Holey Exhaust Collector Box Bat-Man

[laRIKin]

Mainly because you can't weld over it again,so once you done the brazing bit,you're stuck with it.

I agree with you on that, but thats not the reason I was looking for.
It had something to do with exhaust gases reacting with the bronze, or
something like that.

[pete376403]

I agree with you on that, but thats not the reason I was looking for.
It had something to do with exhaust gases reacting with the bronze, or
something like that.

Oh I dunno - my Jawa speedway motor (4 valve) had bronze inserts in the head for the valve seats, Of all the things that upset my Jawa, exhaust gas reacting with the valve seats wasn't one of them.

And Rudge had a motor back in the 30s of which the entire cylinder head was bronze.
http://ulyssesnb.netfirms.com/classi...1933_rudge.htm

[laRIKin]

I just thought that you may not get a WOF if there was brazing on the
exhaust system. I know that when I rebuilt my racing sidecar, I brazed the
collector box to the headers. And one of old hands back then said that it was
not a good idear and one of my mates back then told me why, he is/was a car
mechanic.
I'll have to read up on my old books to find the answer now.
As you said an insert is OK and I agree.
It's more welding (brazing) up the pipe, is where the problem is.
I could be wrong.

Just read your article and it said "The 'semi-radial' aluminum bronze cylinder head"
Now there are bronzes and there are bronzes. I'm not trying to be picky.
Just trying to put this nagging thought to rest.

[What?]

It's coz exhaust pipes get hot. Very hot. And metal expands when it gets hot. But different metals expand at different rates, so the brass fix-it bit will fall out.
Of course, brazing would be fine on a brass pipe...

[Motu]

Well,the whole point of brazing is it's flexability,but an exhaust would have to get to red temp - and yes,that's possible,but not common,there is something wrong if that's the case.If a brazing job falls out just from expansion differentials then the job has been done wrong - there should actualy be a layer of molecular bonding at the joint,the two metals combined.I think that's one of the problems when brazing very thin worn exhausts,it actualy becomes one metal,sort of a matrix of steel and brass,and weaker than both metals.

All the old frames were brazed,but a lugged joint with the bronze in the lug.Later with Reynolds 531 and chrome moly frames there were two camps on how to join the metal - one said welding was too hot and damaged the metal,others said it was ok.My Rickman was a brazed Reynolds 531 frame,my Cheny 531 frame was beautifuly welded - neither broke,so both methods were strong that's for sure.

[Holy Roller]

It's coz exhaust pipes get hot. Very hot. And metal expands when it gets hot. But different metals expand at different rates, so the brass fix-it bit will fall out.
Of course, brazing would be fine on a brass pipe...

Or use an old coathanger for the brazing wire it worked for me anyway. No problem with the different metal types . Typical Kiwi she'll be right mate stuff :sneaky2:

[pete376403]

(See if I can remember what they told us at tech...) with brazing there is no combining of the dissimilar metals, there's still a distinct boundary between the bronze and the steel. Where there are two flat surfaces together there is a capillary attraction between them and its strong as (re your bronzed frame lugs) but with an edge butt joint (ie typical exhaust pipe) theres a much less capillary attraction. Another point, if you get the steel too hot the bronze volatilizes and the steel crytals end up with a coating of impurites, that greatly weaken the steel.
(Petone Tech block course 1972)

[laRIKin]

Well I can't find anything to say not to bronze weld an exhaust pipe.

I actually found in one book saying that you can, as long as it is clean.
So you do not get any impurities in the weld.
Which could be hard on a old dirty exhaust pipe and that maybe where the
problem is.

[Motu]

We're all trying to find these old books! mine are in storage,but I'll have a look in my workshop library tomorrow - Pete,one of my books showed a photo of a bronze welded joint,and there is a layer where both metals combine,the bronze actualy into the surface of the steel.
But I think you hit it when you mentioned overheating of the joint - this could be what is in the back of leman's mind.When brazing such a thin metal as worn exhaust pipe it's very easy to cook it,big smoky flare ups as the zinc burns out of the brass,overheated steel crytalises,the whole joint is just a metalurgal mess,both metals destroyed and no strenghth at all.Good enough reason not to do it!

[What?]

Somewhere in the above 24 posts lies the truth. Or maybe it's spread through the 24. My welding book doesn't mention brazing exhaust pipes, but does warn of the dangers of old hydrocarbon deposits when using oxy-acetylene and steel wire...

p.s. Bronze ain't Brass.

[laRIKin]

This is proberly a boring thread for most.

Well I read the whole article this time.
In a nut shell he said that he would use brazing to repair small holes.
And use it to build up a web (for strength) around his TIG welded header
flangers. :spudwhat: This is not what I would call building exhaust pipes.
Like I thought when I first read the brief write up, before the main article.
Must remember to read the whole thing before opening mouth.
If you can find anything of interest Motu I would be interested.

[Motu]

This is proberly a boring thread for most.

Well,I've thinking about welding - I don't do a lot these days,and when I do it's mostly with the mig.I'm not arty in any way,but to me there is something special about it - I say to my wife it's kinda like sewing...you cut out these peices then stich them altogether,and out of an apparent mess a shape takes form,and like sewing it's a practical form,something useful....maybe that's why I don't dig art,you don't create to use.Controling molten metal,knowing just how much heat,the flow of heat,so elemental - or like the dike welders I knew - such pretty sparks!

I have only seen one person who can match the perfection of the welds of the man who taught me.''do you move the torch around when you weld?,I don't,my hand shakes just the right amount'' Every weld would be inspected,then redone without rod until he was happy with it,then clean with a wire brush - just for a bloody exhaust pipe at 4.30! never rushed,never let an unperfect weld leave his hands.Every time I pick up a torch I can hear him tut tut the mess I make.

[FROSTY:Me]

probably too late now but--I'd get a piece of panel steel the same size as the whole underside of the box and weld it all around.better sollution than trying to put in little patches

[laRIKin]

RiderInBlack I had almost for gotten about your pipe.
So what gives? fixed or F*****!

[RiderInBlack]

Ya, My butcher patch job is holding up so far. Much better with my welding now (thank guys). Still should replace it but am having a hard time just getting enough money to pay for rego (looks like I'll have to do that in 3month lots) and new tyres (would like to try some Diablos next). Just rekitted the slave brake cylinders and replaced the pads with cinted ones. Wont put cheap brake pads on my bikes now as I have had new mineral pads decintergrate on me (lucky they were on the back brakes, still not a good feel but).