Iridium Spark Plugs

[Terryb]

I read in some Thread recently that Iridium Spark Plugs are resistor type and not to be used with Magneto’s. Can you get Iridium plugs that will run with a magneto?

My reason for asking is that I tried NGK Iridium plugs in my 62 gold flash (iron head) and after about 10 miles the bike began to miss fire and run badly at higher rev’s. Stopped changed back to BP6HS and she ran fine🥴

The iridium plugs I tried were BPR7HIX and seem to improve cold starts🤪 where as the BP6HS tends to be a little more difficult 🥴

[ringding]

I was sure that you used to be able to. I recall running non resistor type Iridium plus on my RDLC, and with a positive outcome.
However looking online I can't find them now. If the part numbering still hold true then you'd want a BP7HIX. But I can't find anything with that code. Perhaps my memory is failing me!

None of that helps, sorry!

[a101960]

If you wish to go to the trouble the resistor can be removed from spark plugs. Here's a link about how to do it.  https://www.google.com/url?sa=t&source=web&rct=j&opi=89978449&url=https://www.youtube.com/watch%3Fv%3D5FOtJUbjpoo&ved=2ahUKEwit2JeJx6yMAxVBa0EAHU11JRUQwqsBegQICRAF&usg=AOvVaw0lHTCta386-ApqeuxLA-hA

[Triton Thrasher]

I read in some Thread recently that Iridium Spark Plugs are resistor type and not to be used with Magneto’s. Can you get Iridium plugs that will run with a magneto?

I always found that 5 kilo ohm resistance made no difference to starting or running with a magneto.

My reason for asking is that I tried NGK Iridium plugs in my 62 gold flash (iron head) and after about 10 miles the bike began to miss fire and run badly at higher rev’s. Stopped changed back to BP6HS and she ran fine🥴

The iridium plugs I tried were BPR7HIX and seem to improve cold starts🤪 where as the BP6HS tends to be a little more difficult 🥴

BPRHIX is one grade colder than BP6HS, so it may foul under conditions where BP6HS would not foul.

On the other hand, plugs faulty from new, that stop working after a few miles, are not unknown.

[CheeserBeezer]

I read in some Thread recently that Iridium Spark Plugs are resistor type and not to be used with Magneto’s. Can you get Iridium plugs that will run with a magneto?

I always found that 5 kilo ohm resistance made no difference to starting or running with a magneto.

My reason for asking is that I tried NGK Iridium plugs in my 62 gold flash (iron head) and after about 10 miles the bike began to miss fire and run badly at higher rev’s. Stopped changed back to BP6HS and she ran fine🥴

The iridium plugs I tried were BPR7HIX and seem to improve cold starts🤪 where as the BP6HS tends to be a little more difficult 🥴

BPRHIX is one grade colder than BP6HS, so it may foul under conditions where BP6HS would not foul.

On the other hand, plugs faulty from new, that stop working after a few miles, are not unknown.

In many cases, particularly if the magneto coil has been properly rewound, vacuum impregnated etc. using a resistor plug or plug cap might be OK (but unnecessary). However, a magneto coil has about 5000 ohms resistance in the windings due to the number of turns of very fine wire. If you attach a massive resistor (another 5000 ohms) onto the end of the HT wire - and don't forget that the HT wire is just an extension of the coil windings- you are making it more difficult for the pulse (spark) to find its way to the plug gap. The spark wants to find the quickest and easiest route to earth which should be across the plug gap. By putting a barrier (resistor) in the way of the spark you are encouraging the spark to find an alternative route to earth. Original Lucas magneto coils will, by now, have very weak insulation and the likelihood is that the spark will take the lazy route home which is by bridging the insulation in the coil and sparking onto the armature cheek. Modern rewound coils, assuming they have been wound by somebody who knows what they're doing, are less prone to this as the insulation is better quality. However, rewinding a magneto coils is a skilled job, and judging by some of the rewinds I see, I wouldn't want to stress those any more than I would want to stress an original Lucas coil. To be fair, the majority of rewinders know what they're doing or they wouldn't stay in business very long.

[JulianS]

I used iridium resistor plugs in an ally head for about a year. Denso IW22. The bike ran well with them and they seemed to stay cleaner than the N4. But the plugs did not last for long. Bought from a reputable supplier and in the course of a year 2 of the 4 I bought had failed. And they were quite expensive. I presume they did not like working with the magneto. Tried an NGK equivalent but the bike was not happy with them. Anyway the head would not stop leaking oil from the joints so I took it off and replaced it with an iron head (which did not leak) I use Champion L6G Gold Palladium plugs on this and I prefer them to the L82c or NGKs. They have a fine centre electrode, not as fine as the iridium ones.

[Rex]

If Americans pronounce "aluminium" as "aluminum" do they pronounce "Iridium" as "I ride'm"?
{Sorry }

[chaterlea25]

Hi All,
While on the sparkplug topic,
Has anyone got experiences with "Brisk" sparkplugs ?

