Spark Plug Gap on a 250SL

[n/a]

Hi,

I realise this is a well healed topic as I have waded through plenty of posts on both sites over the last 6 hours but does anyone know the correct gap for the 114 engine (250SL had a 114 and 280SL's had a 130 according to the Haynes manual). The manual says 0.5mm (notice the use of metric) for 250SL's and 0.9 to 1.0 mm for 280SL's.

I set my gap to 0.5 mm and the first 10 kms were the best I've had. Today however, it felt like she was working on three cyclinders. I will regap in the morning but was looking for advice.

Thanks
A

Andrew
London
1967 250SL

[Benz Dr.]

The 250SL is an M129 engine. The M114 is a different engine mostly used in 250C and other cars from the 70's.
I use the factory plug gap wich is about .035''  Anything less than this and the engine will tend to miss.

Dan c

Daniel G Caron

[n/a]

Thanks Dan.

As regards the plugs. I tried Bosch plugs as outlined by someone recently on this forum.... and they were crap. You get 10 great miles and then you get crap. Gapped at .7 mm you get no spark from Bosch so you have to close the gap somewhat which results in missing.

I have replaced them again with NGK BP6ES on the advice of a mechanic at Roger Edwards (the Pagoda man) and I was amazed at the difference. Strongly recommend NGK and the guy at the store said they no longer stock Bosch due to complaints.

[blairwag]

Andrew,
I've got a couple of tips for you, that I've learned along the way.

1: Bosch makes plugs in multiple places around the world. Others have told me that the copper plugs from Germany fire better and perform better/longer than those made in Korea and Brazil. Personally, I try to atleast ensure all my car parts are German manufactured. I'll not ever put Autolite, Champs, ND, nor NGK plugs in - just out of respect for the vintage of the car.  Does Beru make a plug compatible for this car? That might be a consideration, if you hate Bosch's latest slump in quality.

2: There are 2 different plug gap specs, one for non-resistor plugs, and one for resistor plugs. The resistor plug gaps tend to be much greater (wider) than non-resistor.

3: Plug gap, point dwell, ignition coil output, and ignition wire resistance all play together for the ignition system. Weaker coils and/or higher resistance wires are going to require wider plug gaps for consistent ignition firing, as does a narrower dwell angle.   ...but not too wide, or there may not be enough power to arc the spark!

4: Plug temp range has a major impact on plug life. Hotter plugs in a head not intended for such high heat plugs (low heat transfer) tend to fail quickly after what seems to be awesome performance. Though I've never heard of hot plugs breaking down in as few as 10 kilometers.

Last night I pulled the plugs from my car. I was absolutely SHOCKED to find Bosch W9DC plugs in there!!!   *AND* they were gapped at 1.0mm. This might have been ok if they were WR9DC, but they are not resistor plugs!!!!  I thought I was going radical when I decided to buy the W8DC plugs (a step up in temp heat range than MB calls for). But W9DC[:0]  And the car ran great!  It burns a lot of oil. That's probably why such hot plugs were installed. I'm going with the W8DC plugs, gapped at .8mm, which is the wide side of the spec as per Haynes and BBB (0.7 - 0.8 for non-resistor; 0.9 - 1.0 for resistor plugs).    ...but I'm keeping the W9DC's around incase I decide to go back to them.



--
~~~~~~~~~~~~~~~~~~~~~~~~~~~
William Blair Wagner: blairwag@earthlink.net
Education is not always knowing the answer,
...but rather knowing where to look for it!
1971 280SL US Automatic
~~~~~~~~~~~~~~~~~~~~~~~~~~~

[Benz Dr.]

Really.
 All I use is Bosch plugs and mostly W9DC. Most of these old cars tend to run rich and the somewhat hotter plug helps out in this area. The 9 plug really isn't that much hotter than the recomended 7 plug which is usually too cold for anything but an engine with optimum compression. NGK plugs are OK but stay away from Champion or AC. Anything that's black oxide or zinc plated can sieze in the head and pull the threads out. Bosch plugs are nickle plated - the same stuff that anti sieze is made from. ( never use copper anti seize on aluminum )
I leave them at the factory setting. If you close the gap up they'll miss. There's a lot of reasons why some things won't work right of which spark plugs are only one.

Dan Caron
SL Barn

Daniel G Caron

[Cees Klumper]

On spark plugs and wires etc:

- Beru do make a suitable plug
- I finally got myself a decent ohm-meter and checked the wires and caps on my car that were put on some two years ago. Well, I did not need the ohm meter after all because the caps said "5K" on them in big bold letters. Since all I've ever read is to have the wires, caps and plugs be as low- or non-resistant as possible, I replaced them with 1K caps and checked all the wires. All now read 1K ohm. Now this could just be my imagination, but I think the car starts a lot easier than before this swap of the caps. I just turn the key with the engine cold and within two seconds it runs. Always a bit hesitatant for the first 5 or so seconds, but before it would not start until 5 or so seconds of cranking.

