Help! Sudden rattle from engine?!

[Squishy]

The sprockets are tough as old nails, they aren't going anywhere fast

The chain stretches as it gets older, so the only real way to check if it's within limits is to accuratly measure the distance between a set number of pins (the distance and number of pins will be specified in the manual for your year bike).

Hope this helps,
Bullet5.

Yes, I measured the length exactly like mentioned on the picture in my manual, which is 21-pins. I measured 139.85mm with a digital caliper and the limit is 143mm. I thought it couldn't be right or can the chain really stretch 3mm more?

[bullet5]

3mm takes a long time. The chain should be fine :)

The distance between each pin is 6.66mm (at present) so 3mm more stretch is quite a lot really

I'll play the sound link to my old man later and see if we can knock some ideas up as to what it is.

All the best,
Bullet5.

[Squishy]

3mm takes a long time. The chain should be fine :)

The distance between each pin is 6.66mm (at present) so 3mm more stretch is quite a lot really

I'll play the sound link to my old man later and see if we can knock some ideas up as to what it is.

All the best,
Bullet5.

Ye that's what I meant.. I thought 3mm was a LOT and figured it couldn't be right? (--> What is the default length between each pin?)
Thanks!

[bullet5]

I'm not 100% sure on that one as there is no specified measurement in any B4 manual.

I do however have a brand new DID Cam chain I'm fitting to my B4 VC of which I can check the lengths, but this will be a minimum figure not an "ideal" figure as the chain is new and will stretch quickest while it's bedding in (first few thousand miles).

I'll try and have you a figure for my new and "old" chain (no idea how many miles that chain has done) by this evening.

Bullet5.

[bullet5]

Right, well seen as both of my cam chains are still out of my engine (thanks a lot Wemoto ), I've been able to measure them for you.

I had an assistant hold the chain on a work surface while I measure it with some mechanical verniers. I measured 141mm for 21 pins, from the center of each pin. This actual value may be a tiny bit either side, but only by perhaps .5 of a mm at most.

Quick note though, my engine is a VC varient '93 so the chain may be a tiny bit different (wouldn't have thought so, but there's nothing online to suggest they didn't change that too)

So if yours is actually 139.85mm then that sounds alright to me. Afterall, a chain can't get shorter

Hope this helps somewhat.
Bullet5.

[Squishy]

Right, well seen as both of my cam chains are still out of my engine (thanks a lot Wemoto ), I've been able to measure them for you.

I had an assistant hold the chain on a work surface while I measure it with some mechanical verniers. I measured 141mm for 21 pins, from the center of each pin. This actual value may be a tiny bit either side, but only by perhaps .5 of a mm at most.

Quick note though, my engine is a VC varient '93 so the chain may be a tiny bit different (wouldn't have thought so, but there's nothing online to suggest they didn't change that too)

So if yours is actually 139.85mm then that sounds alright to me. Afterall, a chain can't get shorter

Hope this helps somewhat.
Bullet5.

Thanks a lot for all your effort. I guess it's possible but it does have 60.000km on it. I redid the measurement a couple of times and even on the mechanical on it was 140mm...
Perhaps the rattle isn't caused by the chain - but then I don't know what else it could be. I'll redo the measurement for the chain the next time I can just to be sure.

[bullet5]

It's alright bud I've got a bit of free time on my hands anyway.

Have you checked the tensioner yet, and have you drained the oil recently? If there's any metal filings in it you know you're in trouble.

We'll find the cause one way or another

[Squishy]

It's alright bud I've got a bit of free time on my hands anyway.

Have you checked the tensioner yet, and have you drained the oil recently? If there's any metal filings in it you know you're in trouble.

We'll find the cause one way or another

I've drained the oil 2000km ago.. but will do it again as soon as I can (i'm not at my bike right now).
Anyway bandit 600 and 1200 I think have 'teeth' in their automatic tensioner so when you open it you can check whether it's on the 'last' teeth - and therefore can't tension any further.
Does the 400 have this kind of tensioner? Where the spring pushes the tensioner and then it clicks into a teeth?

like this:
http://www.youtube.com/watch?v=iu9ahRl2NXg&t=1m28s

edit: Though from what you said and what my manual says it would be more like this one:
http://www.youtube.com/watch?v=eGr9aMAg6dU&t=1m7s&hd=1

So basically I could turn it anti-clockwise and manually make it tighter?

