1973 Triumph top-end rebuild…

Brand New Pistons!

MotoPreserve member and survivor of the great 2011 MP tour of the south, Scott, has made some great strides in getting his 1973 Triumph Bonneville back together. After finding out that he needed the cylinders rebored, and some help from Hugh at 6th Street Specials (Hugh seems to be SO old-school, that he doesn’t have a web site I can link to here), Scott was back on track to get this top-end buttoned up….

pistons inside the cylinders...

With all the parts and pieces in place, it was time to get the engine back together. Some people get the pistons inside the cylinders while on the bench, and then hold the jugs above the engine, and attach the pins and circlips to the rods. The new pistons and rings were already attached to the rods, so our technique would be slipping the barrels down over the pistons. After watching some videos on the technique (why does it always seem so easy online????) we commenced hemming and hawing, poking and prodding the rings to get them inside the bore. We had some borrowed tools specifically for this job, but they didn’t seem to help, and the decision was made to do it by hand. This is not easy, and it takes patience.

For those of you who have never done it: we had some luck pushing the ring from the side opposite the gap, and then holding it. With a small coin (a nickel seemed to work well) we each pushed one side of the ring near the gap, so that the gap became smaller and smaller, and eventually was closed enough to allow the barrel to slip down over it. Be sure to do one side at a time, and keep moving back and forth, so the cylinders move down together over the rings. Eventually we got the damn thing down over the last of the oil rings, and we were home free. Instantly the carcass looked like a bike again!

Scott had purchased 2 sets of engine gaskets, and they came with very different head gaskets. One was the typical paper with a small ring of metal (steel?) around the opening to the cylinders, the other, seen above, completely made of copper. The copper one looked more “official,” and that was the one he went with. Next up was to fit the head, and it went on smoothly, after helping it along with a mallet…

...almost there

Scott had replaced the valves and guides with new ones, so the top end should be about as tight as it was when new. He put the studs in, tightened it down, and will be ready for the final stages of getting this engine all buttoned up. After putting the carbs back together with some fresh o-rings and gaskets, he will be ready to fire her up, and see the fruits of his labor. This is going to be one cool looking bike…

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