Noise from engine

[Robert_F]

My engine which has run quite well since I've purchased the car has started making a loud noise.

It starts up fine/smoothly and accelerates "strongly" up to about 2200 RPM but then I start to hear a loud metalic ratteling/banging sound past the 2200rpm point. Best I can describe it, it sounds kind of like if you had a metal rod and ran alongside a metal fence letting the rod clatter in and out of the fence posts, loudly, sort of a machine gun like sound..... this is obviously very worrisome. Sometimes I can make it past 2500 rpm and  the sound subsides till about 3200rpm and then it starts again.

All the while the engine seems to have the power to move ahead if that description makes any sense.... and I feel like it is able to keep accelerating strongly but I back off the pedal because the sound makes me worry I'm doing damage, not to mention the fact it's alarming so I back off the pedal. The noise seems to be coming from the back part of the engine closest to the firewall but I'm not 100% sure.

Could this be the valves? or something worse? Is there any way I could check something to know more before taking it to a shop?

[jameshoward]

Robert,

Could be valve chatter from your description. A few things might help you confirm this. First, have you set your dwell and timings correctly. If you have, then check your valves (remove the rocker cover and follow a very straight forward sequence) and ensure they have the correct clearance using a feeler gauge. What oil do you use and how many miles on the engine since re/build. I am in Germany and switch to 20W-50 in the Summer to reduce valve chatter and beacuse I drive the car a lot for very long periods without a break (600 miles days on trips etc). To check what your valves are doing you could go to a bosch krypton tuner equipped or similar garage and get them to hook up their test kit to your car. A quick check should cost no more than $10 or so and they will be able to tell you how your engine is operating. If you do that before you check your valve clearances they should be able to tell you where you need to start looking for a problem.

Then again, it could be something wholly different. But I'd recommed you start there.

JH

[ja17]

Hello,

Does the engune make this sound when it is cold? What is the oil pressure when the engine is hot? Does it happen only under load or can you make it happen by reving the engine? Inspection under the valve cover is a good first check as James suggests. Possibly a rocker arm retainer spring has come off.

If nothing shows up try removing one spark plug wire at a time and then rev the engine.  You will isolate the problem to a specific cylinder. Hopefully the cause is not a connecting rod bearing.

[Robert_F]

Thanks Joe and James,

Yes it makes the noise when cold and even when it is not under a load. Oil pressuere is usually pegged at 45 when first starting out but now I have noticed that as the engine gets hot (sitting at idle) the oil pressure goes from 45 to 30 after a while, I thought that was odd, could it be the oil I use?

I will inspect under the valve cover and see what I find.

[jameshoward]

Robert,

It's normal I think for the engine pressure to drop from 45 when sitting at idle. When driving it should be at 45.

I only mentioned the oil because I changed mine to a 'thicker' (to use the correct scientific term) one because I was doing lots of miles in quite hot temps. It helped a little. Thicker oil only makes things quieter; it masks the valve chatter a little for me. It's a placebo. The reasons the valves (on my car) make a noise is because the engine is worn and there are problems...So the oil won't, I think, be at the root of your problem.

My only other tip is to listen to what Joe says and to do that!!

JH

[ja17]

Hello Robert,

It sounds like your oil pressure is pretty good, so I am hoping for an easy fix.

[Longtooth]

Another possible reason --- Check the operation of your vacuum at the distributor.  Vacuum retards the spark with increasing rpm (makes spark occur later in the compression stroke).  If vacuum line (to distributor) is broken or not attached somewhere, or leaking, then your spark isn't getting retarded (or retarded enough) so could be a detonation problem in all cylinders (most cylinders) at 2200 and above rpm.

Also, check whether your vacuum rod in the distributor is free to move easily or not.

By the way, "valve chatter" is term that has many possible interpretations.  It's a term that's often applied to or mistaken for detonation issues... i.e. "pinging".  

If the engine recently started making loud noises, how long ago (in miles or km) was the last valve adjustment done?  Last tune-up (dwell and timing adjusted)?

[jameshoward]

Longtooth,

I have the Bosch 051 distr, so it vacuum retards I think. Anyway, just how easy should the mechanism to be move, i.e. the rod that goes from the plate under the rotor arm into the vacuum pot? Mine is pretty hard to move, to the extent that I would be amazed if the little thin airline from the air inlet could ever build up sufficient vacuum to move the thing. Or could it?

Is there anyway of checking do you know? I wonder how much a new vacuum pot is. Think I'll check SLS.

Grateful for your experiences, even if just to tell me whether yours moves easily or not.

James

[wwheeler]

Checking the vacuum retard on the 051 is straight forward and I checked mine last night.

I have a hand vacuum pump with a gauge and I connected it directly to plastic tubing that goes to the vacuum diaphram. My diaphram (and the points plate) started to move @ 5 in hg. It also held the vacuum for a long time so I know that it does not have a leak.  Be careful not to put it under too much vacuum. I would say no more than 15 in hg to be safe.

Hope this helps!

[Robert_F]

Thank you all very much for your help and advice.

The plot now thickens. I was all set to start taking off my valve cover and then read some of the latest comments and I opened the hood and started looking around based on what you have noted and have discovered some interesting things.

