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Mercedes 560SL: Lifters keep knocking


I have an '88 560SL that got a valve job 3 years/1,000 miles ago, give or take. Last year my engine began to tick. My mechanic replaced, at no charge, one of my lifters which solved stopped the noise. About 500 miles later he had to replace another lifter, then another, then another. We have now replaced four I believe. I joked “four more and we’re done.” But when he said “unless it starts to cycle all over again…” I decided to ask for your help. I’m moving out of town in a couple weeks so bringing it back, charge or no, is no longer an option.


I would suspect a problem with oil pressure, especially the oil pressure at the clearance adjusters. I am not sure on the 560SL but I know a lot of Mercedes have the adjusters at the tip of the rockers. They are easy to replace but you seem to be replacing a lot of them.

How many miles on this vehicle? Has the oil been changed according to schedule and is the oil of correct grade and type? Is the oiling to the valve train up to snuff?

I’m also curious how many miles? I’m assuming you have good oils pressure and are using the correct oil (weight and spec). Personally, I would probably just replace all the lifters and be done with it.

Sorry. The car has 135,000 miles on it, 120,000 when I did the valve job. After about 10,000 miles (two years) the first lifter began to tick. Since then my mechanic has replaced four different lifters (about every 700 miles), each had an obvious flat spot where it had been hitting whatever it is that a lifter hits when out of whack. The fifth lifter is now ticking. My mechanic only works on Mercedes, is always booked solid, and seems to be a very good and honest mechanic…then again, what do I know? Since he has never charged me to replace lifters and is clearly willing to stand behind his work I haven’t minded, but if this is going to start all over again once we replace the 8th lifter…
I just want to understand why this is happening and how to correct the problem once and for all. I’m not sure replacing the lifters is doing anything more than quieting the problem?

I’v done a little parts research online and it looks like the part my mechanic is replacing is the Rocker Arm; is that the same as a “lifter?” What might the rocker arm be hitting that would cause it to knock or tick and produce a flat, worn spot on its rounded surface very quickly? And what would cause the rocker arms to, one at a time, fall out of alignment, so to speak?
And, yes, oil weight, pressure, etc. is good.

Thanks, Guys!

No, a rocker arm is different from a lifter. This is the rocker arm for you car:

I don’t know why they are wearing, but I would suspect that something is not aligned correctly. At some point you may want to have another shop take a look.

Without seeing the rocker/lifter wear, I am assuming that the flat spot is worn in the surface that rides on the cam. Yes if this surface wears you will exceed the clearance adjusting ability of the hydraulic adjuster. Mercedes has a complex heat treatment process for the cam lobes and the rocker surfaces that usually wear well and give many maintenence free miles. Once the wear breaches the surface heat treatment, the wear progresses quickly. If there is wear in the bushing of the rocker, it is possible that pressure is being lost at this location on the way to the clearance adjuster. I am still assuming that the adjuster is in the rocker and rests against the valve stem.

When the shop did the valve job, were they meticulous about returning each rocker to the exact cam lobe it previously ran on. Mercedes is very particular about keeping the same rockers riding on the same lobes once they have bedded in. Was the cam changed during the valve job? Usually a new cam requires new lifters in this case it would be rocker arms. I gather that your mechanic has not found any problems with the cam lobes of the replaced rocker/lifter. I hate to suggest it but you might need to replace the cam and all the rocker/lifters to solve this problem.

You might give a few more particulars on the reason a valve job was done. 120K sounds a little early to regrind the valves and seats, replace burnt valves, and/or install new guides. If the valves and/or seats were ground, the clearance adjuster range has to be checked and reset for the new geometry. However, if this isn’t done you would be short of adjusting range to the tight side, i.e. possibly risk burning a valve, so that is probably not your cause of the valve noise.

Also, I believe this is a V8 so you will not be clear of the problem until you replace 16 rocker/lifters.

it sounds like you like this car alot to keep putting monet into it. I would just have engine rebulit and replace cam lifters rocker arms
timing chain oil pump. look and see if you can buy a complete rebulit engine at a parts store this better because the engine is done out side the car the block to cleaned well. and the engine will have a warrenty.

You do understand that a good rebuild for this engine costs in the $7-8000 range (not available at the “parts store”)?

Good Lord, why would you go to the expense of rebuilding the the bottom end when it’s not exhibiting any symptoms???

Make sure your mechanic installed factory OEM rockers and not after market. We’ve had a 560SEL in with top end clatter that was ultimately caused by the non-factory FEBI rockers. Additionally, the rockers need to go back into the same spot they were removed from. If they got switched around during the valve job they will talk back to you. Also, make sure the oiling tubes are not blocked or broken. I’ve seen after market oil additives with Teflon partially block the tubes causing oil starvation on the top end.

I think the top end of a 117 engine should go farther than 120k before needing attention, but that depends completely on the oil change intervals in it’s earlier life. If it was neglected when young, you pay for it at about 100k miles. On the subject of oil, use ONLY Mobile 1 15-50 in this engine. if you’re not using this exact oil now that may well be a source of at least some of the noise.

The bottom end of this engine is VERY stout and with proper maintenance will go well past 300k miles before needing any attention.


16 rockers, yikes! Yes, it is a V8.

My mechanic suggested the car has more miles on it than the odometer shows and shouldn’t have needed a valve job at 120K. It was about 8 years old and had 33K miles on it when I bought it from a salesman who worked at the dealership it was traded in to; I did not buy it thru the dealership, he was selling privately. I suppose he could have rolled back the milage, is there a way to tell…15 years later?

The valve job was because the car was smoking, burning oil and leaking oil; since the valve job there is no evidence of continued oil leakage or burning. When the first rocker was replaced, he blamed the machine shop he sent the engine part(s) to. I have no idea how careful they/he was about replacing the rockers to their original positions, but for the first several thousand miles the car ran perfectly, no issues at all. Now it’s cycling thru one rocker ever 500-700 miles? Once the noisy rocker is replaced, the car is perfect again for about 500 miles, then it starts over, with a different rocker ticking. The noise starts our very quiet, within 200 miles or so it is very loud at which time I take the car in. Again. And again.

As far as replacing the cam and all the lifters, I’m willing to do whatever necessary (within economic reason) to correct this. You think if I don’t, the car will continue to cycle thru rockers? Until all 16 have been replaced or will it just keep cycling thru rockers indefinitely if the camshaft is not replaced as well?

I have to take it in in the next couple days for the 5th rocker to be replaced, anything specific I should say or ask that might get him to step up and finally fix the problem, not just address the symptom?

I guess I should bite the expensive bullet and take it to the dealer to have them check it out…

Thanks for all the input! It’s really helping me to begin to understand what might be going on with my poor, old car. At the very least, you have convinced me my mechanic should know more about this “mystery” than he says, which makes me fear he fears a big re-fix???

I’m taking it in again next week, I’ll keep you posted.
Thanks Guys!!!