Mk1 exhaust manifold & Vibration noise?

[Grendel]

I have a feeling I have another hole in my exhaust manifold and wandered is it worth getting a S/S Performance manifold or just get a 2nd hand standard. I vaguely remember there being a thread about the pros & Cons of performance manifolds but can find it?

[kevin..in]

pro's :- they are light
cons:- they break, they cost fortunes, don't necessarily make any more power, they are louder (this maybe/should be a pro!)
you need to address why you are breaking manifolds, ignition timing can be one reason making the manifold run too hot, this if it destroys a cast std. manifold will make short work of a tube one

[Grendel]

Well it turns out the Mongoose down pipe to the Manifold is leaking AGAIN. Yet the bolts are tight so looks like I’ll have to replace the gasket/ring thing yet again. Only changed them a year ago.

[kevin..in]

Well it turns out the Mongoose down pipe to the Manifold is leaking AGAIN. Yet the bolts are tight so looks like I’ll have to replace the gasket/ring thing yet again. Only changed them a year ago.

yes they do tend to break up, could be excessive movement in either engine mounts or exhaust rubber mounts causing this (the weakest) joint to fail

[Grendel]

Just ordered some new O-Rings from TCB and will stick them in with liquid gasket to make doubly sure it's a good seal this time.

Mind you did have some welding done in that area on the Manifold to pass MOT a few months back so that may of weekend them.

[kaiowas]

Might be worth using new studs/nuts as well. I had a problem for ages where the exhaust would burn the gaskets out and start blowing no matter how tightly I did the nuts up. I eventually worked out that the threads on the studs had rusted to the point that although the nuts felt tight they weren't actually clamping the exhaust together properly.

[j0nathan]

Years ago I had a similar issue. Ended up unbolting everything, taking a wire brush mounted on a drill to thoroughly clean up both faces, reconnecting everything with new gaskets and then having to torque everything back up again after a couple of hot and cold cycles. Never had an issue again.

[Grendel]

Can anyone recommend a good exhaust sealant to make an extra seal when I put the O-rings in from the mongoose to the manifold joint?

[Grendel]

Well the old O-rings where FUBA came off resembling springs. So have now put new ones in smoothed in Exhaust paste after giving the pipe ends a good clean so no more leak from there.

BUT I’m STILL getting a rasping/vibration noise when I throttle off yet there is no exhaust leaks.

Any ideas?

[SuperRedMR2]

Is your exhaust slip jointed? This can often blow if not fully closed up

[Grendel]

It's a Mongoose exhaust fitted to normal manifold. I've been under the car with it running and the only leak I found was the manifold to down pipe joint. But need to check it this weekend to see if the bolts are still tight so will check the whole lot again.

Is it possible the baffles could have loosened over time?

It’s not a loud rattle just a bit of a rasp when you throttle of like something loose?

[jimi]

I get a similar noise off my magnex on acceleration for the first ten minutes or so, after the exhaust has warmed up it goes away, I put it down to a loose baffle.
Also used to get a noise like that at a certain rpm with the standard exhaust which I eventually tracked down to a heat shield rattling.

[Grendel]

Found out the rear mounting bracket on the car was shot so the box was rubbing against the heat shield. All it appears the middle clamp/hanger is bent out of shape so guess it has been pushing the whole system back gradually over the years. But just spoke to Mongoose who will sell me a new clamp/hanger for £24.

Beginning to think I may just put up wit the vibration noise.

Out of interest how far should the box be from the heat shield since there is only a 5-8mm gap between mine?

[Grendel]

Might be worth using new studs/nuts as well. I had a problem for ages where the exhaust would burn the gaskets out and start blowing no matter how tightly I did the nuts up. I eventually worked out that the threads on the studs had rusted to the point that although the nuts felt tight they weren't actually clamping the exhaust together properly.

Well after hanging the exhaust properly with all new brackets looks like the manifold gasket I changed in April has gone again but the bolts are tight so looks like its going to be new threads as well as gaskets ands bolts.