W108 3.5 temp related drone
 

The car has recently started to make a droning sound from the vicinity of the front of the engine. It is about the same pitch as a large flying wasp (no wasp, I've checked), and gets louder and higher pitched as the revs build. The sound is there whether the car is in gear or not. It is not the same sound as low power steering fluid which is more of a groan and is related to the fluid levels and turning the steering wheel. As the engine warms the sound gets more and more faint until it disappears entirely. Before I start pulling belts off I was wondering whether anyone had any suggestions for the cause.
Finally, how do you loosen the belt enough to remove it?

Hi Alastair
check the aux air valve, may have a small restriction build up and its droning as it sucks air from cold and then as it closes off as the engine warms up the sound disappears :confused:

how is the megasquirt holding up?
cheers
barri

Check the power steering reservoir while the engine is idling .

Only two things I can think of that would be temp related, aside form the PS reservoir which is louder when low and cold, as in 25°F or colder, and may buzz or moan even when not moving the wheel and not low in very cold temps.

1) Timing chain. Like the tensioner is not building enough pressure. Or excessive stretch that goes away as it does.
2) Water pump failing, and as the thermostat opens and it's under less stress, it's able to "Relax".

I suppose it could be other things, but judging by how you describe the sound as a buzz/drone versus a scrape, I'm going to rule out blocked cam oiler tubes and other things, although you might want to check those just to make sure. It could be the aux air valve, but I would think that would make more of a whistle or whine versus a drone.

That's logical Barrie - it's also the only thing that I have tinkered with recently. This weekend I'll remove the aux air valve assembly and see.
As far as the MS is concerned, I removed it from the car and it is now in a box, complete with my handmade loom, TPS and all the other wires and connectors. It took about 3 hours to remove it and reinstall the old system. I reckon you could 'plug and play' it in a M116 or M117 in about the same amount of time.

I found that it worked really well in the car, but am considering another project for it. I tidied up the original loom and reinstalled it. The wide band AFR gauge makes interesting reading with the d-jet. As you'd expect it runs richer throughout the rev range.

Update - I removed all the aux air valve hoses and checked them for oddities and replaced them. No improvement.

After listening carefully and trying to locate the sound I'm now sure that it is coming from the rocker cover, radiator end of the right hand bank - that is US passenger side of the engine. This suggests that it might be a tensioner problem. The chain was replaced a few years ago when the heads were done. Is the tension adjustable? If so, how?

Nope, not adjustable. Either the tensioner is bad, or there may be a cracked rail. The tensioner may be rebuildable, since it has a large hex cap on it - but I've never tried and I don't know of anyone who has. Take it out and test it to see if it seems to put out a lot of pressure. If it feels weak, it may be time for a new one.

To test a tensioner (which I doubt would make any noise) you measure the length of the extended plunger . You measure from the mount face of the tensioner to the tip of the plunger.. you hold the tensioner so the mount face is vertical and the plunger is pointing upwards when you look at the tensioner from the side.

You measure on the lower side ,so that you are measuring the long side of the plunger.
The length should be 21mm . Any less and the tensioner is worn out . There is a spring in the plunger which pushes it out against the tensioner rail and it's length without a load it should be 78mm long.

Below the head on the front of the block is the oil filter. Check and see if that engine has a oil cooler. The lines to a oil cooler run from the fliter body through a sound damper, if the damper has failed you will strange noises from an engine ,particularly the sort that you describe.

Glad to see that someone else has a wideband AFR on a D-Jet!

I just love mine. I was not sure what you meant about running rich. I adjusted the load mixture using MPS so car runs at about 14-14.5 AFR when warm.

Using the ECU idle mixture control knob, I set it on rich side(12.8) and this along with idle rpm at 1000 in P or N seems to really help during hot starts. Previously I would see AFRs around 17/18 during hot starts .

Regarding your drone - I thought it might be something vacuum related too - like the check valve (or orifice) on the breather from the left side valve cover needing cleaning. Or maybe something to do with the small line that goes from distributor to the throttle via the small valve. Maybe line broken or leaking? But if just temperature related, it could be something to do with oil viscosity, so tensioner may be a candidate. Otherwise, maybe alternator bearing?

I once had a mystery noise (turned out to be starter just not fully disengaging) Checking with a stethoscope or listening tube didn't help because noise was "everywhere"! But in your case it may help.

Good Luck

Miy 3.5 is listed as a 300SEL W109 , Are there W108 3.5's too?
mak

lots of them!,I have had four myself. A really high performance sports saloon before the concept was thought of.

Funny how hard it is to place sounds with the human ear alone. I've checked the damper with a stethoscope and yes it is making loud buzzing sound, but the sound appears to be referred to higher up the front of the engine. The buzzing goes away as the oil heats up and the viscosity drops. So Mercmad6.3, I reckon you might be on the money with your diagnosis. I will replace the damper and report back. Thanks to everyone for help with this.
Mine runs at about that too. Down as low as 11.2 with WOT and occasionally as lean as 15.1 at cruise. However, with the MS and using tuning software I got the car to run well leaner throughout the rev range. I may have a go at adjusting the mixture with a spare MPS.

This problem persisted despite replacing the oil damper - in fact it was getting worse. The drone sounded angrier and lasted for longer. I started to think it might be something to do with excessive oil pressure, so today I drained the oil when it was hot and removed and blew through every oil line and oil gallery that I could access. Noticed in the old oil a wad of what looked like mattress ticking. Could this have been causing a partial block somewhere. Replaced the oil with a good quality Penrite, added a new filter, and the problem seems to have been solved. A total cold start will be the final test but there was no sound when I started it with cold oil in a warm engine. Fingers crossed.

I think I would have dropped the oil pan and had a look at the pump if something came out with the oil ..:eek: it sounds like an old rag left in the engine after a chain change or something because there is nothing in the engine which could have left something like that. if a oil filter collapses it sends bits of paper through the engine in small lumps.

Shavings from a failing chain guide?