Reoccurring exhaust manifold leak

[Pedey]

Hi everyone,

So we've been having problems with our headers leaking at the flange of runners 3 and 4. This first occurred the day we picked the car up after purchasing it. I replaced the gasket, then bolted everything together. When we then ripped off all the fuel injection gear to go to carbs, I noticed that the same area was once again blackened, though it hadn't gone right through yet, (mostly because it had only been started once or twice in that time). I replaced the gasket again and the leak has reappeared now that I've driven it a couple of times.

My question is - is there a way of telling what's causing the problem without having to pull the headers right off and take them to someone ie - is it that the manifold flanges are uneven and might need linishing, could it be those horrible sandwhich type bolts that aren't doing a good enough job of holding both the manifolds on? Any suggestions of things to check before I have to pull it all apart once again?

Thanks!

[djz]

Were the bolts still tight when you've replaced the gaskets? You might want to measure the thickness of both manifold flanges, if there is a difference then the thick washers won't be sitting flat which could cause the nuts to come loose.

The exhaust manifold flange not being flat is the next thing to check.

[nzeder]

also get a good gasket - those that have had zed for a long time will not use a gasket without the metal around the exhaust ports - these are ordered from Japan via ST-Hi-Tech in Mt Wellington Soichi Tate is the owner/operator. They come in 2 sized 39mm and 41mm version - we get the 39mm version as if your ports are bigger than 39mm you are one up on most of the race cars putting down lots and lots of HP - you don't need big ports to get big HP - just everything done right = $$.

[Baker93]

Hi

Yep all of the above. Just pull it apart and check the lot. They do not leak generally on road cars if all faces are flat of the same thickness and you use a good gasket. Mine always leaks towards the end of a season on No2. But i dont care certainly cant hear it ! If building / buying extractor / headers for the Z ensure flange is Min 12mm thick. Some of the cheap headers have very thin flanges !

[big sam]

I think the twin su manifold flange thickness is around 14mm and the typical header flange 12 mm. I encountered this when fitting some headers recently, my solution was to make some stepped washers to make up the difference, so both nip up with equal force.

[Pedey]

Ok thanks for your advice everyone, appreciate it

[ZMAD]

I also made stepped washers when fitting a tripple manifold due to unequal thickness. Scored thick washers, clamped in vice, angle grinded the required amount. Worked sweet.