YZ426F having problems

[barty5]

Ok so picked up an 01 426 to repair for freind of a freind any way. It broke a tooth or 2 on the exhust cam was stripped down had full rebuild from the bottom (so ive been told ) big ends been done etc. Once back together was very hard to start kick it for ever (ask 4stroke he was there ) it spits flames out still wont start. once started it has a real bad knock inthe motor sounds like its from the top??. Shop pulled it down 3 time before they gave his money back.

Ive pulled the cam cover off timing checks ok have checked the flywheel hasnt stripped the keyway did look at the crank being 180 deg out makes no diff and yes it dose have fuel just incase your wondering.
ive tried a compression test but at this point none of the guages i have access to well get down the plug hole starting to think there in as bent valve. Forgot to add have check valve clearances all in spec although one was out by 1.5 thou but is ok now.

ANYONE GOT ANY INPUT BEFORE I STRIP THE HEAD OFF AND DO ANOTHER HEAD GASKET WILL BE THE 4TH AND IT STILL DONT GO ???????????????????

[4stroke]

you rmemeber how willy said it had aftermarket cams in it, wonder if they are on the wrong way round ie in on the out side etc or the cams are the wrong ones full stop.

[motorbyclist]

Once back together was very hard to start kick it for ever (ask 4stroke he was there ) it spits flames out still wont start.

my mate had that once, where it was a bastard to start one morning (fine the night before), and it was spitting flames and shit and seriously misfiring.

got it riding and 5 minutes later it was fine.....


ive tried a compression test but at this point none of the guages i have access to well get down the plug hole

got much experience starting these bikes specifically?

to compression test mine i just dont use the decomp lever and the kickstart will hold me in the air until i really jump on it. if it's been sitting a while the valves get a bit sticky/dry and i can push through the compression stroke and it's a bastard to start, but comes right after a bit of oil circulation


where in auckland are you?

[barty5]

my mate had that once, where it was a bastard to start one morning (fine the night before), and it was spitting flames and shit and seriously misfiring.

got it riding and 5 minutes later it was fine.....



got much experience starting these bikes specifically?

to compression test mine i just dont use the decomp lever and the kickstart will hold me in the air until i really jump on it. if it's been sitting a while the valves get a bit sticky/dry and i can push through the compression stroke and it's a bastard to start, but comes right after a bit of oil circulation


where in auckland are you?


workshop is in newmaket ive had a 01 426 before had it for 2 1/2 years was never like this thing is to get started (or not started is the real truth)

should add ive also now got an 08 yz450f which is piss easy to start

[barty5]

you rmemeber how willy said it had aftermarket cams in it, wonder if they are on the wrong way round ie in on the out side etc or the cams are the wrong ones full stop.


yehive had both cams out they are fine they have replaced the exhaust with a 450 auto decomp cam.

[motorbyclist]

workshop is in newmaket ive had a 01 426 before had it for 2 1/2 years was never like this thing is to get started (or not started is the real truth)

should add ive also now got an 08 yz450f which is piss easy to start

good - you know what you're doing then :)

i'll be riding through that way at about 7 or 8 tonight on my way to go watch motogp at a mate's, and i'll be in epsom working on bikes for most of tomorrow so could have a look then, but it sounds like there's not much i could help with that you havn't looked at already

[barty5]

good - you know what you're doing then :)

i'll be riding through that way at about 7 or 8 tonight on my way to go watch motogp at a mate's, and i'll be in epsom working on bikes for most of tomorrow so could have a look then, but it sounds like there's not much i could help with that you havn't looked at already

that part the reason im thinking bent valve but with out a compression tester anit going to find out with out doin it the hard way. Would have thought a bike shop after havin a damaged cam would have checked them especailly after stripin it 3 times but maybe not???

[motorbyclist]

Would have thought a bike shop after havin a damaged cam would have checked them especailly after stripin it 3 times but maybe not???

which bike shop? - i gave up on shops to do satisfactory jobs many years ago, though atleast your one gave you your money back

if it was henderson yamaha, lets just say i'm not surprised. I'm told mt eden isn't any good either.


a damaged cam would very likely give a bent valve, and fucked piston - if there's no marks on the piston then the valve should be ok

[barty5]

which bike shop? - i gave up on shops to do satisfactory jobs many years ago, though atleast your one gave you your money back

if it was henderson yamaha, lets just say i'm not surprised. I'm told mt eden isn't any good either.


a damaged cam would very likely give a bent valve, and fucked piston - if there's no marks on the piston then the valve should be ok

was down in chirstchurch then he moved back to H town and they didnt want to know about it.

[laserracer]

Hey Barty ask grey racer on thumper the yz426/450 FORUM HE'S THE 426 EXPERT

[laserracer]

Check your messages Barty i have sent you something from greyracer on yz 426 cams with auto decomp and cam timing

[barty5]

Check your messages Barty i have sent you something from greyracer on yz 426 cams with auto decomp and cam timing


cheers for that ill try it monday not got much to loose at this point heaps pullin the head.

