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Exhaust manifold studs and brass nuts


Colin Lindsay
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Just tried to fit new exhaust manifold studs to my Herald cast manifold and not had great success.

The manifold has been shot blasted and the old studs removed, but on fitting the new ones (bought from an eBay supplier) I found that the socket-type stud puller I was using to fit them damaged the metal very easily - the studs seemed very soft and the threads just flattened. I decided to try using a nut and spanner to seat them but the threads didn't fit anything I had, I suspect they're not UNF, so used one of the brass nuts. It went on very easily, in fact too easily - no Gorilla hands needed - and continued right down over the unthreaded section of the stud with very little pressure required, so has stripped the threads clean out of the brass nut. I can't believe they distort that easily. It would never have tightened sufficiently to hold an exhaust against the gasket.

So: before I order replacement studs and nuts, who do we recommend? Are there any alternatives ie stainless?

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I'm not using alloy on this setup; it's the original cast manifold to a stainless downpipe. I've already got stainless manifold studs rather than original copper / brass whatever. Whatever threads these are, none of my other brass nuts will fit but they fit the originals, which are too corroded to reuse.

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Hi Colin,

can you weld a steel nut to the studs and unscrew them that way. The heat may also loosen the stub in the manifold.

Do not go the Stainless direction.    Quite often the steel studs for the manifold are copper plated to resist corrosion. Stick with the brass  nuts.

 

Roger

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Old studs are out, no problem - it's refitting the new. They were too stiff for finger tightening alone so a hand-held stud puller was employed to fit them, just hand pressure but the threads went flat almost immediately. I tried a brass nut and spanner but the brass was so soft the nut just stripped once any resistance was met. I can't tap out the manifold as they're not UNF so have tried my best to have clean threads lubricated with copper grease. It appears these are just cheap repro studs, so am currently checking Paddocks for replacements

I was just wondering what everyone else uses.

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26 minutes ago, Colin Lindsay said:

Old studs are out, no problem - it's refitting the new. They were too stiff for finger tightening alone so a hand-held stud puller was employed to fit them, just hand pressure but the threads went flat almost immediately. I tried a brass nut and spanner but the brass was so soft the nut just stripped once any resistance was met. I can't tap out the manifold as they're not UNF so have tried my best to have clean threads lubricated with copper grease. It appears these are just cheap repro studs, so am currently checking Paddocks for replacements

I was just wondering what everyone else uses.

Hi Colin,

to get the studs in use the double nut method. That usually works.

Rimmers appear to have the studs in stock.  I would have thought the thread would be either UNF or UNC.

Good luck

 

Roger 

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20 minutes ago, Badwolf said:

Just ordered three of those; I like the look of them already. 

23 minutes ago, RogerH said:

to get the studs in use the double nut method. That usually works.

Couldn't do that, Roger, they weren't UNF. Even my old brass nuts that came off other Heralds wouldn't fit the threads. I've gone for the ones that BW has linked to, they look very solid. I'll need two sets but not committing until I see the first one.

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The Spalding stuff that I have had has been first class with fairly quick delivery. Ironically a friend of mine owns a nuts and bolts company but does very little unf these days so it's Spalding for the first search. Let us know what you think when they arrive.

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Colin demonstarted by his post how brass nuts are unsuitable for exhaust manifolds.  Brass is too soft.

The correct material is bronze.

If you have difficulty sourcing, try a yacht chandler!

John

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Stainless studs and tight stainless nuts, not the best. Stainless tends to pick up . Its strength is not in tension. We have had machines that have sheared heads when put under stress.

