ZXR DOWN ZXR DOWN!!!! broken down that is...

[JamesLaugesen]

Well I headed off early thismorning up the freeway to Mt White.
Just wanted to get my exhaust label & plug and scoot back home.
Sitting on the freeway nicely at 110, bike running like usual and "twangshhhh" kinda noise from the engine then about 1/4 power, still responsive to throttle input but only just enough power to maintain speed.

Pulled over into an emergency lane and the engine was (almost) idling with a yucky ruff sound until I backed off the throttle completely and it stopped with a slight "ding" noise.

Now the engine wont kick over though the starter motor is definitely trying to.

HUUUUUUUUUUUGE THANKS to Samhasa636 for driving a long way to pick me up and get me home. Bloody unreal - Thanks mate!

So now I'll look into my options and see how cheaply/easily I can get the bike fixed sad.gif

So the list of symptoms I can think of:

@ Twangshhhh noise while cruising around 8000 rpm and loss of most power
@ Still able to maintain speed for a few hundred metres (until pulling over)
@ Throttle input still had an affect
@ Stalled when trying to idle with a "ding/clunk" noise
@ Engine doesn't kick over with starter now
@ Sounds like something has jammed stopping either the starter or crank from turning
@ Can hear exhaust back pressure valve open when trying to start
@ No visible damage, no fluids leaking, etc.

[Felix]

Ouch, sounds bad...

Umm, don't know where to start. Pull sump off maybe, then head?


Things that have been known to happen include:

* something falling through carby (like a bolt) into a port, jamming valve
* something letting go
* something breaking
* helpful, eh?

So I guess you need to start looking for evidence of what is wrong, but resist the temptation to try and turn it over...you wouldn't want to scratch bores or risk really fudging something up more than it already is.

[I-K]

@ Twangshhhh noise while cruising around 8000 rpm and loss of most power

Can you flesh that out a bit more? Was the twang sound metallic, like a solid metal component letting go, or like a cable snapping? Did the ssshhhh sound represent escaping gas (air?) or was it more like a rustle?

@ Still able to maintain speed for a few hundred metres (until pulling over)

Maintain 110?

Did it sound normal while it was doing so?

@ Throttle input still had an affect

Within the drastically reduced power range you describe earlier, ie. if you gave it more gas, the bike would pull harder, but nothing like as much as it should.

@ Stalled when trying to idle with a "ding/clunk" noise

Again, were these metallic sounds? Tinny, like they were coming from close to the outer skin of the motor, or was there more bass to them, like they were coming from deep within?

@ Engine doesn't kick over with starter now

But you are hearing a metallic engagement sound, like the starter taking up the slack in the gear train between its output shaft and the flywheel, yes?

@ Can hear exhaust back pressure valve open when trying to start

Exhaust back-pressure valve? On a ZXR750?

If you're referring to a brief whirring sound coming from somewhere within the bike when you first turn the key, that would be the fuel pump coming up to pressure.

To be honest, some kind of failure inside the engine is a distinct possibility.

Since you don't hint at you and Sam having had much difficulty in getting the bike onto his ute(?), presumably that means that it rolls around freely in neutral. Hopefully, that eliminates the gearbox from the list of likely suspects.

To check whether something's let go further forward, pull the right-hand fairing and the timing sensor cover off. At this point, you'll be able to see the camchain on approach to and departure from its crank sprocket. If either the approach or departure runs are visibly and unnaturally slack (kinks between the links, that sort of thing), search over; you've snapped your camchain. The next step is to pull the head off to see which valves have made a mess of which pistons.

It's probably a good idea to also pull off the tank, airbox and whatever else is necessary to get at the cam cover, so you can remove it and have a look at the cams and valve buckets. If anything in there's done a suicide bomber, it shouldn't take much staring to spot.

If everything still looks ok, then get a socket onto the ignition trigger rotor retaining bolt and see whether the crank spins freely. Pulling the plugs out makes this easier as you don't have to work against the compression of the motor, but then you miss out on the cool hiss sound of air escaping the cylinders at the first crack of the exhaust valves, not to mention that you'd think it would take more than 175cc at a time worth of 11.5:1 compression to pose a problem to someone with some Viking in his name.

If the crank stops against something solid, stop. Back it off a bit, try again. If again no go, try listening out for the clash of whatever is involved in the blockage. Where is it coming from?

At a stretch, pull out the starter motor, see if that frees it up.

If it's turning over smoothly, hoick it up on a paddock stand and put it in gear; see if it'll still turn over smoothly. What about second gear? Third? Fourth? It'll, of course, require more effort at the ratchet hanging off the crank bolt up front, but, cylinders hitting TDC on the compression stroke aside, if there are no issues, it should still turn over quite smoothly.

Ultimately, it could always be nothing, but it's an 11-year-old bike, and you've alluded a number of times to the relatively hard time you give it, so it's far from impossible that it has gone bang.

Report back with how you go, ok?



This probably belongs in the engine discussion forum, btw, mods.

[Ment]

* something falling through carby (like a bolt) into a port, jamming valve...

Has this happened to someone other than me before?

Honestly mate, sounds like its not going to be good whatever it is.

... and I.K., it doesnt really matter where this is posted does it? This isnt netrider ya know

[Felix]

Has this happened to someone other than me before?

Yes

[JamesLaugesen]

Thanks for the great reply IK!!! Awesome awesome stuff!!!

I'll try to answer all your questions.

@ Twangshhhh noise while cruising around 8000 rpm and loss of most power
Sounded like a cable snapping and a very quick increase in internal revs (only for 1/2 second or so until returning to normal), without a change in exhaust note (but maybe I didn't notice). And a rustle sound, only for 1 second or so.


