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Last weeks carrion…..

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.

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