[bullet5]

Yep, it's just like the adjuster in the 2nd link

I would not advise you to manually tighten it as you may get it stuck, then the chain will run far too tightly and you'll rapidly wear the guides and increase wear rate of the chain.

I know you've said you've checked the valves, but they can cause a right racket. Get them all dialed up exactly the same while you've got the cover off. :)

Another think to check is oil on the bearing plates for the cam shafts. If they're not getting enough oil or a feed line is blocked that can cause a issue.

The next thing I would do is make sure that all bolts on the bike are tightened up correctly. Something like a loose battery box or rectifier could cause a horrible noise. Make sure nothing can vibrate against any other part of the bike.

My only other thought is piston slap, but that really shouldn't happen yet as the engine only has 60,000km on it so unless it's been abused all it's life that shouldn't be the case.

As I said before though, if there's any metal in the oil then we know it's something in the engine causing the noise, not just some other part of the bike vibrating, which it could well be seen as it only happens at low rpms.

Bullet5.

[Squishy]

Okai.
Well, I wanna rule out the cam chain adjuster. (since from the sound, location, behavior @ low rpm it's my first guess)
What if I turn it clockwise, as said in the manual. Would it snap back into position if I release the screwdriver like on the 2nd youtube video? This way I know it's not stuck/malfunctioning. Right?
Perhaps I can give it 1/4 turn tighter just to make sure it's not the cam chain? (I doubt 1/4 turn can do much harm?)

Yes I've checked and adjust all valves. Some were tight (e.g. 10mm barely fit through some intake). But like I said if the valve clearances were off it should've rattled all the time?

I've got everything off (tank, carbs, ignition coil, waterpump, radiator, etc.) and checked for any loose parts.. engine mounts, radiator mount, battery, shock, couldn't find anything. Then again I'd say the sound is coming from the engine area (or waterpump).

Engine's not been hammered. Carefully ridden by previous owner and I always make sure it's warm before revving it.
I'll drain the oil next time.

[bullet5]

Yes you can turn the adjuster clockwise to see if it springs back, but remember it won't give much of a kick as it's being pushed by the guide and chain. :)

Yup, the valves would've made a continous rattle, and if they were tight they'd actually have been quieter upto a point. If you couldn't hear the valves then something would be wrong

Ah! Water pump. Now that could be the answer. With 60,000km of miles under it's belt those bearings may be on their way out, but again it's just one of many possibilities.

The engine doesn't sound very healthy at all in the video you posted. Even if you've got the standard exhaust on (which I hope you have) it shouldn't make that much of a racket.

I really hope that oil is clear.
Bullet5.

[Squishy]

The engine doesn't sound that rough at all in real life.. It's because I used my mobile-phone very close to the engine. Yes I have an aftermarket exhaust but the engine sound is way louder than the exhaust sound in the recording.

One more thing.. does the waterpump pump continuesly or does it get triggered at a certain temperature? (since the 400 is officially water/air/oil cooled)

Will report back in some days (might be a while) but I'll have some days off soon.
Thanks for the help up to now :)

[bullet5]

Glad to hear it! That did sound like one very noisy motor

If the water pump didn't run constantly then you'd have steam forcing it's way though gaskets.

I believe it speeds up when the revs increase, and once the engine gets warmed up the fan cuts in aswell to help cool it down.

Look forward to hearing your findings.
Bullet5.

[Squishy]

I just thought about what you said about the cam chain having only slack at the bottom of the chain.
Well, I think it's possible to measure the slack at the top because if you'd push the chain at the top (between the two cams) the cams could just rotate and allow for slack. The cams aren't fixed?

Ps would you say I need a new enginecover gasket? It's only half a year old

[bullet5]

Indeed the cams aren't fixed however they are held stiff by the valve springs pushing on the lobes.
You'll have one hell of a job trying to turn a single cam by hand.

As long as the gasket isn't damaged/ripped then it's fine to reuse it, so long as you make sure it and the mating surfaces are perfectly clean.
Bullet5.