Td5 Exhaust Manifold

[DaveSIIA]

I had to remove the manifold from the head to fix a blowing exhaust gasket. The manifold was tight to remove from the studs (nuts came off ok), and there were witness marks of the threads inside the through holes. Come to put it all back together and the manifold wouldn't fit back on to the studs.

If aligned with the centre studs (cylinder #3), the holes for #1 & #5 should each have been ~2mm further out from the middle to slide over their studs. The holes for #2 & #4 should each have been ~1mm further out. It appears that the manifold had shrunk. I had to elongate the holes to get the manifold back on.

Has anyone experienced a similar problem, or know what the cause could be? It's a '99 110 with 81K miles on the clock. The engine has been chipped & intercooled by Jeremy Fearn and runs sweet as can be.

[western]

RAVE manual doesn't mention any special way to refit the exhaust manifold, just says fit gasket/refit manifold,tighten to 25Nm or 18lbft

[Mo Murphy]

Isn't the exhaust manifold in 3 pieces normally prior to fitting when new, 2 tubes and the turbo mounting bit in the middle. Therefore could it be that the 3 pieces have been fitted more tightly together than they should have been thus effectively shortening the length of the manifold ?

Mo

[western]

On a TD & Tdi it's a 3 parts on a Td5 it's a one piece casting.

[Ally V8]

Its because you have been thrashing the t-ts off it ! TD5 motors get very hot when chipped/intercooled and thrashed.One customer of mine got through 3 manifolds,a couple of refaces and worst job was the end studs pulling threads out of the head.

I bet the shrouding round the oil pressure switch wire is melted too.Other than that they seem to stand up to it well,topend oil leaks become more common,just keep your cooling system in top order.

[Mo Murphy]

On a TD & Tdi it's a 3 parts on a Td5 it's a one piece casting.

Ah! Well, we can rule that out as the cause then Progress !

Mo

[Guest diesel_jim]

on one of the sites (i think it was devon4x4) they had a tech report on the cure for the manifold warping...

It was a cge of milling out the webbing in between each port, then facing the whole thing up accurately.

Thay way (without the webbing), it allowd the ports to expand and contract individually, without cracking the thing.

[DaveSIIA]

Thanks for the replies. I was fairly certain that there shouldn't be anything special about fitting the manifold.

Its because you have been thrashing the t-ts off it ! TD5 motors get very hot when chipped/intercooled and thrashed.One customer of mine got through 3 manifolds,a couple of refaces and worst job was the end studs pulling threads out of the head.

I bet the shrouding round the oil pressure switch wire is melted too.Other than that they seem to stand up to it well,topend oil leaks become more common,just keep your cooling system in top order.

Oops, I must have been spotted driving in my normal style! It doesn't need to be thrashed too hard as the torque delivers a lot of the performance boost, but the whole exhaust side must get fairly warm. The shrouding round the oil pressure switch wire looks like it has been a bit warm at times.

on one of the sites (i think it was devon4x4) they had a tech report on the cure for the manifold warping...

It was a cge of milling out the webbing in between each port, then facing the whole thing up accurately.

Thay way (without the webbing), it allowd the ports to expand and contract individually, without cracking the thing.

The top stud on #1 sheared about 18 months ago. The exhaust manifold was warped when I removed it, so I milled out all the webs between the ports - nothing to lose. The manifold came true (checked on a face plate and within 0.005"). On that occasion, the manifold fitted straight back onto the studs. It has probably done 30K miles since, so would have been heat cycled a few times.

Is it possible there is some sort of stress relief process happening through the heat cycles?

BTW - in the light of discussions on other forums about this problem, I have decided to remove the studs on cylinders #1 & #5. M8x30 Cap Heads (there wasn't quite enough depth to go to M8x40) have been fitted in their place. This gives much deeper engagement into the head, and hopefully may reduce the likelihood of the studs pulling out.

[JimAttrill]

We drill out the holes in the manifold a little bit and this seems to stop the studs breaking. I get lots of practice helicoiling the threads in the head, which should have been done as standard IMHO.