Hi, I am a new member of this forum. I have just purchased a 1987 560SL with 94k well documented miles on it. The timing chain, rail, tensioner, and tensioner rail were replaced at 85k miles, about 2 years ago. I bought the vehicle knowing that it has a mechanical problem. It runs very rough & has a fairly loud tapping sound. The seller chose not to have the vehicle repaired.

I did a compression check and cylinder #4 has a very black, apparently fouled spark plug, and the compression seems low. All other cylinders check out OK & spark plugs look OK.

Any recommendations on how I should proceed ? Could this be a bad rocker, or, perhaps a worn cam lobe ?

thanks in advance for your help/suggestions !

Brian

Bad rockers/worn cam lobes won't give you poor compression. A bent valve however will.

I'd remove the valve cover to see if the valve is closing fully.


Jonathan

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Hi Johnathon,

Thanks for the reply. When I said that the compression "seems low", that may have been an incorrect statement. When I tested the compression, I the max value it went up to was the same as the other cylinders, however, my wife said (she was my assistant) that the needle on the guage was bouncing up and down quite a bit.... a lot more than with the other cylinders.....when I attempted to remove it, the hose spun around and the bolt at the end did not....I ended up having to remove the guage using a long pair of needle nose pliers. I then recrimped the hose after that test, which was the first test. I am thinking that I need to retest that one as, possibly, the guage was giving a bad reading because of the loose hose.

The spark plug did look bad though, it had a bunch of black deposits on it while the others looked clean.

Assuming that the valve is not bent (I will verify this at my next opportunity) what would a spark plug look like for a cylinder with a bad cam lobe or rocker ?

Thanks,

Brian

I would replace the plug on principle. The miss may be caused by a badly fouled plug, or a bad plug wire or possibly a cam or rocker worn so badly that the valve is not opening, or all of the above.

The best way to test this IMO is to attach a inductive timing light to the wire, start the engine, and see if it flashes. I would est all the cylinders this way.

As noted, the noise could be a bad ball stud, or worn cam lobe/rocker arm. Use a 2 foot piece of hose or an engine stethescope to see if you can isolate it to a cylinder, then pull the cam cover on that side and have a look at the valve gear. Do a search on "ball stud" and you will find a lot of information on how to check them.

__________________
Chuck Taylor
Falls Church VA
'66 200, '66 230SL, '96 SL500. Sold: '81 380SL, '86 300E, '72 250C, '95 C220, 3 '84 280SL's '90 420SEL, '72 280SE, '73 280C, '78 280SE, '70 280SL, '77 450SL, '85 380SL, '87 560SL, '85 380SL, '72 350SL, '96 S500 Coupe

What is a "Valve Gear"??

John

It's not a physical gear.

I used the term as a quick way to refer to the cam lobes, rocker arms, and ball studs - everything that gets touched to open the valves and allow them to close.

__________________
Chuck Taylor
Falls Church VA
'66 200, '66 230SL, '96 SL500. Sold: '81 380SL, '86 300E, '72 250C, '95 C220, 3 '84 280SL's '90 420SEL, '72 280SE, '73 280C, '78 280SE, '70 280SL, '77 450SL, '85 380SL, '87 560SL, '85 380SL, '72 350SL, '96 S500 Coupe

Thanks Chuck:

Was not trying to be a smart-- but I thought I was missing something!

I was use to the term "valve train"!!

John

Hi,

I have removed the passenger side valve cover, which is the side where the #4 spark plug appears to be carbon fouled.....I can't seem to find anything that looks bad, although the #4 ball studs appear slightly lower than those of the other cylinders.....can someone give me an exact link or thread that describes how to determine if a ball stud is bad ?