Cees Klumper in Amsterdam
'69 white 280 SL automatic

[blairwag]

Hi Dan,
Eeeks. Now, you've got me worried!!!!
Never use copper anti-sieze on aluminum heads? Why?  I've been using copper based anti-sieze thread treatment for years on aluminum heads. ...namely only my 1990 Honda 1100 V-twin Shadow, and on my old Toyota 4cyl 4x4 pickup truck.  PU truck is in the great graveyard in the sky, now, but only after 250,000 miles, and due to body rust.

When I pulled the W9DC plugs out, they were drenched with anti-sieze treatment. I cleaned up the head and threads, but then applied more thread treatment. What's the deal with copper anti-sieze on aluminum?   Damn, I just treated the bolts on the thermostat housing, that I just installed too.

Okay, If I detect misfiring, I'll open the gap back to the factory delivery, which was 0.36" (0.9mm I think). If still problems, I'll put the W9DC's back in at the 1.0mm gap. The W9DC plugs were black, but otherwise, in good shape. Thanx for the tip.

Let us know what the deal is with the anti-sieze thread treatment.  Thanx!


--
~~~~~~~~~~~~~~~~~~~~~~~~~~~
William Blair Wagner: blairwag@earthlink.net
Education is not always knowing the answer,
...but rather knowing where to look for it!
1971 280SL US Automatic
~~~~~~~~~~~~~~~~~~~~~~~~~~~

[ja17]

Hello Andrew,
Guess I'll throw my two cents worth in also. The factory spark plug gap spec was originally intended for spark plugs manufactured at the time of the W113 production(such as Bosch W175T30). These plugs are now obsolete. These original plugs were inferior to most of the spark plugs produced today.

So as far as gap what should you use? Should you use a Mercedes factory spec for Bosch plugs no longer produced? Maybe. Consider using the spark plug manufacturer's specification for the current plug for your engine. I am sure that their are many plug types and gap settings being used by the list sucessfully.

Ngk plugs were one of the first to come out with the copper core to accomodate the demands of high rpm Japenese motorcycle engines. These copper core pugs were noticably supperior. Champion  was the next to produce copper core plugs replacing their (N7Y) spark plugs with their new copper core plug (N7YC).

Eventually Bosch came out with their "Super" plug  with their improved coppper core(W7DC replacing W175T30). Bosch was a little behind it seems on the change over to copper. However as far as I know Bosch are the only plugs with the nickle plated threads which tend not to get stuck in aluminum heads as easily as the non-nickle plated plugs.

A healthy engine should perform well on many of these modern brands. I have had very good experience with NGK plugs in my own engines. In the early days I prescribed the NGK plugs in problem engines when the other brands would not perform. However I think most of the copper core plugs of today are very close in performance. I use both Bosch and NGK copper core plugs these days and would consider the Champion copper cores also except the non-resistor champion plugs seem to be especially difficult to find these days.

Champion spark plugs seem to want to bind a little more in the aluminum heads if left installed  for extended periods of years. Non resistor spark plugs should always be used if original type resistor spark plug wire ends are in place.

I have used .028" plug gap for years. This spec came out of a 1975
Bosch catalog  and was recommended by Bosch for their current spark plugs in the W113 cars at that time. This is a little tight according to earlier Mercedes literature (1971).  It has worked fine. However I may try Dan's .035" setting to compare next chance!














Joe Alexander
Blacklick, Ohio

[Benz Dr.]

I don't know. I was told by someone who does know and he works at a power generating station. They use atomic grade anti size and he was very clear about what to use and where to use it. Copper would be good for manifold nuts and certain brake pieces.
I assume that it reacts with the aluminum whereas the nickel won't. I simply use one type and never gave it much thought.

My injection pump rebuilder had a 250SL for a few years. One day he bought a new set of plugs from me ( Bosch) and put them in is engine gapped at the book setting of .024''  It ran like ****.
 He ended up taking his IP off and checking the calibration which was perfect. In frustration he put his old plugs back in and it ran perfectly. He called me about this and I asked him the details of which he told me the plug gap he used. I asked he why he changed them from the factory setting and he said, '' The book said so.''
I told him not to believe everything in books and to re gap the new plugs, which he did. Last time he drove it did 200KPH no sweat.
This car is in Vancouver BC right now. White with blue interior.

Dan

[n/a]

Dan,

That's pretty much what happened to me but when I regapped them... no action. Maybe I damaged them in the gapping process but I doubt it. Anyway, very happy with the new plugs (NGK). It's like a new car!

Cheers
Andrew

[n/a]

This has been a great discussion.  Thanks!
Could Dan and Joe discuss this in terms of the later 280sl cars?  Proper plugs in today's world and the proper gaps?
Thanks again.
Don

[Benz Dr.]

