would you do this

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he wants me to exstend  it 4" not shure if i wantto get involed, its a 1980s 550 honda what size pipe do you think it is Attached Images
Reply:I have worked on many Hondas, chopped a few. My friends called me Honda Mike for a while, we won't discuss what I called them. The swingarm is the heaviest steel on a Honda , but it is still paper thin. Noone would ride Japanese bikes if they knew how thin the steel is. The swingarm on my 88 hurricane is a 1x2 box with a sidewall thickness of less than a 16th of an inch. If I was gonna stretch that I would weld an entire new arm and just use the stock  arm as a template from which to get dimensions. It is not under the stress that it would be with a mono shock but I would still go with a from scratch approach.Mike
Reply:I agree.  It's not pipe, it's thin tubing.  If you just extend it (whether internally or externally sleeved), it will put an additional load on the thin sections where they meet the new tubing that you add.  From a liabilty standpoint, I would agree that the entire arm would need to be replaced with somewhat thicker wall tubing.Miller Syncrowave 350Millermatic 252/ 30A spoolgunMiller Bobcat 225g w/ 3545 spoolgunLincoln PowerArc4000Lincoln 175 Mig  Lincoln 135 Mig Everlast 250EX TigCentury ac/dc 230 amp stickVictor O/AHypertherm 1000 plasma
Reply:agreed the second you start replacing sections with larger diameter or thicker pipe you increase "notching effect" or disrupt stress flow lines and it will become a weak point. Welding repairs on frames such as this is not a wise idea. As stated i would fabricate a whole new frame which wouldnt be hard to do at all.
Reply:Lengthening those types of swing arms is a common practice on street bikes that are used in drag racing. Best route to go would be to build a new one using chromoly, however if you are stuck with using this one I would suggest making additions that can be added to the axle adjusters, that is also a common practice.