Turbo exhaust manifold stud size problem

**HighLife** · 21-04-2009, 02:13 PM

I have a custom steam pipe turbo exhaust manifold to mate a T28 turbo to my 4AGE which I purchased a while ago 2nd hand. I've started to assemble things and have struck a problem - in that the exhaust manifold flange that mates to the turbo has been drilled for 3/8 UNC studs - which if fitted are too big for the holes on the exhaust housing of the T28

I've considered a few options, some less favorable than others, and am just wondering what the gurus suggest?

1. Drill the turbo exhaust housing bolt holes larger to accomodate the 3/8 studs.
2. Cut off the flange on the manifold and weld on a new one with correct stud thread sizing.
3. Find some step down studs from 3/8 unc to something smaller (not sure if these exist?)
4. Helicoil the existing threads to use a smaller stud.

Now number 1 seems the simplest solution but it will also mean modifying the gasket holes and could cause some clearance problems for the larger stud nuts? Number 2 is the probably the best long term solution but costly as I have to pay someone to do it. 3 I'm not sure these exist. I'm leaning towards 4 at the moment?

**off-road** · 21-04-2009, 05:39 PM

If possible drill out the exhaust housing on turbo.
The bigger the bolt the better in terms of coming loose due to heat cycling.

Is it possible to drill the thread out and use an 8mm nuts and bolts as they are easier to keep tight than studs and nuts.

**AAAAGZE** · 21-04-2009, 08:21 PM

without drilling the thread out, you could run M8 throught the centre of the 3/8 tapped hole as the tapping drill is 8mm. it would be a snug fit.

use conelock nuts, as they will be heat resistant and vibration proof. it is an all steel "nylock" nut.

**HighLife** · 22-04-2009, 09:12 AM

Ok I thought the M8 bolt through the holes sounded like a workable solution but after checking it out there is just not enough clearance at the back of the flanges to feed a bolt through a couple of the holes

I have to go the exhaust shop today to grab some exhaust studs for the head, so I'll grab some M8 studs and see if I can do something with them using a nut on both ends?

**AAAAGZE** · 22-04-2009, 07:14 PM

could you weld the stud where it pokes through where the nut would have gone on the tight clearance side.?

**BradW** · 22-04-2009, 10:05 PM

How about welding up the holes in the manifold and redrilling and tapping to the size you need. Not sure if this can be done, but possibly another option?

**HighLife** · 22-04-2009, 10:07 PM

M8 studs look like they might work but I'll need to grind the exhaust manifold a bit to provide enough clearance for a couple of the nuts. I suppose they could be welded in - its bit of a permanent solution though - I'd hate to snap one?

**HighLife** · 22-04-2009, 10:09 PM

Originally Posted by BradW

How about welding up the holes in the manifold and redrilling and tapping to the size you need. Not sure if this can be done, but possibly another option?

I thought about that,but figured cutting the flange off and welding a another one on with correct hole sizing would probably be just as much work and a neater solution?

**web** · 23-04-2009, 12:57 AM

Might be unusual but there's not much wrong with nuts on both ends if you can reach em - down the road it gives you 2 shots at loosening a seized one, too

So I wouldn't bother with cutting and welding. Especially on such a thin stud, it makes them more prone to break.

Either that or try a 3/8 nut with your tools on the turbo and if it fits, drill out the holes.

Replacing the flange completely seems unnecessary.

**The Real Roadrunner** · 23-04-2009, 06:12 AM

get a machine shop to make some studs for you? 3/8UNC - M8 should be easy to make, just get them to make 10 so you have spares for later on (and would make the price cheaper.

cheers
linden

**HighLife** · 23-04-2009, 09:08 AM

Originally Posted by The Real Roadrunner

get a machine shop to make some studs for you? 3/8UNC - M8 should be easy to make, just get them to make 10 so you have spares for later on (and would make the price cheaper.

cheers
linden

Yeah I have a knowledgeable mate(sports sedan race car mechanic) coming around on the weekend to have a look, he thinks it might be possible to get some 3/8 to M8 studs too. So we'll see how we go.

Cheers...