crank pulley bolt - washer or no washer

[smestas]

Wayne,

I have a pulley made for AC but my question is do I or dont I use a lockwasher under the pulley bolt. All the diagrams I have show a lockwasher under the bolt but in the apendix A of your book it only refers to the lockwasher only for the non-AC pulley. Could this be the reason for the two different torque settings?

I aso wanted to know if there are two different part numbers for a crank pulley bolt? I ordered one (K-093-005-02) from you guys but noticed that in apendix A the AC pulley bolt has a extra measurement listed from the non-AC bolt. Did I get the right one?

[Wayne 962]

There have been a gazillion versions of the front pulley. It's probably best to use a lock washer if the factory originally called for it. I would compare the bolt that comes to the one that was in there before. I know, not a scentific and definitive answer, but it's probably the easiest thing to do...

-Wayne

[Damomma]

My 78 with AC pulley had no lock washer. It hadn't been off since 1987.

[Jim Sims]

Some background from an almost disaster with a '73 T air conditioning pulley installation; during which a concern developed when a manual (Porsche specifications book) appeared to be recommending tightening an M12 class 8.8 screw to 110 ft-lbs which would almost surely fail the screw.

In most of the early 911's prior to 1978 the crankshaft pulley screw was a M12x 1.5 x 22 mm long hex head plated cap screw of strength class 8.8 (PN 900.083.001.02) and it was used with a 12mm spring or wave washer (PN 900.028.014.01). This screw could only be tightened to 80 Nm or 59 ft-lbs due to it's strength class. This combination was used for both A/C and non-A/C equipped engines. A spring or wave washer is almost worthless as a fastener locking appliance so it is interesting to note that in the mid-year Turbo's and Carreras with A/C that the pulley screw changed to PN 999.093.005.02 (also M12x 1.5 x 22). This screw is of the "Durlok" form (http://www.franciskirk.com/screws.html) and is of strength class 12.9; this screw is tightened to 170 Nm or 125 ft-lbs (which is higher than a normal plated class 12.9 screw tightening torques of 140 Nm or 103 ft-lbs) due to the Durlok locking features consuming some of the tightening torque. A spring washer was not shown being used with this screw. Beginning in 1978 the spring washers were not being used on any of the pulleys but the pulley screw for all cars (through 1989) was the 999.093.005.02 part number.

If you received a Porsche part number screw 999.093.005.02 you have the correct part. The head likely has the number 12.9 embossed on it and under the head there may be serrations. A wave washer is not used with this type of screw. The extra number (22) in Wayne's book is the screw's length in mm. All of the pulley screws were 22 mm long (length is measured from the bottom of the head to the tip of the thread). Tighten to 125 ft-lbs (no lubricant on the threads). Cheers, Jim

[smestas]

Originally posted by Jim Sims
The head likely has the number 12.9 embossed on it and under the head there may be serrations. A wave washer is not used with this type of screw.

Jim,

Thanks for the explanation and good info! I checked my bolt and I did receive a bolt with a 12.9 stamp and serrations on the bottom. Woooo Hooo! I can sleep tight now.

Now if I can only find a used non-a/c pulley......

PS - Anyone need a FREE pulley bolt washer?

[Wayne 962]

Great info Jim!

-Wayne

[KTL]

Just as an aside, those Durlok screws can be a bear to get off as well. The serrated head bites into the pulley just right and can make for some serious torque needed to get that bugger loose. If one is removing the Durlok with the motor in the car, an impact wrench is the way to go if you don't have much room to get your breaker bar in there.

Thumbs up to Jim. Always provides excellent fastener info.

[Gregsgroup]

The value of this forum contains to amaze me. Even a post from 5 years ago is still relevant. Makes we want to continue to support our host. Thanks Wayne.

[Blauhaus]

Very helpful info on this thread. Rather than start a new thread, thought I would resurrect this one and add few related questions:

Is it OK to reuse these Durlok type bolts?

