1500 Exhaust/Manifold Gasket

[Howard81]

Driving my 1500 yesterday, I had to go over a million speedbumps that London councils kindly distribute around the place. On doing so, the rear exhaust mounting split, which in turn caused a blow at the exhaust to manifold gasket. I didn't realise what it was at first, but the car was making grinding/creaking sounds on acceleration/braking up to 15mph. I put on a new mounting rubber, but as I was tightening up the bolts on the exhaust/manifold join, and one of the studs fell out I've put a bolt on there now, but it's still blowing a fair bit (at least it doesn't sound like a tractor now ).

However, now the exhaust knocks against the driver-side chassis rail slightly as I go around corners, and occasionally on accelerating. With the gasket replaced and bolted up properly will the exhaust just fall back into position? I've checked the two exhaust mounting rubbers, the rear is new, and the one just forward of the rear axle is still in place. Is there a third up front? I can't really see under there without jacking the car up.

I'm thinking to replace the whole manifold. The flange that meets the exhaust is pretty manky, and the remaining studs are pretty corroded.

[mbellinger]

IIRC there should be a third stay up front that attaches the manifold down pipe to the bell housing. This stay is often left off or missing, but without it you will only re-experience the manifold blowing problems. Geoff at Wins is the man for a recon manifold with new studs etc.

I think xvivalve may do the front stays....

[Howard81]

Thanks Martin

I am almost certain there is no stay on the manifold, so that is one more item for the shopping list. Anyone have a photo of one, or a parts diagram so I can see what it looks like?

[Jon Tilson]

The support is between box and downpipe and is a must fit if you want the joint to last more than 5 minutes.
Fit it back with new stainless studs and brass nuts and a plain and spring washer under each nut. tighten til the brass sqeaks when warmed up...then again when cooled down. then it lasts a year if you are lucky...

Jonners

[tinweevil]

The bracket makes no difference IME. 3000 miles per gasket regular as clockwork for the last 50K miles. At some point late last year when changing it I found the U clamp that attaches the pipe to the bracket had escaped. It's made no difference.

[Jon Tilson]

oh well...I'm going mostly by 1850s....

It defo makes a difference on them but then they have no flange gasket as such, just a clamp ring and only 2 studs with zero out of ten for access to one of them...

Jonners

[Richard the old one]

I am assuming that you are talking about the exhaust manifold to exhaust downpipe joint. If this is the case I recommend that you check that both of the mating surfaces are flat. I have found that they are often convex which means you will not get a gasket to last long.

In respect to the mounting bracket that you are missing. If your car is a manual a non Overdrive it is part number UKC4097; For 1500 manual OD car the part is UKC4098; and for an auto UKC 4099. You will also need an exhaust clamp part number GEX7509

[Howard81]

Thanks for the part numbers, I've phoned a few suppliers but no luck with it yet! Being an automatic, I think it's probably going to be very hard to find one.

I fixed the clonking exhaust, it was right up against the chassis leg rattling away. I fixed that by giving the exhaust a few persuasive (but gentle) kicks Now the manifold join is only leaking ever so slightly from the rear stud (which also has a bolt through it). I've got some gaskets on order and will look into getting a refurbished manifold from Wins

[Jod Clark]

The longevity of the OHV gasket joint has a great deal to do with the condition of your engine mountings. As the engine is free to rock from side to side and the exhaust system is held to allow small movement laterally but not vertically, the looser your engine mountings become, the more torque is transmitted through the manifold to downpipe joint. As the engine leans over on the mountings under torque reaction, the exhaust system is actually being pushed upwards towards the floorpan or down towards the road thanks to the 70ish degree bend just behind the gearbox. Three little studs really aren't up to the job of fighting this torque, especially when they're getting very hot and have some high-pressure gas behind them.

I fixed mine by making some new engine mountings from stock Dolomite ones, some box section spacers instead of the Dolly rubber block and some MG Midget 1500 mountings. Then I had the manifold joint face machined flat and the top of the downpipe as well. The little studs were removed and the holes reamered-out and retapped 7/16 unf. I fitted some short sleeves to the inside of the manifold that passed throught the gasket and into the downpipe, plenty of Holts Firegum around the sleeves and both sides of the gasket, then fitted the manifold and downpipe to the car as one unit. Once connected to the rest of the 'system' on my car, I remade the gearbox to downpipe bracket to hold the downpipe in exactly the position it wanted to be in and clamped it all up nice and firmly.

It worked very well and never blew, even when the mount holding up the side-pipe 'silencer' gave up after a good seeing-to from a speedbump. Instead the bloody thing blew a chunk out of the downpipe just below the manifold flange, leading me to receiving a 'fix-it' ticket from M25 plod. EDY never saw the street again.