Dynamic Balance

worntorn said:

Rob ss said-Once more - dynamic balancing (this is, without altering the BF) should not involve touching the flywheel.
Not sure how one can dynamically balance a Vincent crank without touching the flywheel(s)
Flywheels, big pin and mainshafts make up the entire crank. You have to touch ( drill a hole, or machine some thickness away ) in order to get rid of the side to side imbalance or rocking couple, should one be found to exist.

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Sorry Glenn - my comment was directed a the Norton twin crankshaft - I should have been more specific.
You comment holds true for singles' crankshafts as well - although I personally don't see much merit in dynamically balancing those as the mass of the flywheels is very narrow/central.
The same logic could be true for Vincents?

Rob

I can't say for sure as I have only had the dynamic balancing done to this one Vincent crank and we also changed the bf dramatically.
John Mcdougall, who rebuilt scores of Vincent engines, swore by the dynamic balance after trying it on one engine and getting an excellent result.

Glen

so, my reciprocal weight is
2 piston assemblies - 930gm
2 rod pin ends - 380
total - 1310gms

if my desired balance factor is 46%, then .46 x1310=603gms
subtract the fixed pin ends 603-380=223gms
then I would expect my Pit Posse rig hanging balance weight to be 223gms.

It seems I measured 220gms.
close enough?

You bet!

Glen

Finally some decent riding weather!
Tried out the bike again to determine the sweet spot for rpm to see if a gearing change is needed.
The standard Vincent is already very high geared at 3.5 to one overall for " relaxed touring" as Irving put it.
This compares to a standard Commando with about 4.39 overall gearing when using a 21 tooth cs.
In trying to quell the vibrations of this 1360 I had mounted a 22 cs sprocket and 42 tooth rear sprocket for an extremely high overall ratio of 3.04 to one.
This works out to 2800 rpms at 70 mph, barely ticking over. It didn't help much with vibration, it was unbearable at anything over 50 mph!
With the dynamic balance done it's a world better as mentioned earlier.
Today I found the engine to be smooth at almost any rpm above an idle .If anything, things are smoother yet as the revs go up.

Starting in top gear at about 2000 rpm, with the Dakota Digital speedo/tach switched to full screen, tach only, I tried cruising at ever increasing rpms . Things started out well and got very smooth at 3500 then stayed that way to 5000 rpm at which point the windage on my body was getting quite strong. So I held it at 5 k rpm for awhile , engine just purring along at about 1/3 throttle, mirrors clear.

Went home and did the speed calcs.
5000 rpm is 125 mph.
No wonder the wind pressure was high!

Private road, of course.

Now very happy with this engine !

Glen

Sounds brilliant Glen.

Glad to see you have such big, long, private roads near you... like me!

The scary/nice thing was that opening the throttle at 125 mph resulted in strong acceleration.
I think the bike would easily pull to 6500 with the tall gearing.
It would be good to have at least a 1/4 fairing like the Thruxton has in place for that . And maybe a racetrack rather than a private road!

Glen

Impressive. What max speed would that equate to do you think?

If it will pull to 6500 that figures to 162 mph.
One day I would like to see whether it will actually do this, but it will have to be on a track.

Glen

Went out on Tuesday and rode all over this Valley until the 18 litre tank was on reserve.
I've always thought that a hotrodded 1360 would be a real gas guzzler, that's why the tank is fairly capacious.
What a shock when it computed to 65mpg, Imperial.
This was fairly gentle running at 60-70 mph with just a few blasts.
Jetting is as prescribed by Terry Prince, seems right on.
Plugs are tan coloured on Ethanol free 94 Octane Chevron Supreme.

Time to hook up the O2 Sensor and double check things before heading up into the Mountains.

My standard Vincents seem to get 50-55 on a similar run, so 65 with the big engine was a pleasant surprise. I was expecting about 35 and live with it.
65 gives a theoretical range of 250 miles, which is useful.

Glen

Well, yes it’s bigger, but because it’s bigger (and pokier) it’s having to work much less hard at a given speed I guess Glen.

I’m sure that if you tried harder you could get that mileage down to about 35mpg, but you be travelling rather rapidly I imagine !

worntorn said:

Ideally you would take the crank with bare mainshafts to the Dynamic Balancer. My guy also wanted the pistons, rings circlips, rods, rod bearings and all collars for weighing on his scale. I had the numbers but it was good that he wanted to weigh the items on his scale to be sure.
With a press apart crank, there was a lot of work for me , most of which I detailed in the first post.
With the RE crank you don't have to do any of that.
The Balancing shop will spin the crank up on their machine and balance it by drilling holes in the appropriate location. Hopefully it won't need weight added as this is more involved and expensive.

Since Royal Enfield was the only Brit twin builder to dynamically balance their cranks, yours should already be fine. As long as you keep piston and rod weights matched as pairs and similar to the original components, you shouldn't need to bother with another dynamic balance.
It might be a little tricky finding the weights of the OE components.

From my reading the RE Interceptor crank BF at factory was 65 %, that much is known.

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The dynamic balancer insists on a 58% factor, he says it will shake badly otherwise( Truimph, BSA expeipence) and Hitchcocks , the rod supplier recommends a 72% . I am completely lost and ignorant. I cannot make a decision , as I do not understand.

Jimbo - Dynamic balancing is simply trading off inherent vertical vibration (360 degree twins are just like singles from a vibration perspective) for some horizontal vibration.
The factor (say 72 %) just means the vertical vibrating force is reduced to 28% of what it was - at the expense of increased horizontal vibration.
It really depends on how your rolling frame/engine/etc responds to the exciting vibrating force. It's not the same for all bikes of the same kind - although the "rules of thumb" are a good guide.
You can also change the "smoothness" of your bike by reaming and fitting critical mounting bolts - that changes the natural frequency of your bike.
The "stiffer" you make your setup raises the natural frequency, minimising the potential for the annoying "buzzing" feeling.
Cheers
Rob

I just had a Norton Dominator crank balanced at the Balance Shop in Reseda, CA. It was dynamically balanced to suit the new rods and pistons that Jim Schmidt sourced for me. It cost $85, and he did it in a week. (818) 881-9046

L.A.kevin said:

I just had a Norton Dominator crank balanced at the Balance Shop in Reseda, CA. It was dynamically balanced to suit the new rods and pistons that Jim Schmidt sourced for me. It cost $85, and he did it in a week. (818) 881-9046

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Thanks kevin, What was your balance factor before you went with JS Performance parts? Any data?
What was your Dominator balance factor after dynamic from the Balance Shop in Reseda, CA.? Any data?

Since the Dominator crank has a central counter weight, is there any visual/photographic evidence of asymmetrical drilling to account for dynamic balancing?

Thanks

I don't have the paperwork handy with me right now. I delivered the parts to Phil Radford at Fair Spares to build the engine. I believe it was 58%. To memory, there were some asymmetrical drill marks. I did get a computer print out from the Balance Shop. One of my pistons had a hole in it so, I had custom lightweight forged slipper pistons made to match. The end result was slightly lighter than the originals.