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Making exhaust studs


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I broke some exhaust manifold studs stripping my engine down this week. There are two sizes, the smaller ones are available so I can get replacements for those however the long ones are about 58mm long which seems to be a ‘weird’ size. 

I thought I’d have a go at making one, so I cut down an M8 bolt (8.8 grade) and cut a thread in to come up with the below, next to what I’m trying to replicate:

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Is there any reason why I can’t use this on my engine? Or are they made from something special that means I have to buy new?

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6 minutes ago, miketomcat said:

The cut thread will be slightly weaker than the forged end but I'd happily use it.

Mike

We must "assume", without any engine information, that it is an aluminium head, so the fastener thread strength is of no concern.

Like I say, the biggest problem is the zinc coating melts.  Best to be unplated.

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Thanks guys. It’s an iron head on the Mazda SL35Ti engine. I suspect that I can buy the studs for a price, I’ll make enquiries after the weekend. 

I could remove the zinc coating I guess if it’s going to be much of a problem.

I also need to replace the nuts. The ones on there are brass and are self-locking. They are the type that are slightly oval in shape which presumably grips the thread to resist undoing. I might replace them with standard brass nuts and locking washers instead so that they’re all consistent. 

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53 minutes ago, Red90 said:

We must "assume", without any engine information, that it is an aluminium head, so the fastener thread strength is of no concern.

Like I say, the biggest problem is the zinc coating melts.  Best to be unplated.

I guessed what engine they were off hence my comment. 

Mike

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Afraid not, it needs to have the correct lengths of threaded section. These are the two sizes required:

8EF845B9-36C6-4A2B-80DD-1D32BDB0DB33.thumb.jpeg.dd4555c3eb3f31ec55c96b2bfb2eb411.jpeg

If I don’t have any luck procuring the pukka ones, or they’re super expensive, I’ll get a non-BZP bolt from the local hardware place and repeat my effort above to make them.

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any decent fastener supplier (industry type not screwfix etc) should be able to source rolled studs in a variety of sizes. I purchased some long studs for my D2 exhaust manifold to use with clamping spacers not long ago but can't for the life of me remember the supplier I used. Wurth will do them but you'll likely need to find a supplier.

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I’ll take one into the local fastener place and see what they have. If they don’t do studs I’ll get some non-plated bolts to use instead.

Unfortunately the SL 3.5l engine was never sold by Mazda in the UK (or even Europe) so parts are not available through dealers. The HA engine (3.0l variant) was used in some forklifts and shares some parts but I’m not sure if exhaust studs are one of them. 

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A nice take on exhaust studs is cutting the "outside" thread a finer pitch and using a brass nut, means you can torque it up smoothly without stressing the threads in the head and it comes undone when you need to.

For the Rover V8 I buy ones from a mini-spares place as they are 3/8" UNC on the head end and 3/8" UNF on the nut end:

IMG_9277.JPG

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  • 2 weeks later...

Thanks to Ross of this parish I now have some nice stainless studs that are almost an exact match dimensionally for the longer originals. Got some standard studs for the short ones already, plus some longer ones to cut down if the stainless ones didn’t work out.

I also have some standard brass nuts and some self-locking copper-flashed nuts. So plenty of choice! ^_^

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