Discussion in 'Vincent' started by worntorn, Dec 14, 2017.
What is the dynamic balance procedure ?
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.
As noted above in Glen's post Comnoz does Norton dynamic balancing
I will look into it but I think he is set up for Commando crankshafts and is too buzy to develop a set up for my Enfield crank.
When specialists dynamically balance a crank, do they fill them with oil, and plug them somehow?
For this crank, the goal was a 60% dry balance, so oil weight wasnt a consideration.
If the goal had been for a 60% wet balance, it still would have been balanced in a dry state, however the calculations would have been different to allow for the theoretical oil weight.
That’s what I thought Glen.
But it seems to me it’s a complex way of doing things, and that it would be both easier, and more accurate, if it was actually filled with oil.
It’s very well saying that the crank holds X amount of oil, and factoring that in to calculations. But where is the oil, how much is in the journals and how much is in the oil galleries, etc. These factors wouldn’t surely allow opportunity for error?
Reggie had his T140 crank dynamically balanced and, frankly, it ain’t right. So error can be made, and I’d have thought the more ‘error proof’ the process, the better.
I had a crank statically balanced by Owen Greenwood years ago. He was pretty much one of ‘the main men’ then. The bike was like a pneumatic road drill! Even he managed to get something wrong!
I think it should be clarified that "balance factor" is a static balance issue - not a dynamic balance issue.
Dynamic balancing is simply ensuring there is no left-right errors in the static balance
Imagine - if you will - after statically balancing a crank to the desired balance factor, you put a 10g weight on the top of the left cheek and 10g on the bottom of the right cheek
Within error of radii, the unit will be still in static balance - to the desired balance factor
But... the bastard will wobble like shit due to the left - right imbalance
Jim C does not have a setup for my RE crank, still looking for someone to trust with it , the stories above make it clear to find someone that will be able to do it correctly.
The supplier of the new rods recommends a different balance factor at 72% for some reason, I guess they are heavier?
So let me get this straight , all the stuff going up and down, pistons , rods,( but only part of them ?) rod bolts, rings, wrist pins, keepers are weighed ,then two slugs are made at 72% of that weight, and bolted onto the journals. Then static balanced somehow, rolled between stands? , and somehow adjusted. Then somehow the crankshaft is spun dynamically to make sure there is no side to side imbalance, and adjusted somehow. I need someone to fill in the somehows!
No, the bobweight is made to a weight equal to 100% of the rotating weight plus the balance factor x the reciprocating weight.
Adjusting is mainly done by drilling holes unless weight needs to be added. Then holes are drilled and Mallory metal is added.
As far as the "how to" on the dynamic balancer, I can't say because I left the fellow to do his job. Not sure I would have picked up everything he did simply by watching, had he invited me to stay and watch. Interpreting the results is a bit involved, Hines does a course on the whole process of Dynamic balance.
Unless you plan on buying your own dynamic balancer, you probably won't need that knowledge.
A static balance though, is something anyone can do with minimal tools and lots of patience.
Good point Rob.
That type of side to side imbalance is said to cause tingling vibration, maybe the worst vibration to endure when touring.
My Vincent Rapides have a slow pulse which you get accustomed to quickly. Its not bothersome, even after a 500 mile day. They don't have tingling vibration.
The tingling vibration was common in the high rpm Japanese bikes of the 60s and 70s. My CB750 had it bad. I disliked going long distances at highway speeds with it.
I think it would bother me a lot more today, my tolerance for discomfort is much lower.
This 1360 crank had 22 grams of side to side variation, as determined in the dynamic balance. It had tingling vibration by the bucket load, all gone now.
It had that plus the big shakes with the 90 percent BF.
I think I got my money's worth on the balancing job ($180)
I read Paul Goff's article about his long term ownership of an A10, it's a good read.
Crank balancing difficulties are discussed toward the end, between January 2008 and June 2010 after which the bike runs relatively smoothly again.
still looking for a reputable shop in the USA that can balance my crankshaft correctly
As has already been mentioned, didn't RE dynamically balance their cranks at the factory?
If so, you don’t need to do it again.
If you’ve change rods and pistons, you just need to match their weight to the originals. Or if the weight is different, change the static balance.
Either way, I really don’t think you need to dynamically balance the crank again.
I am changing rods and pistons
So weigh them, make them match the old ones, job done!
How do the weights compare to original?
A little variation from the original BF is likely not a concern. There always seems to be a considerable range of numbers that are considered to be the "right" number.
As long as you are +- a couple of percent from your number ( easy to check) then the main thing is that the side to side balance is correct. You already have that done by Gilbert Smith in his lab coat.
One other important thing would be weight matching ( pairing )the rods and pistons.
They are likely very close already, but best to check.
Oh, I see Nigel posted the same with far fewer words used
The supplier of the new rods specify a new 72% balance factor and I am installing JE pistons, so I really need someone to check it out . I might send the whole element to the UK if I have to.
here are a few places I found on the net
Separate names with a comma.