spark plugs for 77 450 SEL - PeachParts Mercedes-Benz Forum

michaeld · #1 05-11-2009, 04:04 AM

I've got a 77 450 SEL. I purchased spark plugs from autowarehouse.com and was sold a set of Bosch Super WR 8 DC+.

But before I actually installed the plugs, I saw that a Bosch part guide called for the WR 6 DC+. And then another one called for the WR 7 DP. According to the first Bosch online guide, the WR 8's didn't fit 116 chassis cars at all, and didn't start being used until the mid 80s.

Since I've got the plugs, I'd like to use them if they work for the car. But could someone give me some clarification on which plugs I should use, and whether these WR 8 DC+ plugs are all right for my car?

Peachparts ITSELF calls for the WR 8 DC+.

230/8 · #2 05-11-2009, 10:58 AM

Personal preference with a bit of practicality coming through here... you will probably be very satisfied with NGK BP6ES plugs, or NGK BP5ES plugs if you do a lot of stop-and-go cold-start driving. The NGKs are easier to find and in my opinion better for Mercedes in US driving conditions. Another item to consider; the originally specified Bosch non-resistor plugs are no longer cataloged by Bosch. The MB Classic Center in Irvine now uses the NGK plugs. (The "R" in the Bosch number indicates a resistor plug...your car should use non-resistor plugs because the required resistance is built into the plug wires.)

230/8

michaeld · #3 05-11-2009, 06:38 PM

230/8 gives a very informed answer about NGK plugs. I'm sure it will help others, and in the future it may very well help me.

But what I'd really like to know is more about the Bosch WR 8 DC+ plugs.

I'm confused why these plugs were listed for later cars, but not for the 73-80 116s (they were listed for 80s Mercedes), but are NOW the right plugs?

Will they run too hot? Too cold?

Anyone know?

michaeld · #4 05-11-2009, 07:17 PM

I re-read 230/8's response after seeing an article that says the "R" in WR 8 DC+ is for "resistor," and he says I do not want resistor plugs in my car.

Want to make sure this is the case. I don't know squat about spark plugs. I've always just checked the book for the right plug(s) and put them in.

This confusion is very new to me.

In any event, it's important that I don't use the wrong plug, as I have to smog test my car. I don't have time to order the 'right' plug for my car; I have to either clean and re-install what I've got or go with the WR 8 DCs.

In any event, if I'm not supposed to have resistor plugs in the car, then why is PeachParts (the host for this site) stocking them for my car?

michaeld · #5 05-11-2009, 11:30 PM

Well, I'm responding to myself. I hope I don't start arguing with myself.

I came across this thread on resistor vs. non-resistor plugs on a 92 Mercedes:

"Here's what the Internet Parts Manager from my supplier wrote yesterday. Do you concur with this opinion? How about another cross-reference non-resistor plug? Any recommendations on succesful substitutions? Thanks, Rob

Although Bosch had been saying for years that resistor plugs couldn't be used in cars designed for nonresistor types, they changed their tune about 12 months ago and said it no longer matters. I do not remember if this preceded the discontinuing of the H9DC plug and it being superceded by HR9DC or if the two events went hand in hand. I am sorry that the plugs we sent you did not work well in your car. Unfortunately, we do not have anything to send you as a replacement. Since the cost of returning the parts would probably exceed their value, their is little point to you returning them so I have approved just issuing you a refund for the cost of the plugs in the amount of $6.30. If you do some searching, you may get lucky and find a distributor that still has old stock of H9DC plugs on the shelf, however Bosch USA states that this part number has been completely depleted and superceded to HR9DC."

The question is, does it matter whether I use the WR 8 DC plugs? To put it in Star Trek terms, is non-resistance futile?

