What's wrong with this starter motor?
 

When cold the starter motor turns the motor over well. The battery is fine, infact it's only about six months old. Once the engine is warm it only just manages to turn the engine over (but being a well tuned SC it fires straight up). If the engine is hot, like I've been stuck in traffic for an hour, nothing, or just about nothing.

My guess is the contacts between the bushes (?) inside the starter are worn and when it gets hot it has expanded that little bit more, so it doesn't make contact anymore.

Or could it be the soleniod. I've got no idea about these.

The wiring contacts are good and clean and the motor is well earthed.

Any tips, tricks, traps, opinons and verbal abuse is much appreciated.

I would take it off and have it bench tested by a parts house.

Thanks Matt, I'll probably do that but I thought if there was someone in the know that could tell me to "just.... and it will be fixed".

So of the more knowlegable elctric guru's like RoninLB, Warren, or JW may be able to shed some more light. The testers should be able to say if it's the starter motor or the solenoid as well. But I wouldn't think after 6 months it wouldn't just need a cleaning, when I believe I changed the original starter on my SC after 21 years of service.

And since you have changed it once before, the project of removing the strater really isn't that bad.

Warning...my knowledge stems from RC cars but it's the same principle........

Magnets lose their strength when hot, often quite dramatically. It is possible, if the starter motor is 20 years old, that the magnets could be on their last legs.

P.S. almost 2000 posts!

Edit: I'm feeling relly stupid now, just remembered that solenoids work on magnets as well, that would most likely be the problem. Give the starter a sharp tap with a hammer next time it siezes.

Re: What's wrong with this starter motor?
 

I would start with a solenoid jump.. if your familiar with that. use a screw driver.

then you go after the hot feed, or
the de-cooking of the 911 sol.. the toased grease and plunger expansion jams it..
don't quote me on the plunger... Ron

Engine is harder to turn over when hot too, I think.

If you have to replace (rather than rebuild) it... try AES - Auto Electrical Spares in Henderson. $350+GST for a Nippon Denso 2kW starter (over 3hp!) which would probably start a jumbo. They copied the size of my existing starter. There was NO Porsche tax.

Auto Electrical Spares Ltd - 25 Parmount Dve Henderson Auckland - 0-9-838 6700

Thanks for the good advice guys. I guess I'll pull it out of the car and check to see whats worn or looks dodgy. If it does need replacing I might try one of those Westies in Auckland :)

I don't think this principle applies to electromagnets (field coils)...

the 12v feed is a common weak point.. maybe a temporary momentary push button wired between the sol feed and the main starter feed, then snake the wires into the cabin for when the problem happens again.. the 14pin engine comp yellow wire/sol connection is a common problem.. and the aftermarket alarm starter kill may break the solenoid connection with smaller wires on the alarm relay leading to voltage drop.
The sol does need routine cleaning and re-grease IMO........Ron

When you pull off the starter you can check the solenoid and the starter motor seperate from each other. With jumper cables put the neg to the starter frame and touch the pos to the small term on the solenoid, it should click and throw the starter drive out and the starter motor will not turn - this means the solenoid is working. Then put the pos to the large term on top of the sole (not the one with the wire hooked to it coming out of the starter motor) and use a jumper from the pos to the small term on the solenoid. This should energize the solenoid thus putting power to the starter motor and it should motor. You can also check the starter motor by itself by going to the lower large term on the sole (with the wire attached to it going to the starter motor) and this will bypass the solenoid.
Hope I made some sense to you. Good luck
jc930

Wow, thanks guys, Ron and JC I'll give those ideas a whirl on the weekend. I've got SSIs and muffler to put on this weekend so I'll be playing cars anyway. I'll keep ypou posted.

Hey Klaus, 2000 :)

Have you checked the ground (earth) strap and associated hardeware that connects the transmission to the body? I was having a similar problem with one of my 912's and replacing the corroded strap was the fix. Good luck.

Bill,

The Bendix mechanism and solenoid both tend to get 'mucked' up with corrosion, old grease, clutch plate dust, and metallic wear particles ... which reduces the power of the starter significantly when hot. I routinely disassemble my starter every 3 - 4 years to clean & lube ... and check for brushes, bushings, shim, and spacer conditions.

I realize most people would never even consider disassembling their starter and would much rather simply replace one that is malfunctioning ... but the job isn't that bad, and can lengthen the life of your starter significantly at very low cost! After cleaning and lubing with a high-quality, high-temperature moly grease ... your starter will convince you it is new again!

Before i take everything apart, do a resistance test of solenoid and starter windings and drop of voltage test to those elements when cold and hot and compare the readings. If you get a higher drop of voltage when hot, it can be a few things actually. If you get the same readings, may be your problem is somewhere else. Check all connections carefully from batteries to cables to starter, including grounds straps.
it can even be the cables themselves. Do drop of voltage test of starting circuit with Digital voltmeter. Very easy to do.
If you need to know how, let me know.
Truly, Filou.

Thanks again Guys. That's what I had in mind Warren, I've fixed enough Toyota starters and alternators with a clean and a pair of $3 brushes to make it a worthwhile bet.

You have hours long traffic jambs in NZ?

Who would have thought

Yea it's a pain in the arse when those sheep farmers forget to close their gates ;)

(BTW I'm half kiwi so no attacking me for being Australian. haha)

Kinda been there done that!

I first added a "hot start kit" which, I know is only a bandaid, but what a bandaid!! It added much more punch to the solenoid before the symptoms showed up again. This time my mechanic says, " the wires from the starter to the solenoid are loose and the starter should be replaced". Well, considering the car is a 1973.5 and the starter is original (would you believe that?), I opt for one of those higher HP rebuild Bosch units. Bingo, hot, cold, bring it on...it starts everywhere.............until that horrifying click after turning the key comes up on me again after a nice run on the interstate. Luckily I get a push start, but I was ready to trade it in on anything at that point. You know the problem was a number of collective things each contributing to each other and culminating into one source........................the battery!!

A brand new Interstate high output battery was installed as a first line of defense against the starter problem. It turned out that I had a bad cell and at times did not get the cranking power
I needed despite all the corrections. So now I have a new battery, starter, hot start kit installed, new ignition switch by the way, new ground wire (check that) and I am back to what I hope is normal.

Thought I would pass on my story. Porsche, a way of life.........

Regards
Bob
1973.5T

Bad traffic is when I drive 'round and 'round the block for an hour :)