knocking noise and a dodgy chain...

[hmmmnz]

the story of the ages,

any way bike : rotax 5 valve engined aprilia pegaso 12k miles (20k kms)

the story: was riding home a few nights back, bike started making a knocking noise under load, fine when sitting still,

what ive done: pulled all the plastics and shit off and thought i'd do the clearances anyway, done the clearances all a bit tight, but nothing major, new shims etc,

what i noticed: when i was priming the oil feed tension'er (hydrolic tensioner) is that the chain gets loose and then tight on the 2 cams
eg

tight
https://i58.photobucket.com/albums/g257/hmmmnz/IMAG1251Medium_zps4bb4fbe3.jpg

loose
https://i58.photobucket.com/albums/g257/hmmmnz/IMAG1252Medium_zps5b97156a.jpg
https://i58.photobucket.com/albums/g257/hmmmnz/IMAG1253Medium_zps89a174c8.jpg

thats with the tensioner out, the tensioner can take up some of the slack, but it almost looks like its going to jump off the cam sprocket or skip a tooth,

its like the bottom crank sprocket is oval

what does the bcf massive think??
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[hmmmnz]

what the fuck, no one has replied in 20 mins.
oh my god this forum is shit!! I'm leaving, fuck all you cunts,
i have a super fast bike and ninjas want to be me and you are all computer warriors, meet me for a fight you pussies if you're not to scared, i kill you


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the humans are dead
I kick arse for the lord
Wiring Diagrams BIDNIP it bitches

[temeluchus]

inb4 bent valves
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[hmmmnz]

umm i did a compression test and was all good,
it hasnt actually slipped any teeth on the cam sprockets, somehow..
so shouldn't have hit any of the valves, unsure if its a non interference engine or not
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[hmmmnz]

seems like im not the only one
https://www.youtube.com/watch?v=g2Ypzdgi9tM&list=UUlJohDIeAoTUDlg6gmvxwog

fucken weird
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the humans are dead
I kick arse for the lord
Wiring Diagrams BIDNIP it bitches

[hmmmnz]

any ideas kids??
____________________
the humans are dead
I kick arse for the lord
Wiring Diagrams BIDNIP it bitches

[MillaMeter]

Knackered tensioner.

It's obvious the tensioner is not doing its job by taking up the slack of the chain.

Chuck it in the biffa and get a new 1.
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2010 Kawasaki ZX6R RAF Performance Edition / 2008 Kawasaki Ninja 250 K8F

[YBR Ric]

My hands-off guess is the slack between the two fixed distance shaft centres is changing because the cam chain tensioner is varying the amount of tension it applies to the chain allowing the secondary shaft to rotate and altering the chain length between it and the primary one.

However there's an outside possibility that if the sprockets are bolted to the shafts, they are somehow running eccentrically. Measuring the distance between the sprockets between tight and slack positions might yield an answer... as might inspection of the pump responsible for the oil feed to the hydraulic tensioner.

[bodger]

If your problem is the same as the one in the utube clip, it looks like the chain is knackered/stretched.

[hmmmnz]

well i can tell you officially that my chain isnt stretched, its well within the rotax manual specs, its almost new,

those pics are with the tensioner out,
the point i was trying to make was that the chain gets tight, and as it rotates around it becomes loose, the tensioner shouldn't have to take that up, it should be there just to but pressure on the tensioner arms

oh and the tensioner is also fine and working as it should,


cheers for the ideas and clues guys, i'll keep investigating
and get back to ya
____________________
the humans are dead
I kick arse for the lord
Wiring Diagrams BIDNIP it bitches

[YBR Ric]

The knocking might be coming from somewhere else and this chain slack 'problem' a red herring. I cant make out the cam positions fully but this is what would normally happen.

In 3 out of 4 cycles one or both sets of cams make contact with the shims and therefore under resistance from valve spring pressure. So the chain is very tight everywhere except between the last camshaft and the tensioner. It's tight between the crank and the first camshaft being turned, then tight between the first and the second camshaft which is being rotated by the first, with all slack to be found between the second camshaft and the crank where it's reduced by the tensioner.

However during one cycle, top dead centre on compression; both cams are free to rotate because they are no longer subject to any valve spring pressure. So it is now possible to position that slack anywhere along the chain's length. Pressing down on the short run between the shafts simply moves all the slack from the front and back vertical runs to the horizontal one.

The chain slack should disappear once a correctly working hydraulic tension is fully primed and operational and would be subject to reappearance after any leak down suffered by the tensioner.

[Vincent]

As above, doesn't the chain tighten up as the Inlet cam is starting to open a valve?

When the chain's tight and/or loose, the number of links between the cams still the same ja ?
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[map]

[hmmmnz]

[temeluchus]

presumably, with the tensioner out, it would get tight again whilst one of the inlet or exhaust valves its being compressed by a cam then slacken off when not under tension.
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[Rogerborg]

My wild guess is that Pete will provide the correct answer.
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[misscrabstick]

If the chains a bit slack then the bagginess in it will move about depending on the loading from the valve springs on the cam lobes , sometimes the pressure will try and turn a cam backwards in certain positions hence you see the variance, this will not happen if the chain is tight, so really the question is why is the chain that slack? most cam chain tensioners can come out to tension the chain but then have a mechanism inbuilt to them to keep them out once they have moved to adjust slack in the chain. Also remember there is usually a little in built slack in the design to allow for expansion of the engine and subsequent engine tightening.

Tl:DR check the cam chain tensioner works properly.

[map]

[Hugh Farking Cant]