Exhaust manifold erosion!

[Jakko]

Finally got my near side manifold off the car. It didn't respond to persuasion, so I bought tungsten carbide burr (not cheap) and carefully ground the bolt head away. Then I was able use a stud extractor to remove the rest.

Unfortunately, just when I thought life was all sweet, I found the the face of the manifold where the gasses had been escaping is badly eroded. Tried 2 local machining companies but their machines are unable to skim the surface to remove the damage.

Has anyone had any experience with plastic metal in an application like this? Any other suggestions would be appreciated.

[AutoAndy]

...apparently I had a slightly destoted manifold which needed machining.
Didn't like to pay 90 quid for it to be skimmed. So I fettled it with an angle grinder.... Very carefully.... It seems to have worked.


Maybe worth a try.

[Griffinr]

In theory plastic metal should work as the manifold temperature next to the block will probably be not much more than 100 degrees C. Worth a try now you have the bolts out as they should come out easily next time (especially if you use stainless). Another option would be to have it built up with braze or weld and then carefully file it back to flat.
J-B High heat is good for up to 250 C and has manifold repair listed under the uses.
Rob.

[phillpot]

Griffinr said:

Another option would be to have it built up with braze and then carefully file it back to flat.

That's how I did mine. Also cut out the joining links so each flange is free to pull up to the head with no restriction (made the filing a lot easier too)

You will need a good quality file !

Edited by phillpot on Monday 2nd December 16:52

[Jakko]

Thanks for the good ideas guys. I like the braze method. Don't have the facilities myself, but should be able to find someone locally to do the filling. I can do the rest.

[glenrobbo]

I reckon the manifold temp at full load would be more like 800 degrees, not 100
The best option imho to get the mating faces flat is to use a large angle grinder clamped in a vice like so....
and a nice straight edge. This was a 2.8 manifold, but it should be feasible to fettle a 2.9 in the same manner. Just check for flatness at regular intervals & keep a steady hand & wear gloves & eye protection, & any other relevant H&S gear obviously.
As previously mentioned, cutting out the webs between branches allows a little more flexibility to the assembly & increases the chances of a better seal of the mating faces. A little exhaust assembly paste can also be beneficial, but don't overdo it, don't want it obstructing the exhaust gas flow.

Edit: Belzona do a hi-temp repair paste, two-part mix, but it ain't cheap.

Edited by glenrobbo on Monday 2nd December 22:57

[Griffinr]

glenrobbo said:

I reckon the manifold temp at full load would be more like 800 degrees, not 100

The flange of the manifold is bolted to the head which is water cooled, so at the joint is going to be around 100 C. I have measured the temp of the the manifold pipes several times, even after a good blast and the highest I have seen is 320 C. At 800 degrees they would be glowing bright red and probably setting fire to stuff.

Rob.

[glenrobbo]

Griffinr said:

The flange of the manifold is bolted to the head which is water cooled, so at the joint is going to be around 100 C. I have measured the temp of the the manifold pipes several times, even after a good blast and the highest I have seen is 320 C. At 800 degrees they would be glowing bright red and probably setting fire to stuff.

Rob.

OK Rob, please excuse me, my poor old brain ain't what it used to was.
I was thinking in degrees Fahrenheit, I would expect around 800 F on our V6's at full chat.
I'll let you do the conversion to Celsius.

Many years ago I used to test large engines on the dyno, and on max overload, 110% power ( this was part of the test procedure ) the exhausts used to glow bright cherry red at the inlet to the turbos. If I remember correctly, the exhaust gas turbo inlet temps were well over 1100 degrees F. You could reach up and light your fag on the turbo outlet pipes, and these were cooler.

I also remember spectating at Le Mans at night in the '70's and the racers exhausts looked like extra rear lights. So yes, they do glow red at full power on high output engines.

[Griffinr]

glenrobbo said:

I was thinking in degrees Fahrenheit, I would expect around 800 F on our V6's at full chat.

Did cross my mind you were talking in old money. I've seen them glow as well on high performance stuff but not on lumbering lazy old lumps that we drive.
Rob.

[glenrobbo]

And I thought I was the lumbering lazy old lump!