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MECHANICALS With a 30 year-old automobile, there will always be discussion here - maintenance, modifications and mechanicals.

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Old 16th April 2009, 05:45 AM
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Default What spark plugs for the M117 and M100

I'd be interested to know what plugs you guys use for your 350/450 and 6.9s and, not to forget, 6.3s - Waxenberger's and abl567's "baby".

For years, I have advocated and used Bosch platinum plugs with an 8 rating. That heat range seems a good compromise for suburban and highway driving, but for sustained highway cruising I have endeavoured to fit the Bosch 7 (one grade colder) range for better engine protection. This is for 6.9s, but I would venture to suggest that the M117 engine be treated in the same manner. I used to purchase those from Repco at about $10.00 each, but for at least the last four years I have not been able to obtain those Platinum plugs from them, nor have I changed them in between times, other than using spare units that I have always had on hand - bear in mind, I have owned my car for fourteen years.

So, just recently I wandered into the Supercheap store at Wentworthville, looking for this, and looking for that, with nothing particular in mind. Then I spotted their Spark Plug cabinet in one of the aisles. Ah hah, what's this ? Bosch Platinum plugs ! Beauty. How much ? $6.00 retail dollars each, and still made in the good, old Fatherland - Germany to the unknowing. They were no different to what I had been buying from Repco. As it turned out, they only had four of the 8 range in stock, but enough of the 7s to satisfy my Gleaming Beauty. So I struck the deal and decided to go for them.
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Of course, we also have a 1999 Holden Statesman with the Series 1 Gen.3 Chevrolet engine. Well, it 's due for its 170k. service, so new plugs would be high on the list, other than Oil and Filters. Naturally, after consultation with the salesperson, I spotted the plugs for the Statesman (very nice car, BTW, more on that later in another section of the board), but the price ? $96.00 smackeroos - wow. Needless to say, I got stopped in my tracks, and walked out with tail between my legs. So, off to the Holden Dealer at Baulkham Hills. I get on well with the Spare Parts guy, and discuss plugs with him.

Yes, of course, we have Platinum Plugs for your Statesman. Denso platinums, and of course, they are $6.00 each trade price. Very good, I'll have them. I then related the Supercheap experience and it turned out that they were 'Fusion" tipped plugs which the Holden dealer also has available, the manufacturer being, again, Denso (made in Japan). The price - from memory, $160.00. I collapsed on the spot, there and then. After a stiff drink and a couple of slaps across my cheeks, he asked whether I had the Series 1 or Series 2 Gen. 3 engine. I stutterd 'well, the former'. Ah alright, just as well, because the plugs for the Series 2 work out to, I think ( I am still dazed) about $360.00 (for eight). Just as an aside, I decided to buy a genuine GM Oil Filter, made in, you guessed right, good old Poland. Regards Styria
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Old 16th April 2009, 06:19 AM
BenzBoy BenzBoy is online now
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Default Re: What spark plugs for the M117 and M100

Michael,
Please stop collapsing all over the place and get to the point!!
What plugs do you have in your Victa?
Regards,
Benz-Boy
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Old 16th April 2009, 06:36 AM
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Default Re: What spark plugs for the M117 and M100

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Michael,
Please stop collapsing all over the place and get to the point!!
What plugs do you have in your Victa?
Regards,
Benz-Boy
Heh, fair go - I just have to tell how it is and how it felt at the time. Victa ? Wot's that ? I crank out the old super-duper GMC that cost me two bucks short of two hundred smackeroos - compliments of the Chinese and the "big" Big W. It's even self-propelled as long as you push hard enough ! Styria
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Old 16th April 2009, 11:51 AM
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Default Re: What spark plugs for the M117 and M100

NGK BP6ES or Bosch W7DC with NGK being the preferred option. Exactly the same as the 6.9, gapped to 0.8mm.
One must ensure that versions with a built in resistor are not used like BPR6ES, WR7DC, etc.

That seems way too cheap for Platinums, which are normally well into the two-figure mark each. I was also under the impression that they are not recommended for use on these engines.

Tim
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Old 16th April 2009, 01:25 PM
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Default Re: What spark plugs for the M117 and M100

I use W9DC's in Six 3, because the MFIS runs richer, 4-5% at idle, they tend to foul the cooler plugs after prolonged idle.
The non resister plugs are no longer made but I found some on ebay so I bought 14 sets of 8 for about $3.20 each
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Old 17th April 2009, 03:18 AM
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Default Re: What spark plugs for the M117 and M100

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Originally Posted by abl567 View Post
I use W9DC's in Six 3, because the MFIS runs richer, 4-5% at idle, they tend to foul the cooler plugs after prolonged idle.
The non resister plugs are no longer made but I found some on ebay so I bought 14 sets of 8 for about $3.20 each
That is a big grin on your face - no wonder as I would call that good buying. You will not do better than that. Regards Styria
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Old 17th April 2009, 03:29 AM
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Default Re: What spark plugs for the M117 and M100

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Originally Posted by TJ 450 View Post
NGK BP6ES or Bosch W7DC with NGK being the preferred option. Exactly the same as the 6.9, gapped to 0.8mm.
One must ensure that versions with a built in resistor are not used like BPR6ES, WR7DC, etc.

That seems way too cheap for Platinums, which are normally well into the two-figure mark each. I was also under the impression that they are not recommended for use on these engines.

