Tuesday, July 24, 2012

Faulty Ignition Switch

1 911.613.011.06 Ignition switch, mechanical portion
1/1 911.613.125.00 Buzzer contact
2 911.613.017.00 Ignition switch, electrical portion
3 - Key
4 911.347.359.01 Reinforcement plate
5 999.219.017.02 Shear bolt (x2)
6 911.613.169.00 Washer
7 911.613.160.00 Rosette
L
ike most vintage Porsche owners, I found myself dealing with a faulty ignition switch. For the last year or so, intermittently it had not been working, then intermittently it worked, and finally it became a bit of a lottery. All key positions were functioning except the last click - engine start.

After reading about the common failure of the electrical portion of the ignition switch (#2 in diagram), I overnighted a replacement. Grabbing my favourite Porsche DIY book - Wayne R. Dempsey's 101 Projects for Your Porsche 911 - I flipped to page 212, Project 91 - Replacing Your Ignition Switch (Google Books and Pelican Parts have some of it online - but you really should buy the book!)

My first challenge was to remove the two shear bolts (#5 in diagram). A shear bolt is a type of security fastener with a head that breaks away after tightening to prevent easy/criminal removal. After some careful drilling and using a Mastercraft GraBit I managed to back out the bolts without needing to remove the steering wheel.

Removing the shear bolts

With a glowing sense of accomplishment I installed the new switch... and had the same problem.

With a now deflated sense of accomplishment, I deciding it would be wise to actually diagnose the problem. First I checked all ground straps and battery terminals. Then I decided to test for power at the solenoid. The main line showed a strong 12.4V but the other two wires were flat when the key was turned to the start position - so I knew it likely wasn't my starter/solenoid.

I then tested the electrical portion of the ignition switch separate from the mechanical portion (what I should have done to begin with) by turning it with a Phillips screwdriver... Eureka! the engine roared to life. I now knew it was the mechanical portion (#1 in diagram) that was faulty.

Looking closely at it, I noticed it wasn't turning quite far enough, maybe 15° short of the full start position.

After several days of driving with the electrical switch swinging by my knees and a Phillips stubby in the ash tray, I figured I either need to dish out the $600-700 for a new ignition switch or try to repair the one I had. If I were to buy a new one I'd need to open it up to rekey it, so I decided to disassemble the old one as practice with hopes of maybe finding an easy fix.

To release the key barrel/tumbler, I used a 1/64" bit to drill out the single pin. With the barrel out I could see it was showing some age and was a bit sloppy.

At the tail-end of the tumbler there are two plates that turn with the key - the thicker outer one turns with the key and the thinner, inner one turns a bit out of sequence. Mine were turning at the same time.

In a functioning mechanism, when turned clockwise, a spring-loaded pin clicks into a hole and turns the inner plate. Then when turned counterclockwise, the pin pops into a notch on the outer disk, preventing it from being turned clockwise again until turned all the way back. This "start lockout" prevents the car from being restarted after it's already been started.

Without taking the tumbler apart, I tightened things up significantly by hitting the two pins at the back with a hammer and punch.

To save the next guy (or future me) some trouble, I tapped the pin hole and replaced the pin with a cone point set screw. Also, when installing the ignition back in the car I used regular bolts instead of the OEM shear bolts.

Here are two posts on the Pelican Parts Technical BBS dealing with the same problem:

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