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Cam chain slap only when cold?

F

Flynn

Husqvarna
A Class
When the engine is cold there seems to be what sounds like the cam chain slapping against the guide blade, but only for the first 5 minutes when the engine is cold.

I have taken a video but I don't think it really captures the noise very well.



I have already tightened the manual tensioner several turns but the noise is still there, I am reluctant to overtighten it and slap the cam chain.
 
If tightening the cam chain adjuster did not change the noise then maybe it is not the cam chain.

Cold be an exhaust leak?

I'd pull the generator cover and see if the chain is hitting the reed valve in the middle.
 
The sound of a cam chain is like ratlling. I suggest you take out you cam chain tensioner, reset to wide open and gently with a thin screw driver push the rod. If you count more than 10-11 eleven clicks then it is time for you tou change the change or you could end up scrabing the chain against the oil reed valve inside the casing which will cause engine failure.

On the other hand if it is a deeper noise, lets say like hitting 2 rocks against each other, only when the engine is cold and in lower than 1500 rpm, it is more likely to be the automatic dicompressor.

Nevertheless you should deffinetly check on the cam chain because it is a very cheap fix in comparisson with the damage that may cause.

in the pdf you will find two pages from the manual for the cam chain and its tensioner.
 

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#ghte is correct it could be the valve clearence a little open, then it is normal that when the engine warms up the metal axpands and does not sound any more. Mine has always been a little noisy on the right hand crank case. I know it is the clutch basket, when the engine is warm it is nearly audible.
 
Hmm, okay, I might back the tensioner off a little then. Also the cam chain is new, I replaced it when I got the bike and have put 1500 hard miles on it. I set the valve clearances to 6mm to make sure that there was some leeway and so that I wouldn't have to touch them for awhile longer.

Btw I have modified my cam chain tensioner, I have ripped all the gubbins out and replaced it with a single bolt to make it a manual tensioner. I thought the plunger was loose and causing the noise but now I have ruled that out.

Anyway I know about the auto depressor noise but what caused me to rule that out is that the idle seems to be a normal idle speed but the noise is still there until the engine warms right up. The trouble is the video doesn't really capture the sound well. I just rewatched it and it sounds like valve noise in the vid but this noise is similar to the auto decomp but as far as I can tell the idle is a normal cold idle.

If I blip the throttle it settles the engine down and the noise becomes less but still audible.
 
Figured out what it is. It is the exhaust rocker arm that I welded the bearing into. When the oil is cold it is really noisy, like a metal rattling against metal sound. For some reason it doesn't pick up on the camera.

Checked at 1500 miles 700 miles ago and still fine:



If I put my finger on the end of the shaft I can feel the pulses compared to the intake side which is smooth.

When I did the valve adjustments I also left the exhaust valves slightly looser than the intake ones which could also be the reason. Or perhaps an in balance between each valve?

It does seem that tightening the cam chain does quieten it down to an extent though as when I backed it off a couple of turns it was more pronounced.

I also have an oil weep coming from here:
DSCF0224.JPG

I shall probably go in and replace the O rings in both arms (part num 8000 59939) and check the exhaust valve clearances. If they are found to be roughly similar then it might be that the welds are deteriorating or that the welds are transferring more shock to the rocker arm compared to when the bearing is swaged in.
 
Okay I figured out what this was.

I was going to pull the cylinder head cover until I found that one of the camshaft bolts had snapped:

DSCF0255.JPG

I double checked the torque in the manual and it is definitely 9NM:
View attachment 71247
My other theory is that the bearing pin being welded in provides less cushioning for the bearing than if it had been swaged in and thus the vibrations and shock from the cam lobe pushing on the rocker arm bearing has fatigued the bolt and snapped the head off over time. Could an over tight cam chain also cause this?

I might back off the tensioner a couple of turns to make certain.

It will be nice to have a quiet and non leaky bike again.

If it happens again I know it's probably to do with the repair on the rocker arm bearing.
 
