Help! Sudden rattle from engine?!

[Squishy]

Well, today I checked the tensioner. Turned the screw a little clockwise and noticed the slack increasing on the chain. When I stop turning I can feel the tensioner wanting to turn back left. When I let go the tensioner snaps into place, just like on the movie. So, the tensioner seems to work. Here's a movie on the chain slack https://dl.dropbox.com/u/22072961/MF/NAKS.avi.

Anyway, I re-checked the valves and put everything together. The bike fired up and luckily nothing exploded. However the rattle is still there :(.

I haven't drained the oil yet.. I said before the rattle isn't constant, but I can now pretty much reproduce it at ~2000rpm. It does really sound like the chain but it's super tight and the tensioner seems to work  

[Chris H]

Hi Squishy sorry for not posting up sooner but with bullit5 being so helpful i kind of left you guys to it,
anyway i can not listen to the rattle because my laptop is crap but looking at the picture of the chain and cams i think the cam chain shows signs of damage.
If you look at the middle links there looks to be silver marks on the otherwise brown/gold chain.
if this is correct and not just light/reflection i would take a closer look.
Also check the guide that is fitted to the cam cover.

[Squishy]

Hi Squishy sorry for not posting up sooner but with bullit5 being so helpful i kind of left you guys to it,
anyway i can not listen to the rattle because my laptop is crap but looking at the picture of the chain and cams i think the cam chain shows signs of damage.
If you look at the middle links there looks to be silver marks on the otherwise brown/gold chain.
if this is correct and not just light/reflection i would take a closer look.
Also check the guide that is fitted to the cam cover.

Hi Chris,

No need to apologize, thanks for the help  
You're right, there are signs on the cam chain.. However I just thought it looked like some of the coating or whatever came off from age. Or would you say the white spots can only be the result of metal vs metal ?
I've looked turned the crank several times while looking at the chain and because it's so tight I really wouldn't know where the chain could rattle against.

[Chris H]

The cam chain simply stretches with age and should not show marks.
I would take the tensioner off and have a good look around with a light.
Look in the hole that the tesioner fits in and around the guides.

i had a similar thing happen to me when a cam sprocket bolt came out and luckily wedged against the top guide, made a hell of a rattle as it keep rubbing on the cam chain.

[Squishy]

The cam chain simply stretches with age and should not show marks.
I would take the tensioner off and have a good look around with a light.
Look in the hole that the tesioner fits in and around the guides.

i had a similar thing happen to me when a cam sprocket bolt came out and luckily wedged against the top guide, made a hell of a rattle as it keep rubbing on the cam chain.

Will do... will open it up again anyway.
Anyway as said, I measured the chain and it's 139.8mm while 143mm is the service limit.. this should mean the chain isn't worn yet?
I will re-measure and make a picture this week.

I'd rather not remove the tensioner as I would have to re-do the timing..or is it very easy?

[bullet5]

Haha thanks squishy

The timing is very easy to check.

To alter/check the cam chain timing you'll need to remove the tensioner, the inlet cam and maybe even the outlet depending on how much out of sync (if any) it is.

However to check the timing on the B4, you remove the front left engine casing, then remove the right side engine crank cover (the little round cap in the middle of the side casing tha screws off), put a socket drive on this and turn the engine over(clockwise) until the timing mark under the left cover lines up with the arrow on inside of the engine (once you see it you'll know what I'm on about).

Next you'd remove the rocker cover, and check the cam positions against your manual specs, and the number of pins between two points on each cam.

Nice simple job.

Bullet5.

[Squishy]

Guess I'll have to drain the oil first before removing the left engine cover? And you have to remove the cams because you can't turn them while in place because of the valves?

Btw, if you look at the picture of the camchain I posted before, you can see the left bolt also has the "white damage" like the chain, and no way the inside of that bolt could hit something and be damaged.

[bullet5]

Yes you'll have to drain the oil, as you need to be working on both sides of the engine.

Sorry, I made that rather hard to understand. No you don't need to remove the cams while you're checking the timing, but if the timing is out you will need to remove the top clamps to be able to move the cams.

I believe you're right about the bolt. If filings were hitting the cam sprocket then there would be damage on other parts of it too.
Still best to check out the chain and surrounding area though, while you've got it in bits.

[Squishy]

Sorry for the silence! I've had some problems on the way .. a mate of mine snapped one of my sparkplugs when turning right rather than left  . Also one of my valve clearance adjuster nuts was dead and I needed to buy new ones.

Well anyway.. I had a mechanic listen to my rattle and he immediately said it was the automatic cam chain tensioner.
I decided to buy a manual tensioner, also when reading about here were some said the automatic tensioner would reach its end before the cam chain was actually worn.

Well I measured the cam chain and it seems fine according to the manual. However maybe I should've also checked the timing marks. But I guess the timing won't go off critically as long as the chain is within this limit? :



So fast forward to solving the stupid sparkplug problem and getting new valve clearance adjuster nuts:



I just did a 30min ride and she runs really good and pulls like it should. I haven't heard the rattle since changing the tensioner so so far so good!! I really hope this solved the problem.

I just hope I tensioned the tensioner right.. What I did now was tension it in such a way that it doesn't rattle idling and revving it. I have no idea how thin the margins are on a good tensioned cam chain. It's now maybe 1/4 turn tighter from the point it stops rattling. Does the chain get tighter or looser as the engine warms up?

Thanks

[erict716]

Squishy,
I just picked up my second 400, and it has the same mysterious noise you mention.  Where did you get the manual tensioner, and was it a bolt in did it require any modifications.
two months down the road, have you experienced any issues?

Thanks,
Eric

[Squishy]

Squishy,
I just picked up my second 400, and it has the same mysterious noise you mention.  Where did you get the manual tensioner, and was it a bolt in did it require any modifications.
two months down the road, have you experienced any issues?

Thanks,
Eric

Hello Eric,

I bought the tensioner on Ebay:
http://www.ebay.com/itm/MANUAL-CAM-CHAIN-TENSIONER-SUZUKI-FRONT-91-93-GSF-400-BANDIT-GSF400-92-1993-1992-/140904106511?pt=Motors_ATV_Parts_Accessories&hash=item20ce8a0a0f&vxp=mtr

It was a direct bolt-on - very easy. I had the rocker cover off but I don't think it was necessary.
I turned the tensioner with my fingers until it I felt tension and started her up.

According to a guy who is well known in my country for being very experienced, a manual tensioner should rattle a little bit with a cold engine. I waited for the engine to warm up a bit and set it so that the rattle just disappeared. Apparently over-tight is at least as bad as too lose. Now it rattles a little when I start her up but it disappears when the engine is warm (<5min).
A bit scary to turn it while the engine is running but I think (hope) it's OK now.
I've only ridden my bike for about 75 miles since (winter lasted more than 5 months) but the rattle has disappeared when it normally would be noticable within 1 mile. So, I hope it won't explode soon  

Hope that helps.