New CRF250X>>>

canyncarvr said:

How much of this is relative to level of use and how much is difference in bikes?

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It's tough to say for sure but here's what I can tell you from what I have seen.

- all single compression ring pistons use more oil than designs with two compression rings. The second compression ring works as much as an oil scraper as a compression ring, so when it's not there you lose it's ability to scrape oil from the cylinder wall.

- With only one compression ring break-in becomes more critical. If the one ring seals poorly the heat transfer and oil control will be poor. This will make the engine use oil and lose compression VERY QUICKLY. These are fairly low tension rings to start with so ring to wall seal becomes crtical.

- The pistons are incredibly short skirt and will lose their ability to stay round after they have some time on them. Pistons that measure to spec aren't necessarily OK if they have a lot of hours on them. Once again with only 1 compression ring you have to pay close attention to everything involved in the ring sealing chain. Fatigued pistons and poor crosshatching during replacement will lower performance and increase oil consumption.

- The intake valves are titanium with a thin hard coating over the valve face. The valves can't be lapped as a result so once the valve seat goes out of spec the valves have to be replaced . Springs generally need to replaced at the same time .

- We've seen a couple of examples of the seat width doubling after about 50 hours. This means the seats need to be recut when replacing valves to bring the seat width back into spec. The seat material on the 250F appears to be much softer than the CRF450. This should help valves last longer but it may increases the need to cut the seats. Not enough data at this point to know for sure. We are keeping a close eye on this.

- Kibblewhite is working on replacement stainless steel valves as well as a higher grade spring kit but at this time they aren't available. This is the standard fix for CRF450s and provides exceptional long term reliability on these engines with no loss of performance.

This is a really nice engine design but don't mistake this for a trail bike. This is a serious racing engine and will have maintenance requirements that reflect that. Guys who just poke around in the woods should get longer life out of the various components, but don't for a second think it will last as long as an XR or KDX before you have to pop the top and do some reall maintenence.

I hope this helps. As Eric and I gather more data we'll pass it along. Mike Perry, R&D Chief from Kibblewhite has also been really helpful in sharing their experience with customers as well as their in-house test programs.

JasonJ said:

I
Also, how much dose a valve job cost?

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You can pull the cylinder head and top end yourself and any good performance shop can take care of cutting the valve seats and assembling the cylinder head properly with the springs set at the proper installed heights. Dealerships seem to lack the equipment and personnel to do good work on these performance oriented engines. It's understandable when you consider that it costs about $30,000 to get up and running with a Serdi valve seat machine.

Most shops get about $25 per valve for a valve job. A valve job will often times be necessary if the valve is badly worn and has compromised the seal at the seat. Some shops charge extra for the assembly/disassembly process some don't. Most will have some sort of package deal on labor if you buy valves and springs through them.

Wouldnt Stainless steel valves be heavier than Ti thus possibly throwing the balance off and slowing the rev rate?

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The stainless steel valves weight a bit more and there is certainly some basis to the theory that stiffer springs will increase the frictional losses at high rpm, but after a lot of testing I've yet to find it a measureable difference on the current crop of MX four-stroke singles. Along with a lot of testing with customers I've done a ton of research through SAE publications on the subject of frictional losses in high speed engines and have come to the conclusion that while frictinal losses do increase with stiffer springs in a test stand motored engine, they appear to be more than offset (at least in the case of MX singles) by better valve sealing as a result of limiting valve bounce at the seat as it comes off of the cam's closing ramp.

What kind of break in do you adhere to for this bike?

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When new, these engines will break in nicely on a couple of easy 15 minute heat cycles and then running them fairly hard. Oil changes after each heat cycle seems to be one of the most important parts of all this. The rings seal almost immediately due to the honing method used by the OEMs. The heat cycles are mostly to allow the crank , rod and main bearings to bed in.

The YZF/WR250s don't require rings or valve replacement as often as the CRF250 but the Yamaha 250F will break the valves and the cranks if you let them go too long. Occurences of this type of destructive failure are far from isolated. Now that the bike have been out there riunning for 2-3 seasons these things are breaking valves at an incredible rate. The guys who seemed to get burned by these failures tend to be second owners who don't have accurate recoreds on the maintenance the first owner perfromed.
This type of failure can happen on the big YZFs but it is much more rare (so far). Given the number of catastrophic failures I have seen on these engines I don't have a whole lot of faith in the two piece OEM Ti valve design or the quality of the OEM springs. All the YZ250F & CRF450 engines we build get one piece stainless valves and the appropriate upgraded springs as replacements for the OEM Ti valves, and we highly recommend them on every YZF4xx we work on . We use Kibblewhite valves and springs exclusively for these engines. As a result we sleep easy and so do our customers. Piece of mind seems to have that effect on folks. ;)

I've yet to see a CRF 450 break a valve this way even when they are hammered to the point of barely sealing. It remains to be seen if the CRF250 will shed parts when they get really tired like the YZF250s.

I don't have enough data on the CRF250X to know for sure if the valve and seat material is exactly the same as that used in the 250R. Intial observations point in that direction but I'll reserve judgement till we get some additional time working with them. We are still waiting for pistons and rings for the 250X from Honda, but it appears they are the same as the 250R. As we get more time to work with these Eric and I will provide additional info.