I also checked the timing chain using the procedure outlined in "http://www.peachparts.com/Wikka/M117TimingChain". I tried to line up the cam marks as good as possible....it was at approx. 2-3 degrees to the right of zero. One thing I noticed, when turning the crank shaft, sometimes the cam/timing chain didn't move right away as I turned the crankshaft....is this normal ? It was as if there was slop in the chain or something. I also noticed that depending on where I rotated the camshaft, sometimes I could lift the chain up & it appeared loose & other times it appeared tight....just wondering if this is all normal.

Thanks,

Brian

Compression seem low, how about giving us the numbers for all 8 cylinders.

The ball stud is a hydraulic lifter it could be collapsed. Put the engine on TDC for that cylinder use distributor as a ref. Then see if there is slop in that lifter, if there is it's bad. If not press down on the lifter with the end of a hammer handle. If you can get the lifter to bleed down over a minute or two its bad.

Chain dident move right away that's OK.

Rails and chain that were replaced do you have a list of the parts. Alot of people forget about the tension rail.

John Roncallo

I will recheck the compression on all 8 cylinders.....can it be done with the valve covers off ? I am wondering if it will splatter a bunch of oil ?

Also, what do you mean by "bleed down" over a minute or 2 ?

Thanks,

Brian

Bleed down means the ball stud will collaps, usually slowly by leaking oil out too fast.

John Roncallo

I have rechecked the compression, this time using the prescribed manner, with all sparkplugs removed, and with the throttle wide open. All eight cylinders are in the following range: 169-175 psi, most of them are closer to 175. Can someone give me a reference/link where I can find the correct compression specs for a 1987 560SL ?

Also, I noticed on a couple of the spark plugs what appears to be some fouling, perhaps due to oil. I am guessing that I will need to replace the valve seals as this is now a 21+ year old vehicle.

Is there someone out there, from whom I can rent the necessary tools to compress the valve springs ? Also, are there any other special tools I will need to do the job (valve seal replacement) ?

BTW, the cam lobes all appear to be shiny, with only minor scratches/abrasions. I can't seem to find anything wrong with any of the rockers/ball studs either.

Question, when I do the valve seal replacements, is there anything special I can do to make sure all of the rockers/ball studs are within tolerance & functioning propoerly ?

Thanks in advance,

Brian

My 88 is running 160 to 165 and it runs beautiful.

You said one ball stud seamed low. Did you check this with the cam lobe on a low spot, as to not be compressing the valve. This should not be visually preceptable. I use a universal KD overhead cam valve spring compressor which was about $20.00, 30 years ago. I don,t know if they still make these.

John Roncallo

I think I was mistaken about the ball stud......everything seems to be OK there....I tried to get a very thin feeler guage between the rocker and the cam lobe & was unable to in any position.

I am more concerned now about the timing chain....as I mentioned the chain, tensioner, & all guides/rails were replaced < 10k miles/2 years ago. I do notice, however, a large amount of play in the chain, when I manually rotate the engine to certain positions. (i mentioned this in another thread as well). I am just wondering if that is simply due to the lack of oil pressure or should the tensioner spring provide a reasonable amount of tension even with no oil pressure ?

(under certain circumstances, I can move/flop the chain up and down probably about an inch or more) I just don't know if this is normal...can't seem to find any info on this in any other thread, or in my mercedes manuals.

Thanks,

Brian

Not normal. The tensioner has a check valve to keep the chain tight. I would replace it before starting the car again. With the new piece installed, pull the green wire out of the ignition unit and crank the engine until you get oil pressure. Then plug it back in and start the car.

This is a common failure. Tensioner bleeds down while sitting, engine starts before it's pressurized, chain jumps.

In fact, this may already have happened. Can you check the cam marks against the timing marks, since you have the covers off?

__________________
Chuck Taylor
Falls Church VA
'66 200, '66 230SL, '96 SL500. Sold: '81 380SL, '86 300E, '72 250C, '95 C220, 3 '84 280SL's '90 420SEL, '72 280SE, '73 280C, '78 280SE, '70 280SL, '77 450SL, '85 380SL, '87 560SL, '85 380SL, '72 350SL, '96 S500 Coupe