[camchain]

I reckon you're onto it with the bent valve diagnosis. Valve stem probably quite bent as well and binding in the guide (making it hard to kick over). Betcha they didn't strip it down, just re-timed the cam after getting it wrong.

[barty5]

Well had a quick look at it today when Oldschool dropped of his car it appears if i follow the link that laserracer PM me it would be 1 tooth out as it now has a 450 auto decomp cam, of which i dont disbeleve the guy that posted it but have to say when i put mine back together i was unaware of this and did it as per norm and it worked fine but hey nothing to loose somill try out tomorrow i guess
AND CAUSE SOMEONE WILL ASK HERE IS THE POST WITH THE INFO
yzf426 with yzf 450 cams will it work?

Hi I'm looking for somebody to give me a answer to my cam question. I own a 2002 426 yzf but would like to convert it to auto de-comp. After reading and searching almost every thread about 426 de comp questions I still haven't found any answer.
Will cams from a 2006 450f yamaha work on my 2002 426?

Any help with my question will be appreciated.
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04-22-2009, 09:59 AM #2 (permalink)
grayracer513

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Join Date: Nov 2003
Location: California
Posts: 22,058

The exhaust cam will, although the cam from an '03-'05 will produce slightly better low end power. Not a real big difference, but there is one.

You don't want to use the 450 intake, however. For one thing, there isn't a lot of difference in them, and for the other, there's no way to time them without one of the original 426 cams, since the 450 timing marks don't line up with the 426 head correctly. The timing procedure, which you must have read by now, is to time the stock intake, then spot the exhaust in with the two top marks on the cams 14 pins apart. The timing of the ex cam will look wrong, but it won't be. Without the stock intake as a reference, you would need to use a degree wheel.

[laserracer]

How did ya get on ?? i probaby have more info if you need it and also access to online workshop manual if that helps

[cheese]

I thought you should borrow the head of Adams 426 that is sitting in bit and try it out.

[barty5]

How did ya get on ?? i probaby have more info if you need it and also access to online workshop manual if that helps

already got the manual ill try the 14 tooth appart thing 1st

[barty5]

I thought you should borrow the head of Adams 426 that is sitting in bit and try it out.


had thought of that think he have most of it back together by now but might be a plan.

[4stroke]

the 14 tooth thing sounds about right, ive come accross a few motors with that sort of a timing set up, i think the drz400 are timed a simular way.

[barty5]

the 14 tooth thing sounds about right, ive come accross a few motors with that sort of a timing set up, i think the drz400 are timed a simular way.

yeh strange cause my 426 had a 450 cam and was set up as per book line up the dots so fuck know could explain the real cool flames its spittin out if the exhuast is being held open.

Another thing i found and as far as im aware every bike ive worked on the flywheel keyway point up at TDC i found this bike to be set up the opposite pointin down which would put it at BDC with the cams in TDC and this was a bike shop that set it up???????????????? WTF

[flyingcr250]

yeh strange cause my 426 had a 450 cam and was set up as per book line up the dots so fuck know could explain the real cool flames its spittin out if the exhuast is being held open.

Another thing i found and as far as im aware every bike ive worked on the flywheel keyway point up at TDC i found this bike to be set up the opposite pointin down which would put it at BDC with the cams in TDC and this was a bike shop that set it up???????????????? WTF

some hairys probabbly been at it:laugh:

[4stroke]

to me that sounds like they've had the crank apart, with the keyway down is the piston at tdc? hmmm strange its sounds all up the fuk aye.

[Buddy L]

adams bikes still in bits, im sure he'll let you use it, and he might even let you put it back together for him as well.

[barty5]

adams bikes still in bits, im sure he'll let you use it, and he might even let you put it back together for him as well.

yeh i was ment to catch up with him yesterday he is after a flywheel puller think he was kinda hinting i could then rebuild it hahaha

[barty5]

to me that sounds like they've had the crank apart, with the keyway down is the piston at tdc? hmmm strange its sounds all up the fuk aye.

Well the way they set it up it was pulled the chain of and spun it 180 deg all good now. Now set so keyway is vertical 0deg and piston is at TDC somy thinking is has to come down to valve set up or some bent ones.

[Boosted]

yeh its still off lol.. you can borrow it if needed and if you want can help put it on my bike mahaha :P

[barty5]

well heads off and all looks good valves seal no leakage timing was correct even doin the set up i was given re have 14 links between cam center didnt help ???????????

[4stroke]

rooted spark plug causing a pre ignition or hows the pickup setup for the igniton system, ie if its got a "air gap" the gaps not set up right? used to have a few issues with the john deere lawn mowers and incorect air gaps causing problems.
does the piston look ok, no marks on it from a hitting somthing.

