Retroanaconda Posted March 31, 2018 Share Posted March 31, 2018 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: 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? Quote Link to comment Share on other sites More sharing options...
Ex Member Posted March 31, 2018 Share Posted March 31, 2018 It should be fine. The unplated ones tend to be better though as the exhaust is too hot for the plating. Better to start with a plain bolt What engine and part number are you saying these do not exist for? Quote Link to comment Share on other sites More sharing options...
miketomcat Posted March 31, 2018 Share Posted March 31, 2018 The cut thread will be slightly weaker than the forged end but I'd happily use it. Mike Quote Link to comment Share on other sites More sharing options...
Ex Member Posted March 31, 2018 Share Posted March 31, 2018 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. Quote Link to comment Share on other sites More sharing options...
Retroanaconda Posted March 31, 2018 Author Share Posted March 31, 2018 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. Quote Link to comment Share on other sites More sharing options...
miketomcat Posted March 31, 2018 Share Posted March 31, 2018 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 Quote Link to comment Share on other sites More sharing options...
Ex Member Posted March 31, 2018 Share Posted March 31, 2018 Are you sure they are brass? It is very common to use copper plated steel locking nuts for exhaust flanges. https://www.belmetric.com/metric-copper-exhaust-nuts-c-3_51/ Quote Link to comment Share on other sites More sharing options...
Retroanaconda Posted March 31, 2018 Author Share Posted March 31, 2018 Well I don’t know for sure but they don’t seem to be magnetic so I had discounted steel. Quote Link to comment Share on other sites More sharing options...
Anderzander Posted April 1, 2018 Share Posted April 1, 2018 Both Brass and Copper get used - but I seem to have only come across classic cars using brass?. If the studs are a standard M8 pitch, can you not buy a generic stud and nut kit? Even if you have to cut them down? Quote Link to comment Share on other sites More sharing options...
Anderzander Posted April 1, 2018 Share Posted April 1, 2018 Something like these any good?: http://www.adl-components.co.uk/5x-bmw--ford-exhaust-manifold-stud-bolt-m8-x-58mm-11122343030-car--motorbike-3592-p.asp Here they are on eBay: https://rover.ebay.com/rover/0/0/0?mpre=https%3A%2F%2Fwww.ebay.co.uk%2Fulk%2Fitm%2F323003557443 Quote Link to comment Share on other sites More sharing options...
Retroanaconda Posted April 1, 2018 Author Share Posted April 1, 2018 Afraid not, it needs to have the correct lengths of threaded section. These are the two sizes required: 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. Quote Link to comment Share on other sites More sharing options...
lo-fi Posted April 1, 2018 Share Posted April 1, 2018 Genuine Mazda studs weren't expensive when I was buying for my RX7. And everything else on that car was expensive! Quote Link to comment Share on other sites More sharing options...
landroversforever Posted April 2, 2018 Share Posted April 2, 2018 Can't see an issue with the BZP.... at worst the coating is going to break down but I can't see any problems with that? Quote Link to comment Share on other sites More sharing options...
discomikey Posted April 4, 2018 Share Posted April 4, 2018 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. Quote Link to comment Share on other sites More sharing options...
Retroanaconda Posted April 4, 2018 Author Share Posted April 4, 2018 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. Quote Link to comment Share on other sites More sharing options...
FridgeFreezer Posted April 4, 2018 Share Posted April 4, 2018 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: 1 Quote Link to comment Share on other sites More sharing options...
Retroanaconda Posted April 7, 2018 Author Share Posted April 7, 2018 Picked up some non-BZP bolts today but the M8 die in my tap and die set broke on trying to do the first one. I’m guessing the high tensile bolt was too much for it. Will revert to plan A but it’ll have to be next weekend now Quote Link to comment Share on other sites More sharing options...
Retroanaconda Posted April 16, 2018 Author Share Posted April 16, 2018 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! Quote Link to comment Share on other sites More sharing options...
Ex Member Posted April 16, 2018 Share Posted April 16, 2018 Put one of each combination in different locations and you can then do a study on which works best. Quote Link to comment Share on other sites More sharing options...
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