Scratch that, I have replaced the bolt and it's still making that clunking noise when cold. Sounds like rocks in a cement mixer, but as it warms up it goes away :headscratch:

Also even when the engine is warm I can feel an impact through the screwdriver handle when I put a screwdriver to the slot on the shaft, yet the other side is perfectly smooth. I wonder if the bearing might have seized?

I have a spare exhaust side rocker arm with bearing but the bearing has worn out with about 2mm of play in it so I doubt that would be any better.

It is also leaking oil still which might be the O ring at fault or it might be to do with the vibrations on the arm shaft...probably the latter.

I am gonna pull the rocker cover and see what is going on in there next week. The only thing I could think is maybe the valve clearances are slightly out of synch and that could be causing the vibes.
 
From reading a thread on advrider regarding the KTM 690

1. Worn bearing usually the exhaust rocker first as it has a bumpy ride with the decompressor pin on the exhaust cam lobe. Varying mileage. Just keep an eye on valve clearances, a large difference between clearances at service interval shows wear point is critical.
Click to expand...

Could this be why when I put my finger on the exhaust side rocker shaft it feels rougher than the intake side?

Still doesn't explain the noise from cold though. Once the engine has warmed up the noise dies down a lot.

I am gonna pull the cover tomorrow and check the shaft, but I am expecting it to be fine as it was last time.

Also I like to overfill the engine oil slightly to account for off roading and wheelies, could that be the cause of the oil leaks from the rocker arm shafts?
 
Okay, figured it out. It was cam chain slap. To begin with when I pulled the rocker cover I thought it was the rocker arm shaft because I found this mark on the inside of the rocker cover:

DSCF0261.JPG

Where I had welded the bearing in looked like it was rubbing slightly so I filed it down. At that point I thought my work was done.

But when I peered down the cam chain tunnel I say that the tensioner plunger was no where near the tensioner blade:

DSCF0269.JPG

I was wary of over tensioning the cam chain because on a certain stroke the cam chain seems to push against the tensioner and get taught.

After a quick Google I found that you should set the engine to top dead centre to tension the cam chain.

I was doing it on the other stroke where the chain was at it's tightest. I didn't want to ruin a new cam chain by over tensioning it.

As it rests the plunger is just up against the blade:

DSCF0271.JPG

The noise was the cam chain slapping against the tensioning blade at low revs, like when the engine is cold.

The cam chain still feels loose, it feels like I can almost lift it off the sprocket with my fingers but not quite.

I might tension it some more but I don't want to over tension it. Strangely the whole time it was loose I didn't get the valve lash sound that I got last time.

Maybe that sound was just the auto tensioner assembly rattling around rather than the cam chain itself.

And as for the exhaust side rocker arm even after sanding the weld spots down there still feels like there is a vibration going through it compared to the complete smoothness of the intake side.

Maybe it is due to the decompression mechanism like on the KTM 690s.

Anyway it's nice to have a normal sounding motor at start up now.
 

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I still haven't reached a conclusion on what the correct cam chain tension should be. When I pulled the rocker cover to fix the oil leak from the rocker arm bushing I had a look at the cam chain and even with my manual tensioner screwed all the way in there isn't a lot of pressure on the guide blade and I can still lift the cam chain slightly off the teeth on the cam sprocket.

There is still a clacking racket as well. I am going to order a longer bolt so that I can tension it more and see what happens.

I mean, this is what my engine has always sounded like, but I figure it has always had a loose cam chain!

This is what it looked like when I tensioned it:

DSCF0472.JPG
 
Still think this is normal Flynn. I would go softly softly on the tensioner especially as its working on a new chain. Expect a little stretching and subsequent noise increase in the interim.
 
Thanks for your input. I have ordered some 80mm m6 bolts to give me a little more adjustment but I'm not going to tension it much more at this point, just see if I can quieten it up by going a couple more turns and if not then leave it where it is as it seems happy.
 
I haven't been able to listen to your video.
My 630 has a rattle on start up, if you give the throttle a blip normally it will quieten, if you do nothing it will keep rattling or sometimes stop rattling in a short period of time.
What i was told is it is the auto decompression sticking on
 
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