The ones suitable for Alloy head A10's are non resistor  and from what I have read about them the insulator is "glazed" as other brands were years ago.
According to "F2" motorcles (shop) in UK they are resistant to oil and fuel fouling.

I searched online for a supplier.
UK Ebay seller wants £10 each for them
F2, you need to phone as they are not an online seller
I found a shop in Germany that sells them for about € 3.50 plus VAT and post
Anyway I now have two grades 14 and 15 equivalent to B7 and B6 approx as they have a wider heat range
I bought 8 plugs and they work out about €6 each . Germany post is expensive at €20
This is shared with a friend who also wants to try them.

My SR always runs well on NGK's but they do not last very long.
After 800/1000 miles stop for a coffee or fuel
And the bike refuses to fire up again. Fit new plugs and it starts instantly. ( i have had the mag checked out, it's a proper BTH)

Time will tell how the Brisk plugs work out

John
 

[Rex]

I like Brisk plugs, and they can be cleaned and reused unlike other new plugs.
Particularly good in the somewhat oily environment of a Scott engine.

[jhg1958]

Sorry to ask a stupid question but how long do the plugs last?  I know the electrodes wear but I have seen little evidence of this on any bike. If they are dirty I wire brush them until they clean. Am I pushing my luck?

I had iridium plugs on my ancient Ford Cmax and they lasted 5 years, about 40,000 miles. Being mean I replaced them with NGK but these only last 2 years around 15000 miles.

The BSA only does about 1500 miles per year but I did not plan to change the plugs for a year or 2. I have 2 sets so if I have a fouled plug I just change them over.

John

[Swarfcut]

 Way back when the motoring magazines carried adverts for Champion Plugs and on cars at least, 10000* miles was the service interval....reckon some of us still have a good few perfectly serviceable plugs lying dormant in sheds and garages. Unless the electrodes are eroded away I reckon they will do. Got caught out with some modern plugs, centre electrode "worn" to a cone. New plugs came exactly the same, my originals were fine. (MGTF, K Series engine)

 Now whether a magneto spark is any different from an ignition coil spark is the deal breaker, and yes, for a magneto you need as many cards stacked in your favour as you can muster.

 One other aspect of changing plugs is the cylinder heads we have now. Back then cast iron was virtually fool proof. These days an alloy head plug thread can easily be damaged, so If an engine is running fine I leave well alone.

 Our Mazda has done 85000 on the same set of plugs. Truth be known I don't know where they are....

 Swarfy.


 * Champion would say that, wouldn't they?

[chaterlea25]

Hi All,
I have read that wire brushing modern plugs is Bad for them
I don't think I have ever "worn out'" a sparkplug
Regular changing the plugs on the 98 civic we had for 23 years would return the mpg  to its best so was worthwhile. Although the plugs looked perfect when removed. I used to keep a few of the old ones to use in the B&S v twin on the old ride on mower.
I haven't looked at the plugs in the replacement Honda v twin powered mower

John

[trevinoz]

This is all interesting.
I had the plugs changed in my Ford Falcon recently. The original were still in it and were working fine but I thought that after some 230000 km it was time to change.
They were Iridium and the replacements are NGK @ about $20 each.

[Joolstacho]

Iridium = waste of money?
I learnt that iridium plugs were designed specifically for V6 car engines, where the plugs in the rear bank were very hard to get to, so the Iridium plugs were developed particularly to be longer lasting, (not better performing) therefore fewer (difficult) plug changes.

Discuss?

[BagONails]

There was a time back in the nineties when DFI/electronic ignition and computerised engine management all came together with Euro and Californian (CAFE) emmision standards and lead free fuel to vastly clean up the way IC Engines run.  At the same time spark service intervals started to increase until by the noughties 60,000 miles was about standard. Spark plug tech also improved in response to these demands and I think iridium plugs started to appear around the same time so its horses for courses.  Not a waste of money in a modern engine maybe as NGK gives the life expectancy of their iridium electrode plugs as 100,000km and that is probably a conservative number... In a BSA though, most probably not worth it!

Generally speaking our plugs really don't wear out but they do foul. Due to variable running conditions (air/fuel ratio, ignition timing scatter, unburnt fuel and oil etc. etc.) our dirty old engines will slowly or sometimes very rapidly deposit carbon on the electrode ceramic insulator and the spark will track to earth instead of making a bid for freedom across the gap.  Most of the time this occurs down in the well away from the tip and no amount of wire brushing will do any good. There used to be spark plug cleaners which basically sand blasted the tips but I've not heard of anyone doing this for years. An iridium plug will foul up just as quick as a standard plug.

Standard plugs are relatively cheap, toss it and fit a new one seems to be the go like so many things these days.

More info here or in your own country's equivalent site.
https://www.ngk.com.au/products/spark-plugs/