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[JamesV6CDX]

Time to change your garage TD!

The head design of a bolt has nothing to do with the thread (obviously).....its the use of a torque wrench which is important, something it would appear they do not use :-/

Their comment is when trying to undo the bolt......not tightening it.....but then i guess as they tightened it the time before.....its there fault its too tight.... :-/

I can vouch they have three torque wrenches   Wether they use em all the time.....is a different matter.....you got a torgue wrench yet James  

Plus they make an excellent coffee while you wait  

Yep, I have (and used) a torque wrench capable of 8nm.

The bolt stripped well before the required torque, though...

[Marks DTM Calib]

Why avoid helicoil.....if done correctly, its better than a tapped thread and is much smoother.

Most top race engines have helicoiled everything!

[TheBoy]

Why avoid helicoil.....if done correctly, its better than a tapped thread and is much smoother.

Most top race engines have helicoiled everything!

I don't have much understanding of such things, but if you have room to retap, isn't that a better fix?

[Marks DTM Calib]

You cant re-tap reliably.....by stripping the threads, the extra metal required to get a good tap has been removed, you can only go over size.

And over size isn't as good and as strong as a helicoil.

[TheBoy]

You cant re-tap reliably.....by stripping the threads, the extra metal required to get a good tap has been removed, you can only go over size.

And over size isn't as good and as strong as a helicoil.

Yes, I was referring to drilling and retapping to a larger size.

As said, don't really understand why helicoil would be stronger that a (oversize) retap.  Not in anyway disagreeing with you, just lack of understanding on my part.

[Martin_1962]

The helicoil is quite a hard steel, AFAIK the sump is aluminium

[TheBoy]

The helicoil is quite a hard steel, AFAIK the sump is aluminium

But it can never be stronger than weakest point - in this case the helicoil against the sump?

[Martin_1962]

The helicoil is quite a hard steel, AFAIK the sump is aluminium

But it can never be stronger than weakest point - in this case the helicoil against the sump?

Not moving though, so should last, Mark seems to know about this.

I made my own equivalent once for an exhaust bolt on a bike barrel, Drilled and tapped bigger hole, made one on a lathe with bolt hole in the middle and a bigger thread on the outside, it lasted

[Marks DTM Calib]

Not wanting to be to technical but....

The shear strength of the female thread in the aluminium will limit the axial load on the bolt (hence it strips IF its over tightened.....). If you then fit an insert, the area under shear increases as radius squared, and you can allow the bolt to take more of its design strength axial loading. This is because the yield stress in shear of the helicoil material is much higher than that of the aluminium.


Basicly, the aluminium thread is now longer and hence gives more support, the stainles steel helicoil is way stronger than the aluminium and the result is....a much stronger thread.

Plus they are much easier to work with as the helicoil is a precision formed thread and not a rough cut thread in an casting!

 

[TheBoy]

Not wanting to be to technical but....

The shear strength of the female thread in the aluminium will limit the axial load on the bolt (hence it strips IF its over tightened.....). If you then fit an insert, the area under shear increases as radius squared, and you can allow the bolt to take more of its design strength axial loading. This is because the yield stress in shear of the helicoil material is much higher than that of the aluminium.


Basicly, the aluminium thread is now longer and hence gives more support, the stainles steel helicoil is way stronger than the aluminium and the result is....a much stronger thread.

Plus they are much easier to work with as the helicoil is a precision formed thread and not a rough cut thread in an casting!

 

Makes a lot of sense once explained.

Thanks for the explaination - as said, certainly wasn't disagreeing with anyone, just trying to understand

When undoing, does the helicoil ever come out?

[Marks DTM Calib]

No, there usualy stainless (although other types are available like phosphorbronze for nasty salty environments) so dont corrode to the bolts inserted and they are designed so they are larger then the hole they are being fitted into hence you have a sprung setup applying contact to the outer material into which it is inserted over the whole area of the helicoil....

....in fact they can be a swine to remove unless you bend one end in and wind them out...

[JamesV6CDX]

Really stupid question, how do you fit a heliciol, and how does it hold in place? Never done one...

[lee4206]

Really stupid question, how do you fit a heliciol, and how does it hold in place? Never done one...

Quite simple you just tap out the existing hole with the tap supplied with the helicoil screw in the helicoil insert break off the tang and its as good as new. The insert holds itself in place because of the spring tension on it

[JamesV6CDX]

Really stupid question, how do you fit a heliciol, and how does it hold in place? Never done one...

Quite simple you just tap out the existing hole with the tap supplied with the helicoil screw in the helicoil insert break off the tang and its as good as new. The insert holds itself in place because of the spring tension on it

If I don't have any luck mate, I may take you up on the offer of lending the helicoil kit. OF course, I'm happy to cover cost of postage insured both ways, if we do go that way

[lee4206]

Really stupid question, how do you fit a heliciol, and how does it hold in place? Never done one...

Quite simple you just tap out the existing hole with the tap supplied with the helicoil screw in the helicoil insert break off the tang and its as good as new. The insert holds itself in place because of the spring tension on it

If I don't have any luck mate, I may take you up on the offer of lending the helicoil kit. OF course, I'm happy to cover cost of postage insured both ways, if we do go that way

I'll double check that i've got the right kit tomorrow and let you know.  I've got sump bolts and washers too so im sure i'll have something to fit..