"Gusset" under downtube

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jimlews
Posts: 299
Joined: 11 Jun 2015, 8:36pm

"Gusset" under downtube

Postby jimlews » 4 Oct 2019, 9:18pm

I recently acquired a frameset from a member of this forum (many thanks, Bill; it's built into a lovely bike). The frame has a reinforcing piece of metal plate (Gusset for want of a better term)under the downtube immediately behind the headtube. It is TIG welded to the headtube at its forward end and to the downtube along its length. The lower end is not welded and there is a distinct gap between plate and downtube. The frameset is made for touring from Reynolds 725 steel.

While I understand that the purpose of this gusset is to strengthen what is a highly stressed area, I can't see that it contributes much that is useful on a frame whose purpose is general touring and one that is made from one of Reynolds posher tubesets. Touring bikes have successfully done without such addenda for generations.

But my main concern is the open lower end. Given the often appalling weather conditions that touring bikes are required to endure and the known propensity of water to find and penetrate close interstices, it seems to me that we have here the perfect rust trap especially as I very much doubt that there is any way the manufacturer can have painted inside the gap.

And now to the question. I am very tempted to remove this gusset by filing away the welds. I don't think there would be any adverse effects, as long as I can refrain from filing into the down tube. The bike will obviously need a respray post surgery, but as I wish to reposition certain conflicting braze-ons this is going to happen anyway.

What do the 'Wise Owls' of this forum think of my scheme?

landsurfer
Posts: 5030
Joined: 27 Oct 2012, 9:13pm
Location: Rotherham

Re: "Gusset" under downtube

Postby landsurfer » 4 Oct 2019, 9:21pm

Fill the gap with clear silicone and leave it alone ...
Be a do'er, not a watcher. Be a Sceaphierde, not a Sheep.
Mike Hall, Jenny Graham .. Respect. .... The Road Goes On Forever !

fastpedaller
Posts: 2143
Joined: 10 Jul 2014, 1:12pm
Location: Norfolk

Re: "Gusset" under downtube

Postby fastpedaller » 4 Oct 2019, 9:26pm

Squirt some waxoyl or similar into it.

Bez
Posts: 1200
Joined: 10 Feb 2015, 10:41am
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Re: "Gusset" under downtube

Postby Bez » 4 Oct 2019, 9:50pm

I wouldn't remove it. It's been designed to be there, and an open end is common because a closed gusset creates a stress riser which can eventually cause the tube to crease.

Open gussets do tend to harbour a little rust, yes. But if you want to avoid that then, as above, rather than file the gusset away fill it with something that won't transfer stress to the tube. If grease isn't permanent enough for your liking then I would use framebuilder's putty, Sugru or even some form of glue.

slowster
Posts: 1037
Joined: 7 Jul 2017, 10:37am

Re: "Gusset" under downtube

Postby slowster » 4 Oct 2019, 10:08pm

jimlews wrote:I can't see that it contributes much that is useful on a frame whose purpose is general touring and one that is made from one of Reynolds posher tubesets. Touring bikes have successfully done without such addenda for generations.

1. For generations touring bikes were overwhelmingly lugged, not welded.

2. I think you'll find that there is a gusset on most - possibly even all - 725 touring frames, e.g. Genesis, Dawes, Ridgeback etc. That suggests to me that it is needed and that Reynolds themselves probably specify that a gusset is fitted. I suspect that Reynolds may have had a choice between making the 725 down tube a lot thicker and heavier to allow it to be used without a gusset, or designing the tube to be used with a gusset which would allow it to be lighter and yet just as strong or even stronger.

3. Given the location I would not have worried about water ingress (I take it you are keeping the mudguards on the bike), but spraying Waxoyl into the gap sounds like a good option.

4. If you want an answer from the horse's mouth, ask 531Colin, since he designed the frame.

Brucey
Posts: 36138
Joined: 4 Jan 2012, 6:25pm

Re: "Gusset" under downtube

Postby Brucey » 4 Oct 2019, 10:57pm

fastpedaller wrote:Squirt some waxoyl or similar into it.


yes; just turn the bike upside down, warm the area (eg with a hairdryer) and apply the waxoyl; it will quickly wick into the space under the gusset.

Gussets like this are a cost-effective way of reinforcing a part of the frame that sees the highest stresses otherwise. The favoured design is as decribed; welded up with sides but not at the end, and the end is often scallop shaped, so that the stress concentration at the ends of the welds is reduced. Don't go taking it off!

cheers
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~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~

reohn2
Posts: 36745
Joined: 26 Jun 2009, 8:21pm

Re: "Gusset" under downtube

Postby reohn2 » 5 Oct 2019, 12:02am

fastpedaller wrote:Squirt some waxoyl or similar into it.

