Hi Evros, hi all,
as some of you know already, a little "TR1 bike family" can be found in my bike shed. (Some of them „projects/wrecks" only, which could serve as part donators.) Most of the bikes are the early ones (code 5A8), and one bike is a late model (code 19T). Apart from the design, you can tell the difference also by the serial number on the frame and engine housing: The early models have a 5A8-00XXXX, whereas the late models have a 5A8-01XXXX.
Concerning the reliability and/or weak points of the TR1 as a second hand bike, the most important point might indeed be the
cylinder head gasket topic: The cylinder head gaskets of all the TR1 bikes were quite „special“. This concerns both model years 1981 and 1982 (also sold 1983-1984) and the TR1 as well as the early XV 750 and XV 920. When Yamaha developed those head gaskets, their idea was to produce only a
thin ring, containing a sandwich mix of asbest (for thermal stability) and several thin sheet metal layers (for smooth ductility which shall lead to a tight gasket that covers eventual geometrical tolerances). As the gasket ring is so thin, most of the surface between head and cylinder would be able to have a
direct contact, leading to a good thermal exchange between those two aluminum parts.
So far for the „good intention“ of Yamaha. But unfortunately, the first series of the cylinders had a little „gap“ between the gasket ring recession and the vertical tunnel for the timing chain. It was that „gap“ that caused the issues: The compression pressure found its way from the combustion chamber to the timing chain tunnel.
So, the TR1 riders developed several workaround options: 1) Closing the gap by welding and machining the cylinder or 2) putting in a filling piece, similar to a tooth seal (as in the photo below), or 3) putting a slim „bow shape piece“ of sheet metal into the gasket ring slot, which will work as barrier or blocker. That sheet metal piece shall have a material thickness of 0.5...0.6 mm, a width of about 5...6 mm and a length of about 50 mm. (Suited just to fit into the gap, similar to the adjusting work that we all know so well from our dentists...
.)
For the late series, Yamaha tried to solve the issue by closing/leaving out the gap. They did that by modifying the shape of the casted aluminium cylinders. Yamaha also helped customers with early bikes that had shot their gaskets: Those customers got a replacement, containing cylinders of the second series.
Quite often, the blown head gaskets are affecting the rear cylinder (which gets a little bit warmer when riding), and the blow through area can be found on the timing tunnel side. Bikes that begin to blow through are sometimes making funny noises (similar to a hammer beating on a steel base plate). That noise is
no deep „buff, buff“, but a more metallic and sharp „tak-tak“ noise, comparable to a worn out piston rod bearing or a valve play that is much too big.
One of my project bikes is a fine example of that kind of issue: It has a broken rear head gasket (with the area between cylinder and head all covered in oil). And, funny enough, it is just the
late series model - whereas all my
early model machines have tight gaskets. (Knocking on wood...).
From the today point of view, I think there will be not much difference between the early and the late models. The gasket solution still seems quite "special" (or let's say "weird") for both models. Most aftermarket gaskets are not suiting well. And original Yamaha gaskets (NOS) are not so easy to be found today. So, the most reliable solution would be to swap the cylinders against XV 1100 cylinders (allowing to use "regular" cylinder head gaskets, which are still available at Yamaha, as they also fit for the Virago series).
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