"

michaeld · #6 05-11-2009, 11:44 PM

And I came across this quotation on this thread regarding NGK plugs:

NGK site says this

Quote:
As well as reducing electrical noise for radio, television and mobile telephones etc, many modern ignition systems require resistor plugs to stop electrical noise from interfering with the vehicle's on-board electronic control units (ECUs). If non-resistor plugs are used in place of resistor ones, the result can be malfunction and in some cases immobilisation of the vehicle. Resistor spark plugs should always be fitted, therefore, where specified. NGK resistor spark plugs contain a single ceramic monolythic resistor of approximately 5000 ohms. Because of the type and construction of the resistor (ie no springs), the problems of vibration and sudden changes in temperature that can occur with some other brands do not apply. The function of the resistor is to reduce electrical noise generated by the ignition system. The most effective place to situate a resistor in the high tension circuit is as close to the spark plug as possible. This makes the spark plug an ideal place to house the resistor. Because the resistance value is only approximately 5000 ohms, there is no detrimental effect on engine performance, power output, vehicle emissions etc. It is also a fact that many motor sport world champions only use NGK resistor spark plugs. In nearly all cases - apart from some very old low output ignition systems - resistor spark plugs can be used in place of the non resistor versions

winecountryone · #7 05-12-2009, 02:13 AM

My understanding of the reasoning why non resistor plugs were called for is that the wires used are a solid core with resistor end caps.Most vehicles use resistor wire and MB doesn't,one of the reasons why these wires are much more costly.
The resistor ends with resistor plugs will cause a small drop in spark energy,but I doubt it will be enough to cause issues with emissions testing.
Many older motorcycle engines called for non resistor plugs,you might have luck sourcing them through outlets that cater to the classic cycle community.

michaeld · #8 05-12-2009, 01:18 PM

Winecountryone,

Thanks for interrupting my conversation with myself!

Since I've got these plugs, and since I've procrastinated on my smog test, from what I've discovered and from what you think, I guess I'll put in the WR 8 DC plugs and tune 'er up.

I checked the local parts store and they have 15 plugs that they list as "fitting" - including several different platinum-style plugs. It gets real confusing when you have to ask yourself which part that is listed for your car actually should go in your car or not.

Tomguy · #9 05-12-2009, 04:39 PM

Ok, here's the problem.

you know how those resistor plugs have a 5K ohm resistor built in? So do your spark plug connectors (the big honking metal ones that go over the plugs). They're big, they're brass, and they have 5k resistance each. This was before resistor plugs existed or were common to reduce interference. The silvers have 1k.

You can put in the "R" type IF YOU REPLACE THOSE BOOTS WITH THE LATER-STYLE ONES. The ones that have 1k resistance. That isn't "That big" of a deal and your car will probably run just fine. But with a total of 11k ohms of resistance with a resistor plug, you are NOT going to have a properly running engine with those plugs!
Distributor cap connector = 1k
Plug boot = 5k
Plug = 5k
total: 11k
VS Stock:
Distributor cap connector = 1k
Plug boot = 5k
Plug = 0k
total: 6k
Or the other possible way:
Distributor cap connector = 1k
Plug boot = 1k
Plug = 5k
total: 7k

Vintage ignition systems need vintage non-resistor plugs or newer boot caps from something like a 420SEL or 560SEL.

michaeld · #10 05-13-2009, 12:20 AM

Tomguy,

I'm glad you pointed that out - because after I installed two of the resistor plugs I chickened out and decided to clean/gap and reuse the NGK BP5ES plugs that were already installed. As much as I hated messing around reusing rather than replacing, I just had my Spidey sense tingling and didn't want any unforeseen issues.

michaeld · #11 05-15-2009, 01:46 AM

Well, a story should have a conclusion.

I took the car through smog yesterday. She sailed through with none of the numbers being even remotely close to "failure."

I have to say this about the M117 engine: it is the easiest and quickest car to tune up that I have ever owned. All I did was clean and reuse the NGK plugs, set the idle slightly high, slightly retard the timing (about 1+ degree ATDC), and through she flew. The spark plugs are amazingly accessible on this engine. I've had cars that I had to jack up and remove the inner wheel shroud to .... just barely ... be able to reach the plugs. And every other car I've ever owned had at least one plug that was just a ***** (usually the driver side due to the steering wheel shaft). Them practical Germans.