@ Still able to maintain speed for a few hundred metres (until pulling over)
Yep maintaining 110, sounded like it was running a bit behind itself, quieter and laggy... didn't notice any different vibrations.


@ Throttle input still had an affect
Yeah basicly no power, and a tiny tiny bit of pull, but not much. Also noticed the exhaust note change a little.


@ Stalled when trying to idle with a "ding/clunk" noise
Hard to remember everything as I was concentrating on pulling the bike up on gravel and then 'clonk'. Definitely more bassy than a mentalic ding though. Like something faily big stopping... that's not good is it? haha.


@ Engine doesn't kick over with starter now
Yep there's a metalic engagement sound, sounds just like you suggest taking up slack in the drive.


@ Can hear exhaust back pressure valve open when trying to start
Hmmm, I guess not then.
Definitely sounds like a valve of some sort opening though, very short delay after hitting the starter I hear the "flick pop" kinda sound of opening/closing a well sealed valve.


Thanks again
Yep I do give the bike a bit of a flogging I suppose (only had it a couple of months) and I think it's had a fairly tough life in the past.
I never jump the revs around really fast though, never wheelie, excessive engine brake, etc.

Greg from the twincam forum says it sounds like the cam chain tensioner has shat itself and the cam chain skipped a tooth.
He said that would explain the ability to maintain speed but once the engine has slowed/stopped there wouldn't be enough compression to fire it up. And if the valves ended up out enough to hit the pistons that could explain the jamming now trying to start.


My dad was on the phone and offered to come down to give a hand (I just wasn't in the mood before, damn weather) so I'll see how I go today working through the tests you suggested.

Cheers

[JamesLaugesen]

Oh I forgot to add that while I was in bed in sadness (after getting the bike home) my housemate had moved the bike and parked it on it's side-stand... on dirt... hurry! 1 broken left rearset later and my day got worse hehe.

Luckily though a friend was randomly stopping by for a visit (Rick from the twincam Across forum) and helped me pick the fat bugga up (btw yes viking in my name but I'm not built like one unfortunatly, hahaha, Danish, haha.).

Now this thread is officially a technical one I think it should be moved to the engine forum yep.

[I-K]

very short delay after hitting the starter I hear the "flick pop" kinda sound of opening/closing a well sealed valve.

???
OK. At this point, I'll fire a confused flare up into the sky. It's orange in colour and has special fins which make it inscribe a trajectory like a question mark...

Greg from the twincam forum says it sounds like the cam chain tensioner has shat itself and the cam chain skipped a tooth.

Camchain tensioner failure is a possibility, but not the chain skipping on the sprockets. For a long time now (my 1990-model ZXR250 had this design) Kwaka have been casting the camchain tunnel with little longitudinal ridges that shadow the chain closely enough to make it impossible to pull the chain off the sprockets far enough for it to skip teeth. There's a similar little cradle that cups around the bottom half of the crank sprocket, plus there's the top guide on the underside of the cam cover.

He said that would explain the ability to maintain speed but once the engine has slowed/stopped there wouldn't be enough compression to fire it up.

That would require the chain to skip a fair few teeth, like five or six. Retarding the cam timing by a tooth or two wouldn't be enough to make the engine unable to fire.

And if the valves ended up out enough to hit the pistons that could explain the jamming now trying to start.

Not quite. If something happens to make it possible for the valves to clash with the pistons, the engine stops pretty much instantly. If your engine ran on for a bit, managed to idle for a bit more, and now can't turn over on the starter, then something a bit funnier would be going on...

Make sure you report back on what you and your dad discover.

[JamesLaugesen]

Thanks IK

Not sure how else to describe the valvey sound when try the starter, haha.
Dad didn't end up coming, I slept instead... so didn't get anything sone today.
Thanks interesting about the cam chain, pretty cool of kwaka too (Greg doesn't know anything about them).

Bit of a worry "something a bit funnier" is going on though That sounds expensive.

Will keep you updated.

Oh and I forgot to confirm before but yep the bike rolls fine in neutral.

James

[JamesLaugesen]

Just found out that the bike had a new cam chain tensioner fitted a couple of weeks before I bought it.

Could that mean anything?

Btw, still haven't had a good look at it, just gathering info today coz I'm in a bit of a grumpy mood.

[mike-s]

if your in a shitty mood, stay away, far far away from the bike. There's always a chance you'll crack the shits and do something that causes bigger problems (ergo me and my old bike had a timing prob, i got the shits, tried to refit the timing differently because i confused what friends said and the japlish from my manual.

Result = broken cam followers and $800 later (yes i suspeect there was a "idiot penalty" in there somewhere) a top end rebuild to make sure i didn't put a hole in my piston or bend a valve. On the upside, new rings and a hone made it perform like a new bike .

[JamesLaugesen]

Haha yep my thoughts exactly Having done something similar to my mountain bike (still in peices) I've learnt to stay away.
Ironicaly Samhasa636 was going out for a ride (mountain biking) after taking me home which was a nice reminder

A mate suggested that I first check for internal mechanical damage by dumping the oil and sifting through for metal debri. Will that be reliable enough to determine if there was any damage to the valves or pistons?

[mike-s]

somehow i doubt it would be 100% as there's parts of the motor that barely touch the oil, i.e. head, bottom of valves, though if something binned into the side of the cyl there'd be a fair chance of bits of metal floating about

[JamesLaugesen]

somehow i doubt it would be 100% as there's parts of the motor that barely touch the oil, i.e. head, bottom of valves, though if something binned into the side of the cyl there'd be a fair chance of bits of metal floating about

Ok thanks mike.

[mattyv74]

... and I.K., it doesnt really matter where this is posted does it? This isnt netrider ya know

yes yes, I'm with you Ment, lets make some more stupid RULES.