ray check pm

Kind of on the same subject, but how often are you supposed to change the cap and rotor?

i dunno i did it yearly but prob every 10,000 miles

Oh, oops... I change mine with every oil change. Although I only change my oil once a year.

I've always just waited until they start to show wear on the terminals, thinking that's all that matters. Is it possible that the plastic and internal contacts deteriorate too?

In this case both the rotor and cap had some miles on them, but other than the blow out in the rotor, they still look pretty good (see the pictures above). Only average wear on the terminals, no pits, grooves or excessive corrosion. The cap has the copper terminals (or is it brass), which makes me think it's one of my OEM ones.

I don't think this rotor button blowout was caused by a faulty cap or rotor, something weird happened and it was probably related somehow to the loss of compression in the rear rotor.

Incidentally, as Ben and I suspected, that rear rotor really is toast, I just went out and checked it more carefully, it's got nothing coming out of the spark plug holes and the T2 hole seems to be messed up, I can only screw the plug back in half way before meeting some resistance.

In any case, I won't be putting that dizzy back in anything soon, until I figured what the connection between the rotor button blow out and the rear rotor blow out is.

Quite possible that whatever caused the compression loss (side seal, maybe?) also dead-shorted the plug, which could cause overcurrent conditions in the trailing circuit, which in turn heated and melted the dizzy button.

Shorting the plug is like removing most of the resistance off the circuit, and with electricals, as resistance drops, current rises in proportion - - it's like unclutching a motor at full load. Very much the scenario Kentetsu was talking about.

i am gonna go with the grounded plug at high load too. ray i think somehow the seal apex or side slammed into the trailing hole as small as it is i guess it could happen. Grounded an overloaded the lead and it had to go somewhere.

When you take that motor apart its gonna be interesting to see what is embedded in that tiny as pin hole they call trailing lol.

Now that I can see the photos, I still think that's what it is. The spark found an easier path to take, which seems to have involved the shaft of the distributor. I wonder if it might have cracked on installation, making it even easier. So, once the plugs were more effort than the dizzy shaft, things started getting hot.

"Quite possible that whatever caused the compression loss (side seal, maybe?) also dead-shorted the plug, which could cause overcurrent conditions in the trailing circuit, which in turn heated and melted the dizzy button."

Wow that's deep. Thanks DD. You know that might explain why that trailing plug hole in the rear rotor is a mess and won't accept a plug anymore.

You guys are smart, I owe ya'll a beer.

CSI: Intarwebz

nothing a couple of brains cant figure out :)

i once had a similar problem. it didnt end up destroying the engine but it did make a nasty nois. this lasted a couple of days driving the car, progressivly getting worse and i just couldnt take it. i looked at some other things first and then pulled the cap. suprisingly the engine was still running ok. here are the pics of what i discovered:

http://i636.photobucket.com/albums/u...b/DSC07206.jpg

http://i636.photobucket.com/albums/u...b/DSC07205.jpg

i'm still intrigued by this, the last couple of days i've noticed slight hesitation on take off, also more backfiring than the usual and a jumpy tack, so today i started looking around my plugs and wires and this is what i found:

http://i88.photobucket.com/albums/k1...08-09_2015.jpg

car's still running good, idle is good. i just replaced this like 5 months ago i think... my leading plugs were nice and brown, but trailing were quite black, which i'm guessing is from a weak spark due to the burnt rotor. timing is where it should be set to.......:dunno:

Whooo hooo, that rotor button looks just like mine, it must still be good. Glad I didn't throw it out!

it's actually two of them, diagonally so if you were to trace a line through them it'd form an " X " right down the middle lol.

i took it out and installed the one i had in there before, it was good only reason i replaced it was because i'd owned the car for 3 years and had never changed it, so i don't know how old it is lol.

Yours looks like it has the same problem as mine, melted plastic that looks like a bullet got shot through it, probably caused by arching at the electrical contact inside. The difference of course is that mine was associated with a rotor going bad, which could have caused the rear trailing plug to ground out.

Yours is still functioning in a running motor, I wonder what caused it to do that?

ray, on our camry we didn't replace the cap and rotor and it messed up the coil and the ignitor. it left me stranded 50 miles away from home.

now we replace the cap and rotor. its a much cheaper thing to do maintenance

This is turning into a very interesting mystery!

mystery of the drive-by rotor lol

We actually transplanted the dizzy from the White One that fostered that rotor button melt down into the Silver One today as part of our efforts to fix a problem in that car. It didn't fix the problem; I should have checked the rotor button for bullet holes, will do so first thing tomorrow morning.

took a look at my old aftermarket rotor and found this
http://i3.photobucket.com/albums/y89...oto062_001.jpg

i now bought a new one from mazda. although my old rotor was working okay, its a good inexpensive maintenance item to replace. also replaced my cap too with one from mazda.
http://i3.photobucket.com/albums/y89...oto061_001.jpg

The dizzy from the White One, which was in operation when that rotor button melted down, seems to be working just fine after I transplanted it into the Silver One, using another rotor button I had sitting around (not OEM, but in reasonably good shape). Here's the Silver One idling with the White One's dizzy with the fried rotor button replaced:

http://i259.photobucket.com/albums/h.../th_silver.jpg

We are working on that overly expressive exhaust system today to quiet it down some.

So I'm guessing in my case at least the melt down was caused by the rear rotor failure, as predicted by the dizzy gurus in the earlier posts, probably due to grounding of that rear trailing plug by a piece of the apex seal (what a brilliant analysis, I want to believe it's right even if it isn't!)

But I agree with boyee, the Mazda OEM cap and rotor are probably worth the small fortune that Mazda (and Mazdatrix) gets for them. They have the brass terminals in the cap instead of the aluminum terminals you get in the aftermarkets and they just look prettier, as you can see in boyee's photo above. Thanks for posting, I'll order today!

Hope I'm not too late to say thisbut if you're going to order from Mazdatrix be sure to ask them if it is a genuine Mazda part. I've been deceived a few times getting aftermarket branded part when I thought I was paying for a more expensive OEM part. Just my .02