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Iridium failure? (top end carnage) top end time...

Started by m in sc, May 24, 2021, 11:32:46 AM

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m in sc

#30
Left side looks much hotter than right side.  Looks like it's run lean but when it's detonating, the temperature rise tends to mask everything else.

The left appears to have eroded the front (exhaust side) and blown the particles down the pipe.  I prefer fine wire plugs on high performance motors and have never experienced that sort of meltdown with iridum or standard plugs caused by the plugs even with plugs of too low heat range - say B7s or 8s.

Working back a step or two:  If the old iridium plugs misfired, the exhaust temperature would probably be higher.

disagree. it think it (unwittingly)  misfired =  'rich' with the iridiums for a long time now. I then tuned carbs to run with those back when i put the flatslides on. However, I think i cured suspected (high rpm iridium) misfire with different plugs and i think it was what caused the issue. (at high rpm). def not a heat range thing.

  If standard plugs improved the burn, the motor should have made more power and exhaust temps should have been lower because the burn would have been more complete.
i see what you're saying but .... with the timing retarded up over 9200, if it was misfiring slightly before and not now, would yes, complete the burn, but later due to the programmed retard and cause the front of the piston as BOTH did (look closely)  keep in mind, i rode this home about 2 miles very carefully after this happened, so the mismatch of piston colors has zero to do with the blowup. (look at the plug pics)

What else changed?
larger main jet and one clip richer. thats it. should have had reverse effect if anything else.
Was it perhaps a different fill of gas that wasn't as good as prior fills?

same tank i rode it in last time so nope.

Could the ignition timing have changed electronically for some reason? nope. i checked it when i got back on the programmer and the mzb drum did not move, i have witness marks when i installed it

The answer should be No F'n way, but stuff does happen. Did it happen at high revs/load and were riding conditions any different.

typical day, was about 75 degrees. nice morning. was ridign normal till it warmed up, then yes, i railed on it. was shifting around 9.8- 10k.
I'm sure you already asked yourself those questions and more, but that left piston missing the whole exhaust side ring land suggests that the problem was exhaust temperature prior to detonation.  Was air density very high that day?
again, look closely at pics of both pistons they actually have the same damage. ignore the color.


I know... its a loopy theory, but that was the ONLY thing that changed was the plugs and slightly richer jetting. and i will say, it took the needle position and main change well. flt better until it did what it did.

Think back to the old days when people would mistakenly jet leaner because of weak spark. I think this is basically what was happening here.
 
i wouldn't believe me either but i know exactly what changed. also, intakes, gaskets, etc look great, no signs of an airleak.  Also, as stated my local guy said they quit running the iridiums in the race bikes over the past year or 2 because they were having spark issues. this was a few days before i installed them and bough the regular plugs from him. (actually bought them for the LT250 grom, they both use same plug)

   

teazer

Thoughtful response.  That misfire thing still doesn't sound right to me.  Doesn't mean I'm right, but let's walk through some of the possibilities.

If there's a misfire (electrical), some of the fuel and oxygen did not ignite.  That absolutely happens with most ignition systems but we mere humans can only detect that missed cycle if there are lots of them - relatively speaking.

So, on that cycle without ignition, fuel and air pass into the exhaust where they may, or may not burn.

In terms of gas analysis, we see that as a high HC level but the Air:fuel ratio which measures unburnt oxygen, doesn't really make a huge difference to the Lambda reading, and the unburnt fuel makes little to no difference to the plug color because nothing burned so no heat effect to see.  That's what we see with poor fuel atomization too.  If fuel droplets are too large, not all the fuel gets vaporised and burned.

If the spark is "weak" and lights the fire, the flame propagation rate arguably is slower because the flame kernel is smaller and less intense, so we might expect that to show up again as more unburnt fuel and oxygen passing down the pipe.

If that is the case, we should expect lower average combustion chamber temperatures and therefore lower plug tip temperatures which we read as "rich".  We know that when we read a plug, all we are really doing is to look at the temperature the plug reached, so rich jetting leads to lower combustion temps and sooty looking plugs.  "Hotter" plugs like say a B6 run higher temps and self clean at lower running loads, with the same Air:fuel ratio we read hot plugs as if they are lean and harder (e.g. B10EGV) will tend to look rich with the same A:F.

