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Discussion Starter #1
Hi , friend has 89 sl v8. he bought it a few years ago, ran well. sat in his garage for last 3 years. he took it out to move it and drove around 50 miles. knocking from rear of engine around no 8 cylinder. he cant remember if it was like that the last time it was out driving, as mostly its just sat in his garage.at first i thought it was just a hydraulic tappet that has gummed up from lying there. checked it and it wasn't. he drove it again and thought the power was poor, by accident rather than by design i pulled off no 8 plug leed and 2 thing happened, the knocking stopped and the power went up. so the current suspect is timing, if the no 8 cylinder is firing too early its working against the engine rotation rather than with it, causing the knock and the power reduction. iv read "How to Set R107 Ignition Timing" by okyoureabeast.
the only problem is why is just one cylinder knocking even if the timings out , not all of them? or is it the case that they are all out by the same tiny amount and and no 8 has some wear in the big ends or piston rings or cylinder that allows it lag a few degrees behind the rest of the engine. I'm going to slightly retard and advance the distributor and see if it improves which would support the timing, and if not effective, will do a compression test to see whats the state of play across the cylinders.
 

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1986 560SL: '84 500SL: '84 280SL 5 speed: other 107s
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Beasts procedure does not apply to '86-'89 models. The timing is set electronically. From your your location I gues you are working on a 420SL?
 

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Head gasket failure between cylinders will also create knocking. A cylinder leak down would rule that out. On a simpler note try removing #8 plug wire from the loom to rule out arc over from another cylinder and pull the spark plug and inspect.
 

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1983 380 SL
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There is a world of difference between a knock and a tap. Knocks are solid and deep in tone and appear to be coming from deep within the engine, they are caused by rods, pistons and bearings (not to be confused with piston skirt slap). Taps are much lighter and usually sound like something on the top of the engine. A tap is usually rockers (tappet noise) or sometimes can be caused by an exhaust leak. Which is it... a knock or a tap? Having said that, in my 380 a blown piston made a sound exactly like a tappet sound. Go figure.

Engines don't run better with one plug wire removed under any circumstances and the timing in your case (ignition that is) is not adjustable. The only other timing is physical and is set by gears and chains so if one cylinder is out... then they're all out... well, on one side anyway.

You have described a perplexing problem. Is there any way you can post a video with sound so we can hear it?
 

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Discussion Starter #5
Beasts procedure does not apply to '86-'89 models. The timing is set electronically. From your your location I gues you are working on a 420SL?
Hi , i was a bit tired when i wrote,
its 79 not 89
thanks
 

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Discussion Starter #6
Head gasket failure between cylinders will also create knocking. A cylinder leak down would rule that out. On a simpler note try removing #8 plug wire from the loom to rule out arc over from another cylinder and pull the spark plug and inspect.
Hi ,
Yes I was going to do the easy version of just taking off the black heavy duty rubber style mat wrap that shrouds/ protects the leeds as they exit the distributor and before the get separated into the leed retainers on top of the cam cover individual lees cross
 

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Discussion Starter #7
There is a world of difference between a knock and a tap. Knocks are solid and deep in tone and appear to be coming from deep within the engine, they are caused by rods, pistons and bearings (not to be confused with piston skirt slap). Taps are much lighter and usually sound like something on the top of the engine. A tap is usually rockers (tappet noise) or sometimes can be caused by an exhaust leak. Which is it... a knock or a tap? Having said that, in my 380 a blown piston made a sound exactly like a tappet sound. Go figure.

Engines don't run better with one plug wire removed under any circumstances and the timing in your case (ignition that is) is not adjustable. The only other timing is physical and is set by gears and chains so if one cylinder is out... then they're all out... well, on one side anyway.

You have described a perplexing problem. Is there any way you can post a video with sound so we can hear it?
Hi,
should have mentioned to all that the leeds are correctly sequenced, confirmed by the distributor cap numbering, and the firing order marked on the cam cover . and the engine running better with the leed removed could well be an arc across the leeds, should also have said my friend took it to an engine rebuilder, who may not be a mechanic in the convention sense , he said the sound to his ear was big end, rings or cylinder wear , maybe due to oil starvation at some point in its life and being at the rear of the engine it was more susceptible to oil starvation, but that's a slow process and does not tie in with the car simply sitting in a garage undriven and being ok to the best of friend knowledge/ ear back then .
 

