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+--- Thread: Misfire After Valve Clearances Adjusted? (/showthread.php?tid=74501)
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Misfire After Valve Clearances Adjusted? - markus2066 - 16-12-15
Hi All,
Got abit of an intermittent misfire on my 99 fzs600 since adjusting my valve clearances last weekend. Got a few working theory's about it but thought I'd get a post on here as people always have something helpful to add.
I have had the cam cover off again to triple check the clearances which are all nicely in spec. I've ordered some new plugs, seems unlikely to help but they are over due a change so cant hurt.
Main concern is my timing. In you experience how precisely should the timing marks line up on the fsz6? When I've done timing in the past on other bikes I know the marks can seem off by a few degrees. I was loosing light when doing to job so had to rush the end abit (not ideal), when the cam marks are perfectly lined up I'd say the crank is about 8mm below the mark I couldn't seem to get it any closer (do you think that's ok).
Could slight timing cause an intermittent misfire, surely timing is right or wrong?
Thanks All (Happy Christmas)
Re: Misfire After Valve Clearances Adjusted? - Bretty - 16-12-15
Timing marks should all line up spot on.
It's a bit of a faff, but it's easy to get things one tooth out either way, especially when the cams rotate when you tighten them down.
I don't know how critical it is for the running of the bike though.
I did mine with the engine removed from the bike and it took me about 4 attempts as I'd never done it before.
Get the crank lined up, keep the chain tight and install the front camchain guide, this will stop it jumping teeth on the crank, then fit the, the chain over the cams, then there's a combination of tightening everything, fitting the top guide and chain tensioner, and tightening down the cams without it jumping teeth.. Which is what it wants to do, as the valve springs push against the cams and try to rotate them out of sync.
I'm sure there is a technique to do it easily but for me it was a combination of trial and error, swearing and throwing tools!
Re: Misfire After Valve Clearances Adjusted? - Ferg - 16-12-15
Have you rebalanced the carbs after adjusting?
Re: Misfire After Valve Clearances Adjusted? - markus2066 - 16-12-15
Looks like I'll be taking it apart for a 3rd time them, I can certainly relate to the cursing and tool throwing.
I have balanced the carbs since I did the clearances yes.
Thanks for your replies guys I'll let you know how it goes, rain tomorrow to looks like a job for Friday. Hope I can get it running right before I start my new job.
Thanks
Re: Misfire After Valve Clearances Adjusted? - Bretty - 16-12-15
Are you doing this with the engine in the bike?
Re: Misfire After Valve Clearances Adjusted? - markus2066 - 16-12-15
Yeah with the engine in. Not too bad the last time I did it, getting to know it now......
Re: Misfire After Valve Clearances Adjusted? - Gnasher - 16-12-15
They don't always line up spot on perhaps 1mm but 8mm is quite some way off I'm surprise you've not hit a piston/bent a valve or 2 which could be the reason for the misfire :eek .
Keep us posted
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Re: Misfire After Valve Clearances Adjusted? - Bretty - 17-12-15
8mm at the crank is not as bad as 8mm on the cams (it's a bigger diameter) I guess that's a tooth out. I doubt the pistons would have hit the valves though, With the plugs out you can turn the engine over by hand, so should have checked that!
You have my sympathy though, it's a pig of a job even with the engine out! I couldn't see how you get the front camchain guide out with the engine in the frame.
Nightmare job, The cams only want to go in and out if they are square, you have 12 cam holder screws to tighten down evenly, and torque, everything is fighting you, you try and skip one tooth on the cam and it jumps 2 or 3 and you have to start again. The cams naturally want to sit 5degree outwards from each other due to the cam profile against the valve springs.
You have to line up the crank, then get the front cam on the right tooth so that when it's tightened down and the cam guide is in the place they are both in sync. Then get the rear cam in the right place (count the links between the cams) so when that is tightened down it is synced with the front cam. Then put the top chain cover on and install the chain tensioner without anything moving.
Check, run the engine through a few cycles by hand, check again. Everything should line up. If not. Start again.
The guides prevent the chain jumping teeth as they force the chain on to the sprockets. But when the cam chain tensioner is out I think the crank can skip teeth when turned by hand but only in one direction.
Haynes manual says to lube all the cam bearing surfaces with molybdenum grease, but I'm sure this now causes my clutch to slip!
Can you tell I have relived this nightmare in my head a few times?
Re: Misfire After Valve Clearances Adjusted? - Bretty - 17-12-15
3am fourth time lucky!...
Re: Misfire After Valve Clearances Adjusted? - Gnasher - 17-12-15
Being able to turn the engine over by hand isn't a grantee it's timed correctly.
One tooth out on the crank will put you in the danger zone of the valves hitting one another when the engine is started. They only have to slightly touch and they will bend, they will bend by points of a mm but the valve seal will be destroyed and it only take one to bend and that's it game over!
Re-time the engine correctly, all the timing marks must be aligned. Then do a compression check fingers crossed you've got away with it, if the compression is low in any cylinder chances are you've bent a valve.
Good luck.
Re: Misfire After Valve Clearances Adjusted? - markus2066 - 17-12-15
Hi Guys,
Today I took it all apart again, managed to get the engine closed before it started to rain.
