James Roccasano

I am reassembling my 915 after replacing some of the internals. I put the castellated nut on the input shaft but when I torque it to 116ftlbs the hole for the roll pin is obscured. What do I do?

1. Torque it to a lower spec to allow the pin to go in
2. torque it higher to get the pin in (this would be fery high indeed)

I can getthe roll pin in with a torque of about 95 ftlbs on the nut

Any suggestions would be a big help

thanks

JIm

art

Are there shims available that allow you to get the torque value and the position? I've never worked on a 915(just 901&016), so just an ignorant suggestion.

James Roccasano

I just received info on my club's message board that indicated the torque value suggested by the Bentley manual is too high and that using this value has been known to snap off the end of the input shaft. Now I am wondering how many other values in the Bentley manual are wrong and how much damage I could do as I return the engine and transmission to the car.

This kind of error really disturbs me. I am tentative enough about doing my own work as it is without having validity of the "bible" I am using being called into question.

Anyone out there have a list of errata for the bentley book (84-89 carrera)? Are the factory manuals my only source of valid info?

Thanks

Peter Zimmermann

Don't know what year your car is! If it's an '81 or earlier your torque spec is 120 - 140 nm (87 - 101 lb/ft), if it's an '82SC - '86 Carrera your spec is 160 nm (118 lb/ft). If you torque the nut and the holes don't line up, remove the nut and grind a small amount of metal away from its contact surface (I use the flat side of a precision grinding wheel), or sand it down using emery paper, oil and a surface plate. It might take you a few tries to get it, but as you work you'll get the hang of it, just be sure to keep the nut flat against whatever you use to remove material. Do a little, retorque the nut and see how much you've gained. It is critical that the nut be tightened to spec!!! Your patience will be rewarded!

Chris Bennet

Peter,
Educate me, why is the torque on that nut so critical that it can't be over/under torqued a little to line the hole up?
In my mental model of things, the goal of the tightening that nut is to produce a stretching of the shaft and a compression on the gear stack. If I return that nut to the same position it was when it came off won't I have duplicated the shaft tension it originally had? If I trust the torque instead, the first few times I torque that nut the torque to tension relationship will change as the threads become smoother (less friction) and the nut turns further for the same amount of torque.
Chris the Eternal Student

P.S. Love your book! I recommend it every chance I get to people looking for a used 911.

Peter Zimmermann

Hey Chris, don't overthink the torque issue! Sure, the threads might be altered, but ever so slightly. Torque is a number established by engineers educated to assign such values. They are trained to understand the way two metals work with/against one another, and can establish a number that won't overstretch metal, or loosen over time as it's subjected to internal stresses. There is nothing in the factory manual to suggest replacement of the nut is needed, so we have to believe that its threads will not be harmed by on/off procedures. I think Porsche went a long way toward simplifying the whole deal when they changed to flange nuts in later transmissions. Those nuts have a shoulder which is peened into a recess after they are tightened - much easier! Good lick with your project, and thank you for your kind words about the book!!

Peter Zimmermann

Chris - a follow-up that might help. Without mentioning names a friend of mine was asked to drive a fellow's 996 recently. The worrisome symptom - noises that seemed to be related to the rear suspension. My friend heard those noises, investigated, and found loose hardware holding rear suspension bits together. Now the rest of the story: The car had been in a pretty big shunt, costing thousands to repair. That repair required removal of the rear suspension in order to facilitate repairs. The "qualified" shop that did the work put the suspension back in using the old hardware. It states in the factory manual that much of the hardware is designed as use-it-one-time-only, and defines those parts. Guess what? The old stuff was used over, and had already started to loosen, after only 2500 miles! Your car, on the other hand, is assembled with "use it over" hardware. The rear shock bolts, trailing arm hardware, etc. is unaffected by removal. Of course, common sense is still important - replace the lock washers on brake caliper bolts, etc., but for the most part everything stays tight. Think about lug nuts. How many times do a car's wheels get removed over a lifetime? Have you ever heard of anyone replacing lug nuts, for other than aesthetics? Nope, put them back on and torque them. Most of the internal hardware in the 915, like the M/S castle nut, is designed to use again. The ring gear bolts are an exception, as are flange nuts, which should be replaced every time. I've found flange nuts used a second time (two peened areas), during repairs, and that's a big no-no. I hope this helps!