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#1
09-06-2004, 06:27 PM
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Spark Plugs
I just changed the spark plugs in my car, and the spark plugs I think are oil fouled. They look similar to this picture,
http://www.bullittarchive.com/Maintenance/Reading_Spark_Plugs/oilf1.gif Althought not as bad in the picture, how can I stop this from happening? I read it would eventually damage the catalyc convertor.
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87' 300E champagne - Euro headlights and corners, 8-hole rims, 140,000miles/220,00km. 
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#2
09-06-2004, 06:36 PM
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Most likely valve seals are leaking by..
If high miles , could even be valve guides are worn , [ common] Most try the seals first before doing the high $$$ valve job...
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#3
09-06-2004, 09:29 PM
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spark plugs
well for a short time fix you can go to w9 spark plugs instead of w8. A touch hotter which will help [but only a smidgin] burn some of the oil foul. but that's not a cure it's a bandaid. look at your stem seal asap and they can be done without taking the head off.
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Thanks Much! Craig 1972 350sl Red/Blk 117k 1988 420sel charcoal/Blk 140k 1987 420sel gold/tan 128k See My Cars at:http://mysite.verizon.net/res0aytj/index.html Pound it to fit then Paint it to match! There is only First Place and Varying degrees of last! Old age and deceit will overcome Youth and Enthusiasm every time! Putting the square peg in the round hole is not hard... IF you do it fast enough! Old enough to know better but stupid enough to do it anyway! Last edited by afmcorp; 09-06-2004 at 09:31 PM. Reason: spark plugs
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#5
09-06-2004, 11:38 PM
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The seals are on the valve stems and they keep the oil up in the valve cover from seeping into the cumbustion chamber past the valves.
They are under the valve springs and can be changed without removing the head or valves... a little tricky , but not hard nor expensive. While doing the job, a tech can feel the play/wear in the valve stem guide and determine if they are also shot. In that case , you are in for a full valve jobs and $$$$. Also, as a poster mentioned , if they are not too bad and the engine is not using lots of oil , a hotter plug will burn the small amount of oil off and keep the plugs from fouling, but it is just a matter of tme before this no longer works. Undergapping the plugs a little helps here a bit too, but a bandaid approach, I agreee...
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#6
09-06-2004, 11:46 PM
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[QUOTE=afmcorp]well for a short time fix you can go to w9 spark plugs instead of w8.
If his '87 300E has the 12 valve M103 motor, it would use either the H9DC or H9DCO plug. The latter is a tad more desireable.
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Mike Murrell 1991 300-SEL - Model 126 M103 - SOHC "Fräulein" Last edited by Mike Murrell; 09-07-2004 at 12:20 AM.
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#7
09-07-2004, 12:33 AM
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mike
you're right i had my head up my 420sel's pipe. good theory so what ever is the next step up in the standard plug's heat range would be correct choice. oasis100 as far as lessening the plug's gap i really think an increase is the correct way. it seems to me in the 60's we ran .032 to .036. now they run a high gap up into the .045's. i believe the theory is the more available physical spark the greater or more complete ignition you should get. frankly though i'd probably leave the gap at standard dimension. again however this is only a stop gap measure. you really need to discover what is causing the problem.
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Thanks Much! Craig 1972 350sl Red/Blk 117k 1988 420sel charcoal/Blk 140k 1987 420sel gold/tan 128k See My Cars at:http://mysite.verizon.net/res0aytj/index.html Pound it to fit then Paint it to match! There is only First Place and Varying degrees of last! Old age and deceit will overcome Youth and Enthusiasm every time! Putting the square peg in the round hole is not hard... IF you do it fast enough! Old enough to know better but stupid enough to do it anyway!
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#8
09-07-2004, 12:41 AM
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Craig:
MBDoc has mentioned a .040 gap for M103 motors. The book calls for .032. On the flip side, Gilly once commented that .032 was the correct gap and I detected in his post that he believed in the factory spec. I'm just a diyer, but have used a "half way" approach in my M103 motor, that being a .036 gap. I get a slightly smoother idle and 22 mph using 93 octane if I drive 65mph-70mph. Whatever works I suppose.
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Mike Murrell 1991 300-SEL - Model 126 M103 - SOHC "Fräulein"
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#9
09-07-2004, 11:12 AM
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Closing the gap increases the heat range and my extensive experience with oil burning engines has found it works quite well on keeping the oil deposits down.
Opening willl give a better idle on tight engine , but not on a smoker..believe me ................ Regardless..change the seals.
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