E-Loc540

I just dumped nearly $1,000 bucks into my 05 CRF250 top end to make it a rocket. I ported it, Webb cam, stainless steel valves with conical springs wiseco high comp. piston. Bike was running awesome....frigin rocket. Then it locked up, it would turn over but it was hard so I knew I didnt drop anything and the whole time I was thinking it was prolly my lower rod bearing...well I tore it apart tonight to find out my lower rod bearing was destroyed....upon inspection of the valves I noticed the tappets were wearing out and letting the spring retainer slide up the valve...another 10 minutes on my bike and the intake valves woulda dropped...just my luck....thats was sucks when you highly modify any motor....its run time and reliability is drastically shortened.

Armenian

dang that sux dude--i hate doing motor work!!

moorport

That sucks, I threw a rod right throught the front of the case on my crf450, I still havne't got it fixed

Goodluckmonkey

CRF450's are known for throwing rods, sucks big time.

And all the 250F's eat valve gear like it's going out of fashion, wether modified or not. Earlier CRFs stretch valves all the time too.

All performance oriented 4-stroke dirt-bikes have their weak points.

400/436/450 WR/YZF's eat 3rd or 5th gear all the time.
KTM EXC/SX/SMR's chew the top ends and do 5th/6th gear on the EXC/SMR
CRF 450's throw rods with alarming regularity - valve seat recession was a major problem with the pre '03 bikes.
Italian bikes are even less reliable, but still better than 650 husabergs.

The safer thing is to buy a lower powered bike like a DRZ, or an XR400, which are really tough, and put SM wheels on it.

Or just live with the constant engine bills.

E-Loc540

lol. you corrected us, now its time to come back at you....Valves dont stretch. The face gets worn down as it smacks the valve seat.....the valve slowly sinks into the head as the valve face wears away; tightening the valve clearance...sometimes to the point of 0 lash. Its all in fun, thanks for the info

E-Loc540

The earlier model YZ250Fs had a problem with the wrist pin end of the rod letting go....lets just say mines a 1st year bike and ive had to replace much of the motor. Looked like a mini terrorist detonated himself in my motor. Cowards.

Goodluckmonkey

You're confusing it with valve seat recession, which is a completely different thing. On the first 250F's it was actually a problem because of the really slim valve stems, choice of valve material, and the high revs involved.

Either way, **** happens, and MX bikes have ridiculous maintenance schedules. Hope you get yours sorted.

E-Loc540

yeah mines good....and not to be a dick but theres another correction...I am almost positive all the 250 4 strokes (intake and exhaust) have the same diameter valve stems (I think 6 mm. for all 4 Jap. bikes) and that hasnt changed from debut year till now....I can take my 01 YZ250f and put 07 valves in it. Yamahas YZ250f has a very reliable valve train. Its mostly the honda crf250 with the intake valve problems due to the spring and super hard seat. Haha this is fun, fire back your thoughts....:YEAH

Goodluckmonkey

My point was that the stem size was too small for the materials used, and then it's been corrected by changing the valve material, not by increasing the stem size.

As you'll know, the smaller the stem, the better the gas flow. The slimmer valves are fine for a race bike that's being rebuilt all the time, but for a bike that you don't wanna be opening up to check all the time, it's none too great.

As far as I know, yeah, you're right, the problems seem to be more down to the Ti inlet valves on the early CRF's.

Just looked into it more, and stole this from the 'net: (of course the only really applies to bikes that are being raced, as stunters, or trail bikes don't get revved so hard)

From here: http://www.carqna.com/motorcycles/1315-carqna.html

E-Loc540

yeah I just put kibblewhite valves in mine with stock retainers and keepers and wmr performance springs, bike has a Webb cam also......I thought that everything would work together...I guess its a good thing my lower end rod bearing on my crank went out because when I pulled the head off I took a good look at the valves and found out that the knuckle on the keeper that fits into the indent of the valve stem was wearing out. There was barly any knuckle left on the intake valve keepers...another 5 minutes I woulda dropped a valve.....the exhaust valves are fine just the intake valves had that issue..Im going with a complete kibblewhite set....because I questioned using different companies products...

Schooler

yeha dude thats why im keepiugn ym 250 all stock except for a pipe air filter and all the normal ****...if u want more power get as 450....by the wya you have any spare parts for the yzf250

Goodluckmonkey

Good plan - I'd take reliability over performance anyday. My 426 runs a YZ450 exhaust cam, and has had a port job with a big skim.
Normally runs a full titanium Acrapovic, hates the stock system, doesn't like normal fuel, only runs properly on super, makes too much power for the crap Yamaha gearbox, and subsequently bashes out big-ends like there's no tomorrow.

I'd rather have a stocker given my ability and what I use it for.

E-Loc540

yeah...power and reliablility/longivity...you can be one one side or the other or somewhere in between. Its all a trade off. You want power you lose your reliablity...same thing with engines, you want good low end power you loose top end and vise versa. Find what you want and roll with it.

Goodluckmonkey

Not quite, due to the inefficiencies of the standard bike, mine made gains everywhere, with another 8hp at peak. It makes about 5-6hp over stock everywhere.

But beyond that, yeah, if i wanted more, I'd have to make a sacrifice somewhere.
Not gonna happen though, as it may as well be stock for stunting.
It's actually YZ timed to take some of the bottom end grunt off it at the moment.

E-Loc540

I went backwards, I turned my YZ250F cam to the WR timing to make the motor pull lower RPM's without cutting out. That may change now because I ordered a 60 rear sproket (now have a 12/53) (stock 13/49) and a flywheel weight. We will see....

Goodluckmonkey

Makes a lot of sense with a 250F. The beauty of the Yams is that you can effectively tailor your power characteristics to the type of riding you're doing in a half hour. It's almost as like choosing what tyres you want for a track session.

As you'll know though if you've ever had a shot on one, the WR is a total tractor as standard.
Mine pulls like a stock WR off the bottom with YZ timing, with WR timing, it's pull trees out of the ground. Just a little too much for stunting. Would rather have something like an XR250 for stunting, but I'm just riding what I've got.

Splash4195

08 CRF 450! Fuel Injection!

E-Loc540

Im with you on the XR250....very smooth power, and when they chug out it wouldnt nearly be as harsh as the high compression 250f's. But the 250f's are sexier:YEAH