Fullauto, JS short stroke build pics

worntorn · Apr 8, 2015

Doug, would those be standard 850 cases?

Also, I'm curious about the displacement of 763ccs. I have read about various methods of destroking or sleeving engines to get displacement at or below 750ccs in order to run in vintage 750 classes, but it would seem this engine is 13 ccs to big for those. I imagine you also want to avoid running in classes which would allow much bigger displacement engines like the Many 1007cc, so what class will this bike run in?

Glen

elefantrider · Apr 8, 2015

Those internals are a work of art and it is too bad to hide them inside an engine.

nickguzzi · Apr 8, 2015

Very nice looking parts. Wish you every success with them.

The measuring device is a thickness calliper or bowl turners calliper. Come in many flavours.

lcrken · Apr 8, 2015

worntorn said:
Doug, would those be standard 850 cases?

Also, I'm curious about the displacement of 763ccs. I have read about various methods of destroking or sleeving engines to get displacement at or below 750ccs in order to run in vintage 750 classes, but it would seem this engine is 13 ccs to big for those. I imagine you also want to avoid running in classes which would allow much bigger displacement engines like the Many 1007cc, so what class will this bike run in?

Glen

Unless there's been a recent rule change, AHRMA allows a .060" overbore above the displacement limit for twins in the vintage classes, including F750 and BEARS. With the 80.4 mm stroke, displacement would be 749 cc with 77 mm bore. At 78 mm bore, Doug's engine would be legal for those classes, and still have another .020" left for future rebuilds.

Ken

Doug MacRae · Apr 8, 2015

Hi Glen- Ken is correct you are allowed .060 overbore or 5% over displacement limit of class in AHRMA and in VRRA in Canada. I am starting with some 850 cases for now and will be bumping up to Maney cases soon, can't afford the whole world all at once.

Hobot · Apr 8, 2015

killer Diller engine with better views than a center fold. The 850 cases may well stand the JMS piston kit but curious to know what red line will be used.

Doug MacRae · Apr 8, 2015

With this stroke, the party will probably be over around 8000 so no need to rev beyond that. We will see what the dyno says.

RennieK · Apr 8, 2015

SupHerb! SupHerb work and great products by all involved. Thanks for sharing Doug!

Hobot · Apr 8, 2015

Alrighty 8000 sounds survival-able for the valve bounce we now know is going on even before that. Does ignition system allow a rev limiter for missed shifts in adremalized excitement or AMC box breaking? Hope this engine is not a smoker insect repeller. Glad you have a rear view camera to see those being left behind.

Doug MacRae · Apr 9, 2015

It will have the right wrist rev limiter...

Hobot · Apr 9, 2015

Ok sure - trained to resist a few 100 over 8grand in a pinch -even if it'd get ya ahead. Rooting for ya not wishing any surprise let downs.

acotrel · Apr 10, 2015

The impeller from the supercharger.

Dances with Shrapnel · Apr 10, 2015

ludwig said:
What is that ? :

It is a custom spacer that goes behind the timing pinion on the crankshaft. The three machined divits allow access for the jaws of the pinion puller.

lcrken · Apr 10, 2015

Now that's a clever idea! I can't count the number of times I've cursed the design while trying to get the factory puller to fit. I've ground down the corners of the puller arms for more clearance, but it's still a frustrating process. I think I'll have to copy your solution.

Ken

Doug MacRae · Apr 10, 2015

Herb put the custom spacer in there and I was wondering when someone would ask about it. John wins the small stuffed animal.

X-file · Apr 10, 2015

It seems to me that the 35mm diameter intake ports would be better suited to an engine of that size that's capable of making maximum torque at around 8,970 rpm.
At any rpm below that, they're likely to cause a loss of torque and power.

Doug MacRae · Apr 11, 2015

Well, we won't know until we try it. All that matters is what the dyno says, not a calculator. It will make big power or it won't. If it doesn't then we will change something. Theory quite often goes out the window at the dyno when you do some big exotic change that theoretically should make an increase in hp but ends up with no increase at all. Everything from the carb size to pipes etc has to be played with to work together.

CanukNortonNut · Apr 11, 2015

Doug MacRae said:
Well, we won't know until we try it. All that matters is what the dyno says, not a calculator. It will make big power or it won't. If it doesn't then we will change something. Theory quite often goes out the window at the dyno when you do some big exotic change that theoretically should make an increase in hp but ends up with no increase at all. Everything from the carb size to pipes etc has to be played with to work together.

Theory can commonly mean everything but the truth!
Cheers,
Thomas
CNN

milfordite · Apr 12, 2015

Herb is pretty good at figuring things out. Years ago he was running some huge carbs on his racer that flew in the face of convention, but they worked!

gripper · Apr 12, 2015

I was wondering what the red coating is inside the crankcases?

Fullauto, JS short stroke build pics

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