OK, guys, I need some help. As some of you might remember, I've been battling a light knocking/ringing sound in my engine. Appears to be coming from #1 cylinder. It sounds kind of like a big diesel does when it idles. It appears that I can minimize it by dropping the timing. The sound always occurs at about 1500 rpms, typically as the engine crosses through 1500 on it's way down. Right now I've got the timing set at about 33 or 34 degrees at 3000 rpms. The car DEFINATELY runs better at 38 or 40, but the knock is noticably worse (but still at 1500 rpms). At idle (1000 rpms) it's at about 10 degrees, right where it should be.

Just to refresh what I've done: Replaced the timing chain and tensioner. Had lower end of the engine inspected (pulled the oil pan - don't ask) and everything was like new. Last summer I replaced the centrifugal advance springs (one WAS broken), and I thought I had it licked. But it's still there, and not getting any better.

Any ideas anyone?? PS, my mechanic (who does the hard stuff I can't do...) says "just drive it".

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Bill Streep
San Antonio
'57 190SL (toy)
'08 S5500 (mine)
'09 CLK550 (wife's)
'06 SLK350 (daughter's)
'11 GLK350 (daughter's)
'03 CLK310 (spare)

Bill, you post the most interesting challenges for remote car repair. My first thought was gas and "engine knocking" but you ruled that out when you say it knocks going down in RPM. I think you have two noises. Distributor timing will only affect combustion and combustion noises; Decreasing RPM's mean no or minimal combustion so what you hear then is most likely not a combustion sound. The only sound from the cylinder would be a valve touching piston, which would happen at all RPM's. That leaves a harmonic vibration as the most likely culprit. This may not be too much help, but it's the best I can do from here. I would leave the timing where it runs the best.

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Jim Villers
190SL, 230SL 5-speed, 95 E320 Wagon, 01 E320 Wagon, MGB, Boxster 'S', 190SL "Barn Find"

Just to clarify this: If I HOLD the RPMs at 1500, I can generally get the knock to continue... But only at this RPM. If I accelerate THROUGHT 1500 RPMS, there is no knocking.

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Bill Streep
San Antonio
'57 190SL (toy)
'08 S5500 (mine)
'09 CLK550 (wife's)
'06 SLK350 (daughter's)
'11 GLK350 (daughter's)
'03 CLK310 (spare)

Bill, you are not making it any easier on us. A noise only at a specific RPM must be a vibration. The interesting fact is that it changes when the distributor is rotated. With your points conversion, there should be no metallic contact within the distributor at all. Try putting pressure on the distributor cap and see if the noise changes (rotor hitting cap). If you move the timing to 20 degrees advance, does the sound change again? If you hold the RPM's steady and rotate the distributor, the sound should change. Next I would very closely inspect the distributor and the advance mechanism, looking for places of metallic contact or anything that may not look correct. Did you retrieve both pieces of the broken spring? Probably just suggesting things that you have already done.

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Jim Villers
190SL, 230SL 5-speed, 95 E320 Wagon, 01 E320 Wagon, MGB, Boxster 'S', 190SL "Barn Find"

OK, here we go. Just got off the phone with my mechanic/friend. He owns a shop that works only on German cars (5 or 6 mechanics), and Randy still works on cars. I went thru all of the symptoms. He still swears it's chain noise. When he pulled the oil pan off a year ago, you could see where the chain was hitting the oil pan - in the casting there's a section that comes up right under the chain. He replaced the tensioner, I replaced the chain (the old chain had no stretch in it as it turns out). But still the noise.

Now, he says that the tensioner is supplied with oil from the oil pump, and he thinks that the supply port may be clogged or partially clogged. This would allow the chain to slap the oil pan upon decelleration, and at a specific RPM (where there's not enough pressure from the pump to keep it tensioned at that speed). In other words, at 1000 RPMs, there isn't enough force to make the chain slap, and at 2000 RPMs the pressure keeps the tensioner tight. Then I asked him about why retarding the timing would make a difference... If I advance the timing to say 38 degrees, the "window" of rattle is larger (like 1200 to 1500 RPMs). He said "I can see that". To make this long story short, he says "just drive it!" In order to unclog the port it would have to be steamed... Anybody have any more thoughts??

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Bill Streep
San Antonio
'57 190SL (toy)
'08 S5500 (mine)
'09 CLK550 (wife's)
'06 SLK350 (daughter's)
'11 GLK350 (daughter's)
'03 CLK310 (spare)

Mine did this several years ago and I just drove it. I left Virginia and I was somewhere in Maine when it finally stopped making noise.

