Studs for B&B Exhaust and PMO Manifolds

[Gordo2]

Worn out searching threads...

Anyone know what length studs I need to install:

1. B&B header/exchangers
2. PMO carburetor manifolds

Original studs for 3.2L stock heat exchangers and motronic injection manifold appear to be too long:

(I plan to replace the exhaust studs no matter what...)





Thanks, Gordo

[James Brown]

here they are Pelican Parts - Automotive Parts and Accessories - Porsche & BMW
use the small studs. and, are the manifolds correct to cover the injector ports?

[Gordo2]

James,

I've believe that I have the correct PMO manifolds and insulators - they cover the area where the motronic injectors enter the intake port - but the flange surface are is not quite the same shape and the port diameter is slightly different from the motronic manifold flanges and port (PMO manifold and insulator port diameters are slightly smaller than the intake port on the head).

(PMO manifold flange to left, Motronic manifold flange to right)


(Intake port with cutout for Motronic injector)


(PMO insulator laid on top of the head intake port - the insulator has the exact dimensions as the PMO manifold flange/ports)


At some point, I will pick up a micrometer and measure - as well as give Richard a Fax/call.

Thanks, Gordo

[James Brown]

ok must be the photo, looks like your good to go

[Gordo2]

Actually the top photo isn't deceiving - the PMO and Motronic manifold flanges aren't the same shape. It seemed troublesome at first, but the more I looked at it I realized the PMO manifold flange adequately covered the intake port surface and injector cutout.

If you look closely at the previous picture you can faintly see an outline where the original Motronic flange mounted to the intake port. I expected the PMO manifold to have the exact same shape as the Motronic intake manifold - but there's no real need.

I drew a red line showing where the Motronic manifold shape extends beyond the PMO manifold in the following picture:



Posting this stuff in case someone else scratches their head at the same issue. I searched all over Pelican and couldn't find a picture to confirm fitment.

Thanks, Gordo

[James Brown]

cool, thanks. now how about them exhaust studs? think they will come out in one piece?

[toddu]

Those look like intake manifolds for a 3.0 maybe? What size PMOs are you running? I *think* Richard makes manifolds with different port sizes on the intake side (36mm, 38mm, 40mm). 3.2 heads have a 40mm intake port?

Todd

[KTL]

Why change the exhaust studs to a different length? I guess if you use lock nuts then it makes it easier to get the nuts on. I don't bother with lock nuts, as the exhaust just doesn't come loose

BTW if you know of any spare/junk cam housings lying around, you can steal the studs (valve covers) from the cam housing for your exhaust stud replacement project. Last week I gave my buddy a bunch of long lower valve cover studs for his header installation project.

[Gordo2]

Originally Posted by KTL

Why change the exhaust studs to a different length?

I'm pulling the studs since most are pretty corroded/while I'm rebuilding the motor. The original studs seem bit long for the B&B flange; wondering if I should go with a shorter stud and if so, what length?

[KTL]

SC short studs are 20mm length. The longer studs (typically called "thick flange" when speaking in terms of SSI header installs) are 30mm or 35mm. Parts diagrams are not consistent with length for different SC years and that's why there's two lengths for the long size.

The Carrera 3.2L studs are clearly listed as 30mm length

FWIW I had the B&B headers on a 3.2L and the long studs were fine. But the locknuts were a pain and a test of patience!

Just for reference, since I mentioned them, the upper intake valve cover studs are 28mm and the exhaust valve cover studs are 35mm.

[Gordo2]

Picked up a cheap HF digital caliper to measure the ports. Oddly enough the HF unit was the best I could find locally (actually had some good reviews on machinist boards).

The head intake and exhaust ports measured in at ~41mm (I've seen the ports referenced as 42mm)


The PMO manifold port (that mates to the head) measured in at ~ 36mm


The insulator measured in at ~ 38mm


So, it looks like the 46mm PMO's and manifolds that I have step from 36mm to the 42mm head intake port opening.

I will be calling PMO to confirm I have the right set up.

Another note associated with this thread, the Billy Boat exhaust flanges are 12.41mm or ~1/2" thick.

Probably should have added this as a separate thread for easier future ref, but got rolling.

Gordo

[Gordo2]

Manifold question/problem was squared away - I bought PMO manifolds for the 46's.

With that, I'm back to my original problem, getting good stud lengths for the PMOs and B&B headers.

-------------------------------

I damn near killed a day looking online at various intake & exhaust studs & fastener options.

I started at Pelican, but everything listed appeared too be too short or too long / and they lacked specific measurements (length of each threaded end).

Moved my surfing to McMaster Carr, which can be kind of painful in its own way - too many options for some parts, too few in others ...

