Leaking exhaust flange

[dom14]

Vehicle - RB30 Patrol, carby

Hey Guys,
I've been struggling with this problem for a while and today it reached a whole new level.
Basically, the problem has been, that regardless of my careful attention, the flange of the exhaust headers kept leaking. Last time I put a brand new gasket and used exhaust silicon sealant to help with the seating it better. Prior to that, it had been blowing few flange gaskets.

I noticed it started leaking again few days ago. During cold start, I could hear the hissing from the flange & a bit of water dripping out of it(cold start condensation I guess).

Anyway, I decided to tighten the flange nuts and that didn't help, as the nuts were as tight as it could be.

Today, I decided to pull the damn thing out and have a one last look before I fix it for the last time. The nut appeared to have gotten stuck during my undoing and I thought it might have cross threaded. So, I kept turning it clockwise and anticlockwise to gradually undo it. However, it broke during that. There are three flange nuts/studs. I managed to undo the other two without breaking the stud. One of the other studs has thread damage as well.

Last time, I checked the flange surface for perfect flatness & any protrusions that might have been inhibiting the proper seating of the flange, but it looked all good.

So, my guess is that among any possible reasons for this flange gasket seating failure would be the flange studs(which are screwed to the headers) might have been loose and turning over time, effectively causing leakage from the gasket.

Tomorrow, I'm planning to drill into the broken stud and attempt to extract it.
If you look at the picture you can see the broken stud. Unfortunately for me, the broken stud hole is not like the other two, because it doesn't go through all the way like the other two. In other words, the broken stud hole is a dead end hole.

Can anybody shed some light on the possible causes of this problem, other than issues of flatness and protrusions of the flange surface?

If I manage to successfully extract the broken stud, I'm planning to either use,
1)slightly large diameter studs
2)High tensile steel studs.

Does that sound like a better approach?

Thanx in advance for any advice, tips, ideas.(other than suggestions of extractors which is an obvious solution :) )

[Clunk]

Engine mounts ok?

[dom14]

Engine mounts ok?

Yeah, I think so. I can double check to make sure they are not stuffed.
How do the engine mounts affect exhaust flange leaks?

[mudnut]

The high tensile option would make it almost impossible to extract it if it seized and broke. Check to see if the ends of the pipes are actually sitting in the recessed areas properly.

[the evil twin]

X2 and...

Most common things that will cause the issues you describe are
Warped flange mating surfaces
or
Elongated/damaged studs

Inspecting the flange gasket should give you an idea on where the gases are getting past the seal.

[Clunk]

Yeah, I think so. I can double check to make sure they are not stuffed.
How do the engine mounts affect exhaust flange leaks?
Wwll my think was that if an engine mount is stuffed, then the engine would move to the right when revving, and possibly flexing the flange and maybe warping it a wee bit........ not sure if its possible coz I'm not an engineer

[dom14]

The high tensile option would make it almost impossible to extract it if it seized and broke. Check to see if the ends of the pipes are actually sitting in the recessed areas properly.

Two of the stud holes on the exhaust flange, I can make them go through and use either a bolt or stud with a nut on the top side as well. But, on the third stud it won't be possible, as the hole doesn't go through the other side. So, I have to be careful with that. I haven't extracted it yet. Just about have a go at it.
Yeah, I was told by an exhaust guy while ago that the high tensile is a bad idea on exhaust studs. I can't remember the exact reason he gave me for that. But, I think it was the reason you describe above.

I think, because of the high heat involved, the flange studs may be prone to getting seized inside the hole eventually.
If it lasts for few more years without breaking while not giving me trouble all the time with leaking, then that's good enough for me.

I think the reason the flange nut got cross threaded 'cos I over tightened it.

[dom14]

Wwll my think was that if an engine mount is stuffed, then the engine would move to the right when revving, and possibly flexing the flange and maybe warping it a wee bit........ not sure if its possible coz I'm not an engineer

Yeah, engineer or not, that makes perfect sense.

I thought about it along those lines, but slightly different way(more like excessive up and down movement). During my inspections under the vehicle, trying to understand the constant failure of the flange gasket, I thought about the possibility of the excessive movement of the exhaust pipe causing this drama. So, I've been planning to add a combination of rubber+spring to the mount where the exhaust pipe joins the chassis/gearbox mount, so the immediate part of the exhaust after the exhaust flange can move more freely.
Now, following your leads, I'm better off to confirm whether the engine mounts are not on their way out.
They are about four years old and aftermarket ones from memory.

[dom14]

X2 and...

Most common things that will cause the issues you describe are
Warped flange mating surfaces
or
Elongated/damaged studs

Inspecting the flange gasket should give you an idea on where the gases are getting past the seal.

