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1988 560SEL
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Discussion Starter #1
Hi all, my 560 has traveled 330k kms and has a smoking issue that points to the valve stem seals/guides. Only smoking at startup after long idles at the lights on hot days. I am planning to change the valve stem seals, chain, chain tensioner, guides and cam oilers. Because of the smoking issue I'm using 20W60 oil plus Lucas Stop-Leak additive. The car runs fine. Just to make sure that there are no major problems before doing the work I decided to do a compression check, using a quality German "Motometer" compression tester with an upper limit of 12 kg/cm2. With a hot motor and full throttle, all cylinders cause the gauge to bottom out at it's upper limit. I checked the accuracy of the gauge by setting my compressor to different values for comparison. It all checks out OK.

The service manual quotes 8.5 bar to 7.5 bar as upper and lower limits with max fluctuations of 1.5 bar between cylinders. IIRC, bar values and kg/cm2 are almost the same. Should I be concerned or pleased about the high readings on all cylinders? Thank you for your input.
 

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1986/1990 W126
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13,551 Posts
Isn't the service manual the US market version? If so that may explain it as the US cars are low compression.
 

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Registered
1988 560SEL
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18 Posts
Discussion Starter #4
Isn't the service manual the US market version? If so that may explain it as the US cars are low compression.
To shed some more light on my Merc compression issues, I purchased a new compression gauge. According to this,
2613413
2613414
the Mercs compression is perfect. I don’t know what the problem with my old German gauge is. If I check it against my compressor pressures it shows the correct values. As soon as I connect it to a Merc cylinder it bottoms out at the limit of 12 bar (appr. 174 psi). Never mind, it goes into retirement after 50 years of service. The sparks look perfect also. I just need to change the valve stem seals and I’ll have a good motor – I hope.

Merc compression test 9-12-2019. According to the manual normal pressure is between 7.5 bar (109 psi) and 8.5 bar (120 psi). Max deviation between cylinders 1.5 bar (22 psi)

Hot-Dry Test in psi
Cylinder First stroke reading Final stroke reading
1 100 130
2 100 130
3 115 130
4 110 130
5 110 135
6 110 135
7 115 130
8 120 135

Hot-Wet Test in psi
Cylinder First stroke reading Final stroke reading
1 125 145
2 125 140
3 125 140
4 125 145
5 125 145
6 125 145
7 125 145
8 125 145
 
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