Reversed battery connection - engine smoking

[Venezia]

Dumb ass move of the day!
I hooked up the battery in reverse - the engine attempted to turned over and lots of smoke and burning smells came from the engine compartment. I have a positive ground 55 MG so I followed that routine and but on the wrong car!!

Anyway I have removed the battery and decided to ask the Pelican experts what might happen when I reconnect correctly. Is there any risk of further damage and/or fire?
I am assuming fuses/relays, the starter and other parts may need replacing.

Looking for any suggestions as I crawl back into my garage ashamed of my incompetence.
Thanks,
Tim

[grizzfan]

I'm far from an 'expert' but the first place I'd look is at your alternator. Those things have diodes that demand that the "blue-stuff" goes in one particular direction if everything is hooked up OK. Yours wasn't so they might be affected. As well you may have fried your starter.

But what the heck. With all those possibilities, why not hook the batteries up correctly, have an assistant with a fire extinguisher standing by and give her a shot.

Good luck,

Tom

[DaveMcKenz]

Does the starter turn the engine backwards, when polarity is reversed? If so may be mechanical problems too. Hope not.
Good luck,
Dave

[heimtun]

I would disconnect the alternator before you hookup the battery again - the alternator diodes, as suggested above are most assuredly toast - don't want to do more damage to alt and don't want the smoke to turn into flames. The starter most probably did turn backwards - my guess and only a guess is the the starter did not engage the motor - I'm not sure how these starters engage the flywheel. If it were your MG I can tell you reverse polarity would not engage the starter into the flywheel.
Good luck and, if it helps, don't feel too bad and if misery likes company, I did the same thing on my MGB and toasted my alternator - the diodes popped like popcorn.

[MikeD]

I would be concerned with the alternator and DME brain.

[uwanna]

As well as all the possible damage that others have mentioned, I think you will be incredibly lucky if you haven't fried your DME computer with reverse polarity!

[Neel]

Any 'so-called' electronic components might be/ will be fried.. Basic wiring should not be affected..

[Joe Bob]

Radio as well.....

[Porboynz]

The starter should be fine, everything else not so much. The most expensive component will always blow to protect the least expensive component. I agree though, disconnect the large alternator cable at the starter motor and see what still works and what does not. Everybody deserves some luck. When I did this on my boat I only killed the depth sounder, the CDI etc was fine.

Best of luck and don't beat yourself up too much, stuff happens.

[T77911S]

your not the first.

alt and DME would be my first concern.
diodes can take reverse polarity, that is there job, the regulator may not like it.

you can dissconnect the alt at the starter.
if the DME is fried putting power to it wont hurt it any more than it already is.


yea that stupid british lucas crap....just had to be different

[chuckr]

OK, I'll fess up.... I just did this also ! the winter was tough on my battery,so got a new one.
Wasn't paying attention... hooked up wrong... got smoke... altenator fried !!
I did NOT have any other issues ! I did, however, have a hard time getting a altenator.
Pelican was on backorder with them and most other suppliers were as well. I did get one, but it took awhile. Best of luck with this !

[steely]

Tough luck Venezia and chuckr.
What year was your chuckr? glad it worked out.

Venezia - You might be ok (outside of the ALT).
Do a search here, some beat you to it and have done it before and came away with minimal damage.
Your cables behind the ALT may need attention, check all of your fuses and the wiring around them. Some stuff that might still work might fail later, so watch for that.

[chuckr]

I have an 88 911. Pelican did have a new one ,ouch !! but I wanted rebuilt.

[tirwin]

Originally Posted by DaveMcKenz

Does the starter turn the engine backwards, when polarity is reversed? If so may be mechanical problems too. Hope not.
Good luck,
Dave

Will the bendix gear actually turn the motor backwards? Grant and I were discussing this recently. We were thinking that it can't, but certainly could be wrong about that.

[rick-l]

Originally Posted by tirwin

Will the bendix gear actually turn the motor backwards? Grant and I were discussing this recently. We were thinking that it can't, but certainly could be wrong about that.

I don't think a series wound motor will change direction unless you reverse one, but not both, of the magnetic fields.

This is how I subscribe so I can see the pictures that will follow.

[Venezia]

Thank you all for the feedback.

I reconnected the battery, correctly this time and as soon as I screwed down the quick release, the engine began to turnover, including exhaust from the pipe - all this without a key in the ignition.

I can switch the quick release on and off and the starter begins to turn. Fuses and relays are all good but 'Houston, we have ignition without a key' which isn't the way.
Not sure what the next step is but it looks like I will get the 911 to my local expert since I lack the skills to diagnose the problem.

Best, Tim

[rick-l]

Originally Posted by Joe Bob

No such thing as a NEW Bosch starter, unless it is new old stock. They are ALL remans. You just have to have GOOD parts and trust the rebuilder. They will warranty for life, but the labor is on you.....

Do you mean alternator and I think mine was made by Valeo (84-89). An OEM supplier one will set you back $911 new and a genuine Porsche one $951 (but I don't know what the difference would be.

I think you can buy the diodes/heat sink and the diode triple at several places online (with a search). I want to see if the windings are cooked.

This alternator has 6 parallel paths of two diodes connected in series. I wonder if they held on long enough to limit the reverse voltage to two diode drops on all the expensive stuff.

[Porboynz]

Originally Posted by Venezia

Thank you all for the feedback.

I reconnected the battery, correctly this time and as soon as I screwed down the quick release, the engine began to turnover, including exhaust from the pipe - all this without a key in the ignition.

I can switch the quick release on and off and the starter begins to turn. Fuses and relays are all good but 'Houston, we have ignition without a key' which isn't the way.
Not sure what the next step is but it looks like I will get the 911 to my local expert since I lack the skills to diagnose the problem.

Best, Tim

Maybe it is time to seek pro help if you are not comfortable using a multi meter and isolating sections of wiring to find the culprit(s) There might be a semiconductor device of some description connected to the starter solenoid feed that's gone open circuit when hit with the reversed voltage and is now passing current in the wrong direction. Alternately the starter solenoid has stuck in the start position, you can smack the starter hard and often with a wooden or copper faced mallet if you have one. That usually fixes that problem.

[Porboynz]

Originally Posted by tirwin

Will the bendix gear actually turn the motor backwards? Grant and I were discussing this recently. We were thinking that it can't, but certainly could be wrong about that.

Bendix gear? That's a name from the past. I guess you could call the 911 starter clutch mechanism a Bendix but my memory of a Bendix is that it uses a course threaded sleeve and centripetal force to throw the starter gear into the flywheel ring gear when the starter shaft spins up. Crash smash and bash. The 911 starter is slightly more civilised with a solenoid pre engagement of the starter gear on a sliding sleeve incorporated with the clutch mechanism for those who keep cranking after the engine has fired. Could be wrong, I seem to remember the Bendix mechanism had a huge spring that would break when you least expected it and then would not disengage from the ring gear and make a real noise. Any volunteers to see if a 911 starter does run backwards? My bet is not and if it did the clutch would prevent it from turning the engine over. Sorry for hi jacking the thread, none of this is helpful, but it is interesting, sort of.

[T77911S]

remove the 14 pin connector at the relay panel and see if it does it again. if it does NOT then the problem is in the engine wiring harness.