Frame Cracking Alert

[davis]

This may not be news to you guys but I noted a frame crack on the rear motor mount bracket. This is the second frame with the exact same crack pattern I've seen. Note, the weld is small and on the short side of the bracket. Any frames I paint will first receive additional weld to the left top and bottom. Even a little more weld there will go a long way in preventing this failure in the future.

Anybody want to write a service letter on this? Hey that's not a bad idea. Vintage Bridgestone service letters being published after being vetted by the multiple star guys.

[slawsonb]

Nice catch Davis! Vely Intelestink!

Just checked my 3 frames. Results:
21S01306 - No Crack.
21U03456 - Cracked exactly as shown.
21U03783 - Cracked approximately 6mm from top of plate along same path. Crack apparently developing. Cyclic fatigue?

Anyway. this is a precaution to add when restoring a frame.

...bert

[reed]

Frame Cracking,
I rebuild a lot of other motorcycles and i always check frames before power coating because i am are working on older motorcycles etc.
Anyway good call Davis.
Thanks.
Steve.
PS none of my frames had that problem.

[moonpup]

Inspection results from S. Texas.....

21U03665 - U-shaped crack directly under the top weld. 
21W06962 - Cracked exactly as shown but has been welded up by prev. owner. 
21W07032 - Unknown as engine is still mounted. (fingers crossed!) 

[farmerdl]

Fairly common even back when these were relatively new bikes.  Of all of the 350 frames that I have sitting here, three fourths of them are cracked or have been repaired.

[coxy]

mine are cracked apart from the oz delivered frames which I think had low kms .my 175 dt also cracked

[Harry]

THANKS Davis.  I'll pull the winter cover and check mine.  Harry

[moonpup]

As farmerdl noted, this is a apparently a common spot on the 350 frames to develop stress cracks.

Does anyone know of other common spots to be on the lookout for?

[BRT-GTR]

      My latest frame, 21G06738, has a similar crack starting at top of bracket, approx 12mm long. Good call, might not have noticed that. Obviously a weak point, there is enough clearance to weld a doubler to the bracket to beef it up.

 This post reminds me that the rear right engine hanger on my GTR cracked through vertically, behind the rubber engine mount, back in the early 70's. Just 'V'd it out, got it welded at the local Blacksmiths and it was fine. Probably a similar cause to the frame cracks, vibration and stress.         Brian.

[husker]

My frame had the mount cracked through in 2 places and the piece across the back was missing.

[OldSwartout]

Mine cracked and I welded it years ago.  I thought mine was unique until this thread.  Learn something new every day...

[slawsonb]

Amen Karl
...bert

[alan86a]

I had a loose front engine mounting stud break away from the frame.

I countersunk the hole and welded the stud back myself with the usual DIY arc welder but it did not last, had to get a professional welding job done on it.

No problem found with rear mountings though.

[davis]

Moonpup,

Haven't noticed anything else on the frame, but the pedal bar on the center stand was weakly welded. I've seen them broken off, some still trapped loose and some gone. I would highly recommend welding them solid before powder coating, like in the picture. You also might want to look at the thin chain guard mounting tab for cracks or gone missing on the swing arm pivot side.

- Bob

[moonpup]

Thanks Bob, I've got 3 center stands at the moment and one is missing the bar. The other 2 are present, but one IS about to fall out.

Very good reminders. 

[BRT-GTR]

Hi All,
          A few other items you may want to check before having that frame powder coated or painted, all of which I have come across :-

   1)  Arms on frame that hold the rear foot pegs can get nudged inward in a fall.
   2)  Small tab that holds the rear brake stop switch, both sides, straighten up
   3)  Welded pin on frame that forms the rear brake arm stop, check for being bent backwards.
   4)  Battery box steel pressing, check for distortion or bent lugs that hold the battery strap.
   5)  On one of my machines the strap that holds the back end of rear guard to the frame had cracked through. How did that happen? When I checked the frame the rear loop (reduced diameter section) was bent slightly upwards putting the guard strap under a lot of tension. Time and vibration did the rest I guess. How the frame loop came to be bent I cannot imagine, no obvious marks on it, may have even been built like that.

      Brian.