Spark plugs are widely misunderstood. Any new plug will make the car run better for a while - reading that plug is more important than how the car feels. A fresh plug will look clean with a very slight gray or tan colour for the first while. Any straw colour is an indication that you're running on the edge of lean or too hot on heat range. You have to look after 10 minutes of easy driving. Small black specks ( burned up pieces of aluminum ) and you're too late.

If the plugs are black but have a very slight gray colour only on the electrode gap this would be way to rich and or low voltage. Any build up on the plug after a few K's is usually oil going through the engine.
If you can't start an engine that's cold even if you have new plugs in it you will need new plugs all over again. Once the plugs get wet or flooded that's it - it won't start. Put all new fresh plugs in it and it will start on the first hit even though you just spent two hours trying. Hard to believe but it's true.


Daniel G Caron

[n/a]

Dan,

When you say "plugs get wet" and to replace them with new plugs, are the wet plugs ruined or should you just leave them to dry and they'll work again later?

Cheers
A

[Benz Dr.]

This is mostly a problem in cold weather. Once you get the engine started and warmed up it will dry out after you drive it for a while. You may be able to put the old plugs back in a warmed engine but it could misfire.
You know, I just can't say, but it sure makes a difference with new plugs. The engine will almost ALWAYS run better.



Daniel G Caron

[Ben]

I replaced my W9DC plugs, which lasted for 15,000 miles, with a BERU type, dont have the number handy, and the car jumped to life when starting !

I have noticed that they are a bit sticky getting them in or out so I always only remove/install when the cylinder head is warm !  Oh yeah I use anti seize too !!

Regards,
Ben in Ireland.
'64 230SL 4sp.
'03 CLK Kompressor

[Cees Klumper]

I set my valve clearances today and removed the spark plugs to that end. I was surprised to find Bosch W6DC's in there - I got this set from Van Dijk so I assume they always fit these when they service Pagodas. The car runs very well on them, and they have a nice grey color. But, next opportunity, I will swap them for hotter ones and see what happens.

Cees Klumper in Amsterdam
'69 white 280 SL automatic

[blairwag]

Well, I finally test drove my car, after the Cranse XR700 conversion. It started ok, and ran fine. Not much better than before, but fine. It had started it and ran the engine several times after the conversion, but before installing the Bosch W8DC plugs, gapped at 0.8mm (0.32in), but never test drove it. With the W8DC plugs in, gapped as mentioned, it ran great, but did not start as well as it did before the plugs were installed. It used to start within 2-3  seconds of cold cranking. Now, it's more like 5 seconds when cold.

I think I'll regap the plugs to the Bosch factory setting, which was 0.9mm (0.35in) as Dan the Doctore suggested. I'll test run and test drive then, and let you all know how it goes.

As far as teh antisieze thread treatment, I'm still on the fence. Da, you didn't suggest not using any treatment, right? You just recommended non-copper treatment, right? What other kind is there?  I'm still a little bewildered why several Japanese motorcycle shops (Honda and Yamaha) sold me this copper anti-sieze thread treatment for my aluminum head equipped motorcycles.  I need to look into this further.


--
~~~~~~~~~~~~~~~~~~~~~~~~~~~
William Blair Wagner: blairwag@earthlink.net
Education is not always knowing the answer,
...but rather knowing where to look for it!
1971 280SL US Automatic
~~~~~~~~~~~~~~~~~~~~~~~~~~~

[Benz Dr.]

W7DC is the standard recomended plug. Nickel anti sieze is the stuff to use. Copper may be OK but I go with what I know until something comes along that changes my mind.
You don't have to use anti sieze on spark plugs. If you remove them every year they usually come out easily enough. Most plugs that remove with difficulty are actually cross threaded to begin with. ALWAYS start spark plugs by hand - I use a piece of hose over the pug to start them in hard to reach places.

Daniel G Caron

[blairwag]

Anti-seize! A little research goes a long way:

As per http://www.sacskyranch.com/antiseize.htm
Nickel is prefered over copper because it survives temperatures up to 2600 degrees F, whereas copper survives up to 1800 degrees F.

Loctite clearly indicates their copper based anti-seize products are safe for use with spark plugs in aluminum heads.

http://www.midwayautosupply.com/detailedproductdescription.asp?4376

http://www.loctite.com/int_henkel/loctite_us/binarydata/pdf/LT3355v4_MROantiseize.pdf

So, the fear should be squelched. For those of us who have used Copper based anti-seize, we are going to be ok. For those of you who have used Nickel anti-seize, you are going to be ok, too. The Nickel formula gives a higher level of protection than Copper, but the Copper should suffice.

However, the next time I purchase an anti-seize thread treatment, it will be Nickel based!

Thanx to Dan, the Good Doctor, for such an energizing topic of discussion!


--
~~~~~~~~~~~~~~~~~~~~~~~~~~~
William Blair Wagner: blairwag@earthlink.net
Education is not always knowing the answer,
...but rather knowing where to look for it!
1971 280SL US Automatic
~~~~~~~~~~~~~~~~~~~~~~~~~~~