M/B frames with welded gussets or not need to be check regularly for cracks in the frame
My Whizzer frame came with Reinforcement Gussets welded in the stress areas and my frame still cracked in 3 spots
It cracked on the top tube 2" from the neck and the side rails both cracked where their welded onto the center tube.
I figure the side rails cracked first then that put stress on the top tube making that crack.
I welded a 6" sleeve over the crack on the top tube, joining the sleeve to the neck
The cracks in the side rails I welded up and welded more length of the rails to the top tube and reinforced it some more behind the seatpost with a plate joining both side rails to the center tube.
But these cracks didn't happen until after 12 years and 30,000 miles
Now I always inspect my frame for cracks every time I change the oil, which is every 100 miles
It's now been 5 more years and another 10k miles and no cracks, making that over 40K miles on my bike now in 17 years
Here's a pic of the plate I Tig welded behind the seatpost This is where it needed reinforcement
The rear of the frame will flex taking turns at higher speeds and the side rails cracked right behind where they were welded to the center frame tube
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