Do split frames for belt drive bikes need special screws?

Question

I have a belt drive Cube bike, and the frame is Aluminium.

The rear triangle has a split to accommodate the belt, there's a screw right above the rear sprocket, on the right side of the bike - see picture below.

The thread for that hole in the frame is stripped and I need it repaired. I've talked to a bike shop and I was told a special Gates screw is needed there, and since they're not an authorized dealer, they have no access to Gates parts. (the screw will need to be replaced because repairing the thread will make it wider)

This seems surprising to me - isn't this just a regular screw to hold the frame together? Can it really not be replaced by something standard after the thread is repaired?

In other words: once I have the screw hole repaired, does it make sense that I would need to use a special screw from Gates? Or would any matching screw do?

Answer 1

Looking at the Gates catalogue, they do not make bolts for frames. They do not sell bolts for frames.

Different frames use different split systems to allow the belt in and NONE OF THEM ARE MANUFACTURED (or designed) BY GATES. (though they will be endorsed by Gates if submitted for approval)

You can have the frame repaired though. Either a helicoil repair or moving up to the next size bolt are the most likely courses of action with the helicoil being preferable. The frame manufacturer may have a suggestion.

The bike shop you used probably don't deal with belts very often but they could have given better advice.

Answer 2

It is a bolt, not a screw. The difference is that a bolt has a matching thread in the receiving part, whereas a screw cuts it's own thread.

You absolutely require a matching thread in the part for the bolt to work.

Given the cost of the bike, it is definitely worth repairing. There are three workable repairs and one dirty bodge.

1. Thread-inserts. Often called Helicoils for the earlier brand name, these are a steel coil which replicates the original thread internally, and has a larger diameter thread on the outside with the same TPI or twist rate.
   The kit can be expensive, but comes with a proper-sized drill bit, a specific tap, an installation tool, and normally 10 or 15 inserts.
   The process involves drilling out the hole, then tapping it with a new thread, and finally installing the coiled thread insert, with optional threadlocker etc.
   You require to know the thread on the existing bolt, which can be discovered from documentation or measured by using a caliper/micrometer, and some thread gauges.

2. Use a larger thread. This is generally a bad idea because the hole needs to be enlarged, leaving less "meat" around the bolt. This differs from option1 in that there is no insert, and you will need to find a larger bolt of sufficient tensile strength to do the job, but with the same head size.

Both of these options are sensitive to alignment - you can't just shove a hand drill through the stay. Instead a pillar drill or drill press is the bare minimum to do it well.

3. Buy a new stay and fit that. The stay will have to swivel to get the belt in, so the other end will likely be bolted too. If you can get the part, do this. It will be the best long term solution provided you use a torque wrench when reassembling.

4. the bad bodge is to replace the existing bolt with a longer one that passes through the hole and is secured on the outside by a separate fastener like a nut.
   Downsides of this is that it is ugly, you'll have a protrusion which could catch, and failure to use a strong-enough bolt could result in shearing under load.
   Also the nut will need to be retained against vibration. A nyloc might be enough, or you might need to drill and pin it in place. If the outside of the frame is not flat and orthogonal to the bolt centerline, then the nut will have poor contact encouraging unwinding, and there's always a risk that the frame member will be crushed.
   This would be my very last resort and I would not recommend this, though I might choose to do such a repair on my own bikes knowing the risks.

All of the above solutions will likely void your warranty. But if you had a warranty then you'd not be asking.