There is white residue on the pulley bolt I removed...thread lock? However, Wayne's manual does not indicate thread lock and nothing regarding thread lock in the parts catalog. Is thread lock recommended or not recommended? At 125 ft-lbs and Durlok, thread lock seems unnecessary to me. But that's for steel-steel contact...

I'm installing an '83 3.0L (originally with AC) into my '72 (non-AC). So I'm replacing the pulley with a non-AC type. I've purchased the Rothsport aluminum pulley. Should the fact that this pulley is aluminum change the torque spec? Seems like the teeth on the hardened steel Durlok bolt would tear through the aluminum pulley. In this case, would it be better to use a non-Durlok bolt and combine with a spring washer? Or, lower torque spec and combine with threadlock?

Thanks for any input!

[Walt Fricke]

From what I can gather - from Carroll Smith's books on race car engineering for the unwashed - spring washers do absolutely nothing to help hold parts together. It is the force created by the stretching of the bolt which clamps the mating faces together, and it is the friction between the mating faces which prevents rotation of clamped faces. For these pulleys, there is also the locating pin, but that will shear off in an instant if the bolt loses its tension.

A spring washer or Bellville washer isn't going to add anything significant to this clamping force, per Mr. Smith (RIP). A bolt can only provide so much clamping force. If tightened beyond its elastic limit, it won't clamp any with any more force with extra tightening. If tightened beyond its plastic limit, it will break. If you tighten below the elastic limit, you should be able to reuse the fastener. This is especially so with a fastener like this, which is not subject to additional tension forces (unlike, say, rod bolts or case through bolts or head studs).

Washers are good, if of a good grade of steel and thick enough, for spreading the loads and avoiding maring surfaces when tightening. I've always used one on my crank pulleys, but never paid too much attention to any of it and never had a problem. Torque it down and move on. Makes sense to pay attention to the bolt grade. I am sure that the steel of the cranks is easily able to take all a 12.9 bolt can throw at it.

I'd contact Rothsport, though, for specs on their aluminum pulley. They ought to know.

I know how you feel, as I have an aluminum flywheel and haven't gotten how much to tighten the six bolts holding it clear in my head. On steel flywheels of this configuration I use 150 lbs/ft per Bruce Anderson's advice long ago. Works fine, 8,200 rpm doesn't shake them loose. But the aluminum ones are uncharted territory, and engine troubles have kept me from enough experience.

[KTL]

Don't use threadlock on that durlok bolt. The serrations under the flange provide all the locking that is needed.

Regarding the aluminum pulley, agree with Walt it'd be good to ask the guys at Rothsport their thoughts. They know their stuff and are not just some guys pushing parts that have no idea about the usage details. Intuitively, i'd agree the high torque spec of the durlok bolt would make me hesitate to crank 125 ft-lbs onto it for fear of crushing the aluminum.

[Blauhaus]

Thanks Walt and Kevin

I had the same thought to contact them directly. I got an email reply from Rothsport yesterday and per Jeff they recommend 150 ft-lbs with the Durlok bolt. I didn't expect the torque spec to go up but these guys know what they're doing. Nothing in their message about thread lock, so I assume it's correct to leave that out.

By the way, the pulley is beautifully made. Fits the crank perfectly with no slop whatsoever. It's a shame it will be hidden once the engine goes into the car.

[Blauhaus]

I should add that the Rothsport pulley is black hard anodized, which substantially hardens the surface of the aluminum.

[KTL]

BTW I would not hesitate to reuse that durlok bolt. It's a high quality 12.9 bolt.

Thanks for sharing the response you got from Rothsport. Good to know for future reference!

[hassanov]

you absolutely get the right one.

[Harpo]

I thought I would bump this really old thread when I removed my crank pulley bolt to install my serpentine belt pulley and found a surprise. For starters my bolt is only an 8.8 not the 12.9 and I got a wave washer to boot. The bolt is 22mm long but Clewett is recommending a 30mm bolt most likely due to the increased thickness of the aluminum pulley. Also the bolt they sell is only as 10.9, not 12.9 grade as mentioned above. Now I have to wait to Monday to get a bolt from work to replace this POS.

[Harpo]