Exhaust manifold

[Callum 13 1 Cars]

Is this a later reinforced manifold? Also it's meant to be heat treated what's good about that? Thanks 

[Callum 13 1 Cars]

Can anyone answer for me? 

[jackherer 543]

The reinforcements are the braces between the ports, they don't all have those so that is a so called reinforced one. You still need to check it for cracking though as they are still prone to it.

 

 

[Callum 13 1 Cars]

Great that's what I wanted to know, my current manifold only has one of the reinforcement braces like your first photo, the issue I have is all my engine mounts are worn and I can hear a blowing noise under acceleration, I've looked at the downpipe and manifold joint and it looks pretty rusty and also the manifold and studs are pretty rusty too and the manifold gaskets look old. I couldn't see any cracks on the manifold but unsure where I need to be looking could you tell me where? 

[jackherer 543]

A cracked manifold normally makes a ticking noise. They crack around the runners from the two outer cylinders normally.

 

Get someone to hold a rag over the tailpipe and it'll force more gas out of the leak so you'll be able to locate it more easily.

[Callum 13 1 Cars]

Brilliant thanks I did put a rag over the end and listen but I was on my own so I will try it with someone else 

[jackherer 543]

My money would be on the manifold to downpipe join based on what you say.

[Callum 13 1 Cars]

So I've changed all the engine mounts and the blow isn't anywhere near as bad so I guess the culprate is the manifold to downpipe gasket as jackherer suggested and the engine movement was making it worse 

[Callum 13 1 Cars]

I've just changed the manifold to downpipe gasket and was expecting to find a split downpipe that would need welding on the end but there wasn't a split at all! Does anyone know where i can get a centre section with a split downpipe? 

[Miles 331 1 Cars]

You won't these days as it costs too much to make

[Callum 13 1 Cars]

Is there an alternative? 

[Miles 331 1 Cars]

Just a non split one

[ArthurH 7]

We hadn't noticed while it was on the car, but having taken it off as part of a head skim, I spotted that my son's manifold had been previously welded.  Unfortunately, on inspecting the underside, that weld has now also split .  Most concerning to me is that the weld has split in straight line along its center (where I would have thought it would have been its strongest).  I assume from the posts above this is the usual place for the splitting?   This is a 'reinforced' manifold, with both of the extra strengthening 'straps'.

 

My plan is to grind the weld off, 'V' it and reweld - but I don't claim any welding expertise.  I assume the manifold is cast iron?  My MIG wire is mild steel, will that be an issue?  I could preheat the are with a gas torch if that will help.

 

[SRDT 182]

This is the "reinforced a bit" manifold, you need the "reinforced again" one that you can find on a 405 mk2 or Xantia:

 

 

 

This cast iron manifold is hard to weld because it want to crack by design.

If you really want to try welding it you need to kill the crack:

 

[Tom Fenton 1,542]

You’ve the right idea but MIG isn’t the weld of choice that will last in this application. MIG puts the heat in quickly and in a localised area, not ideal for cast, plus you can’t get suitable wire either. A good vee prep, preheat the whole thing, then stick welded with appropriate cast rods (hi nickel), then controlled slow cooling down, is the way that is likely to have most success. Plenty written about it on the web.

[ArthurH 7]

Thanks both Baptist and Tom.  It doesn't look as though the crack has propagated further, just opened up again in the same place.  I think we will try welding it in the short term, but perhaps look for a better one in parallel. 

[SRDT 182]

You better start to look for one, even welding this one as good as new isn't enough. Also check if the flange is still straight.

 

This is the other side of the latest model manifold and you can see why this one doesnt crack:

 

 

On a cast part with no stress you can get away with TIG and some stainless steel rod, this manifold on the other hand need every trick on the book.

[hoodygoodwood 70 3 Cars]

With regard to the manifold blowing I have found that the outer 2 gaskets can break down and this combined with corrosion of the manifold and the steel within the gasket itself can allow the joint to blow - it doesn't help that the gaskets can be fitted round the wrong way . I have a granite surface plate which is perfectly flat and I have used it to check all my manifolds for distortion , they are all noticeably bowed by 0.5 to 1.0 mm , once placed on the plate they always sit on the middle 2 ports and you can slide a feeler gauge under the outer ones . Getting the manifold flanges machined would be the best solution but its a very difficult shape to hold so I settle for carefully filing it flat - its a solid hours filing normally !

[Callum 13 1 Cars]

2 hours ago, hoodygoodwood said:

With regard to the manifold blowing I have found that the outer 2 gaskets can break down and this combined with corrosion of the manifold and the steel within the gasket itself can allow the joint to blow - it doesn't help that the gaskets can be fitted round the wrong way . I have a granite surface plate which is perfectly flat and I have used it to check all my manifolds for distortion , they are all noticeably bowed by 0.5 to 1.0 mm , once placed on the plate they always sit on the middle 2 ports and you can slide a feeler gauge under the outer ones . Getting the manifold flanges machined would be the best solution but its a very difficult shape to hold so I settle for carefully filing it flat - its a solid hours filing normally !

Okay that's useful to know I will get a steel rule and see how flat it is when I renew the gaskets 

[ArthurH 7]

13 hours ago, hoodygoodwood said:

 ...it doesn't help that the gaskets can be fitted round the wrong way...

Thanks Miles, so for the avoidance of doubt , which is the correct way around?

[hoodygoodwood 70 3 Cars]

If you put them onto the bolts 180 degrees out the big hole for the exhaust gas is out of position , try them on head or manifold before assembly and note the position of the little rounded tag that sticks out then make sure its in the same place once you have it all back together . I stripped one down once that had 1 or 2 wrongly fitted and had probably been there for a decade partially blocking the gas flow . For your own interest you might want to measure the size of the exhaust port in the head and the manifold and then the diameter of the hole in the 4 gaskets - i had some Moprod gaskets once that were about 2mm smaller than the port size . The size varies between gasket make , i found the ones i bought from Peugeot had the largest hole so no gas flow restriction .

[ArthurH 7]

Thanks Miles, when we get our head back, I'll have a careful check - and post the results for these Victor Reinz gaskets.

[hoodygoodwood 70 3 Cars]

While on the subject of gaskets , many full kits come with 2 very similar items for the inlet manifold to head join , make sure you use the one with the holes that look like a little house - LOL - not the rectangular hole type as that one is for a carb engine and will cause serious running issues if fitted to a GTI .

[DamirGTI 342]

Maybe try finding someone who can do cast iron "spray welding" (powder welding) , might fix that manifold better with metal spray than stick welding it .

 

I tried arc welding three spare cracked manifolds , with an nickel rods , drilled out the cracks , pre heat , cool down in the ash/sand etc. - not so easy to do and the nickel rods are expensive ! only one turned up good , the rest started cracking again after a while along the weld area .

 

As said the manifold base tends to distort , best to check it and resurface if needed so you don't end up with leaky gaskets :

Edited January 22, 2019 by DamirGTI