70.4 crank with ac...bummer

[speedo]

I just found out the difference between an AC and non AC crank. There is a "nub" on the pulley end (as well as the pin hole) for mounting the pulley.

This sucks...I am stroking a 2.2 engine and I live at 8100 ft...don't need AC. The pulley I was going to use (166mm) just has the pin on the backside, with no added detent for the "nub". I check through my box of pulleys and it turns out I have a 133mm double AC pulley with the recess and pin, but it weighs 1730 grams vs the 360 grams of the single 166mm pulley. My coices are...1) grind the nub off the crank end. Not likely as I am in the middle of assembling the engine, and it would be a rough job. 2) drilling the necessary coresponding recess in the back of the 116mm pulley to accomodate the nub. 3) Using the 133mm pulley for better cooling (air movement) and using a lathe to turn down the second pulley to leave me with a single pulley...so I don't need to mess with the crank end.
I am inclined to go with door number 3)...but open to suggestions.

Speedo

[Flieger]

The bigger pulley will flow more air. I would make whatever pulley diameter you want to use fit the crank, and take off the second pulley if you use the AC one.

[Flat6pac]

The hole in the end of the crank should be at 9:00 giving you TDC/Z1 on the pulley. From the picture something is out of wack and you dont need to be drilling random holes.
Bruce

[Walt Fricke]

Lars

Which of the two holes in the end of the crank are at the 9 o'clock position at TDC per Bruce?

If one of them is, use it. You should be able to pull that "nub" pin out if it is not in the right place.

Per the parts books, there is only one crank part number from '72 through '77. It only has one hole. And only one pin is specified: 5M 6x10 DIN 7. There is an inch drill bit size which is close enough to this to be used as a substitute in a pinch - another reason to keep some broken drill bits around.

[Walt Fricke]

Oh - If you need to use the "nub", pull the pin out of your pulley. Shouldn't matter whether pin is in crank or pulley as long as one of them is a reasonably tight fit. It just locates the pulley timing marks - the clamping force of the bolt is what keeps the pulley from moving around.

I know, because I once missed a shift, and the pin sheared off. The pulley stayed on and seemed tight, but I was baffled trying to use a strobe timing light until I realized the pin had sheared and the pulley rotated some.

[speedo]

There is only one hole in the crank, and I presume it is at TDC. The nub is a protrusion...it is the issue. And per Walt...there is not enough sticking out to get any purchase. I think the crank hole is ok, and rather than mess with it...potentially buggering it up trying to remove or grind down the nub, I am going to use a mill to lathe-down the secondary pulley. It was machined as one piece with the crank pulley. I'll post pics when it is done.

Speedo

[Walt Fricke]

I have trouble believing that the nub is part of the original crank forging. How would you machine around it? Has to be an insert.

But why not just drill a hole in the pulley you were planning to use to accept the nub? It wouldn't even have to be a tight fit. The collar of the pulley does the axial locating of the pulley on the crank, and you have the stock pin for radial location.

['78 SC]

The conflicting comments above about TDC v pin location led me to check a stock non/AC pulley:




The outboard end of the locating pin is visible at 9 o'clock. Here's the back (note Z1 and 5 degree notches):

[Flat6pac]

The crank picture with the hole at 2 oclock, someone put that there as the hole is too close to the threads. The nub is the pin and needs to be removed from the crank, The nub is the factory part. Heat the crank and get it to release the pin or drill the pin and easy out it.
Bruce

[speedo]

I could drill an offsetting hole in the pulley to accomodate the nub(pin) that could be a loose hole. Now that I am milling the extra AC pulley off...it isn't a big deal. I have never seen the end of a crank that has been this compilcated...usually just the one hole for the standard pulley pin. A friend has a big lathe and I gave him the pulley to attack today. We'll see how it comes out.

Speedo

[Walt Fricke]

I tend to listen to Bruce - he knew without having to go look at a pulley that the locating pin is at 9 o'clock. I didn't know that. I took a picture to show you, but I see others have done the same.

Notice that Bruce says the nub has to be the locating pin. And that the other hole is (or at least appears in your picture) to be too close to the center of the crank. Which means the locating pin won't be in the right place.

If your AC pulley has two pins, or holes for two, perhaps it is off this crank? And for some reason someone drilled another hole through the pulley? Perhaps because something had happened to the locating pin and it got rounded off? So this was supposed to be a fix? Perhaps the bolt got loose and things wobbled around? And the pulley got tossed and another one substituted?

Sounds like the extra hole is not factory, in any event.

Anyway, seems a good idea to have Z1 and the other markings in the right place relative to the crank.

[304065]

Hmm this brings me back to a thread from nine years ago. . .

High Rpm Pulley Upgrade