daveo90s4

The original Porsche 914 starter motor is not powerful enough to happily turn over the 6-cylinder high compression Chev Corvair engine that I have installed in the 914.

A 911 starter motor will fit and will do the job, but none are readily available at sensible prices.

A 928 starter motor will physically fit and these are readily available at not silly prices and have plenty of oomph- but the 928 starter turns clockwise and for my application I need anti-clockwise starter rotation.

So I have two simple questions about the possibility of modifying a 928 starter.

1. Can the electrics on a starter be readily modified to change the rotational direction of the armature (Yay/Nay), and
2. To then have the pinion throwing in with the 'new' rotational direction would it be possible (in principle, assuming all parts are the same size) to swap over the starter front internals to install counter clockwise parts into the 928 starter in place of the 928 original clockwise orientation parts?

Clutching at straws here and trying to be a bit innovative. A rebuilt 911 starter here is close to $1,000!! and I'm keen to avoid that.

Also, if anyone knows the 928 starter 'pinion at rest' length and the length of travel of the pinion when engaged that would be very useful too (cant find that in the Bosch specs).

Thanks all

DaveO
Australia

FredR

Dave,

FYI- There is a current thread with some poor chap who had his starter motor recently rebuilt and apparently it spins the wrong way- maybe reversing a pair of cables within the motor can get it to go backwards - it is DC after all so no great rocket science involved

Rgds

Fred

daveo90s4

Hi Fred,

Thanks for the quick reply.

I too suspect that getting it turning the 'wrong' way should be doable. But then the trick is to get the pinion throwing in with the new orientation. This directional piece looks from various exploded views to be separate from the central armature shaft (says me, hopefully).

Anyone know this for sure on a 928 starter?

Thanks all

DaveO

FredR

Dave,

As I understand the solenoid throws the pinion out,, the teeth mesh into the starter ring gear and then the motor spins as the juice only flows with the pinion in the engaged position. The motor spins in whatever direction it is configured to [Fleming's left hand motor rule if my decrepit memory serves me correctly]. Whether there are any engineering issues related to spinning the motor the other way it was designed to rotate I have no idea. Last thing you want is the pinion shattering the ring gear!

76FJ55

There is a helix on the starter pinion. This is designed to hold the gear in mesh with the ring gear while the starter is applying torque to the ring gear. Once the engine speed increases to where it will overrun the starter, the helix will drive the pinion gear back into the starter and disconnect it from the ring gear. You would need to swap the pinion and helix from a starter that spins the correct way for your application.

Think of it like this. If you accidentally try to start the engine after it is already running; you will get a horrible sound, but aside from that you only get minimal wear on the ring gear and starter pinion.
If you have the wrong helix; as soon as the pinion hits the ring gear, the helix will drive the pinion into mesh with the ring gear and the engine will drive the starter. the torque from the engine into the starter will hold the pinion in until the starter over speeds and centrifugally explodes.

Bigfoot928

...

WALTSTAR

daveo90s4

Hi all,

Thanks for your comments. Up until now I had no idea that there are companies that make one-off starters.

I've found a company here in Australia that will make me the required starter and will also modify it slightly to increase the normal 'pinion at rest' length from 33mm to 40mm so that I get much better full pinion to ring gear engagement when cranking. For any Australians reading this, the company name is CA Enterprises in Melbourne.

Once again thanks all,

DaveO