spark plug porcelain shattering
 

:scratch: * I need help finding the cause of spark plug ceramic shattering only in R2, both L2 & T2 when run hard. L1 & T1 are ok. I think it is ignition related since I has not changed my jetting.** Here are the details: holley 4barrel carb, racing beat intake manifold & header, 2.5" exhaust tubing, racing beat power pulse prima flow muffler, 1974-78 RX4 13B engine swap to 1993 B2200 pickup, no turbocharge, no supercharge, no nitrous, just naturally aspirated street ported, atkins 3mm apex seals, high volume oil pump, oil pressure regulated to 85psi, no oil cooler, 87 octane pump gasoline, holley blue fuel pump, fuel pressure regulated at 6psi with a deadhead holley regulator, two msd 6a ignition boxes, two msd blaster2 ignition coils, brand new ngk spark plug wires, ngk BR8EQ-14 spark plugs, 1981-85 electronic breakerless ignition distributor.* I think it is cross triggering the pick up coil signals or the problem may be related to the amount of timming splitting between leading and trailing. What do you think is causing this?:wallbash:

You give me too much credit. I've never had this problem so I don't know of any solutions for it.

What it *might* be is perhaps a cast air bleed of your holley was malformed (it can happen) and causes a slightly incorrect mixture at high RPM. Or maybe a jet is slightly clogged on that side of the carb. Or perhaps the MSD boxes and/or coils are causing problems. Can you swap parts to known working ones and recreate the driving conditions which cause the breakage?

What the problem most likely is, is a timing split that is incorrect. A 13B likes 10°. Try that.

no oil cooler? thats no good

I don't know the answer to that problem, but I will tell you to get an oil cooler on there ASAP. You might as well take the radiator off if your going to do that. On a rotary the oil cooler is not there for the sake of keeping the oil cool, it is there to cool the oil for the sake of keeping the ENGINE cool. We all know rotarys run high engine temps, and not running an oil cooler will cost you your engine. That's why even a budget performance car came with them from the factory. Could be that if Jeff's thoughts about fuel mixture are correct, the higher block temp could be auto igniting the A/F mixture, although last I checked that would ruin your seals not the plugs.

Try switching all the rear rotor and front rotor ignition components (ignitors, coils, wires if they're long enough) one at a time, and see if the problem follows those components.

"You give me too much credit."

It's your brain, the way you investigate and the way you find solutions that makes you a unique member of this board. A true gearhead if I ever saw one...just the stuff you tossed out with some testing tips to boot, proves I made a good call bringing this to your attention...stick around and see how many more "baby seals" you can save...:lol:

The ONLY time I've ever had this happen was on my old Firebird street machine when I ran the Accel spark plugs...the tops of each of them (and even the NGK's we use now...) had tips you had to screw in...I used to mount the plug in a vise and SCREW those suckers on when I was a BYM noob. Microscopic cracks developed I couldn't see were the results of such nonsense and they failed in a week...they didn't blow up, the car just ran like crap and when I pulled the jackets, yellow crap was everywhere. My Pontiac guru back then saved the day and laughed when he saw me starting to do it again with the next set of plugs. Some things just don't "strike" you as wrong when you're first getting started.

Mario III

Thanks for the interest in helping me find the problem. By the way, the part of the plugs that is shattering is the one that goes to the inside of the engine, around the spark plugs electrode, not the outside whitch goes to the high tension wires of the secondary circuit. The engine is not running hot, my autometer procomp gauge needle raise only to 180 F degrees even when running hard. Thanks again, I really appreciate any help.:)

I had this happen once on one of the trailing plugs. I don't know exactly WHAT was causing it.

However, I do know that the plugs were a couple heat ranges too hot. (NGK sidefire experiment, all four plugs melted the electrode tips a little after a couple 1/4mi passes) I was also running a bit lean, no color at all on the plugs, but this had never hurt anything before...

PS - The insulator disappeared, passed through the engine. Didn't hurt a thing as the engine went another 20k or so before I overrevved it and blew it sky-high. Perhaps I was lucky, I have had the same thing happen to the check valve weight in a Holley accelerator pump, too :eek:

In my case the porcelain remains traped by the 4 negative electrodes of the spark plug. The engine do not miss a bit even with the broken plugs. Drivability is perfect. By the way, I do not run an oil cooler, but I modified the oil injection jets on the eccentric shaft with weber carburetor air corrector jets as to provide larger oil supply to cool down the rotors.

Your basically running lean on that rotor and your getting pre-ignition or detonation on that rotor and the pressure is breaking the ceramic core. Thats my best guess.

I would check to see if it follows the ignition components as was suggested by swicthing them one at a time. If it doesn't then I would seriously look into the carb because its leaving one side of the intake lean for some reason.

