Iridium sparkplugs?

[NighthawkNZ:Me]

Do you bother spending the extra on them? Is it really worth it?

I asked the mechanics at Advanced Motorcycles that the other day...

He said unless you are racing not worth it, you won't really notice it unless you have had other things done to the bike etc... you will be paying twice as much for no real extra anything...

[The Stranger:Me]

I had a set of iridium plugs in my FJR for a while. I couldn't tell the difference between them and the stock NGKs.

There should be no difference in performance, only in longevity.
As noted if they are difficult to get at, go the iridium's. But also the plugs in a bike are working way harder than a car in general. How many cars rev to even 8,000 rpm, let alone sit there all day at that figure?

Not sure how many cars run a redundant spark these days but quite a few bike motors do, which may add even more work for the plugs.

[AllanB]

Spark Plugs - service book says don't even have a look at them for 12,000 kms. Replace at 24,000 when the head gear gets checked for the first time.

Modern engines are good.

[AllanB]

Which makes me wonder - how come the engine does not need anything looking at for 24,000 kms - apart from regular oil & filters before that period, nothing really gets touched.

So the days of torquing the head etc early on are long gone - how come? Better materials, better machining etc I presume.

[SS90]

On a 100mm long conrod that is a 0.3mm change in length...

That is a lot less than I would have thought, but then again that is a performance conrod, a factory one would probably be a lot worse.

It's fairly well accepted that an engine revving to 12,000 RPM would see an approximate stretch in the connecting rod of (up to) 0.5mm

That is why on some performance two strokes (with a cylinder head/piston clearance of 1mm) will show signs of touching the head occasionally.

Sadly, if a valve touches the piston on a four stroke the damage is quite serious.

Which is why, as you point out modern 4 strokes tend to have expensive rods, and lately more engines comes from the factory with Titanium valves (which resist stretching better, BUT work harden, and require replacement far far more often than Crmo valves of old.)

[imdying]

He said unless you are racing not worth it, you won't really notice it unless you have had other things done to the bike etc... you will be paying twice as much for no real extra anything...

They do last longer; they spec them on cars with plugs that are difficult to remove so that there's little chance of having to replace them under warranty (sad but true)

On a two stroke they're golden, I get plenty of extra kms out of them on those... probably not enough to justify the $/km, but it's worth paying the premium to not have to change them as often. Admittedly I try never run a two stroke in a 'bad' state of tune, but I have noticed that I've never had one foul on me. I'll also admit that I've never had a standard one foul though... but I don't leave them in till they're buggered either.

[vifferman]

Interesting....
That piece of literature is worthless.

Aircraft run Iridium Plugs (they are able to run non-iridium too)... and we service the plugs all the time... Fouled ones clean up easily.
Slight difference in construction though, but shouldn't make a difference.

Yeah, it sounded kinda bogus to me, so given that there was no reference to any real data, I gave it the credence it deserved.
But thanks for that!

[FastFred]

Not quite!

As the piston comes to TDC (let's chose the compression stroke here), the inlet valve closes JUST before the piston gets to the top.

Not quite

Actually both valves are closed when the piston comes to TDC on the compression stroke.

On the compression stroke the inlet valve closes a little ABDC thats after bottom dead center.

On the exhaust stroke the inlet opens a little BTDC and the exhaust valve closes a little ATDC

Its the exhaust valve that gets hit by the piston. Because at high rev's it can be to slow getting out of the way.

[SS90]

Not quite

Actually both valves are closed when the piston comes to TDC on the compression stroke.

.

Oh yes, I meant "overlap", not "compression". (sometimes referred to as "both valves rocking")

But, the inlet valve can indeed be hit by the piston, as the "overlap" phase denotes the time between the exhaust valve closing, and the inlet valve opening.

The piston comes up to TDC, the inlet valve is opening, and the exhaust valve closing. Both valves are open, (only just) as the piston come to TDC

That is why you check both valve clearances at TDC compression.

At high RPM, situations exsist where the valves (inlet or exhaust) can hit the piston.

It depends on the duration of the cam in question (inlet or exhaust)

Particularly now that 4 stroke engines rev so high.

This is why you measure your "piston to valve clearances"

Ask Thomas. (Toot Toot)

[insane1]

keep away from sintered pads they will chew discs real fast,try ceramic pads.

[vifferman]

keep away from sintered pads they will chew discs real fast,try ceramic pads.

Really?
Even though ceramics are almost always harder'n than many metals?
And (AFAIK) sintered pads are just a mixture of glue and metal fibres?

[Ixion]

Wouldn't bother on a four stroke. Doubtful on a two stroke. I've tried just about every 'fancy" spark plug ever. Unconvinced that any of them were worth the extra money.

[Blackbird]

Iridium plugs are standard on the 'bird and I changed them on the advised schedule at 60,000 km. Needn't have bothered as they looked perfect and the gap hadn't changed. Some of the UK 'bird owners don't bother until 100,000 km!

Oh, and sintered pads don't necessarily cause a high wear rate - depends what the sinter medium is. The EBC HH pads I fitted are copper and they are pretty kind to rotors. I think you'll be impressed with their stopping power. I certainly am compared with the SBS ones I had in previously.

[insane1]

sbs sintered pads stuffed my rear disc it"s only done 38,000 kms $210 later brand new ebc disc .

[jono035]

sbs sintered pads stuffed my rear disc it"s only done 38,000 kms $210 later brand new ebc disc .

As per usual there are probably 40 or 50 different variables at play here so saying 'such and such stuffed my discs' is probably a little disingenuous...