The only other thing I did was fill the tank (didn't know if being full, or half full, or near empty was best for smogging a car, but they DO now do a test where they pressurize the gas tank with nitrogen gas, and the tech thanked me for filling the tank) with 89 octane gas (I usually use 87).

winecountryone · #12 05-15-2009, 11:33 AM

So glad to hear you got through the smog check.These cars do run pretty good,even without OBD-2 and 17 tons of electronics.
These early cars such as yours are the MOST likely victims to fail.There rather primitive systems and the increasingly stringent regulations explain why the most common place you see them now is in the wrecking yard or more likely crushed for scrap!
California wants these type cars off the road.The "buyback" programs now include models as new as 1985.This was one of the primary reasons I selected a 1974(permanently exempt) when buying my 450SL.
Good luck and may there be many more miles of happy motoring!!

michaeld · #13 05-15-2009, 06:05 PM

Winecountry,
My problem is that I'm just not that bright. When I bought the 77, I was under the impression that the smog exempt status applied to cars more than 30 years old. Of course, it didn't. At the time I bought it, it had just flown through smog, and I figured it would only have to go through one more time and I'd be through with the stupid bureaucracy and the stupid regulations. I should have made sure about that.

But it has flown through smog the last couple of times.

Thanks for your comments!

winecountryone · #14 05-15-2009, 10:55 PM

Quote:

Originally Posted by michaeld

Winecountry,
My problem is that I'm just not that bright. When I bought the 77, I was under the impression that the smog exempt status applied to cars more than 30 years old. Of course, it didn't. At the time I bought it, it had just flown through smog, and I figured it would only have to go through one more time and I'd be through with the stupid bureaucracy and the stupid regulations. I should have made sure about that.

But it has flown through smog the last couple of times.

Thanks for your comments!

You aren't totally mistaken...(no need to down your intelligence level)
There was a time when it rolled back each year.Our "fearless leader" Gov. movie star changed it so it quit rolling back as of MY 1976.Too many vehicles were being exempted,state was losing too much money!
If it wasn't for the efforts of the old car hobby,the exemptions would have been done away with all together!
My best friend lives in Nevada...No smog ever on any vehicle in his county.Where I just moved from farther north they only did checks when a vehicle was sold.
Too bad you don't live in one of those areas!

Graham · #15 05-15-2009, 11:29 PM

Quote:

Originally Posted by Tomguy

Ok, here's the problem.

you know how those resistor plugs have a 5K ohm resistor built in? So do your spark plug connectors (the big honking metal ones that go over the plugs). They're big, they're brass, and they have 5k resistance each. This was before resistor plugs existed or were common to reduce interference. The silvers have 1k.

You can put in the "R" type IF YOU REPLACE THOSE BOOTS WITH THE LATER-STYLE ONES. The ones that have 1k resistance. That isn't "That big" of a deal and your car will probably run just fine. But with a total of 11k ohms of resistance with a resistor plug, you are NOT going to have a properly running engine with those plugs!
Distributor cap connector = 1k
Plug boot = 5k
Plug = 5k
total: 11k
VS Stock:
Distributor cap connector = 1k
Plug boot = 5k
Plug = 0k
total: 6k
Or the other possible way:
Distributor cap connector = 1k
Plug boot = 1k
Plug = 5k
total: 7k

Vintage ignition systems need vintage non-resistor plugs or newer boot caps from something like a 420SEL or 560SEL.

I put the resistor plugs in my '72 M117 (350SL). But, I also put in a new Bosch wire set. Cost about $65.00. They work just fine.

The packaging for the Bosch wires is misleading saying that they have spiral conductors or something - But in fact I think they are solid copper cored, but without the end resistors that the originals had.

If you really want to use non-resistor plugs and you need new wires, it may be necessary to buy MB wires at great cost or hard to find Beru wires. Either way it will cost a lot more than using resistor plugs and a new set of Bosch wires.