Exhaust manifold nuts loosening

[grogee]

I've got a 4-2-1 manifold and the car's been sounding rough and getting fumes in cabin so I checked manifold nuts (and bolt) and they were all loose.

Any tips for preventing them rattling loose? Was thinking of another locknut behind the existing nut, plus maybe some high temp thread lock if such a thing exists.

Other cars I've had used those 'squashed' nuts that grip hard on the thread, I think I've got some spares so might try that.

 

[zinc2000]

red harlemar should do it or blue, can never remember which colour is best for heat, but normally the heat from the manifold is sufficient to keep them tight.
so maybe worth checking what is causing them to loosen, is the exhaust missing a bracket somewhere

 

[DOH]

There is no need to use any thread lock. There are a few options for nuts to use on the exhaust manifold to cylinder head studs.

First determine the thread size , so if it takes a 13 mm socket , then it will usually be an M8 thread. If it takes a 14 mm socket then it will be a M10 thread.

Then go onto ebay and look at the various options .
The Japanese engines( including Yamaha) , often use a nut with an integral washer, the washer has serrations so that it grips onto the manifold surface.

Other options include plain nuts with corresponding spring washers .

Whichever option you go for, re tighten up the nuts after its warmed up as you will get a bit more of a turn on them.

Have you still got a flexi joint somewhere between the replacement manifold and exhaust system, if not that will be the cause of your problem & you will need to fit one.

 

[grogee]

Spring washers don't work. Ever. The serrated ones might though. There is a flex joint in the system. From memory the studs are M8 but I'll double check. Good tip on tightening when warm although I'll have to watch my fingers as access is tight and that manifold gets toasty.

 

[DOH]

Something like these as I recall there are 5 of them for £2.89 posted:

https://www.ebay.co.uk/itm/Flange-Manifold-Nut-Stainless-Steel-A2-M8-x-1-25-Pitch-Inlet-Exhaust/392790195028?hash=item5b741ebb54:g:awkAAOSwEK9UFIxa

 

[RICHARD MANSFIELD2]

Hi,
On the old A series engine as fitted to the Mini the exhaust manifold nut were brass. The expand when hot and therefore clamp tighter to the stud. In addition they always come undone very easy due to the fact they are non corrosive.
Regards,
Richard

 

[YOG]

Hi,
On the old A series engine as fitted to the Mini the exhaust manifold nut were brass. The expand when hot and therefore clamp tighter to the stud. In addition they always come undone very easy due to the fact they are non corrosive.
Regards,
Richard

Plenty of brass nuts on eBay.

 

[DOH]

The only problem with brass nuts is that they don't take as much torque as a steel nut and therefore strip the nuts thread easily.
The mini & Metro also had a clamping bracket from one of the downpipes to the gearbox.

Kwikfit historically deliberately left that off when replacing the exhaust and told the customers that they needed new engine mounts quoting £100's in the 90's.

Without that bracket the brass nuts always worked loose , so I don't think they are as good for a FWD car such as a Puma.

Brass nuts would still work ok for a longitudinal mounted engine with rwd, where the engine isn't putting as much strain on them as a FWD car.

The amount of cars I sent customers back to Kwikfit was very many,telling them that there was nothing wrong with their engine mounts but to get that bracket refitted leaving Kwikfit very red faced indeed!!

If you are concerned about the nuts rusting, you can of course purchase stainless steel nuts.


The correct engineering solution always depends on the application when recommending a solution . :thumbs:

 

[grogee]

I've bought some pricey locking stainless ones. The equivalent of nylock but ok for high temps. Quite pricey!

https://www.ebay.co.uk/itm/123691176490

I agree about the brass nuts, too soft for this. There are only five fixings holding the whole thing on.

Regarding the bottom manifold to gearbox fixing like A-series: the standard Ford Puma cat is supported by a bracket on lower engine block. The aftermarket manifolds like mine don't have any provision for support at the bottom (near the 90deg bend) so I've cobbled together a bracket that uses the original engine block fixings.

 

[mmc757]

Those are some nice looking nuts!

 

[DOH]

The problem you have is caused by the missing stabiliser bracket to the exhaust. If at all possible try and affix your made up clamp/strap around both of the down pipes . The reason for this is otherwise eventually the manifold flange plates weld can fracture due to the stress of the engine moving back and forth on gear changes and on /off throttle situations.

It is recommended that you also check the condition of the lower gearbox to floor mount, which reduces this movement.
It is common for them to wear and need replacement by now , if it hasn't already.

With regard to the nuts you have purchased, I have no experience in using them. It will interesting to know if they are tight when fitting all the way along the thread.

I am wondering at a later date when you try to undo those nuts, whether they will unwind the studs in the head instead of the intended nut coming off them?

 

[grogee]

I agree about manifold needing lower support. I'm surprised it's not built into the manifold really.

Don't know about the undoing of nuts but you may well be right. If the studs came out I might well fit new ones.

BTW don't do what I did and guess the thread... It's not M8. It's M10.

 

[DOH]

If they are M10 , do the current nuts take a 14mm socket?
I think that when I removed a exhaust manifold off a Lotus Esprit that it had the style of factory fitted nuts you have purchased, but they were not stainless steel.

I still have some of the studs in my workshop with the nuts on.
As a matter of curiosity ,I will check and let you know if they were of the same style but in mild steel .

 

[grogee]

I think 14mm yes. There are also zinc plated versions of the nuts I bought but my thinking was this wouldn't last long at 900 degrees...

 

[grogee]

Bit of an update. I've been told that the Toyo manifold I have is a bit suspect in terms of flatness of the gasket face. I've been recommended to get it skimmed.

And there was me thinking it was a bargain (£21 plus postage)

 

[Brian']

Make sure you don't use stainless hardware. That's not going to work. On my turbo manifold I had problems of exhaust stuff working loose. I now used just plain steel hardware (10.9) and copper nuts. Never worked itself loose again.