That said, if the fine wires are not generating a sufficiently strong spark, they will run cooler that they should.  We read that as rich and jet down.  If replacement plugs generate a stronger spark which creates a more complete burn, then you get the result you describe.

The problem that causes me is that fine wire plugs are supposedly deigned to fire more consistently with inconsistent combustion conditions.

Your situation suggests that Iridium plugs are not only not better, but are actually worse in a high performance two stroke.  I have not tested standard plugs back to back with say B*EGV or Iridium, but it's an interesting hypothesis.  Needs a multi gas analysis on the dyno which are not typically available on dynojet but are on eddy current dynos we were lucky to have access to a few years ago.


Hawaii-Mike

Witness marks?  Are those small scribe marks to line things up?

m in sc

#33
teazer, you're over thinking it soemwhat but yes.... this is what im driving at to quote your reply:  "
That said, if the fine wires are not generating a sufficiently strong spark, they will run cooler that they should.  We read that as rich and jet down.  If replacement plugs generate a stronger spark which creates a more complete burn, then you get the result you describe."

the iridiums are presumed defective and misfiring. or actually missing spark. like a bad coil. (I am making this assumption/theory on the fact that my local mx guy who i bought the plugs from had fouling issues on his racers bikes using the same ones). this would require less fuel up top to run what seemed to be ok.  Im not saying irridiums are bad by design. I'm saying i had a bad batch of them. there no other reason it would have failed like this.  I'm not demonizing irridiums overall, hell, i ran them in my rz for 7 years and -NEVER- had a failuire.

I can 100% confirm this bike would do 120+ on the open road for good long runs prior with no overheating or detonation issues with water temps not going over 190. i added jetting and changed plugs and boom inside a half mile.


Mike, i always make witness marks on the ign rotor and bolt. if it moves, you'll know immediately by looking at it.

teazer

Mark,

Me overthinking things?  Puleeze..... OK. Guilty as charged.

So with absolutely no hard data to work from, I decided to browse the source of all knowledge - the might interweb and there are so many opinions and half baked theories that it's kinda hard to draw any useful conclusions.

Some believe that Iridium plugs have a different thermodynamic profile and that the same heat (number) is misleading and that while Iridium and standard are the same temp at full load they are different at light load conditions.  No data to support the theory but sounds interesting.

Others say that Iridiums improved power or smooth operating compared to Standard.

Odd incidences of Iridiums failing completely or misfiring.  Not well documented but could be there's some bad plugs out there.

Some suggestions that Iridium is mandatory in high power motors and others saying that standards must be used.  Two stroke sled manufacturers seem to like Iridiums and in some cases they want extended nose plugs and others say never use them.

The only good comment I found so far was that different applications need different plugs.

So if we discount all of the opinions, it comes down to why do some iridium plugs fail and are they actually any better in our low mileage applications, since none of us is expecting to get 100,000 miles between changes of plugs.

And in your case when the motor and jetting was set up running iridium plugs, did a simple change to standard plugs need the jetting to be revised?.   Looks like it needed a large jetting increase. When you rebuild it and set it up for standard plugs and jet it on a dyno or butt dyno, it will be interesting to see how much more main jet it likes and to see the difference if you run that setup with iridium plugs after setting it up.

m in sc

i wont run irridiums again. no point really as after i get one dialed in it never fouls plugs.

like said, i have experience with them but not in the past 5 years or so, except for THIS bike. and i ran them in the triples, and the rz with no tuning changes. I'm marking it up to a bad batch. as with anything mass produced, just a matter of time before some bad ones get out.  I thnk i'll be in the 280-300 range. was at 260's which seemed small even on a p6 jet tube.

m in sc

as an update:

pulling everything down and inspecting, i found no other possible issues (whew). I had to borrow a hone as they were on back-order for 6 weeks, so frank b came thru for me. after a light hone, was able to measure up and down the bore using a t gauge and then feeler gauge to piston skirt, all was in spec, hair over .0024" so luckily, no bore damage. checked all down the bore w the gauge and mic, on both cyls a BUNCH rotating the gauge and then the piston, seems good. due to lack of material transfer and the water temp never going over 220.. i figures as much but always safer to check.   cleaned everything up, repainted, and am adding a temp switch int he head for a fan if its needed (haven't run one since 04 but I had it laying around so, why not). also moved the temp sensor for the gauge up into the upper hose so some plumbing updates. swapped back to studs on the exhaust, utilizing brass VW air-cooled exhaust nuts, and trying to get a better setup for the petcocks since its a dual feed tank w no crossover provision in the tank.
endless project.  :devil: :toot:




finally found an actual useful purpose for the pergola.  (paint curing in sun)







compression was tested as assembled, not yet run. both cyls dead even. so.. the lesson here is.. always keep the clutch covered




