best sparkplugs?

[doug s.]

hi all!
(sorry about the repost; i also posted this here: https://forum.bevelheaven.com/viewtopic ... 952#p23952 , but realized it might be better posted in this sub-topic.)

i found this thread (in the other sub-topic) because i was looking to update my '78 darmah sd's spark plugs, and i was wondering if there was any thoughts as to "the best", now that my darmah is up and running again. (the noise i posted about earlier has somehow managed to disappear - i do suspect the clutch may be at play, as i did notice, before it went away completely, that it did quiet when i engaged the clutch.)

so, i was investigating different plugs type, heat range, etc. i noticed that steve's last post mentioned the bp6sh/bp7sh. but it seems that bevelheaven also now has available the iridium ngk's as well as bosch's. i was going to order iridiums, because it seems they must be better, right? when looking up the ngk iridiums, i discovered "ruthenium", which is supposed to be even better. but ngk doesn't know when this plug will be available in the 0.500" reach needed for our bikes ("hopefully soon; the pandemic has pushed our schedule back...")

so, now, i'm pretty much settled on the iridiums, unless ngk can give me a better estimate of what "soon" means, for the rutheniums.

the next issue is heat range - 6 or 7? i understand that 7 is good, unless you have fouling issues, then go to 6? if the bike will run on either, is there a preference, why you'd want one over the other? if a bp6sh works where a bp7sh works, but is marginal, would a 7 be fine in the iridiums? enquiring minds want to know!

and, here's an interesting wrinkle on my bike - i pulled the plugs to see what was in there; both plugs looked fine, re: color, wear, etc. but the forward cylinder had a bp6sh and the rear cylinder had a bp7sh - wazzup w/that? the only visual difference was the rear plug had just the tiniest bit of oil residue on the threads, where the front had none.

any reason as to why one might wanna use different heat range for front and rear cylinders? should i keep both the same on replacement, and if so, which? or replace w/different heat ranges?

thanks!

doug s.

[robax]

Ideally one wouldn't try and offset one problem with something else.. i.e. try to not fix carb issues with spark plugs. The ideal situation is to install the correct plugs and deal with any other issues from there.

You should be able to get the NGK BP7HS as a standard type/heat plug for your bike. The Iridium equivalent is BR7HIX

The 6's are a little hotter. That just means the plug heats up and cools down a little quicker than the 7. The lower number is for lower power engines that need to heat up quickly. The higher number is for engines that produce a lot of heat and need to resist it. Your engine uses a 7 by design. You should not notice a difference between a 6 and a 7 in any case so just get the 7's and then you know you're on target.

I use the Iridiums, but frankly, I've found them to be a little delicate. If you're fouling plugs, then use a non-iridum plug until you've stopped the fouling issue. It'll save you some money. You can't reliably clean or gap Iridiums so once they're messed up, you're looking at replacements.

Get the NGK BP7HS or the Bosch equivalent now and when everything is running well, get yourself a set of Iridiums if you like. I'm running the latter now, but only because everything else is sorted.
Rob

[doug s.]

hi rob,

thanks for your input. the bike is actually running great; i just thought i should check into new plugs, as i've never replaced them, and have put >10k on the bike since i've owned it, over the past 20 years. (ya, not much miles, i know, but i also have two other bikes, that aren't quite as vintage, so i tend to put miles on them instead.)

i figured the 7's would be the correct heat range, but i wanted to pull the plugs to see their condition prior to ordering, to check what their heat range was, and to check their condition. i was surprised to see a 6 in the front cylinder and a 7 in the rear - both the standard bp*hs's. as both plugs look good, (no fouling at all), i think i will order a set of the br7hix's. ngk got back to me and said they don't think the ruthenium's will be available before early next year at soonest. maybe i'll also get a single bp7hs, so if the iridiums seem to not be performing well, i'll at least have two bp7hs's to install, instead of one 6 & one 7.

also, interestingly enough, i've found info that says the darmah sd & ssd should have stock '6' heat range, not 7; it's the mhr iteration that gets the 7. and, there seems to be some discrepancy as to whether or not to use the bp*hs or the b*hs (protruding or non protruding tip). same w/the iridium plugs - br7hix or bpr7hix? altho they both have the same 0.500" throw, so both should work? and what are you gapping the plugs at? i've seen 0.6mm and 0.7mm. ngk says 0.7mm for the b/bp*hs's, and 0.8mm for the iridiums. and the darmah sd factory manual says 0.6mm and a bosch w7b, which is equivalent to the ngk b6hs...

thanks again,

doug s.

[Craig in France]

Honestly, Doug ? I really think you're worrying about something that simply doesn't merit it ...

Short version:
Fit standard-gaped NGK B6HS and sleep easy at night .... Millions of pain-free miles have been notched up by now by bevel twins using these plugs.

Explanation:
If you want to get more life out of your plugs, by all means fit Iridiums. But don't expect to see any great performance change. And given the fact that a) standard plugs are cheap; b) the plugs are easy to get to, I really don't see why you would. (I have Iridiums on one of my Laverdas simply because removing the plugs requires dismantling half the bloody bike ...)

If you want to fit projecting tips, again feel free (I guess you've checked for piston clearance?). But they weren't originally specified; and again, I wonder what benefit you anticipate? The plugs are already centrally placed, so I'm a bit doubtful about any improved flame spread ... But I stand to be corrected.