Tim
Hi Tim, regarding price, you're quite correct as far as "usual" cost is concerned - as I said, some years ago I paid far more than the other day. I have indeed compared old and new side by side - they're exactly the same and made in Germany....and yes, they are Platinum plugs.

The plugs for the Statesman, whilst still Platinum, are completely different with a huge gap set as 'standard' - one would think that the plug would never fire, but that is the intended design.

Some years ago with the debate raging as far as leaded vs. unleaded petrol was concerned, I did ring Bosch Australia and they did in fact suggest that Platinums were not suitable when coupled to leaded petrol. I therefore took their advice and fitted conventional plugs - for one week. They did not burn nearly as cleanly and showed definite signs of coking up. I then refitted the Platinums, and have stuck with them ever since with no apparent ill effects.

I can tell you that even after about a thousand miles, the Platinums were still showing the wire brush marks when I cleaned them on the bench grinder prior to installation - that's how cleanly they burn. Regards Styria
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Old 17th April 2009, 10:36 AM
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Default Re: What spark plugs for the M117 and M100

Interesting. I think I might have to get a set for the 450, as it's due for a new set. I was having issues with no. 4 fouling, which seems to have just happened again.

Tim
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Old 17th April 2009, 11:36 PM
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Default Re: What spark plugs for the M117 and M100

This was my request for information here a year ago

http://www.topklasse.net.au/forums/showthread.php?t=263

There seem to be problems finding NGK plugs with screw off terminals but I agree BP6ES gapped at 0.8mm would be the sound choice.

My 6.9 has run cheerfully on the Bosch WR9DCX+ gapped at 0.8mm without missing a beat for the past year and the hospital gardener (a retired mechanic) remarked last week about how even and regular the idle was.

There have been lots of comments posted around the traps about problems associated with using resistor plugs in these cars but as that was all I could find when I last changed them I am pleased to report not a single problem over the past year.

In my experience the start is more immediate and it idles better with a gap of 0.8mm than WR9DCX+ plugs designed gap of 1.1mm.

Bill
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Old 18th April 2009, 04:53 PM
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Default Re: What spark plugs for the M117 and M100

I'm sure you are aware the non resister plugs are used because the required resistence is provided by the plug ends and the distributer cap ends, If the leads have no built in resistence the resister plugs will work well IF their resistence is the same as the leads should have, 9000ohms I think?
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Old 18th April 2009, 05:52 PM
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Default Re: What spark plugs for the M117 and M100

My memory says 5K ohms. Can someone check?
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Old 18th April 2009, 06:20 PM
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Default Re: What spark plugs for the M117 and M100

The plug ends are either 5000 or 1000 ohms, the former for M100 the later M117, the balance comes from the wires and cap ends, the coil lead also has resistence. This is all from memory
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Old 19th April 2009, 03:48 AM
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Default Re: What spark plugs for the M117 and M100

Hi everyone, resistance, ohms etc. and how it affects the running of the car is a subject I have never understood.

6.9 engines have suppressors that show 5 ohms resistance - not sure about 6.3s, but I believe that the suppressors have 1 ohm resistance as well, and I am fairly certain this also applies to 117 and 117 engines. Speaking to people over the years, but never really coming to grips with the discussion and their points of view, some will tell you that it doesn't make one iota of difference whether you fit 1 or 5 ohms suppressors, yet others maintain it does make a difference. So, do we have anyone on our board that could really clarify this once and for all ?

Furthermore, high tension leads - some insist you must go genuine, others say that convential after market leads are okay to use. I have always gone genuine, but am I being pedantic in the process ? Regards Styria
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Old 19th April 2009, 02:39 PM
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Default Re: What spark plugs for the M117 and M100

Hi Styria,
There was plenty of discussion about this on the M-100 site.
As I recall the resistence provides a spark of longer duration, remaining active while the flame front moves through the compressed mixture.
Ron B explained it best with his description of clearing fouled plugs on worn engines by unpluging the lead at the cap and holding it close enough to arc to the terminal, this gave a longer arc at the fouled plug helping it to fire properly, the combustion then burning of deposits.
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Old 20th April 2009, 02:40 AM
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Default Re: What spark plugs for the M117 and M100

I haven't really looked into the effects side of things until now, but you are effectively placing two resistors in series, when using resistor plugs.

A standard resistor plug already has a 5k ohm resistor built in, so you now have a combined resistance of 10k ohm rather than 5k ohm with an M117, or in the case of a 6.9, 6k ohm.

So, given that the gap is 0.8mm on both examples and the coil is capable of emitting the same values, the 6.9's setup allows a higher energy spark across a shorter duration. It is also less likely not to fire due to slightly fouled plugs, which increase resistance drastically, hence no spark.

As with most things, it is all a compromise between RF noise emissions and engine performance.

Basically, the resistor is there primarily to suppress RFI, which occurs as the spark is produced and emission levels are directly related to the speed at which the coil's energy is discharged.

A lot of aftermarket leads have a special spiral winding that is also a built in resistor, so that would then lead to a spark of lower intensity than specified and one that lasts for an even longer duration, if used with resistor plugs and MB suppressors as well!

There are also many diffent conductors used as well. Leads manufactured to the OEM specs are without doubt, the safest option.

If you wanted to use resistor plugs on an MB and retain the factory setup otherwise, you would have to remove the suppressor ends and replace them with conventional versions.

BTW, I don't claim to be an "expert" in the subject of spark plugs. I'm just passing on some acquired knowledge. The way spark plugs function in the system as a whole is rather complex.

Tim
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