Proper Cylinder Stud Installed Length

[dkirk]

Gentlemen,

Reassembly of my 3.2 engine is proceeding well (I think). All 24 original studs were removed and replaced with Canyon-brand steel studs. In Wayne Dempsey’s book, he states a gauge length for studs should be 5.315 inches above the flange of the case. I assumed “flange” meant the machined surface of the case that the cylinder seats against? The picture on page 137 shows a steel ruler resting against the cast surface on the crankcase, adjacent to the stud. This surface is some .100 lower than the machined flange surface. What gives?

With 24 new studs held in with Loctite 271 and each installed with the gauge dimension being 5.315 inches above the machined flange surface, are the studs too long to let the barrel nuts engage the Allen wrench tool properly?

I’m getting a little paranoid in that all cylinders are back on the case, baffles are installed, and I’m awaiting the heads to be returned from rehab. I don’t want to repeat pulling everything apart again just to screw 24 studs in another two turns.

Experts please voice your opinion and help out a first-time 911 engine student.

Thanks in advance.

[Flat6pac]

The worse possible senario is you would have to double washer the capnuts.
Why did you replace the top ones, they are steel too and are the correct depth.
Bruce

[Henry Schmidt]

The simple cure would be to just change the nuts.
The factory nuts are kind of goofy anyway.

Use a 10x1.5 flanged nut with a 15mm hex. Most hardware supply companies will carry them. With these nuts, installed height has little or no effect. In fact if the studs are long enough you can thread them all the way into the case.

Grade 8 nuts
Material: Medium Carbon Steel, Heat Treated
Proof Load Strength: 150,000 psi min

[cgarr]

Yep, goofy is it. I hate those nuts!

[dkirk]

Bruce and Henry,

Thanks so much for your rapid response. Now I at least have 2 different back-up methods by which to proceed....much appreciated!

Reason behind replacing all 24 studs was due to the advice of an ex-Porsche R&D executive engineer (and friend). He states that even though the studs are not torque-to-yield fasteners, they are torqued close to yield and after 23 years of many thermal cycles, it is prudent to replace them all. I realize the subject is somewhat controversial, but I thought while the engine was disassembled to this point, the $330.00 cost for 24 new steel studs was good insurance money. My biggest nightmare would be to have a stud break on my freshened-up engine.

[4sd911]

I don't have the spec in front of me but I believe the height of the stud is 135mm which is the same as you show in inches. If you have case savers installed they can get very tight around 138mm.

[dkirk]

Thank you 4ds911. I'm resting a lot easier now.

Starting to make some assembly progress now. Still waiting on the cylinder heads from Anchor Atlantic Enterprises.

[dkirk]

Well, cylinder studs were slightly long by about 2 threads so Dempsey's measurement of 5.315 inches is from the cast surface of the crankcase and not from the machined cylinder mounting face. I tried the original socket head nuts and washers and got ample engagement of the Allen driver to torque nuts to the proper value as recommended in the Bentley manual (torque to 11 ft-lbf then rotate through 90 degrees).

All is progressing well at this point. The cylinder heads from Anchor Atlantic were things of beauty. Bob Hirst did a first-class job on reconditioning and I'm very pleased with the quality, price, and rapid turn-around.




With heads installed, cam housings were next:




964 camshafts are being installed in this 3.2, so the RH cam had to have the power steering drive stub cut off:



With both cams installed, timing was set using .490 intake lift @ TDC, corresponding to the 4 degrees BTDC inlet opening point.



Hope to have it all back together in the next few days.