In one photo you will see the wire from the condenser to the distributor is broken! I'm kind of surprised the engine starts at all with that situation but I must admit I'm obviously as far from an expert as you can get.

In the second photo I discovered there is no vacuum line at all connected to the distributor connector!, as well as the last photo where I discovered I apparently have another vacuum? hose missing from the housing leading to the air filter canister. I'm not sure what type hose I should use (one that fits right?)or where to connect the other ends to? does one hose connect these two together or are they unrelated? I guess I need to do some research and figure out what should be connecting where before I start pulling the valve cover off, at least I think? Sorry I'm so ignorant about all this.


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[Raymond]

Robert,
Don't apologize for not knowing stuff.  Those of us who have been doing this a while are constantly learning how much we don't know.  

The green wire comes from your condenser.  You need a new one obviously.  But look below to the little cap with the rotating cover.  That shouldn't be open.  You'll want to put some oil in there and rotate it so it's closed.

The vacuum line is available at most any auto parts store for sale by the foot.  

It's odd that this would happen suddenly.  Anyone you know of been messing around under the hood?  Where did your hose suddenly go and what cut the condenser line?

[Robert_F]

Hello Raymond and thanks,

This condition had to have been this way since I purchased the car several months ago, at least the missing hose part, I guess the wire could have come apart since then, I have not driven it much though since I purchased it. It is garaged and I am the only one who has had access to it and it has never been to a shop. I've never had to bother with anything before because it has run fine, maybe not perfect but certainly no major problems before this all started. All I've done prior to this was to change the oil.

So is it one hose that connects those two fittings ?

quote:Originally posted by Raymond

Robert,
Don't apologize for not knowing stuff.  Those of us who have been doing this a while are constantly learning how much we don't know.  

The green wire comes from your condenser.  You need a new one obviously.  But look below to the little cap with the rotating cover.  That shouldn't be open.  You'll want to put some oil in there and rotate it so it's closed.

The vacuum line is available at most any auto parts store for sale by the foot.  

It's odd that this would happen suddenly.  Anyone you know of been messing around under the hood?  Where did your hose suddenly go and what cut the condenser line?

[graphic66]

Yes, one hose. Connect the two together. I would pull the cap and check the vacuum solonoid and make sure it is all moving good. You can hook a vacuum pump to test it, or just suck on it to see if you can move it a little or see if  it leaks. Don't worry about that extra condenser too much. It is just for radio suppression. You might as well fix it though. It is not the condenser for your points.

[glennard]

Would not run it at all- until all the static checks are made.  Visual under the valve cover, wiring , hoses, valve adjustment, chain, chain guides, cam shaft, springs,- whole bit.  Running risks too much damage.  If everything is right, these engines purr! If it doesn't sound sweet, stop the beat.

[jameshoward]

Graphic66 and any others with working dissys,

Are you suggesting that the advance plate could be moved, albeit a little, by creating a vacuum by sucking on the pipe? If that's the case then mine is most definately buggered.

I don't suppose anyone has pulled the vacuum pot apart; is it possible?

Robert - when you purchase your vacuum line, it runs from the air intake, over the top of the engine, through the bracket that holds the fuel lines at the front of the block (you should see a little hole into which it threads) and then down to the vacuum pot. If that doesn't make sense let me know and I can take a photo, or look on the site for an engine bay shot.

Wallace - thanks. I don't have a vacuum pump, but I do have a vacuum gauge; perhaps I can rig that up to test it somehow. I will have a think.

Thanks.

James

[hands_aus]

Does the rotor spring back if you move it by hand?
If not, this indicates that the flyweights and springs need freeing up.
Maybe oil on the felt wick below the rotor and in the external oil port will help.

[tuultyme]

Robert
If you have a 70 280SL it is probably equiped with the US Exhaust Emissions setup.  The vacuum line from the intake manifold should run to a 2-way valve which is control by the Speed Relay.  Another vacuum line then runs from the 2-Way valve to the distributor.  A PO may have removed the vacuum lines because the Speed Relay may not be working properly.  I had my Speed Relay bebuilt by Beckman in NC.  Or the PO could have replaced the distributor which may change this setup.

[Robert_F]

Thanks Tuultyme,

I'm guessing the PO probably did remove the hose for that reason because the engine ran pretty well when I purchased it.

Where is the speed relay? what does it look like?

I'm going to put the hose and such back the way it should be but I may take the car to a knowledgable mechanic for the under the valve cover part, I'm thinking I'm only at the point right now where I know enough to do some damage and it may be time for a pro to touch it instead of me this time but I'm definitely learning a lot here! thank you all.

quote:Originally posted by tuultyme

Robert
If you have a 70 280SL it is probably equiped with the US Exhaust Emissions setup.  The vacuum line from the intake manifold should run to a 2-way valve which is control by the Speed Relay.  Another vacuum line then runs from the 2-Way valve to the distributor.  A PO may have removed the vacuum lines because the Speed Relay may not be working properly.  I had my Speed Relay bebuilt by Beckman in NC.  Or the PO could have replaced the distributor which may change this setup.

[tuultyme]

The Speed Relay is just left of the coil along with the 2-Way valve and two other relays.  This series of relays work with the 062 distributors.  Use the Search function and search "Speed Relay" and you will see posts showing the relay and it function.  If you do not find the information report back.