug factor[ass up] they tell me a longer swing arm linkage improves it. It stalls at low speeds as the EFI is unable to monitor low RPM.
The clutch or ass up didn't improve in the later years, 2010-2012, don't know if they solved the EFI problem.

I've got an 09 450 and love it. I didn't notice an ass up factor but then maybe my suspension is set to counter act that? Clutchwise I couldn't comment as mine feels like new because the previous owner renewed it before I bought it and I put a magura set up on it. The efi low revs thing did cause me to loop it on my first day out. On the plus side I like the narrow body, steering dampner is great and efi means really consistant starting.

A top end rebuild isn't actually too expensive and do-able by yourself with the right tools.

[ktm84mxc]

A modern 4 stroke will last a long time if the maintance is kept up eg check your valve clearances every 50 hrs, oil and filter change every 10 hrs, check/replace piston every 100 hours.
The problems start when they go bang eg dropped valve or blocked oil lines wrecking the head . As this is by far the most expensive part on the engine.

[brp]

Cheers guys

Yeah heard that about how they ridden but the bro inlaw no slouch and lends it to his 18 year old son for trail rides - maybe the yzf the one togo for ?

ktm84mxc - know the bro uses synthetic on a regular basis

[Boo]

It depends on what you gonna do with it and you. If your a light ass a 250 could be for you, the thing about a 250 vs a 450 is the 250 can be pushed harder due to its size. The problem with that is maintance can be higher. Where as a 450 you don't need to push as hard.
I persoanally think the last of the carby models are nice bikes in particular the YZF and CRF 450, don't know about the others but they could well be the same. The funny thing about the crf 450 the 09 crf 450 is the same price as the 07-08 on trade me.
The 09 will get cheaper because of the new model in 13

[brp]

Cheers Boo

(Read some good reviews on the 09 CR - voted bike of the year by respected crowds)


I'm 100kg, 98 on a good day

Do the 450's have much low down grunt like a big bore 2 stroke ? 400exc rode (about 2003 - 2004) it was all mainly up top - nothing then a big surge of power as the revs built - newer 450 similar power delivery ?

[Boo]

Standard no, but thats a good thing when trail riding, as it does'nt wear you out. At 100kg I would go to the 450 or though a 250 would be faster you would have to ring it, and may increase maintance costs. You would have to get the suspension revalved and the aftermarket clutch [it will go] at some stage on the 450.
A revalve would be anywhere between $500-$1100 with springs. Take it to a suspension guy, tell him what sort of riding you do, the good ones can use the same spring and just change the shims, gold valves are expensive, some say there good others say there not worth it. My experience with them is they are way more adjustable so as you improve and get use to the bike or faster you can adjust. Many justify money on making the bike more powerful and nothing on getting it to stop or handle better. Use oem fork seals they last longer.
Look for a STM slipper clutch for a 02-08 crf450, there are two versions dirt and motard either would be ok if your trail riding and are cheap secondhand, an aftermarket would set you back over $1100, you may need a basket with the STM .

[Boo]

Standard no, but thats a good thing when trail riding, as it does'nt wear you out. At 100kg I would go to the 450 or though a 250 would be faster you would have to ring it, and may increase maintance costs. You would have to get the suspension revalved and the aftermarket clutch [it will go] at some stage on the 450.
A revalve would be anywhere between $500-$1100 with springs. Take it to a suspension guy, tell him what sort of riding you do, the good ones can use the same spring and just change the shims, gold valves are expensive, some say there good others say there not worth it. My experience with them is they are way more adjustable so as you improve and get use to the bike or faster you can adjust. Many justify money on making the bike more powerful and nothing on getting it to stop or handle better.
Look for a STM slipper clutch for a 02-08 crf450, there are two versions dirt and motard either would be ok if your trail riding and are cheap secondhand, an aftermarket would set you back over $1100, you'll need a basket with the STM.

[brp]

How come the 250's can be pushed harder when there's only about 8 kg of difference in weight than a 450 ? (Suppose you on limit all the time so ya just twist the throttle fully open between corners too)

I was looking for something for local mx track ...

Cheers

[scott411]

How come the 250's can be pushed harder when there's only about 8 kg of difference in weight than a 450 ? (Suppose you on limit all the time so ya just twist the throttle fully open between corners too)

I was looking for something for local mx track ...

Cheers

its not so much the dry weight difference, its the rotating mass that makes a 450 feel heavy, bigger piston, crank clutch etc, makes it feel heavier as its harder to change direction,

[ktm84mxc]

for Joe average a 250F will be more enjoyable as you will be able to control the bike even when you get tired and start making mistakes, a modern 450F can take the unwary for a thrilling ride wether you want to or not. A 300cc kit on a 250F makes a good compromise between power and rider ability .

[brp]

Cheers guys - interesting points

[motor_mayhem]

A 300cc kit on a 250F makes a good compromise between power and rider ability .

and largly reduces the selection of pistons and rings you can buy for it and would likely increase the wear on the rest of the engine (may run at reduced RPM but more torque applied to clutch/gearbox). If you want to go somewhere in the middle for weight and power I would suggest you look at a production middle bike like a 300 2T (KTM, GG or Husa) or a 350 4T KTM.

[Boo]

How come the 250's can be pushed harder when there's only about 8 kg of difference in weight than a 450 ? (Suppose you on limit all the time so ya just twist the throttle fully open between corners too)

I was looking for something for local mx track ...

Cheers

Yes its because your closer to the limit on a 450, usually in respect to speed and acceleration. Less time to react.