BigHeads

[tommyg]

Hi All

I decided to go down the "BigHead" route to attach my cycle wings.  However, minimum order size seems to be 25 (at a rather high cost!).

Anybody got any spare ones they would like to sell, anybody also looking at this solution and want to split the cost of a bulk buy, or does anybody know where you can get them in lower quantities?

Thanks!
Tom

[Grubbster]

You can buy them singly here 

[tommyg]

Thanks - I have sent them an email asking for more specs - as there is no size on the website - no response yet.

I noted on Daniel's excellent blog he used the 16mm x 15mm size, so was hoping to get the same....

http://www.caterhamr500.co.uk/2014/03/build-day-twenty-seven-front-cycle.html

Have you/anybody bought them from this website so I could be sure they would the rigth size?

 

Thanks!

Tom

[turbot]

I went down the big head route 18 months ago, but they failed quite rapidly. I have now bonded them directly to the stays with loads of sikkaflex. This seems much better.

[Grubbster]

The issue of Bigheads (or the bond) failing comes up for discussion so often, as I've been using them for 15 years on 2 cars I'll summarise my experience here - 

When bonding bigheads to cycle wings god preparation is key - I clean the areas to be bonded with isopropyl alcohol and scratch the surface just a little.

I originally bonded big heads to GRP wins with Sikaflex 291 (black) and they lasted just a couple of weeks before the bonding failed. Sika 291 is a sealant not an adhesive (but has been used by some for bonding direct to wingstays where the contact area is much larger and can be glooped around the stay.

I then switched to Sikaflex 292 (white, large tubes only and expensive). I've never seen (nor heard of) a bond failure using this, it is used to stick yacht bulkheads together, very strong.

On my Academy car I used Bigheads own 'Big Bond fast set acrylic' with no bonding problems but I did have 2 Bigheads fail (weld failed) and I know a number of other people have experienced this, possibly bad batches manufactured?

Then on my original car I switched to carbon wings and used 'Big Bond fast set acrylic' which was fine for a couple of years then all of a sudden I had a complete bond failure (lifted clean off the wing) on 2 fasteners at Castle Combe (over 100 mph on the straight). No idea why, possibly due to extreme cold (the car was out of the garage overnight and it was icy), but I don;t know.

So now I've fitted new wings with Sika 292 and no problems so far.

I've never had a cable tie break either, even though in the Academy I used very thin ones!

This is how I  go about fitting them.

[ScottR400D]

I fitted the carbon wings to my R400 a year ago using big heads on the front of the stay, screws on the rear.

The big heads I used are 38x15mm with an M5 post. 3 in a line across the stay tube gives a surface area of over 1700mm2. If you examine the spec for sikaflex 291, it is an adhesive and sealant and has a bond strength of about 180g/mm2 so my arrangement theoretically gives a strength of over 300kg. (Disregarding the mechanical grip of the perforations).

As said prep is important. Key the surface of the big head and the wing and clean with an appropriate solvent. Leave plenty of time for a full cure.

Both bonds look fine almost a year and 1800 miles later. Unfortunately, using the post type heads you can't do both ends of the stay but I don't find the rear ones to be so noticeable. For me this is a better solution than cable ties etc. 

I had the same problem getting small quantities but a mate got them via his business as a sample.

 

 

[ScottR400D]

Btw although sikaflex 292 has a higher bond strength than 291, it's less flexible. Either should do the job if properly applied. 

[ScottR400D]

Btw although sikaflex 292 has a higher bond strength than 291, it's less flexible. Either should do the job if properly applied. 

[Grubbster]

I'm not trying to start an argument, just spoke from my own experience, obviously people are free to choose whatever they wish to use. If 291 works for you (and to be fair you have a lot more surface area than I do with just 2 small bigheads per stay, and less stress if the rear stays are drilled and bolted) that's good news.

Sika 291 spec sheet - Fast Cure Marine Adhesive and Sealant 

Areas of Application:

 - General all - purpose sealant

 - May be used for light duty – bonding

Sika 292 spec sheet - Structural adhesive for marine applications

Areas of Application:

Sikaflex® -292 is suitable for structural joints in marine constructions which will be subjected to high dynamic stresses. Suitable substrate materials are timber, metals, particularly aluminium (including anodised finishes), metal primers and paint coatings (twocomponent systems), ceramic materials, plastics such as GRP (unsaturated polyester resin), ABS, etc.

[ScottR400D]

No argument, I quite accept that 292 gives a stronger bond. It's just that the extra elasticity of the 291 is useful and it can be made to work, in my experience, though I did plan it carefully to maximise the bond area and quality.

To be honest, if I did it again I might well just source some high quality, black setscrews and avoid the bond altogether. I think button head sockets in black would be hardly noticeable on the carbon wings.

What I would avoid is what I understand Caterham do which is just plaster lots of sika type material all over the place, bit too permanent and inelegant for me!

 

 

 

[Titanium7]

RIF (Richard in France - Sadly no longer with us) used to sell them singly and also some small Carbon Fibre squares slightly bigger than the BigHead bases with holes for the post to go through. You ended up with the bonding material in a sandwich with the posts sticking through. He also produced a guide for the process of fitting these cycle wing Big Heads. I used his guidance notes and used Tigerseal, worked a treat.

[cr500dom]

I like the ability to remove the cycle wings and stays without splitting the top ball joint, so I went with Big Heads and Tywraps. secured with the acrylic adhesive.

But following on from an earlier post, i will add a third fastener in the middle to increase the bond area / decrease the loading on each.