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  #1  
Old 01-05-2003, 01:38 PM
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replacing lifters / cam followers

I've just had all the cam followers ('lifters' to you in the US?), timing chain, chain guides, chain tensioner, and rockers replaced but even after 700 miles there is a very diesel-like solid knocking noise on starting from cold that only disappears if I hold the revs at 2000rpm for 20-30 secs. Once warm the engine is totally quiet. Mechanic says the noise is the cam followers and some of the new cam followers must be faulty. Is this likely? Is there some trick to fitting Mercedes cam followers that my mechanic might not know? He says he soaked them in oil for 30 mins to 'prime' them. How do I tell the difference between cam follower noise and chain noise? Oh yes - it's a 1989 W126 (500SEL) with 117 engine. Hope someone can help!
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  #2  
Old 01-05-2003, 03:18 PM
ILUVMILS's Avatar
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Hi Chris, find out if your mechanic checked the "basic position" of the new lifters. This is required when rockers and lifters are replaced. A special guage is required to measure the height of the ball which the rocker arm fits over. If found to be out of spec, shims are available in various sizes to correct this. The shim is between the valve side of the rocker and the spring retainer. This is standard operating procedure when performing extensive top-end repair. Good luck and let me know how it goes.
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  #3  
Old 01-06-2003, 07:38 AM
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Really grateful for such a prompt reply. Posted this query first on the MBZ forum I usually use and still nothing! My mechanic had never heard of checking the original position of hydraulic cam followers. Asked him if he found any shims when removing the old rockers and he said no shims, only what he calls 'slippers' - could these actually be shims? In which case could he have created another problem by re-inserting these where they weren't actually required with the new components? Thanks again.
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  #4  
Old 01-06-2003, 12:14 PM
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Have also heard the term "pucks" in reference to the shims. They come in something like four standard thicknesses.
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'73 280SEL 4.5 (9/72)- RIP
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  #5  
Old 01-06-2003, 02:22 PM
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There are no "lifters" in this engine. The cam acts on the rocker arm. which rests on a ball stud on the outboard side of the head. The ball stud contains a hydraulic mechanism which holds the rocker against the cam lobe thus keeping it quiet. These are called "hydraulic lash compensators (HLC's)."

It is not clear from your post if these were replaced.

I just did a cam and ball stud replacement in my 380SL, and it is very important that the pre-load adjustment to the ball studs be done if any of the components are changed. This is basic stuff and you should find a mechanic familiar with this process.

If the engine is quiet when warm, the adjustment is probably OK or close to it. However, it does sound like you have a defective HLC that is losing its hydraulic pressure ("leaking down') when the car sits. Your mechanic may be able to identify it by allowing the car to sit and then checking each rocker arm for looseness by rotating the cam.

I did a post on this that included Herr Fuch's "finger test" for finding bad HLC's.
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'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
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  #6  
Old 01-06-2003, 05:44 PM
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Chuck

Trouble with cross-Atlantic terminology! The items I described as 'cam followers' are certainly what you describe as 'HLC's' and all 16 were changed along with all the rockers. The reason for the repair was to cure a 'ticking' noise when warm that my mechanic had diagnosed as a worn cam follower / HLC. Once rebuilt, the engine has not just a 'tick' but a good solid noise just like a diesel when cold but is totally silent now when warm. I showed the mechanic the reply from ILUVMILS and he admitted that he hadn't known to check the 'basic position' so I hope this will turn out to be the solution but if so I'm a little confused as to why the noise disappears when the engine warms up? It does behave just as though oil is draining out of one or more HLC's - would the oil be more likely to drain if the preload was wrong? I'll certainly try and find your post on checking the HLC's.
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  #7  
Old 01-06-2003, 05:55 PM
cobra
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I agree with chrisgoodman, all it takes is a piece of dirt or trash to allow for leakdown.
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  #8  
Old 01-06-2003, 06:44 PM
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He didn't know about the pre-load adjustment? Bloody hell!

I personally doubt that a pre-load adjustment or lack thereof would cause the noise that you describe, but a bad HLC certainly could. Randy Starkie bought a 380SL that was believed to have a bad rod and the problem turned to be a couple of HLC's (he did several posts on this).

It's not beyond possibility that one of the new ball studs has a bad HLC, or that one of the oil passages that feed it is plugged and so it takes a while to get pressure up.
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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
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  #9  
Old 01-06-2003, 07:24 PM
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Pucks? Slippers? Sounds about right. Mr. Tangas is correct. They come in several sizes. When dis-assembling the valve gear they should be re-installed in the same place! In most cases the majority of rockers will not require any adjustment. If the shims were re-installed randomly it's possible to have several rockers way out of spec. I disagree with ctaylor concerning the possibility of this being the cause of the noise. I've seen it happen many times. On the other hand, I agree with his statement that one of the new compensating elements (that's the "official" MB name) could be bad right out of the box. I've seen this happen as well. Before any parts are condemned the basic position should be checked and adjusted. Only then can an accurate evaluation be made
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  #10  
Old 01-07-2003, 06:39 AM
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Gentlemen.

