Rotor button melting!! Why?

[911-m5]

It's on a 1970 911t. Possibilities anyone?

Thanks

[911pcars]

Voltage should be high through the secondary circuit. Current should be very low. Melted button indicates higher-than-normal current flow. What kind of ignition box are you using?

Sherwood

[rexav8r]

I saw that happen once when somebody tried to put a Bosch rotor on a Marelli distributor on a '70 E.

But I don't want to point that finger at myself right now...



What kind of distributor do you have???

If you bought the rotor recently, odds are it's a Bosch since you can't really find the Marelli components ANYWHERE anymore !

(Anybody out there have any they are looking to get rid of???)

Hopefully you kept the old rotor, if it's a Marelli, mine is fairly user serviceable. Take a dremel with a wire brush, clean it and the cap up (unless you have cracks and/or significant wear) and you may be good to go for a while.

Otherwise you may have to bite the bullit and get a new Bosch unit. There are plenty of parts available for these...

[H20911]

Where has man last been?
Did you change your rotor on a tune up?
New ignition coil?
New ignition?
Resistance in the rotor on a new high current Crane cams ignition will burn up.
Did you change the rotor and it did it again?
I think we need more info to get this one.

[john walker's workshop]

MSD?

[Nitrometano]

May be are too resistance on the spark plug wires.

[911-m5]

Hi again,

I did just replace the points and the rotor button the plugs and wires etc...

The old rotor looked kind of burnt up and after maybe a 2 weeks runnng time this one is starting to melt - the black shiney stuff is whats melting. The car has been popping and sputtering. I took the rotor out after running it yesterday for maybe 10 mins and it nearly burnt my hand pretty good - so its getting pretty hot. It is a bosch rotor and cap. I'm not sure what the distributor is I'll have to look. All other ignition components are stock with the exception of what i think you guys call the c/d box - high output ignition box right? Well, the stock one has been replaced with what I think is probably the first aftermarket one ever made - it's called the SPEEDOTRON I think. I'd have to look again to verify but I think thats the name. I can find no info on it other than somebody who found and old panorama ad for it. Anybody ever heard of this thing?

Thanks

[H20911]

Assuming that the car ran well before the cap, rotor, plug wire change. What is now different then before? Did you have a rotor burn then decided to do a tune up with new and different parts (Brand wise)?
What is the back ground?
I suspect that parts were changed during a retine tune up and now it is burning up the new parts as fast as you can put them in.
You have resistance somewhere..... probably the rotor. Is it a different brand then the original?

From Warren: I haven't done this, since I don't use or advocate MSD ...

But, one possible solution would be to take a new Bosch rev-limiting rotor ... and 'bridge' the Glyptal-covered resistor element with a row of 5 or 6 parallel 30 gauge wires soldered to the brass ends where the resistor element terminates. Brass stock could also be used. The power rating of that resistor element is apparently too low for use with MSD, and I don't think soldering a higher-power rated resistor to the rotor would be a good idea!!!

Here is a thread you should read:

MSD rotor burn problem

[911-m5]

Ok let me go back to the beginning of this saga.. Episode I

In a galaxy far away.....

About two years ago - I think the car was running fine then but it may have started the backfiring and sputtering then - I dont recall. I needed to replace my heat exchangers and as you might have guessed, some of the studs broke off. I was hesitant to drill them out myself, so I took it to a mechanic who said he had done this plenty of times before (lies, lies and more lies). He siad he would drill them out with the engine still in the car on a lift. My car sat there for about three months and I finally got pissed and towed my car back home. Being as there arent any other mechaics in my area that know anything about old Porsches, I decided to take the engine out myself. I didnt remove it for a few months because I had never done this before and I was a little worried, but it came out o.k. I took it to a town about an hour away to another mechanic who said he could do it. Being that it was getting cold and the garafe is not heated I told him I want in a hurry he could do it over the Winter months. They turned into Spring months, but he did get the job done. I did notice that one of the studs turns in its hole though. So, I got the engine back last June. I decided to go ahead and do a valve adjustment and I also purchased the tune up kit from Pelican. I figured it was a good time to do both things. I gave it the tune and installed the heat exchangers and turbo valve covers and put in a new clutch and clutch cable. I did notice at the time the old rotor button was somewhat burned up. I did have a little trouble with the cable installation and John walker helped me out with that. (Thanks John!) So, that was probably around September/October of last year. It ran well for about 2 weeks as I recall and then started the spitting and sputtering and backfiring. I noticed that gas was leaking out of 4 of the accelerator pumps on the carbs. So , I did - as best I could- a rebuild on those and put them back in with no improved results. I did mess with the timing yesterday and you can move the rough spots around on the rev range, so a couple of friends of mine think its an ignition problem b/c of that and the hot rotor button.

