YZ426F having problems

**barty5** · 27th June 2009, 14:13

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** · 27th June 2009, 15:00

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** · 27th June 2009, 15:18

Originally Posted by barty5

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.....

Originally Posted by barty5

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** · 27th June 2009, 15:22

Originally Posted by motorbyclist

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** · 27th June 2009, 15:23

Originally Posted by 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.

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

**motorbyclist** · 27th June 2009, 15:32

Originally Posted by barty5

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** · 27th June 2009, 15:37

Originally Posted by motorbyclist

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** · 27th June 2009, 16:21

Originally Posted by barty5

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** · 27th June 2009, 17:14

Originally Posted by motorbyclist

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** · 27th June 2009, 19:03

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

**laserracer** · 27th June 2009, 19:13

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

**barty5** · 27th June 2009, 21:18

Originally Posted by laserracer

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** · 28th June 2009, 12:31

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** · 28th June 2009, 15:20

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.