Exhaust manifold studs.

[abowie]

The way the E Type exhaust manifolds connect to the downpipes is poorly engineered. The manifold has a threaded stud screwed into it. This thread is 3/8" UNF and the problem with the fine thread is that corrosion accelerated by heat means that the thread in the manifold fails. Then the stud strips and the exhaust leaks because it can't be tightened.

I thought about a helicoil repair but this still leaves you with the delicate UNF thread.

I obtained some studs that have the standard UNF thread at one end but have a 7/16" UNC thread on the other. These are screw in rocker arm studs for short block Chevy V8 engines. Elgin part number was RD1920.

The holes needed to be drilled out and it is important that they are parellel. I made a small jig out of a piece of 1" angle iron so I could bolt the manifold to my pedestal drill.

The studs needed to be cut down 10mm on the coarse thread end to be a perfect fit. The fine threaded end is actually a little longer than the original stud. The minimum crush distance is about 0.65 " which I think will be small enough; if not I will run a thread die further down the stud.

The manifold I chose to do the first repair on was about the worst one I could find and I think it looks pretty good.

[rolando38]

well done Andrew !
I'll have to replace my exhaust soon (delivery next week) and I'm a bit anxious to unscrew the existing one as I might break one/several studs...
any tip to avoid it ?

[mgcjag]

Hi Andrew....how did u get the old studs out of the manifold..did u have to drill them?..Steve

[Duckham]

To save a tiny amount of effort the JEC produce a repair stud that is the similar to your concept but the right length.
I'm sure yours will be a lot cheaper though.

Joe

[abowie]

Hi Andrew....how did u get the old studs out of the manifold..did u have to drill them?..Steve

In this manifold they were all so corroded they came out easily. I have drilled out one one in the past which was irritating.

[abowie]

To save a tiny amount of effort the JEC produce a repair stud that is the similar to your concept but the right length.
I'm sure yours will be a lot cheaper though.

Joe

Damn there goes my multi million dollar patent.
The studs were about US$2 each but the postage from the US to Aus doubled that. I have 3 sets of manifolds to do for my 3 cars so I might see if I can source them locally.

[abowie]

Did another one today; snapped off a stud and drilled it out:



This picture shows how badly corroded the threads are: