Last week – March 8 – 12, I enjoyed what is best described as pure good luck.
Although I could make an effort to deceive and pretend that it was a solution derived from hard work and investigation, that would not be true.
The result of a simple mis-strike on the keyboard delivered me with a perfect solution in a way that I can only attribute to good luck. Good luck not only for me, but also for Pete vB and the ongoing development of PVX, the rocket 912 with the GT3 Cup motor.

PVX has devoured two starter ring gears (SRG) in a total of about 200 engine starts. The installation uses a shortened 993 6-speed transmission, which precludes the use of the original 993 starter with the starter pinion head supported in double shear by a mount cast into the bellhousing (this mount is lost when 26mm was cut from the bellhousing length)

Like all parts of PVX, we started with the lightest solution we could obtain or manufacture. The lightweight IMI starter was a significant weight saving over a 911 starter. When initial starting and running of PVX lead to damage of the starter ring gear, we suspected that the cantilever pinion design of the early 911 starter was at fault, with the lightweight starter having even greater deflections that allowed the pinion gear to “climb”  out of mesh as the burden of the 13:1 compression ratio in the GT3 Cup motor was encountered.

Before totally destroying the starter or the SRG we switched to an early 911 starter and seemed to have the issue under control, but not beaten. Thinking the wounded SRG was destined to fail after the initial damage – when it did, we installed a 2nd unit, which lasted about another 100 starts…..

I was / am still of the impression that the cantilever design is at fault, with the pinion head free to deflect. What we needed was some system that had a double shear pinion head, one that could behave like the original 993 installation, after all, a 993 3.6 litre motor is 11.5:1 compression and that installation is designed to last 200,000 miles +

So my challenge last Monday on the 8th, was to find a way to emulate that design, within the constraints of the short bellhousing on PVX and execute the work quickly while we complete other tuning and preparations for a serious national event in May.

I had prepared Pete for the fact that we were looking at creating the starter system as a whole new configuration, a combination of OE parts, WEVO parts and derivatives of both to create a pinion head in double shear. Many cars use a simple shrouded pinion head, Chevy’s, VW’s all sorts of Japanese cars. A shrouded starter has the second bearing for the pinion head in the end of the “shroud” thereby needing no other pilot or bracket to support the pinion shaft.

I resigned myself to designing and drawing the 4 or 5 parts that would be needed to mount a shrouded starter. Then went to our Bosch supplier SSF to buy a 993 starter (that should work right?) as the core for the adaptation. The SSF website is great, quick to navigate and they carry huge inventory for cars like the 993 that are in the 10 – 20 years old bracket (plus many much older models too). You navigate to the product by selecting manufacturer – Porsche, Year – 1995, Model – Carrera C2, Section – Electrical, starter, alternator. From the drop down menu I select “Starter” expecting a single starter option to appear. As the screen fills, I am already clicking on the part number and the photo….

I am confronted with a thumbnail image of a shrouded starter?? – not a 993 starter as I know it?!? There in a single rushed keystroke I swept away days of design and a couple of weeks delay while expensive custom parts were made. It turned out to be a 993 Tiptronic starter. We obtained our no-core-refund part for under $300 and then crossed our fingers as we tried it into the packaging envelope for PVX, still expectant of some revision albeit reduced.

Within a few minutes we established that the 993 Tiptronic starter was a direct interchange for the early 911 starter – all the physical aspects were the same, the mount pattern, pinion projection, pinion design – all the same.

So with another new SRG installed, Brian had PVX running again 48 hours later. Fingers crossed we have now solved the starting issues for PVX, which has been the only element of unreliability since this amazing car started to accumulate test mileage in December.

Pete has started to attend Bay Area AutoX events and learn the style of driving needed to deploy the power and utilize the grip of massive tires. No doubt it is a science project and we are happy that the car has the versatility to be tuned and adjusted.

More rewarding was the unexpected gift from the Porsche parts catalogue, when by pure accident I discovered the compatibility of the 993 Tiptronic starter (have you ever looked at a 993 tip transmission? – barely looks like a Porsche product at all!) with the starter from a 1972 911.

Oh, did I mention it is just over 3 lbs lighter too?…… fantastic

This entry was posted on Monday, March 15th, 2010 at 8:51 pm and is filed under Design, Hayden, WEVO. You can follow any responses to this entry through the RSS 2.0 feed. Responses are currently closed, but you can trackback from your own site.