Originally Posted by
Trakhak
You can find mentions of Technium frames coming unglued in forums, but there seems to be very little in the way of first-hand evidence. Such failures, if any occurred, seem to have been rare and were possibly confined to a single production run.
@
Trakhak
The attached pictures show a cast aluminum bottom bracket from a 1990 Raleigh USA Team 753 Technium frame with oversize Reynolds 753 main tubes.
The "rings" around the joint between the lugs and tubes are cosmetic additions to conceal the adhesive filled gap. Both rings are cracked which seams to be common with those frames.
The Reynolds 753 straight gage tubes have a 0.6mm wall thickness plus an aluminum sleeve inside at the joints supposedly to stiffen the frame.
The reason that I bring this up is that a lot of the failures in the Raleigh "bonded" frames have been at the bottom bracket juncture.
Notice the small amount of surface contact area between the sockets in the BB and the tubes - see pictures.
Even with the down tube being slightly oversize plus the internal aluminum sleeve, the 0.6mm wall thickness is rather thin for a down tube. This could result in some flexing in the vertical plane from riding over rough pavements, hitting potholes and for some riders, jumping curbs.
Those kinds of stresses put adhesive bonds in shear where they're weakest - see last picture.
What I'm suggesting is that if the BB shells had a larger contact area via deeper sockets they would provide more contact are for bonding.
That's all moot now because these are 25+ year old frames, long out of production.
One last thing, we didn't sell kid's bikes. Occasionally an irate parent would drag in their teenager's 10 speed with the down tube pulled out of the head tube lug....
Their kid had been jumping curbs or BMXing with the bike! The give away was the forks were bent forward from the crown!
verktyg
Chas.