Exhaust manifold nuts

Yes they look like the correct nuts. When installing the studs into the head, you can “double nut” them to ensure they’re seated all the way in and tight, could always add a little locktite as well if needed.


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I have used blue loctite on the studs which helps keep the stud in the head when you have to move the nut.

 

Pinch nuts are best for exhaust studs, risk is pullout when removing. The pinch nut stays put thru the thermal and vibration cycles.
That said, I prefer the solid copper ones vs plated.

 

I'd say that that is a very heavy-duty lock nut with that much circular distortion over the whole length of the thread. IME, the "stock" F exhaust nuts of that era are the slotted type (where, after threading, they cut a slot near the top and then bend the thin part down which gets flexed back up when put on the stud to provides the drag for locking) like these examples:
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Doesn't need as much torque as your "fully distorted oval" nuts to install or remove. Not saying that those won't work, but they have a much greater chance of having the stud come out during removal (or strip the threads in the cyl head during installation), and can make it hard to determine how much of the applied torque is tightening the nut and how much is used up in the thread friction. Did they come from Maranello Classic Parts or some other F part supplier?

 

Solid copper nuts won't cross thread the stud. That's another reason to prefer them.

 

Belmetric also sells the "slit" style:
https://belmetric.com/slit-lock-nut-copper-plated-steel-exhaust-din-14441/

What year/model F do you have (update your profile)? Not sure if they ever changed the style of exhaust flange nut over the run of 308, but if you want something with less prevailing torque to install those would be an option. You might check the SPC figure for your year/model F to see if the picture shows just a flanged nut or a washer with an unflanged nut. There are also other styles that have a smaller localized distortion in the threads (so need less torque), but your photo looks like the majority, or all, of the threads are deformed "oval".

 

I've used these and they are great. 12mm. Same nuts on a VW bug. Cheap from EMPI

 

While a flanged, distorted lock nut would be perfectly OK in that location (if not too heavy duty/friction), your SPC shows a spring split lock washer and a split lock nut were used originally there (items 22 and 23):

https://www.ferrariparts.co.uk/diagram/ferrari/308-gt4-dino-1976/005-cylinder-head-(right)

Don't you need to move "308GT4" in your Profile from "Wanted Cars" to "Personal Ferraris"?

 

That's a small distinction in length difference, and an Engineer expecting the Assembler to tell such a small difference (and never get it backwards) would be a bit of a mistake IMO (and a reasonable tolerance of the thread length on each side of a stud bulge is probably at least +/- 1mm -- so I'd guess that each side was nominally intended to be the same length and the difference that you have is just the manufacturing tolerance). The SPC presently shows a much more asymmetric stud (but it's been superceded so might have been more like what you have originally):

https://www.ferrariparts.co.uk/part/ferrari/13516824

where it has to be the short end going into the cyl head -- as the short end looks too short to accept the header flange, the washer, and a (tallish) locknut.

 

Are you doing that by gently just using your fingers or by firmly double-nutting them in? (The tapped blind hole in the cylinder head can have some taper in the last few threads.)

 

There's a class or fit difference for internal thread and the stud. I'm not recalling off the top of my head what it is at the moment but it's different then the threading for the nut end. So there are studs that are threaded slightly different on each end, it's kinda obvious when holding them, the end that threads into the block/material is 'fatter' and the nuts have more resistance when threaded.
Not all replacement aftermarket hardware is like that though.

 

"I would never have guessed there was so much involved in just exhaust studs!!!"

Me neither! In all the years of engine work I've done the only concern I ever had about exhaust manifold nuts/studs is that they were right size! Never had a "plain ol'" nut or stud loosen on an exhaust fitting.

 

Nut and bolt type and materials are also a concern for aircraft exhaust as well.

 

DinoPoint.it sells the brass one so will not come off