Stud size on the intake side of a 73 1.7

socuriouso · 08-06-2014, 02:59 AM

I have a stripped stud issue with my '73 1.7. Years ago, I had to have a garage work on the heads, and install new jugs due to the previous owner's inability to diagnose a stuck exhaust valve in the number three cylinder. (As a result, I got the car for $1000.00, third owner, and it was never out of the Austin, TX area.)

It was mandatory as I was living in an apartment, going to grad school and couldn't drop the engine in the parking lot. They came recommended by several VW folks and my neighbor who had a pristine 912. They were surprisingly affordable and my experience was great.

Turns out that the mechanic that did the tear-down and reassembly cross threaded the stud in when installing my Webers. I just found this going through the carbs last night; I was checking for leaks around the intake gasket, carbs and heads due to backfiring that has become more insistent. The webers are tuned best lean, synched (aside from a small leak I believe due to this stud that has finally fatigued and is spinning without torquing back in.

I'm fine with re-tapping the head and cleaning up the threads so I can eliminate that barrel as the culprit. I've searched all over the tech drawings, articles and this board and can't find the size or pitch of the stud anywhere.

Anyone have this info?

I'd be much obliged.

The cap'n · 08-06-2014, 10:16 AM

It's unlikely he "cross threaded" the stud, it just pulled the threads out of the head. You'll need an 8mm x 1.25 insert. This is a fairly common problem, and the repair is somewhat more difficult than it should be because of the location and the design of the part of the head into which the stud threads. The original stud would be 8mm x 35mm, and it is designed to go through the insulator/gasket and the intake manifold, leaving just enough room for the nut and washer. If you're using the insulator blocks beneath the Weber manifolds, that stud may be too short. You need to look at that before you purchase replacement studs, and you should be prepared for more threads to be damaged if you need to install longer studs.

The Cap'n

socuriouso · 08-08-2014, 01:46 PM

Quote:

Originally Posted by The cap'n

It's unlikely he "cross threaded" the stud, it just pulled the threads out of the head.

I stand corrected, the threads were pulled. I forgot to factor in (in my slow simmering profanity muttering state) aluminum heads and steel studs.

My next question is:

Are these studs required to be a certain rating? In other words, are they a specialty fastener in the same way the nuts used to torque the heads onto the engine are? Or do they just need to meet standards designated by their alloy combination and minimum tensile/yield strength and proof load? (8.8, 10.9, or 12.9)

Again, thanks in advance!

The cap'n · 08-08-2014, 04:35 PM

Plain old 8.8 studs. The length is your primary concern. I'd choose one with a 12mm or so end, an unthreaded portion as a stop, and the remaining part long enough to get through the gasket or insulator, and the manifold with enough room left for the washer and nut (which should leave a couple of threads exposed).

The Cap'n

socuriouso · 08-08-2014, 09:37 PM

That was exactly why I was asking. I wanted to get longer studs and if I could find them just about anywhere I wouldn't have to wait for them in the mail. I have the 8 x 1.25 inserts and corresponding tap ready to go.

I carefully removed the other nuts, washers, carb and insulator, cleaned, cleaned, cleaned, and just to satisfy my curiosity I tried the fouled hole with the stud that came out. I used the two nut method and I was able to get good threads deeper back held when I pulled hard on the stud, but never found a "tightened" position.

I'm wondering if you might have any tricks to pre-drilling for the tap in that tight space. (I don't have a right angle drill....yet) The offender is on the 1 & 2 side on the upper left as you are looking into the manifold. I have a Foredom Flexible Shaft that might fit in there with a stand-off jig to keep it at the correct angle, but I'm not sure the shaft will have enough room to curve away from the hand piece. I'm no stranger to dropping the engine to be on the safe side, but I'm always on the lookout for sage advice and new tricks. If there is a way I can do it in the car I'd rather; its my daily driver.

Dave at Pelican Parts · Dave at Pelican Parts's Garage

Mr. PET says the overall length is 56mm (53 for the early 1.7s). There are several entries in the list, some with overlapping "application" fields. Notations range from "AM 8 X 53" to "AM 8 x 56" to "CM 9 A X M8 X 56". That last one might be a "step stud" that is 9mm on one end to allow the hole in the head to be re-drilled and tapped.

