Joe Michaels
Diamond
- Joined
- Apr 3, 2004
- Location
- Shandaken, NY, USA
I was asked to take a look at breaks in the frame of a 1971 Triumph Bonneville by the guy riding it. He knew I am an engineer as well as doing some machine work and welding.
The guy picked up the seat and the damage was obvious. The rear portions of the frame tubing run horizontally, and have the rear shock mounts welded to them. Just behind the shock mounts, the top of the frame tubing kicks up slightly and then makes a horizontal 180 degree loop, effectively closign the rear ends of the frame.
The tubing had broken through just behind the shock mounts and the rear loop of the frame tubing was held in place by the rear fender. An additional light crossmember or two further forward on the frame (ahead of the fractures and shock mounts) held the fender as well.
I told the guy riding that Triumph he should have parked it and stripped it for repairs to the frame. He claimed it was riding season and he wasn;t pushing the bike hard, running it locally. I wouldn;t have been out on the road with a motorcycle with that kind of frame damage, but that's my opinion. My own belief is there is flexure of the frame in that area caused by the shock mounts putting concentrated loads into the frame tubing.
My ideas for the repair are to turn a couple of steel pins to drive into the open ends of the frame tubing, spanning the fractures. I would bevel the ends of the fracture for a CJP (full penetration) weld, letting the root passes burn into the connector pins. Welding will be done using DC GTAW.
My questions are: has anyone any knowledge of what alloy steel Triumph made their frame out of the 1970's ? Was it a chrome-moly steel ? Any ideas as to filler metal to use ? I've got DC TIG with lift start, argon shielding gas, so should be OK for the actual welding. I will try to get a piece of 4140 or 41340 round stock to turn the connector pins out of.
I believe the fractures occurred at what I call "inflection points" on the frame- the frame tube laid horizontal as it ran over the tops of the shock mounts. Just aft of the shock mounts, the tubing "kicked up", making an inflection point. At the same time, the rear shocks were putting a concentrated load, as well as some "side-to-side" flexure into the frame at that point. It is my thinking that by going to fitted connector pins accross the fractures, I stiffen that whole area and the repair welds are not so critical as the pins carry the loads. I will turn the pins and hot-bend them as required to fit the frame so there will be good bearing contact before I weld things together. I do not plan to turn any kind of "neck" or groove in the pins at the weld root, just leave 1/16" or so as a root-gap & burn the root pass into the pin.
Has anyone done a similar repair ?
Thanks-
Joe Michaels
The guy picked up the seat and the damage was obvious. The rear portions of the frame tubing run horizontally, and have the rear shock mounts welded to them. Just behind the shock mounts, the top of the frame tubing kicks up slightly and then makes a horizontal 180 degree loop, effectively closign the rear ends of the frame.
The tubing had broken through just behind the shock mounts and the rear loop of the frame tubing was held in place by the rear fender. An additional light crossmember or two further forward on the frame (ahead of the fractures and shock mounts) held the fender as well.
I told the guy riding that Triumph he should have parked it and stripped it for repairs to the frame. He claimed it was riding season and he wasn;t pushing the bike hard, running it locally. I wouldn;t have been out on the road with a motorcycle with that kind of frame damage, but that's my opinion. My own belief is there is flexure of the frame in that area caused by the shock mounts putting concentrated loads into the frame tubing.
My ideas for the repair are to turn a couple of steel pins to drive into the open ends of the frame tubing, spanning the fractures. I would bevel the ends of the fracture for a CJP (full penetration) weld, letting the root passes burn into the connector pins. Welding will be done using DC GTAW.
My questions are: has anyone any knowledge of what alloy steel Triumph made their frame out of the 1970's ? Was it a chrome-moly steel ? Any ideas as to filler metal to use ? I've got DC TIG with lift start, argon shielding gas, so should be OK for the actual welding. I will try to get a piece of 4140 or 41340 round stock to turn the connector pins out of.
I believe the fractures occurred at what I call "inflection points" on the frame- the frame tube laid horizontal as it ran over the tops of the shock mounts. Just aft of the shock mounts, the tubing "kicked up", making an inflection point. At the same time, the rear shocks were putting a concentrated load, as well as some "side-to-side" flexure into the frame at that point. It is my thinking that by going to fitted connector pins accross the fractures, I stiffen that whole area and the repair welds are not so critical as the pins carry the loads. I will turn the pins and hot-bend them as required to fit the frame so there will be good bearing contact before I weld things together. I do not plan to turn any kind of "neck" or groove in the pins at the weld root, just leave 1/16" or so as a root-gap & burn the root pass into the pin.
Has anyone done a similar repair ?
Thanks-
Joe Michaels