Manifold Madness

SimonR · 29th April 2007, 18:55

Hi all,

My R-Series VP Maestro has been suffering from a blowing exhaust for a while and I set about repairing it today. The problem area was where the two manifolds join together and there's a tin gasket clamped between them using three bolts. Part 3 in the diagram below:

The old gasket was completely knackered when it came out and there was a large portion of it missing along one side, hence the blow.

However, I've replaced it and have the same problem.

I'm wondering which way round the gasket should go because there are indentations in it. Currently I've got the indentations downwards (i.e. towards the exhaust manifold) - perhaps it should go the other way?

Failing that I think maybe my exhaust manifold has rusted and/or warped - has onyone else experienced this?

I'm also wondering if perhaps I should have used some exhaust assembly putty on the joint, but I've done this job before sucessfully and didn't do so then. If only I could remember which way up I put the gasket!

Cheers all...

talkingcars · 29th April 2007, 19:45

I trust you cleaned and inspected the mating surfaces, it is possible you burnt some away while the joint was blowing.

SimonR · 29th April 2007, 19:56

Quote:

Originally Posted by talkingcars

I trust you cleaned and inspected the mating surfaces, it is possible you burnt some away while the joint was blowing.

Yes - I cleaned them and they appeared to be true and flat. I have to admit that I didn't put a straight edge over them to see if there had been any erosion. Anyway I'm going to have to take it all apart again tomorrow so I guess I'll be able to measure then.

If there is a fault with the exhaust manifold then it could be quite a big problem. I've no idea where I'd get an R-Series exhaust manifold from these days!

Cheers...

E_T_V · 29th April 2007, 20:47

What flows through the gasket (intake or exhaust gasses) as it isn't obvious from the picture. If it is exhaust then add a load of exhaust assembly or repair paste to the gap and see what happens.

SimonR · 29th April 2007, 21:21

Quote:

Originally Posted by E_T_V

What flows through the gasket (intake or exhaust gasses) as it isn't obvious from the picture. If it is exhaust then add a load of exhaust assembly or repair paste to the gap and see what happens.

Yeah - it's exhaust gas.

Actually thinking about it I can't really see what the purpose of venting exhaust gas into the inlet manifold is. Why would you want to heat the inlet manifold using exhaust gases? Surely it should be kept cool to keep the intake gases as cool and therefore dense as possible?

Maybe I could simply block up the rectangular holes in the exhaust manifold and therefore prevent any gas leakage from source?

E_T_V · 29th April 2007, 21:50

Yes I'd block the holes up if it was me (just fit a piece of metal to block the hole off).

The reason they do it is to improve the cold running of the engine (the same reason the S series got a manifold heater).

SimonR · 30th April 2007, 10:40

Cheers for the answers, Dan.

I agree and will do so. Getting it air-tight might be a bit of a faff but I'll find a way.

Just as long as I don't have to keep taking it apart I'll be a happy camper!

G Force · 30th April 2007, 10:48

Hi Simon it is fairly common for that gasket to blow. It does not matter which way up you install the gasket, all you can do is make sure the mating surfaces are clean and true. The exhaust manifold is susseptable to warping and can sometimes be too badly warped to seal the joint. When you do the job losen the exhaust maifold bolts as well, once you have cleaned the surfaces tighten the three bolts before you tighten the inlet and exhaust manifold. I never use repair paste as it eventually blows out of the joint, if you must use it I would only use a liberal amount.

If you block off the hot spot then you will more than likely have running problems such as stalling whislt warming up and poor mpg and drivability during the colder weather.

Chris Y · 30th April 2007, 17:07

Quote:

Originally Posted by G Force

I never use repair paste as it eventually blows out of the joint, if you must use it I would only use a liberal amount.

Not meaning to nit pick, but "liberal" means "a lot", so did you mean use a small amount, or cover it liberally with exhaust goo?

On the subject of manifolds and warping - a cautionary tale from my own recent experience:

Never, ever use exhaust wrap!

Mine is now totally warped, and will not fit on the cylinder head. As you look at it from the front of the car, the right most port is about 3mm - 4mm closer in than it should be, and no amount of prising or levering will get it back on. It's got more warp than the starship Enterprise

I don't have any means of effectively heating it up to bend it back either, so I'm not going to bother for the moment. May try that in the future.

I've seen it happen to other people's manifolds and exhausts, but I've always suspected they had inferior designs or poor quality metal, but it's actually the wrap, which keeps more of the exhaust gas heat in the manifold. Great for the inlet system and general underbonnet temps, but not so great for the manifold itself

On the subject of paste though, I do use the Fire Gum stuff if I'm not 100% sure that the mating surfaces are totally correct. Provided you just smear it on as an addition to the sealing properties of the gasket you shouldn't have a problem, and indeed I find it helps. I would use the Fire Gum in this instance, if the gasket wasn't 100% or there was some warp on the mating surfaces.

SimonR · 30th April 2007, 18:42

Quote:

Originally Posted by Chris Y

Not meaning to nit pick, but "liberal" means "a lot", so did you mean use a small amount, or cover it liberally with exhaust goo?

Yeah - I think that was just a slip of Gary's keyboard...!

Quote:

Originally Posted by Chris Y

On the subject of paste though, I do use the Fire Gum stuff if I'm not 100% sure that the mating surfaces are totally correct. Provided you just smear it on as an addition to the sealing properties of the gasket you shouldn't have a problem, and indeed I find it helps. I would use the Fire Gum in this instance, if the gasket wasn't 100% or there was some warp on the mating surfaces.

Righty-ho well it looks like the plan is set then - I'll take it apart again and smear some paste into the joint.

Damn this car - it's doing its best to pee me off. Can't believe I've got to take it apart AGAIN - this'll be the third time! Still at least only one bolt sheared on dismantling it and that was on the exhaust manifold, not the cylinder head.

Tax and MoT are due tomorrow so it's about time it was fixed...

G Force · 30th April 2007, 18:50

Quote:

Originally Posted by G Force

I never use repair paste as it eventually blows out of the joint, if you must use it I would only use a liberal amount.

Yes I mean a small amount, I never realised it also meant a lot. Just my ignorance of our language. I meant it in the moderate context i.e. slight amount. I'll try not to make the same mistake again.

SimonR · 4th May 2007, 10:56

Hi chaps,

Thanks for all the replies. I nipped out to a motorfactors and bought some exhaust paste and reassembled the joint with a good dollop of the stuff on both sides of the gasket.

I'm happy to report that it's now air-tight and the car sounds as quiet as it used to.

Just need to get an MoT but that should be relatively easy now because the rest of it's very up-together.

Cheers!