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Hi ,
Yes I was going to do the easy version of just taking off the black heavy duty rubber style mat wrap that shrouds/ protects the leeds as they exit the distributor and before the get separated into the leed retainers on top of the cam cover individual lees cross
Thanks,
I image that the head gasket/ cylinder to cylinder leak wouldn't generate enough crossing over of gasses to generate a very obvious drop in power by and create a substantial knocking?
 

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1983 380 SL
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Hi,
should have mentioned to all that the leeds are correctly sequenced, confirmed by the distributor cap numbering, and the firing order marked on the cam cover . and the engine running better with the leed removed could well be an arc across the leeds, should also have said my friend took it to an engine rebuilder, who may not be a mechanic in the convention sense , he said the sound to his ear was big end, rings or cylinder wear , maybe due to oil starvation at some point in its life and being at the rear of the engine it was more susceptible to oil starvation, but that's a slow process and does not tie in with the car simply sitting in a garage undriven and being ok to the best of friend knowledge/ ear back then .
I'm not sure I agree with the rear of the engine (Vintage Mercedes anyway) being more susceptible to oil starvation. The oil passages that feed the heads are in the rear. The end (rear) cap that holds the rear crank seal also contains the oil supply passages to the heads. I suppose it isn't impossible for the rear to be more susceptible to oil starvation ... just not very likely.

Can you post a video so we can hear it?
 

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1983 380 SL
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I had knocking from the rear of my old 350 engine, it was due to oil starvation to the rear of the cam shaft.
That's odd because the oil comes up through the cam towers and then is channeled through the oiler tubes which drops a steady stream of oil on the cam lobes. The oil then returns to the oil pan via gravity. In other words... the oil takes a parallel path through the cam towers before getting to the oiler tubes. The oiler tubes serve no role in lubricating the cam towers, only the cam lobes.

The oiler tubes get their oil from the cam towers, not the other way around. If one or more of the cam tower oil passages were themselves clogged, then no oil would get to that particular cam tower bearing but the oil tube would still receive oil from the remaining unclogged cam towers and the cam lobes would still receive lubrication. In that way a cam tower could wear out and produce a knock even though the cam lobes remain unharmed.

Other than that... I see no relationship between the front or rear of the engine being more or less susceptible to top end oil starvation in one of these classic Mercedes V8's.

Yes/No?
 

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The lobes were still in reasonable condition, the rear bearing tower was trashed with about 0.5mm of clearance to the CAM. Damage was reduced coming towards the front. I'll post up a pic later.
 

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The lobes were still in reasonable condition, the rear bearing tower was trashed with about 0.5mm of clearance to the CAM. Damage was reduced coming towards the front. I'll post up a pic later.
And to what can we attribute the rear to front diminishing damage? Is it not likely that the damaged rear tower is what contributed to the damage of the cam towers going forward? And if so would we not need to determine what caused the initial damage to the rear tower? If we determine that it was oil starvation, then what aspect of the design would make the rear tower more susceptible to oil starvation?

Perhaps it's the fact that the rear tower is the last tower in the line and therefore the only tower that doesn't have additional support aft of it's own position?
The #1 and #5 towers have support aft in the form of the #2 and #6 towers and support forward in the form of the timing chain tension and the additional mass of the cam sprockets. In like manner, the #2, and #3 have support forward and aft as do the #6 and #7. The only cam towers without dual support are #4 and #8... the rear most towers.

Hmm. We may be on to something.
 

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update. I have done a compression test. all 4 on no 5 6 7 8 all show 150psi with the same duration of cranking the engine. so does not seem to be any leakage or head gasket leakage between no 7 and 8, although it’s not a leak down test. checked all the leads for chafing or possible arcing, separated them , they are all fine. I tried to rotate the distributer anticlockwise which I think should advance the timing. the engine went from approx. 1200rmp cold idle to approx. 1400 cold idle. drove the car , the power was up. disconnected no 8 and the power was down unlike the original test done on first post. so heading in the right direction, but haven’t made inroads to the knocking yet. it could be a big end on no 8 that bangs on power stroke , but with the lead disconnect its just a passenger being towed along by the crank shaft instead of slamming into the shaft/ taking up the play in the bearing when its firing power combustion stroke , which could have happed at some point due to starvation, blockage etc.. getting back to the timing, the distributor has maxed out its adjustment in the long slot that the pinch/clamp bolt sits into, I imagine in the factory it would have been in the centre of this groove, slot. so I think at some point some has removed the distributor and probably refitted it into the engine, 1 gear tooth wrong. so I plan to remove it and see if 1 tooth can allow it to adjust the timing / advance correctly and hopefully increase the power, maybe not fix the knock , but at least there is some positive outcome from all the hours and investigations.
 

