Exhaust stud problems

[Matty B]

G'day everyone,

The threads in my exhaust stud holes have given up.

Rutted dirt roads have vibrated them to death.

They have been drilled and re-tapped twice in a couple of holes (up to 14mm)

the rest are 12mm. One is a strange coarse thread.

 

Tommorrow morning I am removing the heads and having the holes tig welded up, re drilled and tapped to 10mm again.

 

Has anyone done this?

 

Tips?

 

I have provision for 3 studs on each head and will be using the third this time,

 

 

and modifying the flange to suit.

 

Is the cast alloy able to take weld?

 

Should I pre- heat the heads?

 

Cheers

[Beegeer]

Matty B,

 

Your heads are most likly cast of 356a, which can be welded. I weld investment cast 356a parts to aluminum bike frames every day. We heat treat them back up to to T6 before we machine. I have machined non-heat treated parts and they do not cut very well, very soft.

 

Have you tried a helecoil?

[Matty B]

There were the remains of helicoils in the heads when I got them,

I went one step oversize on them @ rebuild,

now they are flogged out.

How did you heat treat the metal?

[BobBrumby]

When my stud stripped i took it to an exhuast shop and they tapped a thread into the steel spacers where the asv valve connects to.

[Matty B]

Bob I am referring to the studs going into the head, (all alloy, no steel there)

 

are we talking about the same thing?

[torxxx]

for the price, just get used heads..

[BobBrumby]

Bob I am referring to the studs going into the head, (all alloy, no steel there)

 

are we talking about the same thing?

 

Oh so these are the dual port heads, didnot read your post fully. I did this on my ea81 but with a closer inspection of your picture it seems it does not have the steel "spacer" thing, that the valve that puts air into your exhuast, through.

[Phizinza]

I've just put champion thred inserts into my heads. I replaced all 4 bolts. The thred inserts are like a big bit of thred with a threded hole in the middle. I also didn't have to take the engine out (i just got under the car and drilled them out.) But these only worked with 13mm drilled holes. Anyway. I done them up as hard as I can with my 10" ratchet. I was supprised I could do them up that tight. But it doesn't leek at all now (I also used new gaskets of cause)

The Champion thred inserts cost about $9AUD each.

[Beegeer]

There were the remains of helicoils in the heads when I got them,

I went one step oversize on them @ rebuild,

now they are flogged out.

How did you heat treat the metal?

 

We use the same schedule as 6061, this is off the top of my head so I might be off by a bit. Any heat treat facility would know the proper schedule…

 

 

 

Heat treat: 950 F for 2 hour soak/ per 0.25 in

 

 

 

Quench:water glycol mix a/b 20%

 

 

 

Artificial age: 350F for 8hours.

 

 

 

This will get the 356a back up to T6.

 

 

 

However I think Torxxx has the best suggestion….

[Matty B]

for the price, just get used heads..

 

I would if I could, they are JDM dual port heads from a factory competition motor, (siamesed exhaust ports)

 

They are matched to my cam and very, very rare.

I only know of one other motor in Australia with the same heads,

I have secured it, but its weeks away from arriving.

Welding is my only option in the short term.

 

BeeGeer, thats great info, many thanks.

Cheers

Matt

[Matty B]

whoops

[Ross]

Because of the geometry of the casting, I would recommend a pre heat to reduce teh risk of cracking. You really need to find out what condition the material is in now and bring it back afterwards.

If you can't find out the actual condition from the manufacturer, you could do hardness tests at various points, you will then be able to estimate what condition it is in.

Take it to a reputable welding shop experienced in aluminium welding, or if your doing it yourself, make sure the head is TOTALLY clean and TOTALLY dry.