Honda CB77 brake stay modification

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I tried sending a private message to Rojodiablo but the system is acting screwing and my message doesn't appear in my sent box.  Accordingly, I will ask the forum at large for some help.I am writing in the hopes that you can offer me some sage advice on my vintage motorcycle racing project.  I'm in the process of building up a Honda CB350 vintage road racing machine (WERA V1 / AHRMA Formula 250).  My bike utilizes a 200mm diameter 2LS front drum brake from a Honda CB77 Super Hawk.  I need to fit a large air scoop to the front drum for cooling purposes.  Unfortunately, the brake linkage gets in the way.  I spoke with an old-timer who recommended I rotate the brake backing plate counterclockwise approximately 135° and weld a boss between the brake shoe pivots for a new brake stay rod mounting bolt.  See the picture below.  The white arrow indicates the original brake stay mounting location, the red arrow indicates the newly fabricated brake stay mounting location.I'm decent with my Miller Diversion 165 on DC.  But I'm not confident with welding aluminum on such a safety critical component.  Therefore, I have enlisted the help of a friend who I consider to be a decent auto fabricator and welder.  He used to moonlight for Ballard Technology (aerospace company) but now he just helps out friends with their projects when needed.  To better understand the process and to help ensure my friend and I are both on the same page, I have a few questions:1) What material should I make the new boss out of?  Alloy 2017? Or alloy 6061?  I have no idea what the original sand cast brake backing plate is made of.2) What filler rod should be used? I see a lot of debate back and forth between using 4043 or 5356.  It seems to be a matter of personal preference.  Which would you recommend?3) My friend has access to a decent TIG welder Miller Dynasty 350 I believe.  Would he still need to pre-heat the brake backing plate with a propane torch if he is using a machine like this?4) Do I need to worry about post-process heat treating the brake backing plate?Thank you for any help or advice you can offer.  I really appreciate it!Miller Diversion 165
Reply:I do not know why you are welding on this backing plate but 6061 would be fine.No heat treating or post treating is needed.Warpage is possible and I would not weld on that backing plate if it is not necessary.Do NOT cool the weldment with water!!The weldment would get soft as butter.Let it cool on its own.I wish you could explain or show WHY you want to weld on the backing plate.That brake reaction arm is too short to pull in a straight line. You need to increase the length of that arm.IS that duel cam front brake from a CB450???IT should be more like this: CB450 front duel cam brake.BTW the spokes in that hub are in backwards.EDIT: Disregared this commentThis wheel looks very dangerous.You better get this looked at by someone who knows what they are doing.Last edited by Donald Branscom; 01-07-2013 at 07:26 PM.AWS certified welding inspectorAWS certified welder
Reply:Originally Posted by Donald BranscomDo NOT cool the weldment with water!!The weldment would get soft as butter.Let it cool on its own.
Reply:Originally Posted by shovelonThat is opposite of what I have come to believe.How did you come to this conclusion?
Reply:copper softens by quenching. aluminum usually requires heating to 700f or so and cooling slowly.miller thunderbolt 250vlincoln square wave tig 175 prolincoln idealarc mig sp250everlast tig 210EXTeverlast power plasma 50chicago electric (hf) 130 tig/90 arcchicago electric 90 amp flux wire3 sets oxy/acet
Reply:6061 t6 will soften to t4 if you heat it to 900+ let it soak at temp and then quench.miller thunderbolt 250vlincoln square wave tig 175 prolincoln idealarc mig sp250everlast tig 210EXTeverlast power plasma 50chicago electric (hf) 130 tig/90 arcchicago electric 90 amp flux wire3 sets oxy/acet
Reply:Originally Posted by Donald BranscomI do not know why you are welding on this backing plate but 6061 would be fine.
Reply:Originally Posted by freedomgliI tried sending a private message to Rojodiablo but the system is acting screwing and my message doesn't appear in my sent box.
Reply:Thanks kidtigger24.  I must have overlooked that feature!Miller Diversion 165
Reply:please post pics of the bike and the air scoop and what you end up doing for weld process.  i'm interested and i'm sure others are too.
Reply:Originally Posted by freedomgliThank you for the reply.  The reason for the modifications are stated above in my original post.  In its normal position, the brake linkage interferes with the ability to fit an air scoop to provide cooling air, a necessary and common modification for road racing.  So the brake backing plate is rotated (or clocked) so that the brake linkage is out of the way and a large brake scoop can be fitted to the leading edge.  In order to accommodate this modification, it is necessary to relocate the brake stay mounting bolt.  I plan to weld a boss to the backing plate and then drill, tap and heli-coil to fit a M10 bolt.I'm basically trying to build a poor man's CR77 front brake by utilizing the existing CB77 brake plate.  Although replica CR77 brake plates are reportedly available as unfinished castings, they are rare as hens teeth in the USA, rather expensive even if they can be sourced (believe me I've been corresponding with folks from around the world for months now, asking many favors and still no luck) and the casting would need hours of machine work and heat treatment (that I don't have the facilities to achieve) in order to be viable.See http://www.eurospares.com/cr72b.jpg and http://www.eurospares.com/cr72j.jpgWarpage is always a concern, especially when doing anything automotive/motorcycle related, as the materials are all relatively thin gauge.  However, fitting a new brake stay boss is necessary in order to fit a sufficiently large brake cooling scoop, which is necessary for the rigors of road racing.Thank you.  Please read my original post and my additional explanations above.I disagree.  The picture shown is an example of what I hope to achieve with my own brake.  The builder of that bike has not changed the effective ratio of the linkage at all from the OEM configuration.  The mechanical advantage is the same as it was before.  Please also compare it to the CR77 brake I linked to above.No.  As stated in my original post, the front hub/ brake drum I am using (and the one shown in the picture I posted) is a twin leading shoe brake from a Honda CB77 Super Hawk, which preceded the CB450.  Both hubs are nearly identical, the CB77 having 36 spokes, the CB450 having 40 spokes.  I'm not seeing the concern with the spokes you describe.  Could you please elaborate? The wheel was built by an experienced fellow who was a successful amateur road racer when the CB77 was new back in the 1960s!  I am inclined to trust him.
Reply:Originally Posted by Donald BranscomBTW..I was a mechanic at a dealership during the period that the CB77 was introduced.I thought the brakes provided worked just fine.
Reply:Originally Posted by freedomgliI'm conflicted about the necessity of a brake cooling scoop.  The gentlemen who relines brake shoes strongly recommends a brake scoop for road racing.  The bikes on the grid are mixed: some have totally worked over brakes (even some exotic 4LS GP stuff from Europe) while others simply drill a few cooling holes in the hub and that's it.  Ideally I'd only upgrade items once I know they're holding me back.  Yet at the same time I have a desire to do things once and do them right!  Fortunately I've got a couple of these old brakes on the workbench so the plan is to build up one front wheel that's relatively straightforward while I tinker with spare brake plate.
Reply:Thanks red devilMiller Diversion 165