Well, I'm excited. Now we have 12.4:1 99mm (1065cc) piston kits for the TR1. There shall be a piston kit only. There shall also be a drop-on kit: the piston kit bored into Virago 1000 cylinders with an appropriate gasket set.
The pictures above are of some 920 cylinders I have on hand. Note that the first two have no aluminum "dam" between the head gasket recess and that for the cam chain tunnel o-ring. These are blow-prone, and I recommend against even running an after-market cam with them, let alone a high-compression big bore.
These pictures are of an actual TR1 from Norway. Note that the stock displacement; stock cammed motor was in the process of blowing its head gasket. Thus, I cannot guaranty that you will get satisfactory results with the piston-only kit -- it looks like one must run cylinders with flat decks. I have put together a tutorial on how to modify your stock barrels, but the results will never be as secure as cylinders manufactured that way. The owner gave the model year as 1982.
Another genuine TR1 top-end from Finland. Note that these cylinders have a barrier where needed for the big bore. This makes me very confused. This bike's owner claims that it is from 1981. I have parts books for '81 and '82 and they indicate different part numbers on the cylinders. Not posted are pictures from a 1985 shaft-drive from Italy that also has a barrier. I hate to do this, but I ask you to tear down your top end before you decide which kit to go with. Or whether you want to try "decking" your barrier-lacking cylinders.
The bare piston kit bored into your stock TR1 cylinders will run a 12.4:1 compression ratio. As the picture shows, it will leave very little "fire ring" between the bore and the head gasket. The aluminum cylinder of the Virago is 0.6mm shorter than the TR1. The compressed gasket is also 0.6mm -- so the compression ratio remains the same.
A 99mm next to a stock 95mm piston. Note the shorter skirt and the dome. Also, those valve cut-aways will provide adequate clearance for up to .600' valve lift. More importantly, they give ample clearance to a .300' lift of the intake at exhaust TDC. These are designed around lifts of over .550" and durations of 300 degrees.
The pistons relative to stock bore cylinders. At the machine shop I use, a 4mm cut costs ninety dollars per hole; many other shops refuse to do it -- it wears out their less-than-adequate cutting heads. The complete kit comes with pistons slid into their respective bored cylinders with gapped rings installed. They also come with an Athena complete gasket set, and clean dowels that are a slip-fit in their bores. All threaded holes will have been chased.
I'm having a problem getting enough Virago 1000 cylinders. Eleven hundreds work, too, but they are almost as rare.. These are shot high-temp black with exposed aluminum fin edges, and heat cured; shot clear, and cured again. They will not smoke upon first start up.. Prices have gone up. I cut all prices to the bone, but the prices listed below still obtain -- and they do NOT include international shipping and insurance.