Low compression on 4,5&6 - Mercedes-Benz Forum

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post #1 of 20 (permalink) Old 11-05-2011, 01:35 PM Thread Starter
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Low compression on 4,5&6

I went out today and did a compression test on the 1972 250 and m130 motor and my findings were not very good --
1 150
2 160
3 155
4 100
5 102
6 100
you guys have any ideas on what it could be? should I start looking at the head gasket or should I assume The back three rings and pistons are bad? I get a little bit of a light knock but nothing that's concerns me. I think it is an exhaust leak more than anything.
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post #2 of 20 (permalink) Old 11-05-2011, 02:18 PM
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What kind of history does the engine have? Miles? Exhaust leaks don't usually cause a knock, more like a rumbling sound. How is the oil pressure and what does the oil look like?

Felicita e un bicchiere di vino con un panino.
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post #3 of 20 (permalink) Old 11-05-2011, 02:41 PM Thread Starter
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The car has 87,000 miles from California. It has signs of low mileage such as oil change stickers with the miles and dates on them. And some service records. The oil is clean of radiator fluid if that is what you are thinking. And visa versa.
Plugs looked good (proper detonation). I recently adjusted the valves and inspected the cam shaft. Wondering if there is some history of the back three low for a reason. I'm used to seeing one low. Can rings be done without removing the engine? Looks like the subframe might get in the way?
Thanks
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post #4 of 20 (permalink) Old 11-05-2011, 02:43 PM Thread Starter
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Oil pressure is max on the gauge most of the time.
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post #5 of 20 (permalink) Old 11-05-2011, 02:44 PM
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Let's start with what made you think of doing a compression test in the first place. What were/are the symptoms?

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post #6 of 20 (permalink) Old 11-05-2011, 02:57 PM Thread Starter
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Quote:
Originally Posted by flyboyike View Post
Let's start with what made you think of doing a compression test in the first place. What were/are the symptoms?
I did one, because it is a pretty new car to me. I figure, before I throw money at it with tune up parts and tranny flush and filter, I should check the core of the motor. Too many times it has been seen that people change everything only to realize that the head gasket is bad. There really are not any symptoms as far as power or acceleration, but maybe I'm just being soft on how it actually runs (ecause in the back of my head, I think it is a 40 y.o. Motor )
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post #7 of 20 (permalink) Old 11-05-2011, 03:00 PM
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I did one, because it is a pretty new car to me. I figure, before I throw money at it with tune up parts and tranny flush and filter, I should check the core of the motor. Too many times it has been seen that people change everything only to realize that the head gasket is bad. There really are not any symptoms as far as power or acceleration, but maybe I'm just being soft on how it actually runs (ecause in the back of my head, I think it is a 40 y.o. Motor )
I see. Any oil on plugs 4, 5, 6?

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post #8 of 20 (permalink) Old 11-05-2011, 03:02 PM Thread Starter
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As I think more about it, could the readings sign toward out of adjustment of the carbs? Twin zeniths.
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post #9 of 20 (permalink) Old 11-05-2011, 03:03 PM Thread Starter
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No on the oil on plugs. All were nicely colored and clean.
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post #10 of 20 (permalink) Old 11-05-2011, 03:09 PM
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As I think more about it, could the readings sign toward out of adjustment of the carbs? Twin zeniths.
If you suspect the carbs, do a dry test (no fuel) and see if the difference is just as dramatic.

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