Monday, July 30, 2007
Tubulars: Part II, Repair
Tubular tires can be repaired, I have done it often, but it is a lot of work. The first obstacle is pulling the base tape away from the stitching.
This used to be an easy matter, but I’ve noticed in recent years with modern adhesives the base tape seems to be permanently bonded to the tire. What I do is pick at the edge with my thumb nail and try to lift just enough of the base tape that I can grasp it with a pair of pliers.
The object is to try to pull the base tape away from the area where the puncture is, but leave it in one piece attached to the tire. In reality, what will probably happen is the base tape will tear off in a short piece.
You will notice this is what happened with the tire I opened up to take these demo pictures. Not to worry you can still glue it back in place after the repair. The next important trick is to find exactly where the puncture is, and only cut about 2 inches (50 mm.) of stitching. An Exacto Knife is the perfect tool for this job.
Under the stitching, is a thin fabric strip or membrane that is lightly stitched to either edge of the outer casing. This strip of fabric is there for two reasons. It holds the inner tube in place while the outer casing is being stitched during manufacture. It also prevents the thin latex inner tube from chafing on the stitching.
Carefully cut the stitching on one side only of this fabric membrane, and pull it to one side to reveal the inner tube. (See picture, below. The fabric membrane is white, the inner tube is green.)
Pull the inner tube out in a loop and the puncture can be patched in the usual way. Before you put the tube back in place, inspect the inside of the outer casing for any sharp objects sticking through that could re-puncture the tube. (This is standard practice with any puncture repair.)
Also, inspect the outer casing for damage as shown in the next picture (Below.) In this case, it will be very important to glue a piece of canvas on the inside, because with 120 lbs plus pressure in the tire, there is a good possibility of a blow out later. Notice I use a piece of rolled up cardboard to hold the inner tube out of the way while I glue the canvas in place.
Canvas can be bought from any fabric store, and any proprietary brand of contact adhesive is good for gluing it. Follow the adhesive instructions, usually you coat the canvas patch and the area inside the tire casing, allow to dry 10 or 15 minuets, then stick the patch in place. Allow it to dry thoroughly (Preferably overnight.) before you put the tube back inside.
There is no need to re-stitch the fabric membrane back in place as long as it is put back over the inner tube, between the tube and the stitching. It will stay in place because you have only opened up two inches or so.
Sewing the tire up again is the biggest chore. You need a sail-makers needle, which is tri-angular rather than round in section. If you buy a proper tubular repair kit, it will come with one of these. (Google: Velox tubular tire repair kit.)
You will need a metal thimble to push the needle, and I use a pair of needle-nose pliers to pull the needle all the way through. If you managed to repair the puncture by cutting only two inches of stitching, you will be glad you did when it comes time to sew it up again.
Try to use the original needle holes to re-sew if you can, and use the same original cross-stitch pattern. If you open up more than two inches of stitching there is a possibility you will not re-sew the tire straight, and you will have a twist in it.
Glue the base tape back with the same contact cement used for the canvas patch. If there is a cut in the rubber tire tread; glue it with the rubber cement that comes with the repair kit. Allow the cement to dry overnight before inflating the tire.
This is part 2 a three part series; here is a link to part 1, and part 3.
Posted by Dave Moulton at 7/30/2007 05:07:00 AM