924Board.org

[Rasta Monsta]

So, I was removing exhaust studs today in order to replace them with superceded (non-breaking) parts. Two came out with fuxxored threads and lovely aluminum chunks (should the machinist have investigated this on the bench. . .should I have reminded him. . .strong maybes to both).

My question: which is better, threaded inserts, or step studs?

In my mind, the advantage of the inserts would be the ability to use the magic superceded studs, the material of which is intended for brutal heat cycling.

The advantage of the step studs would seem to be the fact that there would only be two types of metal interacting in this harsh environment instead of three.

Thoughts? Experiences? Has anyone helicoiled a 931 head before?

Thanks, as always.


rasta
_________________
Toofah King Bad

• WeiBe (1987 924S 2.5t) - 931 S3

[Rich H]

Different metals are only a problem if they get wet, they need an electrolyite. As the exhaust studs a) get really hot and b) live under the bonnet slated down all the time, they are unlikely to stay wet for long enough to be a problem.

I would helicoil them, it also means that if you ever have a problem in future you don't have a mix of stepped threads and normal jobbies.

Aslo helicoils are easy to put in to ali... Just tie a bit of cotton thread around the 'tail' that way you can be sure it comes out...
_________________
1994 Lotus Esprit S4 - Work in progress...
1980 Porsche 924 S2 DITC Turbo - Original spec
1978 Homo-Sapiens - Tired spec
1953 Landrover S1 - Pensioner Spec

[RC]

What Rich said.

Helicoils are the go. Personally did all the exhaust stud holes and would suggest others do the same. Presume this is on your new engine and is not yet fitted. Complete bastard to do with the engine in if at all possible. So easy to do all now and never have this problem again.

Get a M8 kit that includes the correct tap and more than sufficient coils. Usually include the applicator but a slotted rod does the same thing. A kit would be from $20 - $50 and packets of extra coils are quite cheap. Usually dont need drilling but drill size is listed, so only use that, and it is critical to keep drill straight and centred. Some taps have a original (M size starter thread and will enlarge & tap in one pass. Screw the inserts at least 1/2 - 1 threads inside the face.

Haven`t heard of the cotton tail trick. The tangs are notched to break off easy, just twist applicator backwards or knock with a punch. As they`re blind holes will easily come out with compressed air, long nose pliers or gravity if the motor is still on a stand.

These pics are of the oil sender hole but same method used.

[Rich H]

Cotton trick prevents having to arse about with air/pliers/etc
_________________
1994 Lotus Esprit S4 - Work in progress...
1980 Porsche 924 S2 DITC Turbo - Original spec
1978 Homo-Sapiens - Tired spec
1953 Landrover S1 - Pensioner Spec

[Rasta Monsta]

Great feedback, thanks fellers!
_________________
Toofah King Bad

• WeiBe (1987 924S 2.5t) - 931 S3

[RC]

[Rich H]

_________________
1994 Lotus Esprit S4 - Work in progress...
1980 Porsche 924 S2 DITC Turbo - Original spec
1978 Homo-Sapiens - Tired spec
1953 Landrover S1 - Pensioner Spec

[peterld]

Can only agree with Rich and Rog (is that a new pop group?).

If the head is off the block or the whole motor is out, inspect the exhaust manifold side very carefully and reclaim any dodgy threads. As a matter of course I renew ALL exhaust manifold threads.
Forget all the malarky written about the 931 heads - they are a poor and soft casting and excessive heat cycles will only exacerbate the brittleness of a 30+ year old casting.

Oh and don't forget the plug holes while the head is off!
And the timing belt tensioner bolt hole - in fact any thread that will see regular usage or high tensioning force.

Like Rog I use Helicoils, however the boxer motor brigade prefer TimeCerts. There are others on the market as well.
_________________
80/81 932/8 ROW

[Rich H]

I've used Recoil and V-coil inserts - they are all the same pretty much - but get a kit with a drill bit in it - makes life easier than finding a single 8.3mm (~11/64" IIRC) drill amongst your tools...
_________________
1994 Lotus Esprit S4 - Work in progress...
1980 Porsche 924 S2 DITC Turbo - Original spec
1978 Homo-Sapiens - Tired spec
1953 Landrover S1 - Pensioner Spec

[Min]

Problem with step studs is the step becomes a hardcore stress concentrator that can easily double the stress in the stud at the step even if its smoothly radiused. Another vote for helicoil.

Min
_________________
Custom means it didn't come from a box.
1980 n/a with EDIS and Megasquirt II Injection. 7 different colors and counting.