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What size bolt

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fatjames
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Joined: 09 Jul 2011
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PostPosted: 07:32 - 25 May 2012    Post subject: What size bolt Reply with quote
Hi all,

I sheered the head off one of my exhaust bolts on the virago. Luckily there was enough thread left to put a nut on it. The bolt goes into an elbow, that goes into the block. I'm aiming to replace this, but all I can seem to find on places like ebay are studs.

Does anyone know what size I'd need? Looks like M6x30mm, or maybe M8? Or should I just replace them with studs?

Also, to withstand the temp of the exhaust does it need to be made of a certain metal?

https://cdn.bikechatforums.com/files/exhaust_stud.jpg

Thanks,
Fatjames
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DrDonnyBrago
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Joined: 03 Jan 2010
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PostPosted: 08:17 - 25 May 2012    Post subject: Re: What size bolt Reply with quote
fatjames wrote:
Hi all,

I sheered the head off one of my exhaust bolts on the virago. Luckily there was enough thread left to put a nut on it. The bolt goes into an elbow, that goes into the block. I'm aiming to replace this, but all I can seem to find on places like ebay are studs.

Does anyone know what size I'd need? Looks like M6x30mm, or maybe M8? Or should I just replace them with studs?

Also, to withstand the temp of the exhaust does it need to be made of a certain metal?

https://cdn.bikechatforums.com/files/exhaust_stud.jpg

Thanks,
Fatjames


Studs are generally better than bolts for exhausts.

Mostly because torquing down a nut onto a stud puts less strain on the cylinder head threads than torquing down a bolt does.

Also, using studs means you can use brass/copper nuts that wont corrode too badly and if they do, will strip and come off before the stud snaps. Broken exhaust studs is VERY VERY common and can be a royal pain in the arse to fix, if you do it properly now then it shouldn't happen again.

I find that most exhaust studs are M8 in the bit that goes into the head then either M8, M7 or M6 for the bit that you screw nuts on to. I'd be a bit surprised if a stud as thin as M6 was used for the whole stud, seems a bit too snap happy for my liking.

Exhaust studs are made from mild steel, lather them up with copper grease and you shouldn't have a major issue with corrosion. Certainly less likely to have big problems than if you fitted stainless studs/bolts and they galvanically corroded into the head.

You will also need new downpipe gaskets if you are removing yours, otherwise they are liable to leak. There are a few main types, everyone has their preference, for various reasons I prefer the copper gaskets but go for whatever you want.


TL;DR - if it was mine, fit new gaskets, studs and brass nuts.

Last edited by DrDonnyBrago on 13:52 - 25 May 2012; edited 1 time in total
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fatjames
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Joined: 09 Jul 2011
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PostPosted: 12:20 - 25 May 2012    Post subject: Reply with quote
Thanks, very informative. Karma

I've ordered 4 new studs and a set of 3 new gaskets, the gaskets look like hollow copper o rings. I assume I tighten 'til they start to collapse and form a seal. Shall I also put copper grease on the gaskets?

Also, any tips when using Irwin extractors? I purchased the standard set, and the expansion set. I'm hoping very much that the smallest is small enough for the remains of the bolt.

Thanks again
FJ
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Nexus Icon
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Joined: 26 Aug 2010
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PostPosted: 12:48 - 25 May 2012    Post subject: Reply with quote
You won't need extractors to remove the broken piece. If you can get a nut on as well as the flange itself you must have a good 8-10mm of thread exposed outside of the cylinder head.

That's plenty to grab hold of with some vice grips.

Add a bit of plus gas or heat and Bob's your uncle.
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fatjames
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Joined: 09 Jul 2011
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PostPosted: 12:52 - 25 May 2012    Post subject: Reply with quote
Nexus Icon wrote:
You won't need extractors to remove the broken piece. If you can get a nut on as well as the flange itself you must have a good 8-10mm of thread exposed outside of the cylinder head.

That's plenty to grab hold of with some vice grips.

Add a bit of plus gas or heat and Bob's your uncle.


Normally that would work, but there isn't enough room. I tried to put two nuts on and counter lock them, but then I couln't fit a spanner into the gap. It's not an issue though, I've just had the Irwin set delivered, looks quite easy to use.
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DrDonnyBrago
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PostPosted: 13:51 - 25 May 2012    Post subject: Reply with quote
fatjames wrote:
Thanks, very informative. Karma

I've ordered 4 new studs and a set of 3 new gaskets, the gaskets look like hollow copper o rings. I assume I tighten 'til they start to collapse and form a seal. Shall I also put copper grease on the gaskets?


Yeah, the gaskets are exactly that, thick copper foil rolled up into a hoop. They compress when you fit them so there is no need to go mental torquing the pipes down.

You only really get one shot with the gaskets so make sure everything is nice and clean before you tighten the stud nuts, you can get around it if you mess up but nice new gaskets seal the best. Clean both the end of the pipes and the recess in the head where the gaskets fit, if you have a tap and die set then running a tap down the old stud holes in the head is worthwhile. Use plenty of copper grease, on the studs, nuts, gasket etc etc - all the grease burns off leaving a dusting of copper powder to keep everything from rusting together and snapping off again. Make sure you get the old gaskets out too as sometimes they get really stuck in, so stuck in it is hard to tell they are even in there.



Quote:

Also, any tips when using Irwin extractors? I purchased the standard set, and the expansion set. I'm hoping very much that the smallest is small enough for the remains of the bolt.


What do they look like?

bolt extractors:

https://www.toolauthority.com/images/P/78/53916.jpg

or EZouts?

https://www.askmehelpdesk.com/attachments/plumbing/38000d1320932543-have-new-shower-tap-shroud-thats-stuck-small-piece-piping-help-easyout1.jpg


I've never tried the bolt extractors but was under the impression that they are for bolts that still have a head? My snapped studs came out with mole grips and lots and lots of heat and plusgas into the cylinder head.

The EZout type are totally unsuitable for what you want to do and will almost certainly snap off and make the job even worse.
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