I think thats everything. I just really want to have my car back. It's gotten pretty depressing and demoralizing. I never get to drive it - makes me wonder what the point is in having it. I'm just getting very frustrated.

Thanks for the help

[Zeke]

This thread is about a rotor, but I have to toss in a tip about the carbs. I hate to see you get frustrated. God knows I have seen that movie lately!

Take the accelerator pump covers off and lay them on a known flat surface like a piece of plate glass. For this test, the glass can still be in the window or door. It just has to be plate glass, no wavey glass.

Slip a feeler gauge all around. If you can ge more than .003 under the part between the tabs, it's warped due to over tightening of the screws. You simply need to sand the part dead flat on some emory cloth or wet or dry sand paper lubed with kerosene or similar. Finish up with med/fine paper, you can tell when you've got it flat by the sanding marks. It doesn't have to be super smooth, a little "tooth" is a good thing.

Next, put a little Gaskacinch on the gasket, both sides with your fingers. No excess. Install and don't overtighten the screws. Let dry overnight. You won't have any gas leaks if your diaphrams are good.

Good luck with the ignition, you will get this thing running like a top. Just keep coming back here for step by step instructions and advice until you do.

BTW, you won't find the *glass* procedure in your Haynes, so keep coming back for similar tips.

[Early_S_Man]

Assuming that you have the proper rev-limiting rotor for your distributor ... what resistance does the rotor measure form the center brass contact point out to the end of the rotor tip? I have seen rev-lmiting rotors that got cracked [after being dropped on hard concrete floor] in the Glyptal area covering the resistance element ...

If your rotor resistance element was cracked and 'open' ... the burning may be the result of overheating of the Glyptal insulating compound by arcing to jump the gap in the resistance element!

If the rotor measures infinite or open [incomplete circuit] from tip-to-center, then try bridging the resistance element with some fine gauge wire by soldring ... or get a new rotor!

[911-m5]

Thanks guys.

I am going to order 2 rotors and see what happens. If the next one gets burnt... I'll certainly need some advice on what to do. Do any of you know where could get one that doesn't have the rev limiter built in? I would like a garden variety rotor just to try it out. that was the type I replaced. Besides, I like making the choice of how far I rev it.

[john walker's workshop]

get a cheap american made rotor from napa or elsewhere, which doesn't have a resistor. end of problem.

[911-m5]

Thanks John,

One more question: Do I run the risk of damaging anything by using the cheap american variety?

[john walker's workshop]

nope.

[73911guy]

John Walker

I've seen a burnt end on a rotor before but never tracked it back to an MSD issue. So the rotors from NAPA are the best for an MSD application? How about distributor caps?

Thanks

Jim

[Nitrometano]

Were I can buy a non Bosch rotor? Here in PR we have no NAPA? There is another rotor from other car that fix into a Porsche distributor ignition?

[911pcars]

"Do any of you know where could get one that doesn't have the rev limiter built in?"

It's been awhile, but I believe an early VW rotor will fit. Take your current rotor when you go shopping to compare.

Sherwood

[john walker's workshop]

vw bug rotor fits 72-77 for sure, but if i remember right, there's a shaft size issue on the earlier ones, and the rotor will wobble.

[911-m5]

Any ideas what it is if I do put in the cheap rotor button and it burns that up too?