Good thing this isn't a boosted rotary.

agreed, its probably really hot, because the oil is really hot. hot oil = high rotor face tempratures

Change the ignition coils leading to trailing and trailing to leading, the problem did not follow ignition components.It made me think the MSD 6a boxes and the Blaster coils must be good. Example: lets asume the leading MSD 6a or the leading ignition coil is fault, then it would breake L1 & L2 spark plugs. If trailing MSD 6a or trailing ignition coil is damage, then it would breake T1 & T2 spark plugs. Neither is the case. It is breaking simultaniously only L2 & T2 spark plugs ceramics. No electrodes are melted. May be it is running lean only in R2, but I think it is unlikely because the intake manifold is modified with a commom plenum under the carburator where each engine intake port sucks in air/fuel mixture from all 4 barrels at all times, and the wide band oxigen sensor read a mixture of 11.9 air/fuel ratio at full throttle in four gear. The O2 sensor is located at the header collector.

spark plug porcelain shattering
 

how were these spark plugs installed did you torque them more than 15 ft lbs when you were installing them.

Yeah but that o2 sensor is measuring the average of the oxygen from the two rotors exhaust, it could still be lean on the one rotor. I bet one side of carb has a fouling issue somewhere.

Put new plugs in and run the engine up to temperature and check plug colors (hopefully before they break up). Your looking to see if the L1 and L2 plugs are vastly different colors where darker means richer and lighter or none means lean.

Spark plugs were finger tighten so I can check the plugs on the road really quickly, so I Think I do not break only L2 & T2 spark plugs installing them. Lastnight I borrowed the holley street HP 4 barrrel 650cfm mechanical secondaries part# 82651 from my brother 1988 gxl. Results: the same problem, shattering L2 & T2 spark plugs ceramic. This time the wide band read 10.8 a/f ratio.

spark plug porcelain shattering
 

okay those spark plugs need to be torqued or tighten down more firstly. If the problem still occurs we move on but you have to do it by process of elimination . Just because you are getting 10.8 a/f ratio it doesnt mean that both rotors are being fed adequately one side could be running way lean .

That is probably your spark plug problem right there.

Spark plugs cool themselves off by contact with the cylinder head (or in this case the rotor housing). They need to be torqued for a good thermal connection.

Perversely, undertorqued plugs get stuck way more often than properly torqued ones.

you probably have a vacuum leak causing the rear rotor to run lean. if r1 is running 9:1 and r2 is 14:1 youre going to see 11.5:1 at the collector.

This is why the plugs broke.

When spark plugs are not tightened correctly there is two problems. One is that the plug threads are not making good contact to the threads of the cylinder head/rotor housing, this causes a direct elevation of both center electrode temperature and ground electrode temps, the plug can't dissipate heat. The other issue with a loose plug is vibration, which is most likely the issue you are having that is breaking the insualtor.

Tighten the plug to the NGK recommended 18-25.3 lb-ft required for a cast-iron head and you will not have this issue ever again.

P.S. I handle all the US damage claims and under-tightening is the number one problem and cause of plug failures. If you have any plug related questions just let me know.

Regards,

Brandon

Why it does not shatter the finger nontightened L1 & T1 spark plugs? Does R1 rotor housing has a better heat transfer than R2 rotor housing? By the way , problem began November 2008 with all 4 spark plugs Torqued to spec as per original mazda rx-7 1986 workshop manual paret #1131-10-85h page 5-30.

Even if I put on a fresh brand new set of ngk r6725-11.5 spark plugs torqued to spec, it will still shatter ONLY L2 & T2 plugs.

By the way, rotary* engines rotor housings ( where the plugs are threaded) are aluminium, not iron.

I thought that part was cast, thanks for clearing that up. I just bought my first rotary three weeks ago so I am still learning these engines. :)

If you still have the damaged plugs I can look at them for you. Just send them to:

NGK spark plugs USA
ATT: Brandon/aftermarket
46929 magellan Drive
Wixom, MI 48393

List for me your name and contact info as well as mods done to the car and under what conditions you notice them breaking. I'll contact you when I get a chance to look them over/test them.


It is possible that the rear rotor could have more heat than the first housing or worse harmonics, but if you say the plugs also broke when they were correctly tightened then there may be another problem going on.

Regards,

-Brandon

spark plug porcelain shattering
 

If you tried r-6725 11.5 plugs in your engine and torqued them to 15 ft lbs and they still cracked then your problem is not spark plugs or torque specs you need to check intake system first and make sure manifold is seated against engine then check fuel delivery to both sides of rotors. Question has this engine ever been overheated you could have a warped intake manifold.

Did you ever check the plug colors as was suggested? You must have a fuel mixture problem on the rear rotor if we have ruled out loose or over torqued plugs. The plug colors will tell you if the mixtures are different and which are lean. Ignore the wide band for now, its not telling you anything helpful at this point.