Which bolts?

[Mikerb]

I am replacing my JCB 3CX 87 exhaust silencer. The old bolt heads have sheared off, so I'm ordering some replacements while I try to extract the bolts.

The bolt head is 5/8. Which type of bolt do I need? there seems to be a lot of choices; grade 5-8, UNF, UNC, BSP, BSW, 5/8x1/4, high tensile, course, M8, Stainless steel... the list goes on.

Bit confused to be honest

I'm assuming that http://www.ebay.co.uk/itm/111429656606 is what I'm after?

Regards

Mike

[Jeremy Rowland]

Hi Mike, while I am not sure of the thread of your bolts they are not going to be BSP because that stands for 'British Standard Pipe' I would see if I could carefully drill a central hole in one and use an 'easy out' type stud extractor.
Once you have identified the thread and length then I would go for an 'HT' bolt (high tensile) stainless is a good option but still corrodes over time, whatever they are I would plaster them in copper grease before putting them back.
If the 'easy out' stud extractor does not fetch them out then you will have no choice but to carefully drill them out and re-tap the thread, what usually happens is that as your drill size reaches the threads core size then you may be able to get the bits of old thread out with a sharp implement like an engineers scriber.
I would also fit a flat washer with a spring washer under the bolt head to prevent them from falling out as the old threads may be a bit loose after you have drilled out the broken bits.
I would use a local fastener supplier for the new bolts they will be able to give you the higher tensile value bolts.

Jeremy

[Jeremy Rowland]

When you have identified the thread I should be able to tell you the correct size tapping drill to use; either way you could simply tap it into Google there's bound to be the same info there.

Jeremy

[Mikerb]

Thanks for the reply Jeremy.
I've got the extractor, so I'll have to try get the bolts out to find out what thread it is.
That's a useful tip about the engineers scriber, I'll keep that in mind but fingers crossed I wont need it!

Mike

[FOWLER MAN]

Hi,
If a 5/8 AF spanner fits the bolt head the bolt will be 7/16 UNF or UNC.
You would usually expect to find UNF if fitted with a nut, or UNC if screwed into a casting or tapped hole.

On "7/16 Unified" bolts with 5/8 AF heads the spanner size for the nut will be 11/16 AF, (one size bigger than the bolt head).

As far as tensile strength is concerned, (grade), a good rule is "the better the bolt the better the job."
Fred

[FOWLER MAN]

Hello again.
I have just looked at your original post,
I'm a little confused, those bolts on Ebay can't be UNC and Whitworth as they are not the same thing.
Looking at them the heads are far too big in relation to the threaded part of the bolt to be UNC. They must be 1/4" Whitworth
If so they certainly wont do.
Fred

[Mikerb]

It's all a bit confusing, but I have spoken to Vicary Plant Supplies today and apparently they should be on stud and nuts, so the previous owner (when he replaced the engine) must have used bolts instead. I have now ordered the studs and nuts for it so fingers crossed they will fit.

Thank you all for the replys.

Mike

[Jeremy Rowland]

It's all a bit confusing, but I have spoken to Vicary Plant Supplies today and apparently they should be on stud and nuts, so the previous owner (when he replaced the engine) must have used bolts instead. I have now ordered the studs and nuts for it so fingers crossed they will fit.

Thank you all for the replys.

Mike

I thought that it was odd that bolts were fitted but as I am not familiar with that engine type I did not question it; if your fitting new studs secure them with Loctite, but put plenty of copper grease onto the threads where the nuts fit and also on the nuts, this won't stop corrosion but will help to delay the onset of it and should make the nuts easier to remove should the manifold need to come off again in a hurry.

Jeremy

[Mikerb]

I'm struggling to get the old bolts out, they are seriously rusted in! I've drilled them out and snapped an easy out, welded a nut onto the stud, heated it cherry red with oxy/acet but no hope.

The next thing to try is a tap to re thread it. But does anyone know what tap I need to buy, would it be 7/16 UCN like FOWLER MAN mentioned? I have the replacement studs but have no way (or don't know how) to gauge it.

If re threading doesn't work I'll be buying a helicoil set, and again need to know what size to buy.

Regards

Mike

[FOWLER MAN]

Yes Mike ,
If the original bolts had 5/8 AF heads as you say they will be 7/16, and if threaded into the casting they will be UNC.
If you go down the Hellicoil rout you only need to quote the size 7/16 unc and you will be given the drill size and supplied with the right taps for the job.
If you have the correct new studs take them allong and let them sort it out.

Good luck.

Fred