9 replies to this topic

[stitch-86]

Hi all,

Posted this here as technically it's not mini, but........

During the removal of the exhaust on my motorbike I managed to snap 3 out of 4 exhaust studs on the front cylinder head ( bike is a vfr 400)

They all have 5mm stubs sticking out but are badly corroded - how would you go about removing them?

Or does anyone know a machine shop that would do it?

Any help will be greatly appreciated, the studs I believe are 6mm, and not 100% sure but I think the heads are alloy.

Cheers

Richard

[sonikk4]

Can you get mole grips on the stud?? Plusgas the stub and leave for 24 hrs. Keep adding it over that period (do not use WD40) You could try some heat but be careful.

[stitch-86]

I had been soaking the nuts for a good few weeks in plus gas, but the studs had rusted almost all the way through, and I gave them a generous coating the day I broke them, probably could get mole grips on them, but didn't think they would have enough torque - will give it a go.

Someone said about trying to weld a nut on - but your in quite a tight space, which means I will most likely need to take the head off

[Dan]

Take the head to a shop for spark erosion.

[Ethel]

If the stubs have broken reasonably clean, I'd be inclined to use them to centre a guide to drill them.  Helps if there's enough metal to fit helicoils.

[stitch-86]

Dan sorry could you expand on that a little? To be honest I'm ok taking things a
Art why they go back together, but when they break I get a little hesitant so machine shop sounds good.

Cheer's Ethel, someone else said that, people in similar situations have installed heli-coils,

Think I will try one of the external teeth type removers, then the weld a nut, then cut them flat for either a heli coil or extractor!

I I thought rust was a pain whilst I had the mini!

[Dan]

  Exhaust studs are very difficult to remove sometimes even when they are complete because of all the heating and cooling they go through and the head and stud being dissimilar metals.  I seriously doubt you'll get a broken one out with any kind of extractor.  Welding a nut will probably work but as you say it'll be hard to get in there.  Wire spark erosion uses a current to literally decompose the stud out of the head.  A vibrating tool sends high currents through a tiny contact area into the stud which superheats that tiny part and a flow of coolant then washes the burnt parts out.  This happens hundreds of times a second and the tool simply presses its way forward into the stud fairly rapidly.  The tool erodes away the majority of the middle of the stud usually leaving just the thread which can be broken out easily.

[stitch-86]

That sounds like sy-fi!

I don't suppose you know anywhere that does that doff the top of your head? Stuck on my phone at the mo

Will also depend on costs, as just looking on fleabay there are a couple of heads going for between £70 and £100 which have all the studs looking pretty intact - would prefer to keep the engine as it were originally, but a replacement may be easiest if the cheaper options fail.

Thanks for getting back to me

[Dan]

  Google wire spark erosion, there are loads of people who do it.  They tend to mainly work on large scale very expensive industrial machines where binning castings is not a good option, so they tend to be mobile.  They usually accept small jobs like this to fill in time in between so often will let you post parts to them to be done and returned to you if you can't find anyone local.

[stitch-86]

Thanks for that Dan, Just got to work and having a quick google - there a quite a few places that do it - and its quite an impressive process!