Pip Pins for service bonnet

[stevieeg]

My nearside service bonnet hinge/bolt's threads have flattened to the extent that an M6 bolt simply slides inside with little purchase in what is left of the thread. So not only a thirst for fuel and oil, but a need for a replacement bolt very frequently!

I'd been considering drilling and tapping both bonnet bushes and wing points out to M8... but I know this will only begin the wear process again. It's not a very good design.

A mate suggested using pip pins instead. Has anyone else done this and did they work well? I've looked at a few sources online but I'm not convinced that there is enough space within the bodywork for the interference fit.

[BobE]

I'm not sure why you have a problem with the service bonnet fixings. The service bonnet pivots on two socket head cap screws that are tightened into the front bodywork/chassis. Why have the threads worn when they do not move in their threaded holes? Am I missing something here?

[stevieeg]

BobE said:

I'm not sure why you have a problem with the service bonnet fixings. The service bonnet pivots on two socket head cap screws that are tightened into the front bodywork/chassis. Why have the threads worn when they do not move in their threaded holes? Am I missing something here?

The reason is only the thread in the offside wing is intact, the nearside wing thread is worn and the wear is to the point that you can push an M6 bolt through the thread without interference.

Why? Fretting I would imagine. I notice that the bushes in the service bonnet also have threads in them (both worn to the point you can push an M6 directly through too)

So as it stands the offside is secure, but the nearside is not. An M6 will fit into the worn thread, but won't stand much vibration before it simply falls out.

They all either need to be bored and tapped out to M8, or a more effective solution that excludes the possibility of further thread wear is needed... Hence the pit pins idea.

[nawarne]

stevieeg said:

BobE said:

I'm not sure why you have a problem with the service bonnet fixings. The service bonnet pivots on two socket head cap screws that are tightened into the front bodywork/chassis. Why have the threads worn when they do not move in their threaded holes? Am I missing something here?

The reason is only the thread in the offside wing is intact, the nearside wing thread is worn and the wear is to the point that you can push an M6 bolt through the thread without interference.

Why? Fretting I would imagine. I notice that the bushes in the service bonnet also have threads in them (both worn to the point you can push an M6 directly through too)

So as it stands the offside is secure, but the nearside is not. An M6 will fit into the worn thread, but won't stand much vibration before it simply falls out.

They all either need to be bored and tapped out to M8, or a more effective solution that excludes the possibility of further thread wear is needed... Hence the pit pins idea.

Think I'm with Bob on this one.
Would it not be simpler to remove/drill out, then replace the riv-nuts in main bonnet, and then get new M6 shouldered cap screws to restore original fixing?

The service bonnet should rotate on the shouldered part of the cap-screw - as far as I know, the 'boss' (through which the cap-screw goes) on the leading edge of the service bonnet is not threaded

Mine are still the original fixings and seem to be holding up well.
Nick

[stevieeg]

nawarne said:

Think I'm with Bob on this one.
Would it not be simpler to remove/drill out, then replace the riv-nuts in main bonnet, and then get new M6 shouldered cap screws to restore original fixing?

The service bonnet should rotate on the shouldered part of the cap-screw - as far as I know, the 'boss' (through which the cap-screw goes) on the leading edge of the service bonnet is not threaded

Mine are still the original fixings and seem to be holding up well.
Nick

The problem is not on the bonnet itself, but where it screws into the wing. That is the thread that's messed up. I could drill it out and use a helicoil to restore to M6... I wouldn't want to think about the amount of work and potential for disaster involved in replacing the fixing point in the wing entirely!

I agree with you and I wouldn't have expected the Plain Bearing/Bushings in the service bonnet itself to be threaded... but there are thread marks in them which look too deep to have been caused simply by wear from having cap screws without shoulders fitted.

Either way, I do see wear in all of these places and I need to do something about it.

The pip pins seem like a suitable fixing method which would put to bed the problem of any further wear against what's observed, and is also of lower risk than me drilling into the wing and fitting a helicoil... Hence my question if anyone has had prior experience of using them for this purpose.

[nawarne]

Steve, I see where the problem is, I think.

But, IMHO, it doesn't seem to make sense to have the 'boss' on the service bonnet threaded...That is essentially, the 'moving' part of the hinge. Perhaps the wrong capscrews were used at some point, and this has caused the thread in the riv-nut to strip and cut a thread in the grp boss?

I guess you could fix the front end of the service bonnet with 'pip-pins'...take it these are the same fixing used on the trailing edge of the service bonnet?

Might be worth talking to one of the TVR body-shops on the best way forward?
Nick

[stevieeg]

nawarne said:

Steve, I see where the problem is, I think.

But, IMHO, it doesn't seem to make sense to have the 'boss' on the service bonnet threaded...That is essentially, the 'moving' part of the hinge. Perhaps the wrong capscrews were used at some point, and this has caused the thread in the riv-nut to strip and cut a thread in the grp boss?

I guess you could fix the front end of the service bonnet with 'pip-pins'...take it these are the same fixing used on the trailing edge of the service bonnet?

Might be worth talking to one of the TVR body-shops on the best way forward?
Nick

I'll be heading to Bespoke this weekend so I'll discuss the approach with them.

The pip pin is just like a bolt but without a thread on the shank. It has a "pip" feature at the end which can lock into a blind hole. Pressing the button retracts the pips and allows the pin to be inserted. Releasing engages the pips and gives an interference fit. For example:

http://www.wixroyd.com/en/catalog/design-elements/...

So basically a bolt without any screwing involved.

[geoffphead]

Hi Steve my Tuscan S is at Bespoke. Ask the boys to show u my service bonnet conversion. The hinges etc are rose joints and never wear. It may help you figure your problem
Cheers Geoff

[geoffphead]

Hi Steve my Tuscan S is at Bespoke. Ask the boys to show u my service bonnet conversion. The hinges etc are rose joints and never wear. It may help you figure your problem
Cheers Geoff