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03-10-2015, 12:18 AM | #1 |
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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???
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03-10-2015, 11:22 AM | #2 |
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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.
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03-10-2015, 11:41 AM | #3 |
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Re: Crankshaft Counterweights
You could make it look like a "B" crank,..with the add-on weights, if that's
what your after.. |
03-10-2015, 12:23 PM | #4 |
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Re: Crankshaft Counterweights
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03-10-2015, 12:34 PM | #5 |
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Re: Crankshaft Counterweights
Your correct Bill,....why confuse the issue..................lol
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03-10-2015, 01:08 PM | #6 | |
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Re: Crankshaft Counterweights
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03-10-2015, 01:36 PM | #7 |
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Re: Crankshaft Counterweights
Agree, else you will also overhang the mains as well
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03-10-2015, 05:24 PM | #8 |
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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.
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03-10-2015, 05:58 PM | #9 | |
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Re: Crankshaft Counterweights
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Here is a first-class job and picture posted by Bill Stipe in a previous related thread on the same subject. It appears that you started that other thread on 11/19/2014! Of note in Stipe's work, the attachment is through collars on the added side pieces. The side weights present no sheer load to the fasteners. |
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03-10-2015, 06:08 PM | #10 |
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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?
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03-10-2015, 08:17 PM | #11 |
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Re: Crankshaft Counterweights
Evidently more is better,
could someone tell me the total number of pounds of weight that Stipe uses? thanks nick c |
03-11-2015, 12:59 AM | #12 | |
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Re: Crankshaft Counterweights
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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. |
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03-11-2015, 02:03 AM | #13 |
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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.
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03-11-2015, 09:59 AM | #14 |
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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.
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03-11-2015, 10:15 AM | #15 | ||
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Re: Crankshaft Counterweights
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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... |
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03-11-2015, 10:36 AM | #16 |
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Re: Crankshaft Counterweights
Well,...how about this for a "four banger crank"..?
Hollow "pins" anyone ? |
03-11-2015, 10:45 AM | #17 |
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Re: Crankshaft Counterweights
5 mains too
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03-11-2015, 04:40 PM | #18 |
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Re: Crankshaft Counterweights
I think I'm in love!
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03-12-2015, 03:57 AM | #19 |
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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. Last edited by Tom Wesenberg; 03-12-2015 at 06:10 AM. |
03-12-2015, 10:42 AM | #20 | |
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Re: Crankshaft Counterweights
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"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 |
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