flywheel balancing

Here you can talk about all kind of TECH for the B50 B44 B25 And Other BSA unit Singles

Moderator: minetymenace

Post Reply
User avatar
FGF
>80
>80
Posts: 89
Joined: Sat May 11, 2019 3:14 pm
Location: Orleans
Has thanked: 23 times
Been thanked: 1 time
Flag: France

flywheel balancing

Post by FGF » Sat Aug 15, 2020 9:40 am

Hello ,

i 've read many posts about the crank balancing and some talk about the flywheel separate balancing .
i understand the sludge trap problem which cause a big dissymmetry .

i know the dynamic flywheel balancing wich is made on an electronic machine but
what is the static separate flywheel balancing ?

for me, a flywheel without big end can't be static balanced because of the counterweigh presence ...

i make a mistake sure , but wich one ?

User avatar
minetymenace
Gerry1
Gerry1
Posts: 7713
Joined: Wed May 26, 2004 1:00 am
Location: On the edge of Salisbury Plain, England
Has thanked: 33 times
Been thanked: 97 times
Flag: England
Contact:

Re: flywheel balancing

Post by minetymenace » Sat Aug 15, 2020 9:52 am

As far as I understand (and I'm no expert on these matters) the knack is to ensure once balanced, that both flywheels weigh the same, whatever balance factor you use. This means you have to make sure the flywheels weigh the same before you dynamically balance the whole shaft.
There is no evidence to support the notion that life is serious.
Abyssinian Wire-Haired Tripehounds Gnash.

User avatar
kommando
>1400
>1400
Posts: 1970
Joined: Mon May 24, 2004 8:41 pm
Location: Scotland
Has thanked: 10 times
Been thanked: 52 times
Flag: Ireland

Re: flywheel balancing

Post by kommando » Sat Aug 15, 2020 2:46 pm

Static balancing is for the piston and 1/2 ish of the con rod, it only changes the angle the weight is applied at, the weight of the inbalance is unchanged.

Dynamic balancing is to set the weights of the 2 sides of the crank to be equal to eliminate the rocking side to side motion, its pointless making the flywheels the same weight before the operation as the mainshafts are not the same weight anyway. Its a 50/50 call as to whether making the flywheels the same weight aids the difference between the mainshafts or makes it worse, so no advantage so let the dynamic balancer do his thing. As a single cylinder crank is narrower than a twin cylinder crank dynamic balancing is less likely to help on a single cylinder.

Jeff K
>1300
>1300
Posts: 1347
Joined: Sun Jul 13, 2014 12:30 pm
Location: Bay City, Michigan USA
Has thanked: 54 times
Been thanked: 23 times
Flag: United States of America

Re: flywheel balancing

Post by Jeff K » Sat Aug 15, 2020 3:30 pm

BSA, Triumph and the after market used to sell a clip on weight that would go on the main bearing and replace the rod/piston. It has been many years, but I seem to recall that you would then place the crank on a pair of knife edge parallels and drill out enough metal if needed until it was balanced and did not return to the same spot. Much like balancing a rim or tire.
Jeff

Jeff K
>1300
>1300
Posts: 1347
Joined: Sun Jul 13, 2014 12:30 pm
Location: Bay City, Michigan USA
Has thanked: 54 times
Been thanked: 23 times
Flag: United States of America

Re: flywheel balancing

Post by Jeff K » Sat Aug 15, 2020 4:27 pm

From the repair manual.
ws-bsa-B25-B50-part2 00-4188.pdf
(452.89 KiB) Downloaded 42 times
Jeff

Jeff K
>1300
>1300
Posts: 1347
Joined: Sun Jul 13, 2014 12:30 pm
Location: Bay City, Michigan USA
Has thanked: 54 times
Been thanked: 23 times
Flag: United States of America

Re: flywheel balancing

Post by Jeff K » Sat Aug 15, 2020 4:37 pm

I was just checking my old notes and found this. It was from Peter Quick's BSA unit singles site. The 1971 is different due to the change in the connecting rod.
B50 B25 SERVICE BULLETINS 1971 TO 1973xx.pdf
(187.28 KiB) Downloaded 34 times
Jeff

