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Old 05-01-2002, 01:04 PM
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Location: beaumont, texas
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Bosch Spark Plug Question

I recently changed the spark plugs on my 300e with the bosch copper ones. Does anyone know if these plugs come already gapped? I made the mistake of not checking them before putting them in. If they aren't gaped to the oem specifications can this cause a rough idle?

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Old 05-01-2002, 02:33 PM
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I would check the gap. I usually find the gap is either large or small depending ont he plugs.

I always check my gaps before I install the plugs. I also check the gap according tot he old plugs too to see if there are any discrepencies in the gaps.

I would set the gap to factory specs for the gap.

The plugs you buy can probably be use din other cars, so my thinking is the gap may or may not be correct for your car.

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Old 05-01-2002, 02:38 PM
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Location: Indiana
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If you ordered them from Fastlane they generally are set for the vehicle. I just replaced the plugs in my C280 last night (takes a bow) with Bosch Super's and was cautious in checking each one. They were all fine but I wouldn’t be surprised if they weren’t perfect after possibly getting bumped around in shipping. There have even been reports of them getting bumped out of spec on the way in although if you were careful at all I doubt that would happen. If you’re experiencing a rough idle though I would think it would be worth the time to take them out and check.

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Old 05-01-2002, 03:06 PM
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I also recently changed the spark plugs on my 300e with the bosch copper ones. I checked the gap on each and they were within spec. The end of the box will tell you the factory gap settings. If nothing happened in shipping they should be fine.
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Old 05-01-2002, 03:11 PM
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If this is an early, M103 engined car, you will be better served with a slightly closed up gap. You will get a better idle. If I remember correctly, they should be about .036. I would do a search, you will find many posts on this.

Good luck,
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Old 05-01-2002, 08:29 PM
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The correct gap is .032" (.8mm). The gap is ALWAYS larger than that, they need to be gapped.
Damage is rare in transit due to the cardboard rings around the threaded end of the plug.
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Old 05-02-2002, 01:15 AM
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I'm not sure how ordering from Fastlane ensures proper gap? Fastlane doesn't gap plugs, the mfg. does.

All the H9DC/H9DCO I've ordered were almost TOO small. Std. gap is .032. I agree with Larry. M103 motors idle smoother and run just fine at .036. MBDoc has mentioned in the past that .040 is good. I elected to use a gap in between .032 and .040.

Mike Murrell
1991 300-SEL - Model 126
M103 - SOHC
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