-- For the exhaust stud I settled on a black oxide steel 50mm stud that had 20mm of thread at each end & 10mm center (McMaster Car part # 93275A030 - $2.56/stud). Black oxide serrated flange hex nut (part # 94920A500 - $11.43/bag of 25).

-- For the intake, I could used the same part as I had selected for the exhaust - but didn't see the point in spending $2.50 for a stud that would see a relatively mild environment. As such the next best option I could find with the lengths needed was a 50mm plain steel threaded stud (part # 90435A127 - $0.70/stud). Going with Zink coated hex nuts.

I would have gladly gone to an off the shelf, known fitment solution, but didn't find anything for either intake or exhaust. The PMO insulators with gaskets and manifold flange stack to a rather irregular height - or at least to something that stock studs don't seem to match well.

For a bit I considered cutting down a threaded rod - which I've seen others do here on Pelican, but at that point I was too far in to turn back...

Selecting non-standard intake and exhaust hardware parts - isn't much fun...

Oh yea - a happy snap while I was trial fitting a few studs with the PMO's.



Inching along...

Gordo

[Lapkritis]

You would be amazed at what a selection of manifold studs Aubuchon/Ace Hardware carry. Previous owner installed PMO carbs and left the stock intake studs. There were maybe 2 threads on each holding the carbs on and you could see the top of the stud sunken inside the nut. I went longer on reassembly. Very common size, same as VW.

[Gordo2]

Man - this one has me confounded.

The intake manifold studs that I ordered from McMaster Carr won't allow me to mount my PMO manifolds ...

Configuration Details

3.2L engine, stock heads - PMO 46MM carb conversion. Purchased 50mm, full threaded studs for the intake since the stock studs were too long / wouldn't allow a barrel nut or regular hex nut to thread on the stud due to interference between the nut and the manifold body.

Stud Length - Nothing Seems to Work

The new studs are shorter than the stock Motronic studs, and fit perfectly on the outside flange of the manifolds stud (~ flush with the nut) - but they still don't leave room to fasten a M8 nut on the inside studs (the stud closest to the case seam) due to interference with the PMO manifolds.

Not sure how I overcome this one - the nut can't be tightened due to interference with the PMO manifold. You would think this is a common problem but I haven't found any threads describing the same problem:


The PMO manifold bulges out from the mount/flange which makes it impossible to tighten a normal/standard M8 nut (13mm bolt pattern nut) due to interference between the nut and the manifold.

I tried one of the original barrel nuts to see it they would work but they are too tall and contact the manifold - they won't go on the stud.

The stud is fully threaded/seated into the head - leaving just enough exposed threads to allow the outside nut to tighten nearly flush with the stud.

If the studs were any shorter (threaded further into the head or a shorter length stud) the nut would not fully thread onto the stud (the stud would only extend half way or less into the nut).

Seems like there is no good option other than seeking a smaller sized nut (ie. M8 that has a 10-11mm hex nut)

What's the deal?

Thanks, Gordo

[Lapkritis]

Lift the manifold slightly until you tighten the nut down further...same problem with my PMO.

[snbush67]

You need to use the 12mm copper exhaust lock nuts to get the right clearance. Sorry for the upside down pic.

[Henry Schmidt]

We've had issues with the PMO manifolds as well so we ordered AN K nuts to cure the problem.
They are the highest quality nuts available, flanged and self locking (prevailing torque). The thread pitch is 8 x 1.25 mm and the head is 10mm allowing access with a small swivel socket or standard combination wrench.
I found them while hanging around the Indy Car pits.
PMO sells a stud specifically designed for mounting their manifold.
We stock both metric K nuts and PMO studs.

[Gordo2]

Originally Posted by Henry Schmidt

We've had issues with the PMO manifolds as well so we ordered AN K nuts to cure the problem...

We stock both metric K nuts and PMO studs.

Thanks Henry - left a voicemail on your Supertec #, I would like to order a set of the nuts.

I'm good on the manifold studs - the ones I ordered from McMaster Carr (after loads of searching, measuring etc.) seem like they will work well.

Gordo

[KTL]

BTW for anybody searching this, the original Motronic manifold barrel nuts are the same thinner barrel nuts (thinner than typ exhaust barrel nuts) that are used in the cam housing. Not a big deal to massage the side of the PMO manifold since the manifold wall thickness is pretty beefy.

But I agree 100% that the K-nuts are a nice feature with their 10mm hex size.

[Henry Schmidt]

Originally Posted by KTL

But I agree 100% that the K-nuts are a nice feature with their 10mm hex size.

The prevailing torque feature is paramount as well. It allows a tight fit/clamping pressure without over tightening the nut, a common mistake on intake manifolds causing manifold distortion, cracks and air leaks.