Jeff K
>1300
>1300
Posts: 1347
Joined: Sun Jul 13, 2014 12:30 pm
Location: Bay City, Michigan USA
Has thanked: 54 times
Been thanked: 23 times
Flag: United States of America

Re: flywheel balancing

Post by Jeff K » Sat Aug 15, 2020 4:48 pm

I should add that if you do not have the "factory" tool. A old work around was get a roll of electrical or plumber's solder, the heavier 1/8" diameter stuff, unroll it and weight it. then carefully cut off enough to get the proper weight and then just wrap this around the big end . The key word here is carefully cut off until you get what you need. Cut off a inch weigh it and then multiply it by how much you need and add a bit and then cut it off the roll, trim it back to proper weight and use it.
Jeff

User avatar
FGF
>80
>80
Posts: 89
Joined: Sat May 11, 2019 3:14 pm
Location: Orleans
Has thanked: 23 times
Been thanked: 1 time
Flag: France

Re: flywheel balancing

Post by FGF » Sun Aug 16, 2020 10:13 am

Hello ,
Thanks for your advises .
Jeff , you are talking about the crank assembly balancing with this factory weight replacement ? don't you ?
B25_weight.jpg
B25_weight.jpg (14.92 KiB) Viewed 684 times
i 'd like to see a pattern of a '' separate flywheel balancing '' , if possible .
Some think it to be a good thing before the crank assembly work.

Kommando answer that it 's less important for a single crank ( it 's a B50SS )...without doubt he 's rignt.

User avatar
koncretekid
>900
>900
Posts: 933
Joined: Sun Nov 20, 2005 1:22 am
Location: Yarmouth, Nova Scotia
Has thanked: 4 times
Been thanked: 26 times
Flag: Canada

Re: flywheel balancing

Post by koncretekid » Sun Aug 16, 2020 2:09 pm

The B50 is much more difficult to balance because you first have to take off at least one crankpin nut and disassemble the crank, remove the rod and rod bearing, and weigh each end of the rod while it is level.You can do it with one very accurate scale and a support under the other end, and then do the opposite end, each time making sure the rod is level thru the rod ends. It's easier if you have two very accurate scales and can get the rod level with one end on each scale. Let's call the big end B (which includes the needle bearing) and the small end S. Then weigh the piston, pin, clips, and rings together and call this P. The weight of B is added to 58% of (P+S) (if you want a 58% balance factor, for example) and we'll call this pSB. Make a split weight equal to pSB that can be clamped around the crank pin and reassemble the crank. This assembly is then set on the knife edge rollers or taken to someone who has the ability to dynamically balance it. Then you drill holes in the heavy sides to get this to balance. Of course, you then have to disassemble the crank and reassemble with the rod and you're balanced, so to speak. The question in my mind is at what speed did BSA decide to use to find their ultimate balance factor? If they used 50 mph, and you spend most of the time at 60 mph (or maybe 150 mph), will it be ideal?

Here are the balance weights I made for B25. The two extra washers under the head of the bolt was to make the weight symmetrical.
B25 balance weight.jpg
B25 balance weights


Here are the weights attached to the crankshaft.
balance weights on B25 crank.jpg
balance weights on B25 crank
Tom
life's uncertain - go fast now

eebtr7
>200
>200
Posts: 214
Joined: Fri Dec 21, 2007 3:49 pm
Location: Texas USA
Has thanked: 0
Been thanked: 3 times

Re: flywheel balancing

Post by eebtr7 » Sun Aug 16, 2020 2:30 pm

Whoa! This just went WAY beyond my mental capacity. Just a thought...wouldn't it be a bit easier to re-engineer the frame to add rubber engine mounts, like Plymouth did back in 1928? Or, Norton in 1967? Even a perfectly balanced lower end will still vibrate in the solid mounts, won't it?

User avatar
FGF
>80
>80
Posts: 89
Joined: Sat May 11, 2019 3:14 pm
Location: Orleans
Has thanked: 23 times
Been thanked: 1 time
Flag: France

Re: flywheel balancing

Post by FGF » Sun Aug 16, 2020 2:50 pm

Thanks Tom.

I 've read your old post about it and now i understand better the details of this way.
It 's really accurate with a dynamic machine .

