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Re: Crankshaft balancing

Thanks for the input chaps. My engineer will be looking at checking the flywheels for true and static balancing. I've worked out that the dome top +40 piston that's fitted is approximately 94 grams (3.3 ounces) heavier that a standard flat top piston. This is all interesting stuff to me and i'll be using a guy who is not adverse to letting me in on the process. I'll report back.

Strangely These Royal Enfield's don't have a head steady? Maybe it's because of the large oil filled crankcase? But then from memory, nor do the Norton's? Ron

email (option): ronpier@talk21.com

Re: Crankshaft balancing

The 'rule of thumb' is that a piston weight difference from standard of more than 1 1/2ozs. should mean rebalancing...

Obviously the crank should be set up to recommended tolerances regarding 'truth'...An M20 for example should run true to a tolerance of .002" max. on the main shafts and .005" max on the flywheel faces...

Regarding sympathetic vibration and the altering of it, that is the thinking behind handle bar end weights. Increasing the mass here alters the vibration frequency...Maybe you should experiment with internal bar end weights later on if there is still a problem?....Ian

email (option): ian@wright52.plus.com

Re: Crankshaft balancing

Cheers Ian. That's worth considering and easy to do. Ron

email (option): ronpier@talk21.com

Re: Crankshaft balancing

Ron Pier
Thanks for the input chaps. My engineer will be looking at checking the flywheels for true and static balancing. I've worked out that the dome top +40 piston that's fitted is approximately 94 grams (3.3 ounces) heavier that a standard flat top piston. This is all interesting stuff to me and i'll be using a guy who is not adverse to letting me in on the process. I'll report back.

Strangely These Royal Enfield's don't have a head steady? Maybe it's because of the large oil filled crankcase? But then from memory, nor do the Norton's? Ron
Quite right Ron! The Norton doesn't have a head steady. Most proper motorcycles don't. ( As I duck out of the bar before Ian throws a beer bottle at me!):grimacing:

email (option): sam-cormier@hotmail.com

Re: Crankshaft balancing

Ron, is that +40 piston an old original or a modern replacement ? Some of the modern ones seem to be very heavy,with very thick crowns.They also often have very heavy gudgeon pins.The Australian JP piston in my AJS had quite a bit of material milled out from inside the crown to get the weight down,and the pin I think we taper bored as it was so thick in the wall.

Re: Crankshaft balancing

Yes Jon it's a modern Royal Enfield Bullet piston and comparing it with one of Jan's standard bore flat top originals, it's at least 3 ounces heavier. It's with 'Ainsley' now for him to check and weigh and and let me know what he intends to do. I have every faith in Ainsley, He's well known here and apart from the mundane stuff, he builds racing and speedway engines. Ron

email (option): ronpier@talk21.com

Re: Crankshaft balancing

Ron, we are the lucky ones having someone we can trust... I have a good friend who builds allsorts of race engines,including "Mountain Motors".(14 litre v8 drag racing engines)
The point is he looks at every component for all the right reasons,no matter how basic the engine is he is working on.That piston you are using is probably very much a compromise,without weakening it too much it can likely have a fair amount of material removed from inside the crown - Anything your chap can do here will help.
Me and my riding mates often chat about the opportunities we now have to build engines to run sweeter,cooler,more power and last longer etc,than when they had to be almost thrown together to do a job.

Re: Crankshaft balancing

I collected my crankshaft from Ainsley today. The outcome is that when he first checked it, he calculated the balance factor at 43%. After drilling the flywheels at the big end area, he's achieved a balance factor of 58%.

My 'RAF' crankcases arrive from the Netherlands yesterday and I've fitted the new main bearings and ordered new gaskets and small parts from Hitchcock's, so I can proceed with the engine build tomorrow. Ron

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email (option): ronpier@talk21.com

Re: Crankshaft balancing

I've rebuilt my engine into the RAF crankcase and done 2 x 7 mile test runs on Monday and the vibration is vastly reduced. I'm planning another approx 30 mile run in the morning to watch Gedd try and straighten Tim's Indian Chief forks in his frame straighten jig after he ran into a car a few week ago. Ron
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email (option): ronpier@talk21.com

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