Cam Chain Noise

[jkdmag]

Interested in experts opinions as to likely source of engine noise that only occurs between gear changes.

My suspicion is that it is cam chain/tensioner noise when the load comes off the engine. It is a thrashing sound that is not noticeable during normal steady state running.

The ALDL data stream also indicates that the ecu is initiating detonation retard at the same time and there are occasions during cruise condition when retard is generated.

There is no audible or ALDL data indication of detonation under any other operating condition.

Could cam chain noise be responsible for a false detonation trigger or maybe the timing shift from poor cam control causes real detonation.

 

[moon161]

Is the chain stretched?
Is there slack or wear on the sprocket?
Can you examine the tensioner?

 

[04v8s4]

This is probably a difficult problem to diagnose without inspecting the timing components. Can you pull the cam cover(s) and see the cam gears or tensioners?

What engine are you referring to? How many miles?

It's unlikely that the timing chain is stretched. How are the cam gears fastened to the cams? Look for wear in that area if possible.

 

[Tmoose]

Is the tensioner mechanical? In the days of tensioner-less V8s turning the crank back and forth slightly while observing the motion/non-motion of cam-driven distributor rotor was a gage of cam chain condition.

The butt dyno said that a rattling exhaust heat shield had a significant negative affect on the power of an old Volvo 245.
I figured it was probably spooking the knock sensor.

 

[BigClive]

I don't think there would be any noticeable difference in load on the cam or cam chain when the load came off the engine - the cam load being pretty much constant. The noise is possibly more likely to be associated with the clutch or gearbox.

 

[patprimmer]

Clive.

Are you sure there is no inertia in the cam and cam gear.

While drag at the bearings and cyclic loads in both directions have their influence, so does centrifugal force. Bottom line is they all add up to less tension and thereforemore balooning out of the chain as you lift off. It this balooning out is enough to hit something you will get a rattle and a grove worn where it hits and resultant debris.

Regards
Pat
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[MikeHalloran]

I vote for checking the tensioner.
... AFTER checking the motor mounts.



Mike Halloran
Pembroke Pines, FL, USA

 

[patprimmer]

I agree with Mike and also checking crank pulley bolt and clutch and flywheel or converter bolts. Heck I have even seen exhaust baffles rattle on over run.

Regards
Pat
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[jkdmag]

Optimistically, was hoping to have high level of confidence that cam chain was the problem before having to delve into the motor. Lot of work to get to the chain and find it is not the problem.

Unknown mileage on the chain but believe it to be in excess of 70,000km. It is a V6 Buick engine with spring loaded tensioner and balance shaft. Had considered balance shaft bearings a possible cause but the noise only appears during the off load period as the auto changes up a gear, I would expect balance shaft bearing noise to be always present.

Also, as I said the ALDL data says that something strange is happening during gear changes and when light load cruising. High rpm, hard changes are worse. Low rpm, soft changes give no noise and no knock retard data.

 

[moon161]

Rev it and listen at various points using a mechanic's stethoscope.

 

[BrianGar]

Are you sure its just a spring tensioning it?

In some cases, a spring is used for initial tension, on starting oil pressure takes up the the correct tension via an internal piston/rod inside spring. Drilling can be small, and exit block directly behind tensioner mount. A small hole, say .5mm is sometimes bored into the nylon chain shoes allowing some of this pressurized oil to escape from chamber, oiling shoes, and chain.

If it was done this way, (look close) then rattle at idle would make sense, since your oil pressure and delivery is most demanded of at idle, with hot bearings when your pumped volume will be at its lowest. This is why an oil light on an old engine can sometimes flicker at tickover, but be fine up the revs, the engine lasting perfectly fine for a long time after.

If you are >sure< it is just a mechanical tensioner, then it is probably an ancillary as mentioned.

Brian,

 

[BigClive]

JKDM - I am assuming that your Buick V6 is the same (or very similar) engine to that used in the Oz Holden Commodore V6.
The early models of the Comm. engine were famous (or infamous) for their odd, annoying rattly/vibrationy noises from the engine. It was often suspected to be in the cam or cam chain area but changing these parts invariably didn't help. I heard of a few people who had their engines rebuilt only to discover that the odd noises were still present. The later model V6's were better - I did read somewhere that Holden finally tracked the noise down to some resonance problem in the exhaust manifolds - but I don't think that even Holden ever really knew what was causing the noise.

 

[jkdmag]

BigClive, it is the first of the oz holden V6s and yes they are not the quietest of engines. However this particular noise appears to be associated with knock retard by the ecu that I get during auto up changes.

The knock retard issue has probably highlighted the noise and I would ignore it if I can disassociate it from the knock retard problem.

When cruising there are no noticeable engine noises, an advantage of a tall 4th gear ratio and lock-up converter, but I get periods of knock retard for no obvious reason. The only loose correlation of cause and effect I can find is that cruise knock retard generally occurs at around 1700 rpm. I have altered the ecu timing map by retarding the ignition around this rpm without any improvement.

 

[dicer]

If running the engine and throttling up and backing off with the car sitting and hood up and a stethoscope in your ears, and you can hear what you hear driving down the road then you found it.

The chain that can make noise also is the transaxle drive chain. I think that has one.

 

[1gibson]

If it is similar to a "series 2" 3.8 V6, the tensioner will wear and the chain can stretch, especially if using heavier valve springs or higher ration rockers. Usually not with stock valvesprings, although tensioner will wear eventually.

Is the transmission in close proximity to the knock sensor? Known fix on the front wheel drive variant is to install "dynamat" or other acoustic insulation in that area to prevent transmission noise from getting to the knock sensor.

High load / low engine speed situations will cause real knock, adjust your torque converter clutch settings to allow earlier downshift. Do you also get surging/hunting (torque converter lock/unlock) as you go up an incline in 4th?

Finally, if you can somehow verify that the knock is false, increase the low RPM knock threshold to 1800 rpm. Or adjust the attack rate, or adjust the sensitivity. I'm assuming it is OBD2 (95 or newer) and you can access those parameters. If not, there may be different / equivalent settiongs. If not, look for a slightly less sensitive replacement knock sensor. All this, only if you verify it is false!

 

[evelrod]

Ahhhh, the 'timing chain noise'...
Well it bit me last race. Sounded like some little 'whirring' thing caught in a blender. Engine ran fine, no indications of a problem......until the little 1/4" cap screw that had come loose and was rubbing the back of the timing chain finally broke and poked a small hole in the timing chain cover. THEN we could see a problem, oil shot all over the fan and blown through the radiator onto the LF tire.

I guess what I mean is, don't let that noise alone until you isolate it and confirm that it is not a problem that can come back and bite you like it bit my Mini Cooper!

Rod

 

[Pancholin]

I would disagree with BigClive - I think it would take considerably more effort to open the exhaust valve throttle open than throttle closed.