I'll post few pictures of the flange gasket shortly. It's in two pieces now. As soon as it started leaking, it get separated and the bedding material get destroyed. I tried the trick of adding exhaust sealant to the severed middle part(not trying to be cheap, but experimenting) last time, but that didn't last that long either.

[mudnut]

Are you using good quality gaskets. A while back I had a brand new one fall apart in my hands. Can't remember the brand though.

[dom14]

Are you using good quality gaskets. A while back I had a brand new one fall apart in my hands. Can't remember the brand though.

I had no idea about different brands. I usually buy them from Burson.
Flange gasket is around $5.

[dom14]

These are the photos of the flange gasket.

I've been trying to extract the broken stud today from the exhaust manifold.
It's not that easy.
I will have to get hold of a better extraction bits tomorrow and try again.
In the meantime, I'm leaving it with a bit of penetration spray over night(wd40).
Hopefully, that will help with the extraction.

[dom14]

These are stud removal attempts related photos.

I tried pull the broken stud out using extractor bits without any success.
So, I ended up drilling out most of the meat and then tapping off the rest.

[dom14]

This stud hole is not a go through one. It's about half a centimeter hole.
I reckon it's not deep enough.
I would like to drill it bit more and tap it.

However the drill bits I use below doesn't seem to be able budge the cast iron manifold flange.
Is there a trick to it, or do I need a better highspeed drill bits?!!

[the evil twin]

I think you have bugger all chance.
The correct drill size for the plug tap will damage the existing thread
Old cast iron exhaust manifolds can be suprisingly tough and can be a turd to keep aligned without a drilling jig.

Anyway if you want to give it a crack then fair enough...

Rule of thumb is a thread should be minimum of 1 1/2 times the dia IE M8 should be min 12mm thread depth.
Most likely the drill is blunt or of poor quality.
Maybe try sharpening the HSS drill or better still purchase a cobalt jobbie.
Go slow and don't overheat the drill cutting edges

Don't forget to check the flange mating surfaces with a straight edge.
Especially the pipe flange surface as the manifold surface is usually OK most of the time
If either surface is warped then all the effort will be for nought.

If you want to drill out the hole and use a thread insert go for the shallow depth soft casting solutions and not a Helicoil.
Ezilock, Keensert etc are the go

[Touses]

[QUOTE=the evil twin;672769]








Go slow and don't overheat the drill cutting edges

Evil is spot on here. Good advice use it.

Cutting oil or if you don't have it crc wd40 etc will help to cool the bit and clear swarf.

[mudnut]

Show us a pic of the engine pipe please Dom.

[dom14]

Show us a pic of the engine pipe please Dom.

Just took these photos.
Also have a look at the photos on next post with the exhaust manifold & exhaust pipe attached.

[dom14]

These are the photos of the exhaust headers and exhaust pipe attached without a gasket, to check how well they fit.
There's slight gap in one corner. I'm not sure how to correct is at this stage, whether I should file it or use silicon.
It appears the gap is more towards the outer edge of the flange, not towards the inner hole.
It appears the slight unevenness is on the exhaust pipe flange, rather than the manifold flange.
I checked both of them with a ruler. Manifold flange isn't that bad.

[mudnut]

After you have made sure both surfaces are flat, try filing the protruding bits of pipe down a millimetre or two, so they fit snugly into the manifold.

[dom14]

After you have made sure both surfaces are flat, try filing the protruding bits of pipe down a millimetre or two, so they fit snugly into the manifold.

Thanx mate. It's possible the little gap in the picture may be caused by pipe protrusion touching on the manifold flange inner edges. I'll grind it up and see if it fits perfectly. If not, a laborious filing job is awaiting for me.
Machine shops aren't worth it.

[threedogs]

I had a similar problem with the block hugger extractors [350 chev]coming loose all the time to fix it
I put a texta mark on the Exhaust bolt so I could drill them,I numbered and drilled all the bolts.
Then I had a roll of aviation lock wire and continued to lock wire each bolt twisting the wire
between each bolt. ,,,,,,The bolts never came loose again.
This will only work if your bolts were coming loose.

[dom14]

I had a similar problem with the block hugger extractors [350 chev]coming loose all the time to fix it
I put a texta mark on the Exhaust bolt so I could drill them,I numbered and drilled all the bolts.
Then I had a roll of aviation lock wire and continued to lock wire each bolt twisting the wire
between each bolt. ,,,,,,The bolts never came loose again.
This will only work if your bolts were coming loose.

I can't say I understood any of it mate. But, I'm sure you are making perfect sense for somebody who understands the procedure.