Robby Ackerman

It sure doesn't sound like a distributor issue since you say the noise comes from the front of the engine and mostly as revs drop. If it were a knock it would most likely be under throttle and load. And if it were a distributor / timing issue wouldn't it be on all cyl's or more random?

Following up on the theory of plogged timing chain tensioner...how about trying some rislone oil treatment or marvel mystery oil to free up the 'arteries'?

Eric

I don't think that your mechanic's theory about restricted oil flow makes any sense. The chain tensioner has one-way valves that hold the highest pressure and cylinder extension. In the past you have mentioned your special tool to depress the tensioner, which verifies that the valves work and that the tensioner is tight even with zero oil pressure. As I said before, you come up with and interesting set of symptoms. How could turning the distributor affect chain slap? I could create some BS like the combustion impulses and the compression impulse creating a harmonic vibration in the chain. Maybe. If it is chain slap, we need to develop a theory of were and how the chain could slap. Where did your mechanic say that there was evidence of metallic contact? As I understand it, the engine has made this noise with two different chains and two different chain tensoniers; is that correct?

Still meandering in the world of possibilities …… just driving it could be a reasonable solution.

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Jim Villers
190SL, 230SL 5-speed, 95 E320 Wagon, 01 E320 Wagon, MGB, Boxster 'S', 190SL "Barn Find"

OK, here's what he said, probably not repeated very well, 'cause I don't know jack...: By retarding the timing, you "improve" the responsiveness at the top end at the expense of the bottom end,and vice versa. He says that how the cylinders detonate could cause there to be more slack or lack of tension in the chain at the lower rpms...

In any case, there IS evidence of chain hitting both the oil pan and valve cover (which I've since replaced), as the prior owner had the valve cover machined when the engine was rebuilt. The "new" valve cover shows no marks. When the oil pan was pulled, there's a section of the casting that comes right up under the chain that has a U shape to it that conforms to the shape of the timing chain as it passes. This was well beat up by the chain. He REALLY thought it was the tensioner. When he used his sophisticated super dude-dog mechanics microphone, the noise was coming from the lower end near the #1 cylinder. I listened to it as well. When he pulled the pan expecting to find a bearing or crank problem, it was "pristine" - perfectly new. And, there was evidence of the chain hitting the pan.

What I'll do tonight is pull the valve cover and the tensioner (oh joy! I LOVE to reinstall that tensioner) and see if there is an oil feed to it. I'm curious and I need to re-seat the valve cover gasket anyway as I've got a small leak. Any other ideas?

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Bill Streep
San Antonio
'57 190SL (toy)
'08 S5500 (mine)
'09 CLK550 (wife's)
'06 SLK350 (daughter's)
'11 GLK350 (daughter's)
'03 CLK310 (spare)

Bill … I have never heard of the chain rubbing the valve cover or the pan. Perhaps the previous owner also milled the pan to "improve the seal". If the noise comes from the bottom chain sprocket, there are few variables; the chain and tensioner, which you have already changed and the sprocket, chain guides and pan. Robby and I have a pan on the "spare" engine we bought off eBay last year and would be happy to measure the boss thickness for you or with Robby's concurrence, swap the pan with you. If the pan is the problem, you could fit a gasket for it, which would raise it a few thousands, which should be enough. I believe I have a pattern for the gasket if you are interested. Yes, I have also pulled the pan without pulling the engine.

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Jim Villers
190SL, 230SL 5-speed, 95 E320 Wagon, 01 E320 Wagon, MGB, Boxster 'S', 190SL "Barn Find"

Jim,

I went out to the garage at lunch, and I'm not sure HOW you would measure the boss/lip. I pulled the tensioner last night (what a bear to re-tension...) and there IS a lube port going to it. I'm not sure how it works, since it's just a hole that puts oil around the outside of the tensioner. There's only one small bleed hole in the tensioner, and it's on the TOP of the tensioner, the port's on the bottom. I don't see how it could possibly pressurize the tensioner. If, however, the bleed hole was on the bottom, that might make a little more sense?? I looked carefully at the tensioner, and I don't believe that there's a way to re-orient the hole on the bottom...

__________________
Bill Streep
San Antonio
'57 190SL (toy)
'08 S5500 (mine)
'09 CLK550 (wife's)
'06 SLK350 (daughter's)
'11 GLK350 (daughter's)
'03 CLK310 (spare)