Valve Train Geometry

Pay attention: from the 700 to the 1100, the deck height and rod length are the same. The valve springs, guides, seals, base washers, retainers, and keepers, too. The studs and their pattern were the same. In the head gasket (post Gen I) and base gasket, the only difference was the size of the bore; if not for which, the cylinders would have inter-changed.

The 700 and the seven fifty have 43mm intake valves and 37mm exhaust. The bigger bikes all had 47mm intakes, 39mm exhausts. The stroke was same for all but the 1100. The heads may be swapped between models. Exhaust gaskets were the same, and intake flanges and carbs (with breather re-routing and jetting changes) were mix-and-match.

In the main, there is no top or bottom to a valve spring, but -- if the coils are visibly tighter at one end, that is the top. If one end is painted, that is the top. Stock springs can come plain, yellow, blue, and possibly other colors. It most likely makes no difference, but put the painted ends upward -- even if it's not clear why, it's painted for some reason, and the standard is that that end goes up.

Also the same were rockers, rocker shafts, adjusters and jam nuts. The rocker ratio was 1.347:1. The stock valve spring wire is of lower quality steel and the wire is thick in cross-section. At a valve lift of .440" (or there abouts) the coils touch and the valve can open no further. The action is flaccid -- the springs cannot react to direction changes fast enough to keep the valve tip in contact with the adjuster over eight thousand RPM. The valves "float;" failing to close and getting in the way of the piston. Bad news.

After-market spring sets help two ways: they are of finer wire allowing for valve lifts of up to .600". They are also made of higher quality steel and the retainers are made of light (yet strong) materials such as titanium or aluminum, allowing adherence to the cam profile to a much higher speed. When RH/RJ's were current, Team Yamaha campaigned them in Battle of the Twins races. The engines were turning as high as twelve thousand RPM -- where the main bearing outer races spun in the cases.

More to come . . .

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