At the beginning , i was looking to have a better comprehension of the static way working with the flywheel separately
wich is something i never had listened.

My engine is fully stripped , so it would be unfortunate to forget the crank balancing with the sludge trap cleaned.

User avatar
JB
>480
>480
Posts: 495
Joined: Tue Jun 15, 2004 8:32 am
Location: Devon, England
Has thanked: 9 times
Been thanked: 12 times
Flag: England

Re: flywheel balancing

Post by JB » Mon Aug 17, 2020 10:56 pm

I have statically balanced cranks a number of times the limitations of static balancing is that it only balances in one plane, not so bad on a single with a narrow crank, not so good on a twin that really benefits from dynamic balancing that balances in multiple planes. Dynamic balancing uses sensors on both main bearing journals coupled with an angle sensor and can detect differences end to end on a crankshaft that static balancing simply can't detect. The balance weight for any particular motor is the same for both methods

User avatar
FGF
>80
>80
Posts: 89
Joined: Sat May 11, 2019 3:14 pm
Location: Orleans
Has thanked: 23 times
Been thanked: 1 time
Flag: France

Re: flywheel balancing

Post by FGF » Tue Aug 18, 2020 9:42 am

Thanks JB , it 's clear .

But i was looking for an advise wich is to balance the flywheels separately before the crank assembly work.
this way would be choosen by a machinist which make a static work with no modern machine like my French machinist today.

the separate flywheel static balancing is not clear for me.
Geery told me a right answer , i'd like more detailed if it's possible .

User avatar
JB
>480
>480
Posts: 495
Joined: Tue Jun 15, 2004 8:32 am
Location: Devon, England
Has thanked: 9 times
Been thanked: 12 times
Flag: England

Re: flywheel balancing

Post by JB » Tue Aug 18, 2020 10:41 am

Okay, sorry can't help you there as I've no experience or knowledge of doing this, all I would say is that if done separately it would have to be done between dead centres rather than knife edges/rollers and I guess there will always be an element of friction involved.
These users thanked the author JB for the post:
FGF (Wed Aug 19, 2020 9:56 am)
Rating: 25%

User avatar
koncretekid
>900
>900
Posts: 933
Joined: Sun Nov 20, 2005 1:22 am
Location: Yarmouth, Nova Scotia
Has thanked: 4 times
Been thanked: 26 times
Flag: Canada

Re: flywheel balancing

Post by koncretekid » Tue Aug 18, 2020 1:57 pm

I think I've seen photos of balancing with the connecting rod in place. How about putting crankshaft with connecting rod attached in a lathe and lock the spindle of the lathe with the connecting rod at right angles to the crank (rod will be level thru the centerlines of the ends). Then weigh the small end of the connecting rod, say 100 grams. Then weight the piston, pin, and rings to get their weight, say 300 grams. So the small end plus the piston equals 400 grams. If you want a 58% balancing factor, the bobweight would be 400X.58=232 grams. Since the small end already weighs 100 grams, just add a weight of 132 grams to the small end of the rod. The connecting rod with the bobweight would now weigh exactly what we would have made if the connecting rod were removed. Now put the crankshaft with rod and the bobweight attached to the small end on the knife edge rollers with the rod hanging down. Drill holes in the heavy side of the flywheels until it balances.

I don't know if this would work, but I don't see why it would not.

Tom
These users thanked the author koncretekid for the post:
FGF (Wed Aug 19, 2020 9:56 am)
Rating: 25%
life's uncertain - go fast now

User avatar
FGF
>80
>80
Posts: 89
Joined: Sat May 11, 2019 3:14 pm
Location: Orleans
Has thanked: 23 times
Been thanked: 1 time
Flag: France

Re: flywheel balancing

Post by FGF » Sat Aug 22, 2020 2:51 pm

Hello Tom
Thanks for your answer about the crank assembly balancing.

With a bigger piston ( 86mm ) and heavier alpha crankpin and carillo ,
where can be drilled the holes ?

BSA has taken the whole place near the big end with it's two holes :

B50_crank.jpg

the B50 crank design is not easy to drill except if you have to make the counterweigh lighter ...?

Post Reply