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Ref S/S not the bee all it sounds like, in the Water Industry here we had a 900mm Alligator valve simply like a jaw & mouth opened around hinge pins which controlled res inflow between 25 and 650Ml/d (650 flowrate = 2/3 of Melb daily demand)

Obviously at throttled flows there is a lot of vibration and wear on the valve teeth/gums, so the valves require a rebuild every 5 years, a bright spark in out Mech Maintenance Dept decided to fit S/S replacement gums/teeth held on with S/S bolts tapped into the body. The fixture lasted 3 months when the valve leakage increased to 200Ml/d, so after a lot of revalving we dewatered the inlet chamber (the pipeline is 22Klm long between valves as a Transfer pipeline only) and found the replacement gums/teeth missing, so we had to dewater the Reservoir to find the replacement gums/teeth, which showed fatigue fractures in the S/S and the bolts had sheared due to fatigue where they were threaded into the gums/ teeth, so it was back to the drawing board.

Similarily on S/S reticulation pipe repair clamps the threads on the screw down bolts had to be coated with Teflon to stop galling of the thread when tightening down, also the S/S clamps construction welds had to be passivated to stop severe corrosion & eventual failure at that point. 

I'd be wary of S/S studs in a cars exhaust manifold/joints.

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https://www.ebay.co.uk/itm/254809108713

I've tried these as manifold to head studs and nuts... motorcyclists seem to be very fond of them but no doubt time will tell! I reckon there should be less heat at that part of things than the exhaust flange, so it will get the Spalding fasteners as a trial.

The biggest problem with the studs / nuts I bought is that while the studs screwed into the manifold - eventually - none of the nuts I had, either mild steel, stainless or bronze fitted the other end, so I could neither adapt or replace anything else, or even use two nuts to screw the studs to manifold. 

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9 hours ago, Colin Lindsay said:

The biggest problem with the studs / nuts I bought is that while the studs screwed into the manifold

Colin, didn't they come with nuts?  I was looking at this supplier, he's offering me a full set of SS studs nuts and washers but now you have me worried

 

 

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The stainless studs for the head to manifold came with nuts, spring washers, and flat washers. Full kit and I must admit I'm impressed by how solid they feel.

The other kit for the manifold to exhaust also came with the same range of items, but obviously cheap quality and not fit for purpose.

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1 hour ago, AidanT said:

We're these the good ones?

https://www.ebay.co.uk/itm/254809108713

Yes those are the ones. 

With regards to brass / bronze nuts; I understand the reason for them with mild steel studs so would fit them on the exhaust flange out of mere habit; I've no idea if you could get away with stainless there. Some of the gang here will hopefully advise.

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As John said earlier. BRASS is too soft, needs to be a Bronze material. A little touch of "copperslip" or similar dosent hurt either. Stainless Nuts can (and do) seize, the Type/Quality of the Composition can be critical (%age chrome) as the Tensile strength can be affected. I`m not the biggest fan of stainless fasteners with the exception of "cosmetic" area`s. I.E they look pretty.

Personally I would stick with O/E and perhaps Bronze nuts?.

Pete

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17 minutes ago, PeteH said:

As John said earlier. BRASS is too soft, needs to be a Bronze material. A little touch of "copperslip" or similar dosent hurt either. Stainless Nuts can (and do) seize, the Type/Quality of the Composition can be critical (%age chrome) as the Tensile strength can be affected. I`m not the biggest fan of stainless fasteners with the exception of "cosmetic" area`s. I.E they look pretty.

Personally I would stick with O/E and perhaps Bronze nuts?.

Pete

As pete points out, stainless with stainless when done up to a torqued can "seize " what  we call "pick up". If your lucky you can get out of it , plenty of lubrication and winding backwards and forwards to avoid shearing. Then the threads need cutting if needing to use again. Stainless is very hard, gets harder with heat! Its tensile strength is poor, thus its tendency to shear.  As pete suggests stick with standard for a long term solution.

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From a bit of research the manifold studs sizes on a six cylinder are as follows

3/8" UNF stud 6 off @ 1 7/8" L
3/8" UNF stud 4 off @ 1 3/8" L
5/16" UNF stud 3 off @ 1 3/8" L

Can you advise on the lengths purchased as an alternative Spalding Fasteners on do the 1 7/8" ones

Thanks

 

 

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