1976RD400C

Cool, I like that you get right at it and make it go again so quickly. Downtime is a bad thing. What pistons did you decide to go with? I have had those Iridium plugs in my bike for over a year and everything has been ok, but I notice it is harder to start now. Before I had the HPI ignition, the Dyna, stock coils, and regular plugs, would misfire at full load at high rpm (weak spark?). After thinking it was jetting, and many hours later, I put in fresh plugs and the misfire would stop but as soon as the plugs had just a little run time on them it would start misfiring again. The HPI made all the misfires stop and I didn't have to change the plugs any more. I think I will try the standard plugs and see if anything seems different.
'76 RD400 green  '76 RD400 red   '84 RZ350

m in sc

thanks. same as before, pro-x.  Im not a wiseco fan TBH. I have them in the lightweight but, meh.

and like said, i've run iridium's before with no issues.   fwiw, the vape (or mzb) thats on the bike im fixing has been on since 2007.


Kawtriplefreak


m in sc

got 'oh shit' fan wired in on radiator as well. temp switch in head will kick on at 195. (this is primarily for getting stuck in traffic situations). its a small spal fan but it moves a shit tone of air.

carbs on, jetting up to 280 to start.  still need to mount pipes and break in, will have to wait a day since i have family in town coming over for a dinner tonight.


IR8D8R

In theorum... The properties of Iridium are very interesting from a scientific perspective. It is of the platinum group which means that it has catalytic properties when heated to high temperatures. These properties are similar but not identical to Pt. Functionally similar to what you see in vehicle catalytic convertors as an example. The reaction causes rapid oxidation of certain materials including aromatic hydrocarbons and the reaction is self-sustaining as long as fuel is present. The reaction is mostly initiated by heat of the catalyst. It is possible that sudden changes in iridium temperature would result in initiation of this catalytic reaction and fluorescence of the iridium component. That would react similarly to a glow plug and initiate detonation in the presence of fuel. At high RPM this could advance ignition or create a secondary ignition event from wasted spark under the right conditions such as high RPM.

Iridium is chosen for it's high resistance to arc transfer. In high energy ignitions that is desirable. But modern FI systems are better controlled for fuel delivery than carburetion. Fuel quench is available and utilized in charge temperature control and emissions are carefully managed. The amount of unburnt fuel is greater in a 2-stroke no doubt. If hot spots develop in iridium electrodes from high energy ignition spark, in the presence of hydrocarbons, the ignition event could be uncontrolled. In a 2-stroke application where there is a high energy spark and excess fuel I believe that a reaction would be possible.

I'm not saying that this is what happened with Mark's bike. It is just a possible explanation for what occurred with no other identified problems. What this would indicate is that iridium spark plugs are unsuitable for 2-stroke applications using high energy ignitions. Not that there are lot release problems in quality control in the plugs. I have no evidence to support this except laboratory experience using PT as a catalyst. It will self-sustain a reaction in the presence of hydrocarbons at the right temperature. It is only a possible explanation. Under ideal conditions... From my look into the properties if iridium the catalytic properties are less predictable than platinum. It would only take a momentary reaction at the wrong time to propagate detonation. That might present as a timing anomaly. It might not have the perfect conditions in any other engine for this to occur.

IR8D8R

m in sc

i see what you're saying.

except it blew up when i took the iridium plugs out and the copper cores in.  :huh:

IR8D8R

Oh yeah. Well that makes me feel like I wasn't thinking well... :laugh:

I was so fuckused on the properties of iridium I outsmarted myself.

IR8D8R 

m in sc

you know, it was one of those rare instances where only one thing could have been the issue I was able to sort it out. especially since the bikes been put together so long and historically extremely reliable.  I -never- would have even considered it unless for that happenstance conversation with Chuck S.

I was in there 2 days ago buying some fuel line and was talking to his main tech, and he was like 'yeah.. that's all it could have been.... so weird.'.

hopefully i can wrap it up tonight.