[camchain]

Hmm bugga. Would've put money on bent valve/s (been there done that with dropped valve). You'll know a heap more about engines than me but maybe pull all valves out while head off to be thorough. Bearing blue the seats/valves, smooth operation in guides, correct springs, decomp funtioning properly, ie not jamming or even (unlikely) lifting valve all the time - basically rule out every possible prob with head.

If teeth were broken on cam sprockets, maybe some damage lower sprocket? Poke a torch down there and turn engine over? Chain Tensioner/Guides functioning right and look OK? Maybe lack of tension issue that caused broken teeth after rebuild?

Re that thumpertalk post/info - maybe that inlet cam is a 450 one and throwing things out timing wise?

Just fyi and comparison, I've had cam timed one tooth out before (doh), bike started fine and ran smooth but was very down on power.

[xen]

I thought 4 strokes were easy to rebuild :shutup:

[barty5]

I thought 4 strokes were easy to rebuild :shutup:

they are but some cock at a bike shop rebuilt this one and i can say cock cause the crank was set up 180deg out so who knows what else he has fucked up head is off all looks sweet valves seal nicely so they arent bent they move freely startin to think somthin more internal could be set up wrong got a few more thing to try out tommorow if time allows before cases get split as well.

[laserracer]

WOW sounds weird , you could try asking greyracer on the 426 forum on thumper, he is a master yz426 whizz ,before you split the cases ,just in case its something else ,but it sorta sounds like you have the top end covered,Hope its nothing to major
Have just had a search on thumper... it could be the counterbalancer key.... oooppps this may only be relevent to 2000 models as i think newer models had a spline

[barty5]

im hopinnot as it turned out it was the primary gear that lost a tooth not the cam so all that stuff was looked and a replaced hence the did the big end while appart. but i guess if you can get the tdc wrong anything is pos.

[cheese]

Not something stupid like the timing way out? or a sheered key for the flywheel?

[barty5]

Not something stupid like the timing way out? or a sheered key for the flywheel?

nope checked all that

[Danger]

I know you have said several times that the timing is correct but how are you checking this? By the timing marks or with a dial guage or timing light?
I just want to bring up the possibility of an aftermarket crank having been used in this bike like a Hot Rod crank or something. I know they have caused timing problems in YZ250's due to the key being slightly different to the stock crank.

[barty5]

I know you have said several times that the timing is correct but how are you checking this? By the timing marks or with a dial guage or timing light?
I just want to bring up the possibility of an aftermarket crank having been used in this bike like a Hot Rod crank or something. I know they have caused timing problems in YZ250's due to the key being slightly different to the stock crank.

poor mans dail guage and timing maeks it still has genuine crank.

[motorbyclist]

my money is now sitting on it being an electrical problem.... assuming the carbs and air filter are all good.....

[barty5]

Well its times like this you really wish you had bought that compression tester a few day earlier would appear we have a major lack of it going on which could also explain the rattle (piston slap at a guess) Knda strange as it dosent fell like it miss that much when you kick it over but it dont have any guess im more use to my 450 although not a lot a diff in motor size. Waitin on owner to find out if we go any further with it ie new piston kit.

[laserracer]

Ouch sounds all bad...$$$$$:crybaby:

[barty5]

Ouch sounds all bad...$$$$$:crybaby:

$337 retail my price $200 so as it for mate of a mate somewhere in the middle

[barty5]

Well after a lot of thinking on this job. Finally got the go ahead from the owner so pulled the piston out measured it up hmmmm ring end gap big enough for a bur to drive through dang near 1.5mm and piston clearance cant remember now but out a spec.
New piston ordered and fitted (along with another big slice in finger blood everewhere) watch sharp edges on pistons) Anyway all fitted reset timing fit tank hey starts 3rd kick motor still little noisey at top but 100 times better than before and it now starts.

JOB DONE

[krad_nz]

Wow well done mate. Enjoyed watching the diagnostic process.

[barty5]

Wow well done mate. Enjoyed watching the diagnostic process.

Fuck glad someone did i sure as hell didnt enjoy doin it. Real mind fucker you would think a b/shop would have checked the rings and shit while it was in bits given the once out it was rather easyto see it was original piston standard size, You would or at least i would at least wanted to check its tolerances. Especially when you have stripped it for a 3rd time ????????????????? Wonder why i fix my own hmmmmmmmmmmm ill ponder that NOT.

[kezzafish]

yeah well done boss. Glad it was a satisfying escapade for ya lol. The owner of the bike has gotta be pissed off with the shop but at the same time stoked you could sort it out so cheaply

[laserracer]

AAAAHHHH nothing like a good old yz426 to bring on a bit of blood, sweat, and tears, well done mate , :woohoo:what a bunch of noddies at that bike shop not checking ring clearances....