:wink:
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I cycle therefore I am.

pwa
Posts: 10605
Joined: 2 Oct 2011, 8:55pm

Re: "Gusset" under downtube

Postby pwa » 5 Oct 2019, 9:18am

landsurfer wrote:Fill the gap with clear silicone and leave it alone ...

Something like this. Then forget about it.

The gusset probably is unnecessary. My 725 frame Thorn Club Tour doesn't have it and has taken more abuse than any bike should have with no problem, just held together with lovely neat tig welds and no gusset. But just accept your frame the way it is.
Last edited by pwa on 5 Oct 2019, 9:22am, edited 1 time in total.

reohn2
Posts: 36745
Joined: 26 Jun 2009, 8:21pm

Re: "Gusset" under downtube

Postby reohn2 » 5 Oct 2019, 9:22am

pwa wrote:
landsurfer wrote:Fill the gap with clear silicone and leave it alone ...

Something like this. Then forget about it.

As the rust sloowwlllyyyy creeps under the silicone :shock:
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I cycle therefore I am.

pwa
Posts: 10605
Joined: 2 Oct 2011, 8:55pm

Re: "Gusset" under downtube

Postby pwa » 5 Oct 2019, 9:25am

reohn2 wrote:
pwa wrote:
landsurfer wrote:Fill the gap with clear silicone and leave it alone ...

Something like this. Then forget about it.

As the rust sloowwlllyyyy creeps under the silicone :shock:

You think it would? If it is a Spa they are "painted" with an electronic process in a bath, so the hidden surfaces should be painted. Many years ago I had a lugged frame with imperfect braze and a couple of holes where braze should have been. I filled them with wax crayon and never had any rust there.

David9694
Posts: 361
Joined: 10 Feb 2018, 8:42am

Re: "Gusset" under downtube

Postby David9694 » 5 Oct 2019, 9:32am

A picture would be good.

I’ve never seen this before. I note people seem to recognise it, but are you sure it’s not a repair to a front end shunt?

reohn2
Posts: 36745
Joined: 26 Jun 2009, 8:21pm

Re: "Gusset" under downtube

Postby reohn2 » 5 Oct 2019, 9:37am

pwa wrote:
reohn2 wrote:
pwa wrote:Something like this. Then forget about it.

As the rust sloowwlllyyyy creeps under the silicone :shock:

You think it would? If it is a Spa they are "painted" with an electronic process in a bath, so the hidden surfaces should be painted. Many years ago I had a lugged frame with imperfect braze and a couple of holes where braze should have been. I filled them with wax crayon and never had any rust there.

It's not a definite but as I can't see inside the gusset,I prefer Waxoyl and an open end for the gusset to breathe.
-----------------------------------------------------------
I cycle therefore I am.

Brucey
Posts: 36138
Joined: 4 Jan 2012, 6:25pm

Re: "Gusset" under downtube

Postby Brucey » 5 Oct 2019, 9:53am

I've seen quite a few frames which have traces of corrosion lurking under the gusset, so I've always assumed that many painting processes don't coat that area perfectly.

I've also seen corrosion inside frames at about this point, presumably due to condensation. No reason condensation shouldn't occur beneath the gusset too. hence my preference for waxoyl that has definitely run in and penetrated fully.

cheers
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~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~

pwa
Posts: 10605
Joined: 2 Oct 2011, 8:55pm

Re: "Gusset" under downtube

Postby pwa » 5 Oct 2019, 10:22am

reohn2 wrote:
pwa wrote:
reohn2 wrote:As the rust sloowwlllyyyy creeps under the silicone :shock:

You think it would? If it is a Spa they are "painted" with an electronic process in a bath, so the hidden surfaces should be painted. Many years ago I had a lugged frame with imperfect braze and a couple of holes where braze should have been. I filled them with wax crayon and never had any rust there.

It's not a definite but as I can't see inside the gusset,I prefer Waxoyl and an open end for the gusset to breathe.

And top up once in a while? That does sound like a plan.

jimlews
Posts: 299
Joined: 11 Jun 2015, 8:36pm

Re: "Gusset" under downtube

Postby jimlews » 5 Oct 2019, 10:44am

I am thinking that if I remove it carefully, there should be no reduction in the strength of the frame. I understand that 725 steel becomes harder due to the welding process (hopefully, not embrittled), so the aprox 38mm of heat affected area down each side of the downtube should be at least as strong as it was when it left the tube factory.

There is already evidence of rust grinning through at the 'lip'. This can be wiped away, but it is obvious that something untoward is happening within.

In my version of cycle-touring, I am regularly following muddy, empuddled tracks and fording streams, so moisture IS going to find its way into the gap, mudguards notwithstanding.

In my experience in a past life, of restoring old motor cars, Waxoyl makes any subsequent painting problematic,to say the least.

And finally, what better way is there of spending those long winter evenings than by 'whittling' ones bicycle?