Threads!

[Luke Hudson]

I've mangled the thread on my 1972 911's alternator shaft (the shaft that the fan and pulley are attached too) can someone tell me the correct thread for this shaft as I will need to buy a split die to restore the thread (it's a Motorola alternator if that makes a difference)

Also can someone tell me the correct thread for the front ride height adjustment bolts, and the correct measurements for these bolts (M8 fine etc)? My powder coater rather unhelpfully powder coated the thread so I need to get a tap to clean it out

Thanks guys!

[Early_S_Man]

Luke,

Motorola/Marchal threads are M16 x 1.00 ... don't be surprised if a die is impossible to find locally!

[Luke Hudson]

thanks Early S Man, any ideas on the front ride hieght adjusters?

[Early_S_Man]

Luke,

No, I've never measured those threads. The hex head is 11 mm, and if memory serves me right ... the major thread diameter is a bit larger than the hex, perhaps 12 mm.

[Luke Hudson]

Thanks Warren, would you belive that the ride height adjusting bolts are NLA? I've snapped the head on one, so I need to find what thread the bolts are and try my local hardware store.

Oh and luckily my supplier has the correct split die!

[Rot 911]

Luke I too mangled the threads on my old '72E alternator. I couldn't find the correct metric die and ended up rethreading it with I believe a 15/16 fine thread die which was quite easy to find.

[Luke Hudson]

Luckily everything’s a bit more metric in the UK Kurt, I’ve managed to get the correct split die from the first place I tried!

And as soon as some kind gent lets me know the front ride height adjuster bolt dimensions I can get that tap delivered too!

[Luke Hudson]

anyone? please?

I've tried my local Prrsche OPC but they can't tell me either

[djmcmath]

Someplace you might try for obscure metric sized tools is Newman Tools -- 1800-465-1384, or NewmanTools.com. All Metric of Seattle may also have what you're looking for, but they don't have quite the inventory of Newman. I don't know what sizes the threads are, but I know where to find the tool...

Dan

[Jim Sims]

Luke, I have the 72 factory parts manual; I'll check tonight and see if it lists the screw type, thread and length. Jim

[Jim Sims]

The adjuster (if you are referring to item 19 in the below figure) is a special screw and the thread and strength class are not listed in the factory parts catalog only the part number which is: 911.341.115.00. This part was used on most 911's from at least 1972 (probably from 1969) through 1989 and also on the 914's. Pelican shows it to be available at US$34.75 each (ouch!). I measured said adjuster screw on my 1976 911S and it appears to have an M12x1.5 thread; there is an approximately 3 mm long dog (a reduced diameter unthreaded portion) at the tip; about 80mm of thread length and then a small external hex head, 11 mm across the flats (an 11 mm spanner or socket fits). Jim

[Luke Hudson]

Jim, You're a saint!

The screws are NLA in the UK and Europe according to Porsche, which i find bizarre so I'll have to get them from my local fastener supplier I'm thinking they're carbide steel, which may make them hard to source.

[Jim Sims]

Sometimes I believe NLA means: "I'm too lazy to look it up or to inept to find it!" Perhaps you should check with another UK parts source or bite the bullet and buy it from Pelican. How's that for "carrying coals to Newcastle!"

I'm not sure what you mean by carbide steel but carbide is a material typically used for making machining cutters and drills and is not suited for use as a fastener (it's too brittle and lacks fracture toughness). I would suggest if you have to make a substitute screw you make one from a strength class 12.9 (alloy steel) fastener. One possible approach is to obtain a fully threaded fine thread (1.5 thread pitch) M12 12.9 strength class socket head cap screw with an 80 to 90 mm long shank length and have a machinist square up the tip and turn the tip down to make the 3mm long round tip "dog". The outside diameter of the head could also be turned down but not too much as the wall of the socket will become too thin and may deform during wrenching with the hex key. You may have to search a bit to find a full thread length fine thread M12 class 12.9 socket head cap screw. I can also imagine making a substitue screw from a length of fine thread M12 class 12.9 stud and brazing a nut (hex or allen nut) on one end but this approach is more elaborate and runs the risk of annealing the stud if the brazing is not properly done. Cheers, Jim

[Luke Hudson]

Thanks Jon,

I'm not sure what i meant by carbide steel either! But I've managed to find a couple of 12.9 strenght bolts that should do the trick!

[ChrisBennet]

Why don't you buy a thread pitch guage and measure this and any other threads you need? Is the powder coating too thick? A pitch gauge is really are a must have tool.
-Chris

[Luke Hudson]

Chris,

having spent close to 5k (and that's GBP not USD) on the car since October, I have to draw the line somewhere.

So if I can tap the great knowledge of the Pelican BBS and save myself another 50gbp I'm going to do it!

[ChrisBennet]

Originally posted by Luke Hudson
Chris,

having spent close to 5k (and that's GBP not USD) on the car since October, I have to draw the line somewhere.

So if I can tap the great knowledge of the Pelican BBS and save myself another 50gbp I'm going to do it!

I hear ya!
-Chris

[A Quiet Boom]

Luke, do you have an old bolt available at all? I've so you can make a thread cleaning tap by using a triangle file to cut a groove on each side like a regular tap would have. You could take one of the bolts to a machinist's supply store and they can measure the threads as well as sell you the correct tap.