Crankshaft Counterweights
 

I am considering putting counterweights on a spare crankshaft I have. Big ends and mains are all 0.015 undersize so it's a good candidate. I have a set of weights I bought a few years ago from one of the parts suppliers. They are 5/8" thick and should be welded to the shaft but I've heard that a better result can be obtained by putting more weight on than what they provide and that this is done by bolting an extra weight to the sides of the ones I have so they can be removed for any future grinding of the journals. Does anybody have dimensions for these extra weights. I assume we put one each side of the welded on weights.
I think they would be 10mm (3/8" thick) and follow the curve of the larger diameter of the weights I have but how wide are they an how long? 3/8" will clear the con rod easily.
Anything else I should know???

Re: Crankshaft Counterweights
 

I don't have any dimensions but think you have the right idea, just follow the shape of the weights you have added on.

Re: Crankshaft Counterweights
 

You could make it look like a "B" crank,..with the add-on weights, if that's
what your after..

http://www.mtfca.com/discus/messages/29/21612.jpg

Re: Crankshaft Counterweights
 

bb ?

Re: Crankshaft Counterweights
 

Your correct Bill,....why confuse the issue..................lol

Re: Crankshaft Counterweights
 

The common practice of adding this extra weight is to add it to only one side of the primary crank weight. The side to add to is the rod journal side. Study the previous posts of the late crank and you will understand what I am trying to describe.
Good Day!

Re: Crankshaft Counterweights
 

Agree, else you will also overhang the mains as well

Re: Crankshaft Counterweights
 

Firstly, thanks to all those who posted a reply.
I had a revelation during the night (your day) about maybe the weights would foul the web in the block at the main bearings so the first thing I did this morning was to check a block to see. I think the weights would clear the front and middle bearing webs but certainly won't clear at the rear. If Henry did it as the picture shows, that is good enough for me but I can't see in the pictures how the "side weights" are removed for grinding the journals. I'm sure they do but they look to be permanent. The pic also gives me a pretty good idea about the size of the extra weights.
Thanks again, guys.

Re: Crankshaft Counterweights
 

Re: Crankshaft Counterweights
 

MikeK, Gotchya. I was still in the mindset of the weights being welded to the crank shaft.
I do like the look of the crankshaft in Bill Stipe's workshop. I also note the machined main bearing caps. I haven't heard anything about the originals failing or am I just not well enough in the loop? Are machined caps overkill or neccessary on a touring motor?

Re: Crankshaft Counterweights
 

Evidently more is better,
could someone tell me the total number of pounds of weight that Stipe uses?
thanks nick c

Re: Crankshaft Counterweights
 

More is better.
I can't answer your question but anything added to the counterweights will help.
It is not possible to get enough weight in the crankcase to "fully" balance an A/B crank. About 65% is all there is room for and that involves bolt on or press on weights BESIDES installing as much heavy metal (Mallory) in the existing part of the counterweight as possible.
This is a costly option for little gain.
A very good option for achieving a high degree of balance is to weld bearing pads on the left outside of the block and drive a "balance shaft" with a cog belt. Several modern 4 cyl engines use a balance shaft.

Re: Crankshaft Counterweights
 

A balance shaft can help with engine vibration, but will do nothing to help the crankshaft from wanting to bend due to lack of counterweights.

Re: Crankshaft Counterweights
 

regarding the pictured crank at Bill Stipe workshop. Do I understand that the added weights are heat shurnk on the existing crank? That must involve precise grinding of both the weights and crank along with some sort of fixturing to get them in the right spot, very impressive work.

Re: Crankshaft Counterweights
 

Ya,....well...too a point.
Now, are you talking smooth running Model A or touring engine /
performance engine ?
You still have too accelerate and stop all that metal ! The heaver the
crank, the harder the engine has too work to accelerate a heavy
crank,...then think about trying to stop this mass.

What would you rather move and stop,..a 16 foot boat or the
Queen Mary?

The crank in an A is a lot stiffer than the "bent coat hanger" in the
"T's". You want a stiffer crank ?....add 2 more mains!

With the design of the original engine, it's a moot point,..until you
change the internal design of it...

Re: Crankshaft Counterweights
 

Well,...how about this for a "four banger crank"..?
Hollow "pins" anyone ?

http://winbergcrankshafts.com/wp-con...2595882800.jpg

Re: Crankshaft Counterweights
 

5 mains too

Re: Crankshaft Counterweights
 

I think I'm in love!

Re: Crankshaft Counterweights
 

That crank doesn't look good to me. The counterweights are too light to start with, just by looking at them, and then when they made them hollow, it even took away more of the weight plus added to the wind resistance.

"Ya,....well...too a point.
Now, are you talking smooth running Model A or touring engine /
performance engine ?
You still have too accelerate and stop all that metal ! The heaver the
crank, the harder the engine has too work to accelerate a heavy
crank,...then think about trying to stop this mass.

What would you rather move and stop,..a 16 foot boat or the
Queen Mary?"

Dudley, how does rotating mass enter into the problem of bending the crankshaft due to unequal weight away from the crankshaft centerline, which is trying to make the crank flex? If you want less rotating mass, you lighten the flywheel. To counterweight the crankshaft you'd want to add weight opposite the throws that would equal the weight of the throws and lower half of the connecting rod. Adding more mains will give the crank better support to keep it in line, but ideally you still want the weight on each part of the crank to be equal on each side of the centerline.


BTW, a balance shaft is different than a balanced shaft. A balance shaft is a seperate spinning shaft with weights which are to help counter the vibrations of the crankshaft.

Re: Crankshaft Counterweights
 

The best photo I could find, at that moment. Ya,..I don't like the
"counter weights" myself....I think there just wrong.

What I wanted too show is the hollow crank pins, especially the rod
throws. If you lighten the rod throw side,..it's the same as adding
weight too the counter weight,..without adding weight to the crank.

A lighter crank accelerates and decelerates quicker than a heavy one,..
that has to be "somebody's" law of physics ? I think that equals horsepower and drive-ability.

Question;...how much weight do you have to add too counteract
and kill the vibration? If a stock crank weighs (guess) 40 pounds and
you add another 20 pounds does that do it? how about another 20
pounds,...that makes the crank 80 pounds!
I could be wrong, and it wouldn't be the first time,... but adding all that
weight just dampens the cylinder firing..and that's all.

Your a train guy,...look at those 80" drivers and the counter weights.

Yes,...I still thinkthe crank needs counter weights....so change the
crank design instead of adding weight. Better steel (stiffer crank),
hollow rod throws...

Yes, ....I also know about balance shafts and odd fire and even fire
cranks.

Tom, I'm tired of typing..

Dudley