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I had assumed the towers were fed by the oiler tubes and the rear had been starved due to the tube clips being broken and the tube coming lose, someone had tried to RTV it in place.

This is the rear most lobe, perfect condition.

2651949


Every clip glued in place.

2651950


Cam pushed and pulled, you can see the gap in the pic on the right.

2651963


The CAM journal surface.

2651962



The bore of the tower.

2651959


Anyway, not too sure if this will help the OP?
 

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1983 380 SL
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update. I have done a compression test. all 4 on no 5 6 7 8 all show 150psi with the same duration of cranking the engine. so does not seem to be any leakage or head gasket leakage between no 7 and 8, although it’s not a leak down test. checked all the leads for chafing or possible arcing, separated them , they are all fine. I tried to rotate the distributer anticlockwise which I think should advance the timing. the engine went from approx. 1200rmp cold idle to approx. 1400 cold idle. drove the car , the power was up. disconnected no 8 and the power was down unlike the original test done on first post. so heading in the right direction, but haven’t made inroads to the knocking yet. it could be a big end on no 8 that bangs on power stroke , but with the lead disconnect its just a passenger being towed along by the crank shaft instead of slamming into the shaft/ taking up the play in the bearing when its firing power combustion stroke , which could have happed at some point due to starvation, blockage etc.. getting back to the timing, the distributor has maxed out its adjustment in the long slot that the pinch/clamp bolt sits into, I imagine in the factory it would have been in the centre of this groove, slot. so I think at some point some has removed the distributor and probably refitted it into the engine, 1 gear tooth wrong. so I plan to remove it and see if 1 tooth can allow it to adjust the timing / advance correctly and hopefully increase the power, maybe not fix the knock , but at least there is some positive outcome from all the hours and investigations.
If you've got a rod knock it should be most noticeable when you first start the engine. For the first second or so, while the oil pressure is coming up, a rod knock will be quite pronounced but quickly fade to almost silent as soon as the oil pressure hits the rod journal. Is that the case with your engine?

Also, rod knocks are generally at a lower frequency than main bearing knocks. Try to get a sense of the knock frequency and keep in mind that if it's a rod that's only knocking on the power stroke then the knock frequency should be just about 1/4 of the rpm. I should say at this point that I don't have much faith in the rod is knocking on the power stroke theory but I can't completely rule it out either.

You might want to send a sample of your oil out for analysis, if there is bearing wear than there will be evidence in the oil. If the oil analysis comes back clean (no metal in the oil) then you should be able to rule out a bad bearing.

Are you sure the exhaust pipe isn't hitting the chassis some where?

Now I'm just throwing out guesses. Can I assume you can't make a video (w/sound) and post it here?
 

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1983 380 SL
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I had assumed the towers were fed by the oiler tubes and the rear had been starved due to the tube clips being broken and the tube coming lose, someone had tried to RTV it in place.
A common misconception and one that is perfectly reasonable until you realize there is no way for oil to get to the oil tubes other than through the cam towers themselves.

A first glance this may appear to be off topic but if the OP's problem is actually worn cam towers, which may very well be the case, then it's right on topic. I seem to remeber another member posting a while back about a worn cam tower causing a knocking sound.
 

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Connecting rod knock has a double knock when the piston changes rotation. Not sure about the power reduction while it’s connected which led me to a cross firing situation. Main bearing is a single knock per rotation. Rod knock will get quieter when the plug wire is pulled. More so than a main knock. With a warm engine if you remove the wire and blip the throttle you will hear the knock if the bearing is toast.
I would also spray water around the intake manifold at number 8 to see if there is a vacuum leak back there. You can also use flammable brake clean as well.
 
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