If i line up the crank shaft spot on I can either have the cam like this (slight retard):
https://drive.google.com/file/d/1h-dMyN9olAZQ9HWEsZyS6Lm6BSRNbxfLkg/view?usp=sharing
https://drive.google.com/file/d/16fvoibshnHF0p9kT1DKQcI4xJe11aN7bHg/view?usp=sharing
[/size]
[/size]Or one tooth the other way and its like this (slightly more advance):
https://drive.google.com/file/d/18t3z1Fcqpkaldu_45YI3bI17UcD2WsCtrw/view?usp=sharing
https://drive.google.com/file/d/1nOKIpNcY8ZtO3m9ov4OdD3x6UvfVBoD93w/view?usp=sharing
If i line up the cam marks dead center in both above positions I end with with the crank timing mark in either of these two positions:
https://drive.google.com/file/d/19-76bmzojUdlKOs_cP39RD296abZp4LW4g/view?usp=sharing
https://drive.google.com/file/d/1IQA12ibDfEyQpslTrgMR7RoLi7-qi21Vag/view?usp=sharing
At the moment I have gone with the slight retard position as it appears to be closer and safer (further from hitting pistons). I have also cleaned out my carbs and they were abit gritty in the slides.
I'll test ride tomorrow when hopefully it's dry and I'm feeling less down trodden by the whole ordeal (hopefully new plugs will arrive also).
Thanks for your input all.
Re: Misfire After Valve Clearances Adjusted? - markus2066 - 17-12-15
Not sure what its done with my post there....
There are 6 links the second one down has been compressed into a line below the first.
The second two links show the cams one tooth the other way (it cut out my text explaining that).
Hope that makes sense.
Re: Misfire After Valve Clearances Adjusted? - unfazed - 17-12-15
What mileage is on the bike?
Did you remove the cams to change shims when doing the valve clearances?
There are two possibilites
1. A worn cam chain
or
2. One tooth out on the exhaust cam when you put the cams back in
Re: Misfire After Valve Clearances Adjusted? - markus2066 - 18-12-15
Hi,
The bikes done 38k, yes I removed cams and changed shims.
It was running ok before this work was done so hopefully not worn chain as that's quite a job isn't it?
When you say one tooth out on exhaust do you think I should go advance or retard? Both cam marks seem to point to the exact same angle but just a few degrees either way of the marks depending on which tooth I set it on...
Thanks
Re: Misfire After Valve Clearances Adjusted? - Gnasher - 18-12-15
Make sure there is is no slack in the in the front portion of the cam chain.
What you appear to be getting can be a symptom of that, all the slack must be at the rear.
Re: Misfire After Valve Clearances Adjusted? - markus2066 - 18-12-15
Interesting point about the slack in the front of the chain, I did pull it as tight as possible....perhaps if I got someone to hold the crank on the timing mark I could try and pull it tighter.....
the thought of taking it apart in the street a fourth time does make me want to shoot myself, hopefully it will be ok.
Do you think slightly off timing could cause an intermittent misfire? I keep thinking that if the timing a set at a point why would it cause a misfire that doesn't occur at any particular point in the revs or throttle position.
Re: Misfire After Valve Clearances Adjusted? - Gnasher - 18-12-15
Mate try and get somewhere to work on the bike I appreciate that may be difficult but doing this sort of work in the street is really to be avoided. Where are you?
Perhaps there's someone on here near you who knows what their doing and can sort this for you, it's not hard but like most things it's easy when you know how. Yes wrong valve timing can and will cause misfires and all the other things mentioned thus far, it's very possible to wreck your engine in seconds. :eek
You may want to consider paying someone to sort this for you, it will be far cheaper than paying out to replace bent valves or a replacement engine.
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Re: Misfire After Valve Clearances Adjusted? - markus2066 - 18-12-15
I'm in east Bristol. I've been making sure the engine turns over freely before putting it all back together and starting it up. Yes the street isn't ideal.....
Further to the front of the chain tightness point. When you tighten everything down and rotate the crank ccw that tightens the chain at the front, the only other variable in this is the number of chain links between any two given points on the crankshaft and ex cam sprockets.
Perhaps if I went with the advanced timing option shown in the pictures (links) and gave it a run and let the tensioner really clamp down it would tighten the chain enough at the front to be perfect?
Re: Misfire After Valve Clearances Adjusted? - Gnasher - 18-12-15
Mate you shouldn't have to move anything it should all line up with the slack at the rear which the tensioner will take up. If you can move the crank or cam with the chain in place and it doesn't move the chain is buggered there should be no play in the chain?
Re: Misfire After Valve Clearances Adjusted? - markus2066 - 18-12-15
Just taken it for a ride (first since yesterdays rebuild) and it seems to be running perfectly!
The timing is where is was before, I think perhaps the chain is stretched a little and ill have to keep and eye/ear on it but sounds sweet for the time being.
I did clean out the carbs which were quite gritty in the slides. perhaps when it turned them upside down whilst struggling with the throttle cables all the crap from float boat ect ran into the slides? Or anyone of another 100 possibilities....
Glad its all working again though, thanks for all your help guys.