If you do decide to fit projected tips, bearing in mind that according to NGK, "The temperature of a projected spark plug firing tip is increased by 10 - 20°C", you might want to fit a 7 rather than a 6. But even then, I question whether this is really necessary given that, again according to NGK "The difference from one heat range to the next is the ability to remove approximately 70°C to 100°C from the combustion chamber".

As you can see, the figures just don't match up.

chartheatratingflowpath.gif (10.74 KiB) Viewed 17155 times

As to plug gap, here's what you may have heard: "The bigger the gap, the 'hotter' the spark". While that may be in some sense 'true', it is simply because you need more volts to jump the bigger gap. Which superficially sounds good. But is it?

No, not necessarily. What you want from your ignition system is that it provides enough of a spark to fire the mixture. That's all. Once the mixture is ignited, it's game over. And the thing here is 'enough'. Because demanding a higher level of voltage to jump that bigger gap increases the electrical strain on the coils. And why would you want to do that?

So again: stick with what the manufacturer specifies: 0.5mm in NGK's case.

(If you've got a poor ignition mix or poor compression, a hotter spark may help. But it's a 'get-over'; and, despite their many other weaknesses, it doesn't/shouldn't apply to our clunkers).

[doug s.]

thanks, craig. yes, i think i might be making a mountain out of a molehill.

but, it's interesting, the variations in thought - and what's written. for example, you say "stick with what the manufacturer specifies: 0.5mm in NGK's case." but, ngk says 0.7mm for the b6/7hs', and ducati says 0.6mm (and ngk says 0.8mm for the iridiums).

right now, i'm leaning towards the projected tip, and in the '7' heat range; especially considering that a projected tip will run a mite hotter, and considering that one of the cylinders is running a non-projected tip b7hs already, w/no ill effect.

thanks again,

doug s.

[robax]

I'm fussy about the details myself like you Doug. I always want to know every aspect of every little part of the bike before I decide what I'm going to do on mine.

The outcome regarding plugs is to use the stock item and use it as it comes in the box. The plugs are pre-gapped for the best performance and one can't improve upon that. Note that the plug's performance is capability of the plug, not of the engine.

If there are any issues with the engine, then it's not going to be fixed by non-standard plugs... though it might be covered up a little, leading you down the wrong track.

I suggest putting standard plugs in, 6's if that's correct for your engine, don't change the gaps, and then use their appearance as a gauge for what else you need to sort out.. e.g. carbs.

I was doing plug chops after each ride and took photos of each so I could compare over time. Then I would make minor tweaks to jets, mixture, chokes, fuel, check and clean petcocks/banjos, check floats, always aiming for the original spec. Also, get your carb sync skills updated as that has the biggest effect on the engine once everything else is sorted.

And report back how you get on with it all.
Rob

[doug s.]

hi rob,

well, i ordered a set of bp7sh's and the bpr7hix's. i think i should gap them per ducati spec, not per how ngk gapped them - even ngk says it's possible that the vehicle mfr may have a different spec. i'm also going to gap the plugs that are in there now, before i make a final decision.

as i said prior, the bike is actually running as well as it's ever run, since i've owned it. it actually idles steady, w/o wanting to have its revs increase, only to drop and then stall out. i ran some carb cleaner in the tank a couple tanks ago, and i think it may have actually helped - the 10% ethanol gas here really sucks... even tho it's always run well, its idle has never been consistent; the last 200 miles or so, the idle has been much better. it will be interesting to see if the iridiums do anything to improve things. i'm hoping i'm not doing my typical "if it ain't broke, fix it 'til it is" thing - heh!

thanks,

doug s.

[robax]

Ok yep, the idle issues are extremely common and will be anything but the plugs.

You'll need to sort the carbs out with the correct factory jetting, correct floats, float heights, all new gaskets, o-rings etc, pump gaskets, choke plungers/seals, and above all the correct idle mixture and accurate sync.

To improve your fuel, you might try an octane booster such as Silkolene Pro Boost for a couple of rides. The engines were designed to run on far better fuel than what we have today. 10% of a much higher octane fuel (wherever you might get that from) mixed in can make a significant change to the amount of soot on your plugs. A commercial booster like the Silkolene is the next best thing.

You could check compression if you have access to an accurate tester (not one from Supercheap).

I'd still not touch the plug gaps. Ducati didn't design NGK's plugs and they don't know what the best gap for them is. The figures in the old user manuals is just a guide for random plugs. There's only one gap value that provides the maximum spark for a given plug. And if you get some Iridiums, don't gap them at all or they will fail.

My channel has various videos of interest on these things youtube.com/c/Ducati900SS
Rob

[Craig in France]

<snip> ... for example, you say "stick with what the manufacturer specifies: 0.5mm in NGK's case." but, ngk says 0.7mm for the b6/7hs

My source for the 0.5 was NGK at this address:
http://www.ngkpartfinder.co.uk/mc_searc ... engine=900

But it was a few years back and that link is no longer active. However, FWIW, this is what it said:

... and Ducati says 0.6mm

But THAT was for a different plug, Doug! A Bosch W7B!

And as Rob says: DON'T try to re-gap Iridiums. It will end in tears ...