Having learnt the intricacies of this forum's search facility and read literally hundreds of the archived posts to find the references you give, I'm now off to the garage armed with info on everything from the 'Herr Fuch Finger Test' to the 'Updated check valve' in the oil filter housing!

(Along the way I have also learnt that the 'little electric motor' that accidentally became detached when satnav kit was fitted above passenger footwell (RHD car) does actually have an important function!! My [now internationally renowned!] mechanic thought it might be blowing air into the door skins to prevent corrosion!)

I will instruct that the preload be checked (assuming he can borrow the appropriate tool) and see where we go from there. Could someone tell me the checking procedure? Is it performed with the engine warm / Compensator Elements pressurised?

With many thanks.
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  #11  
Old 01-07-2003, 10:25 AM
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If you send me an email, I will send you the chapter from the CD on the test procedure.

But here are some practical suggestions.

The guage gives an indication of the preload, but that measurement is relative to the thickness of the hockey puck. So if a correction is needed, the thickness of the hockey puck will need to be determined so that the appropriate thickness for correction can be obtained.

Hockey pucks (actually called valve pads or thrust washers) come in seven thicknesses in .35 mm increments with 5.1 mm as the mid point.

Example. The guage shows an additional pre-load of ~.4 mm is needed. Remove the puck and "mike" it. It is a 4.75 size. Obtain a 5.1 puck to correct.

Be aware that the pucks can be pitted badly where the rockers contact them and take this into account when determining the correct replacement thickness.

Also, once a HLC has been unloaded by removing the rocker, it can take some time to return. Wait at least 10 minutes to re-measure. Once I made the corrections on mine, I let it sit overnight and then remeasured and found one lobe where a thinner puck was more appropriate.

If you find you need to go below 4.4 or beyond 5.8 mm to correct, you should probably check that valve and HLC out closely. Herr Fuchs told me that he has only used one 6.15 puck ever.

Cheers.
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'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
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  #12  
Old 01-07-2003, 04:55 PM
moedip
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My two cents worth - if it were a shim problem - would not it cause a heavy tick instead of a solid knock? I suspect a bad hydraulic lifter that won't hold it's prime and has to be primed to build up the oil pressure every time the engine is started. After the engine has sat for a while, pull the valve covers one at a time (to prevent too much oil mess) and use an automotive stethoscope to pin point the bad lifter. Even just feeling the rocker arms should find the culprit when the lifter is knocking that hard. I had a bad hydraulic lifter on a VW Diesel that sounded like the bottom of the engine was pounding out - it was so loud. I pulled all lifters and sat them in oil for 30 minutes - all had strong resistance when compressed - but the bad one was like pushing on a sponge. Have your mechanic check for dirt in the offending lifter - or for the price - just replace it. THEN check the preload on all lifters. I could be wrong but for the preload to be that far off to cause a solid knock and then disappear as the lifter is primed after 30 seconds doesn't seem reasonable. The lifter should still tick after 30 seconds if the preload is all that is off. Just my opinion though.
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  #13  
Old 01-08-2003, 05:21 AM
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Moedip

Have to say that you, my mechanic, and I are pretty much in agreement here but it's the ratio of bad
components to good in a set of new parts that seems surprising - after all this is German engineering! If I was driving a home-grown product (not that we've got much left!) I'd just accept it as 'par for the course'. Might know more today.

Chris
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  #14  
Old 01-08-2003, 10:09 AM
moedip
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Chris - just because the part is new does not mean it is good. I speak from experience. 4 months ago I changed the press in German made front wheel bearing on a VW only to have it go bad after 3 days (wheel wobble) Ended up changing it 2 more times. The batch the distributor got in had an abnormal number of defective bearings and only when the second shipment came in did I get a good bearing. Keep us posted
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  #15  
Old 01-08-2003, 03:05 PM
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Okay.......yesterday morning car sounds like diesel (as it has each time started cold in the last 2 weeks) when mechanic collects it from my house to take to workshop 6 miles away, leaves it parked outside. Car again sounds like diesel 5 hours later when mechanic starts it to move it into workshop for security overnight.

However, when Mechanic starts it this morning in workshop to move it slightly prior to carrying out 'Herr Fuchs Finger Test' as agreed - engine is totally quiet! Sees no point in carrying out test.

Perhaps the problem is somehow climate related? Since the original repair the car has been standing outside and has been to Scotland and back where we've been having day / night temperatures a few degrees below freezing recently. Oil viscosity?? Oil (Shell Helix 10w40) & filter were changed when the top end was rebuilt.

As unable to identify any individual 'faulty' HLC's, mechanic decides to 'warranty claim' the full set. But unfortunately MB dealer has no more on the shelf. Dealer agrees refund and suggests mechanic buy HLC's from local TRW outlet so he's ordered same for delivery tomorrow. Is this OK? Apparently the dealer says that even they sometimes use TRW OE spec components when they can't parts get quickly from MB. I'm not really comfortable with this but I'm being told that the only difference is the name and the price.

Given the time zones, you've got 14+ hours to tell me if this is a mistake, otherwise I'll have to see what happens when this set is installed - using preload procedure kindly e-mailed by Chuck.
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