I haven't checked to see if these are available through us or the dealer, though.

If you don't want to pull the motor and you don't have a right-angle drill head, then you need to get the car high enough off the ground that you can use your current drill. I have heard of people using the mounting ear of the heat exchanger itself as a drilling jig--though that does assume that the other holes on that exchanger are in decent shape and the exchanger is not tweaked. That last is a worse assumption with SSIs, which in my experience get tweaked out of shape more easily than the stock exchangers.

--DD

The cap'n · 08-09-2014, 10:29 AM

Personally, I see no way to drill the hole for an INTAKE stud using the HE as a guide, but that may just be me...............................................

The Cap'n

Dave at Pelican Parts · Dave at Pelican Parts's Garage

Oh, oops! I'm so used to stripped exhaust studs on these cars, that my brain totally glazed over the fact that this is a stripped intake stud! So yeah, my post is completely wrong for what you actually need.

Sorry about that!

--DD

porschetub · porschetub's Garage

I think it would be very hard to do this repair with the motor in the car,getting to drill the hole @ the correct angle and stopping drilling going down the intake port would be some of the issues.
Flexy drives or drill rightangle attachments limit how you drill for starters,they are clumsy and hard to use in your situation.
This is a common problem as the The Cap'n points out so there is a good chance the others may 'pull' sooner or later
The best fix is to tap to 10 x 1.5 and get stepped studs made,the larger diameter and thread pitch have improved holding power in the alloy.
I've made these studs in the lathe using a 10mm bolts and have never had any problems again after fitting them,any machinest could pop these out for you in no time.

The one in the pic is an example to give you an idea,cheers.

socuriouso · 06:07 PM

I found 56mm studs at a local import repair who also have a parts counter. The guy behind the counter actually took me back into the garage to the back room to compare the stud I removed to the ones he had available. He gave me a 40 mm and a 56 mm to measure against what is going back into the car. When I asked what I owed him, he just said, "We will settle up when you come back for the other seven." That kind of service coupled with a parking lot littered with vintage Volvos, BMW's and Porsches, most of which look like they drove off the showroom floor impressed me mightily.

I am fairly confident in my hand skills when it comes to precision drilling. I am a silver-smith and custom jeweler and have been doing precision work for over two decades. I am fabricating a fixture (otherwise known as a jig) to keep my angle true, and will mark my bit to the depth needed with paint so as not to drill too deep. I have purchased a right angle drill with variable speed, and as I'm drilling a relatively soft metal will go as slow as it allows. Slower is faster with precision work, and I have the patience of Job.

I have the insulators on the way from Pelican, and will be taking out the other seven studs (30 mm) and replacing them with the 56mm to accommodate the extra that should never have been removed. Instead of grumbling about shoddy work, I am reminding myself that all is being put right, and my growly little piece of driving joy will reward me for doing so.

Again, thanks for the help, and I will keep you all posted with the progress.

socuriouso · 09-03-2014, 08:56 PM

I haven't forgotten about updating the progress, but after listening to the voices of reason (here) and my own experience over the years with various and sundry air-cooled engines, I decided to go ahead and pull the head off and let a machine shop handle the precision work.

I am very happy I did, as I kept having visions of that OH ****!!!!!! What have I done?!?!? moment.

I have it together, idling beautifully and leaned out just where it likes to be. Thank you all for your suggestions and help. Now on to more puzzling issues........

porschetub · porschetub's Garage

Quote:

Originally Posted by socuriouso

I haven't forgotten about updating the progress, but after listening to the voices of reason (here) and my own experience over the years with various and sundry air-cooled engines, I decided to go ahead and pull the head off and let a machine shop handle the precision work.

I am very happy I did, as I kept having visions of that OH ****!!!!!! What have I done?!?!? moment.

I have it together, idling beautifully and leaned out just where it likes to be. Thank you all for your suggestions and help. Now on to more puzzling issues........

Good move and you did the right thing,pleased you had a good outcome,fire away on your other issues