Factory short stroke pistons

Here's something new. Factory style short stroke 77mm forged pistons to fit the factory short stroke fully hemisphered big valve heads. The orignal Omegas on the left weigh a whopping 335 crank breaking grams. The new style on the right are only 216 grams. 3 months in the making but worth the wait. For longer rods of course.

Lovely.

Ken

Good to see new parts for those heads. Looks nice. Would work well with a fully hemisphered big valve Fullauto and Nikasil alloy barrels!

Now if you had done them in 1977 I really could have used a pair 2nd oversize! I still have one that looks like the original in your picture.

But crank breaking? Not really. The Omega was the best available at the time and fairly light in comparison to some.

But my crank was a well balanced and polished MkIII with the extension past the taper cut off. However, as an 850 it only normally ran to 6800, it was letting it go to 7200 that prompted one of the inlets valve heads to bury itself in the piston.

The heavy stock pistons can break the cranks and cases - thats why you see heavy duty cases and stronger cranks with radiused PTO shafts on the market. The Omega piston shown in the top photo is even heavier than stock and adds to the stress on the crank and cases.

Jim, we all accept more reciprocating weight is a bad thing.

And on those 750 Short Strokes with the steel bridge girder rods there will have been too much weight.

Your solution is good and not being criticised, I use and like it.

In the '70s the crankcases I saw blown apart across the drive side bearings were 850 MkIIs with alloy rods and Hepolite pistons.

The MkIII bottom end held up fairly well.

Norton Atlas cranks have been balanced to factors in the high 70s. - Isolastics dont stop your crankcases from being hammered. Higher piston weights affect inertia. The pistons actually stop at the bottom and top of the stroke. Their rate of acceleration affects performance. I suggest fully hemisphere heads to fit bigger valves is nonsense when you lose the squish band. The proof of the pudding is in the eating - do lap times decrease ?