Bottom line is, if you want XR reliability buy an XR. :) If you are willing to do additional maintenance in exchange for a LOT more performance from both the engine and the chassis then step right up and enjoy the four-stroke revolution. It's an amazing ride. :yeehaw:

a454elk said:

Mine has 2 rides after the break in stuff and it runs great. It is cold blooded, which is normal I believe but after that, it seems to run fine. I have the CA model obviously and it could use some more top end, maybe the White Brother's pipe I have coming will achieve that.

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Elk- For you guys in California the 250x has a different carb and much different (i.e restrictive) cam timing than the 49 state 250x models. The 250R has much more appropriate cam timing for making horsepower.

California 250X cam specs
IVO TDC @ .040"
IVC 45 ABDC @ .040"
EVO 45º BBDC @ .040"
EVC TDC @ .040"

49 state 250X cam specs

IVO 10 BTDC @ .040"
IVC 40 ABDC @ .040"
EVO 40 BBDC @ .040"
EVC 10 ATDC @ .040"


250R all
IVO 15 BTDC @ .040"
IVC 50 ABDC @ .040"
EVO 50 BBDC @ .040"
EVC 20 ATDC @ .040"

Look closely and you'll see there is NO overlap on the California cam. :yikes:
Be prepared to have TTR 125s run around you with the stock spec CA cam. :bang:

Your money might be better spent getting Ol89r to swap cams for you, and helping you sort out the jetting. :cool:

a454elk said:

That's an idea, didn't know there was such a difference.

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With no overlap on the CA X there is no real opportunity for the scavenging effects of a good pipe to do their work. As a result there is very little to gain from a pipe other than a basic reduction in backpressure from an overly restrictive stock muffler core.

Flow at TDC during overlap is one of the real keys to making pipes and cams work together to produce real horsepower. No overlap equals NO JOY. :bang:

a454elk said:

damn the lack of overlap

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The good news is, cams are fairly cheap and they are reeally easy to install in this engine. I'm going to talk to Tony Tice from Hot Cams and see what he has in store for the Junior CRF ;)

Rich Rohrich said:

Elk-
California 250X cam specs
IVO TDC [at] .040"
IVC 45 ABDC [at] .040"
EVO 45º BBDC [at] .040"
EVC TDC [at] .040"

49 state 250X cam specs

IVO 10 BTDC [at] .040"
IVC 40 ABDC [at] .040"
EVO 40 BBDC [at] .040"
EVC 10 ATDC [at] .040"


250R all
IVO 15 BTDC [at] .040"
IVC 50 ABDC [at] .040"
EVO 50 BBDC [at] .040"
EVC 20 ATDC [at] .040"



Your money might be better spent getting Ol89r to swap cams for you, and helping you sort out the jetting. :cool:

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:ohmy: HIS MONEY??? What ya talkin about mister. :yikes:

Rich. My local cam grinder has one grind available for the 250X. Also fits the 250R.

In. .332 lift.
Ex. .325 lift.

In. 239 degrees duration @ .050.
Ex. 249 degrees duration @ .050.

In. O @ 12
In C @ 47

Ex O @ 49
Ex C @ 20

Checking @ .050.

I like Holesnots idea of using elks 250 for the guina piglet. :laugh:

Elk. Keep in mind that the more duration and overlap that a cam has, the harder the bike will be to ride in the tight stuff. It would be kinda like a RM 250 where ya gotta clutch it and rev it just to get off of a corner. Who the heck would want that??? :rotfl:

holeshot said:

Whoa..


First off, lets be sure we're getting our terms right -

Doing a search on the web resulted in opening another can of worms - there are things like ramps on either side of the lobe (I assume steeper ramps are beneficial to performance but are a lot harder on the valve train). There's also something called "lobe centers", but my head hurts too much to explore any further. :bang:

What does this have to do with twisting the throttle? Nothing. :joke:

Be sure to set me straight if I've stayed of course a bit.

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Sounds like you got your terminolgy figured out pretty good Hogsnot.

Ramps on a cam have a lot to do with the type of lifter used. Depends on if it is a flat lifter (CRF-YZF cup style) or radiused rocker arm, (XR style) or a roller rocker arm, (CRF exhaust lifter style). And you are correct sir, the steeper the ramp the harder it is on the valve train. The angle on the ramp and the shape of the lobe determine how fast/slow the valve is opened/closed and how long the valve remains open.(Duration).

Lobe centers are used when timing cams. Since few cams time out to the specs that are given in the little sheet provided by the cam grinders, you have to find a happy medium. You can do this by using lobe centers.

To find the center of a cam lobe, in the case of the Exhaust cam that I listed, take the Opening figure of 49 degrees and subtract it from the Closing figure of 20 degrees and you will get 29 degrees. Add 180degrees to the 29 degrees and you get 209 degrees. Divide 209 degrees by 2 and you get 104.5 degrees center.

And, it has everything in the world to do with twisting the throttle. Too much overlap and the bike will be very hard to ride. It may have a tremendous amount of top end but no low end. The transition from low end to top end power will not be smooth, hence the term 'Coming on the cam'. Similar to a early style two stroke without powervalves, 'Coming on the pipe.'

Ok, now my head hurts. :laugh:

BTW. Tony, did not mean to mimic anything that you said in your post. Looks like we posted our response within three minutes of each other.

Ol'89r