2L Mk1 Exhaust Manifold.

[68vitesse]

Wondered about the advisability of making a replacement log manifold from mild steel, I do have a 6 3 1 stainless manifold bought years ago, from a trader who closed down, but never used as not happy with the fit. I.e. Round ports to the head which has slightly oblong ones which reduces the gasket contact area and very tight clearance to chassis.

The other day I made a cylinder head stand from scrap and fitted spare manifolds to the head to give me a better idea of what would be needed. Not much price difference between mild and stainless, temperature range very similar, mild easier to work, less expansion and less prone to stress cracks.

Running out of cast manifolds last one I removed had a good crack in it but found someone who said they would weld it for fifteen pounds. Apparently his method is to drill each end of the crack and then tig weld using cast iron stick weld rods with the flux removed as the filler.

Regards

Paul

 

[Guest]

20 minutes ago, 68vitesse said:

Apparently his method is to drill each end of the crack and then tig weld using cast iron stick weld rods with the flux removed as the filler.

Hello Paul,

That is certainly the correct option is stop the crack creeping, by drilling each end. 

Cast is, oddly enough, quite delicate hence the reason for cracks appearing - as to the welders method I cannot comment as I've no experience on that particular process; but all sounds plausible.

Regards.

Richard.

[Gadgetman]

On 01/12/2019 at 14:26, 68vitesse said:

Wondered about the advisability of making a replacement log manifold from mild steel, I do have a 6 3 1 stainless manifold bought years ago, from a trader who closed down, but never used as not happy with the fit. I.e. Round ports to the head which has slightly oblong ones which reduces the gasket contact area and very tight clearance to chassis.

The other day I made a cylinder head stand from scrap and fitted spare manifolds to the head to give me a better idea of what would be needed. Not much price difference between mild and stainless, temperature range very similar, mild easier to work, less expansion and less prone to stress cracks.

Running out of cast manifolds last one I removed had a good crack in it but found someone who said they would weld it for fifteen pounds. Apparently his method is to drill each end of the crack and then tig weld using cast iron stick weld rods with the flux removed as the filler.

Regards

Paul

 

Are you interested in selling

the 631?

[68vitesse]

Never sell parts as I generally find a need afterwards.

Regards

Paul

[RogerH]

Hi Paul,

The cracking is caused by stresses built up in the manifold.  Eventually it cracks and relieves the stresses.  It will crack no more.

The actual gap of the crack will fill with carbon and other muck and thus not leak.

This is common on the TR4/4A original manifolds.

 

Regarding the repair. The stop drill holes will certainly help to stop the crack running.

However unless the crack has a decent amount ground out of it there will be very little penetration and the crack will still exist under the weld.

You could consider an Ali/Nickle/Bronze brazing technique  - much more sympathetic to the cast steel.

 

Roger

 

 

 

[JohnD]

The problem with welding cast iron is the diffrence between cast iron and steel, the carbon.    If Cast is heated to welding temp, the carbon, present in the grey cast iron as graphite, dissolves in the hot metal around the weld pool.   This is fine, as long as the iron cools down again slooooooooooooooooooooooooooooowly, so that the carbon can precipitate out again as graphite.      But a simple weld will cool down quickly, as the heat is absorbed into the rest of the casting.         The rapidly cooled iron becomes cementite, much harder and more brittle than the pearlite in grey cast iron, so that it's typical for new cracks to appear around the weld.

Solutions include heating the entire casting, to 500-1200C before welding, so that the weld cools more slowly.      Even slower, if you surround it after with sand.     OR, braze the crack.      The braze metal doesn't get the iron as hot and the above doesn't happen, but the iron must be quite clean, and it's a skilled job.

John

[Iain T]

Paul,

The upshot is make sure wherever you take it to be welded is experienced in cast iron repairs. We always used to heat the entire casting but in say some larger press tools this was not possible so we heated the area as best we could. The GTMA (gauge and toolmakers association) website lists some companies that could do the work....but at what price?

Iain