Cracked Rear Struts ????

[Rossco]

Hi. I am new to the site and have just bought a 757 Proflex. I have bought it as a project for my Brother as about 10 years ago his pride and joy 757 and my shiny Orange Clockwork (I know not a Proflex but still a classic!!!) were on the roof of my car coming home from a ride. We parked outside my Mother in Laws for 10 minutes and when we came out the bikes had gone! I always promised myself I would by him another one. I picked it up at the weekend very happy with myself thinking I had checked it over fully. It was a bit dirty though and when I got home and cleaned it up a bit I noticed the paint cracks on the top and bottom of the rear struts (1 side top and 2 sides slightly at bottom). There does not seem to be any movement and I have done some research on here and found out that they are bonded and not welded (I think). Is this a normal part of the frame or is this impending doom or a written off frame? I think I can just see the lines on some of the other photos I have seen but cant really see clearly enough to be sure. Any advice would be appreciated before I strip it and re condition it for him. I am hoping to have it powder coated so if it is bonded will this cause any problem? Thanks for any advice.

[Spokes]

As you rightly say the rear struts are bonded together. The cracks will probably just be caused by paint shrinkage and I wouldn't worry at all about it. As far as powder coating goes that should be fine as I don't think it uses heat in the process. Just avoid any process that uses heat incase it melts the bond in the strut. Don't uses stove enamel.
Good luck and post photos of your build.

Chris

[w2zero]

Powder coating requires heat in either an oven or by infra red emitters to achieve flow and cure on the paint.   How much heat is an issue with a bonded joint such as the struts have.  The amount of heat soak to produce the finish and not damage the bond would be critical to the performance of the parts by the end user.

The bond is heat sensitive so that is what you are seeing at the least.  The epoxy or methacrylate bond system is more or less affected and that will show as a crack from creep during the heat/cool cycle. 

Worst case, overheating will cause a failure of the joint.  Far more usual, there is a line in the paint finish which shows up on all my Proflex struts.

If it ain't moving, it's okay.

[Rossco]

Thank you for your advice. I will definitely talk to the powder coaters about the rear struts and the bonding before I have anything done they are experienced in doing bike and motorbike frames so I hope they have come across it before. I will post pictures of the build as it gets underway. Thanks again.

[fyrstormer]

The joints are designed to be stable in compression (i.e. the parts have to be pulled before they will separate), so the likelihood of catastrophic failure while riding is slim to none. But yes, it's worth letting them know that the parts are epoxied together, and that the epoxy is about 15 years old now.