Crank shaft counter weights

[Synchro909]

Hello all. I have a set of "C" shaped weld on counter weights which, now that the Burlington cranks are no longer available, I think I will use on the engine I am (re) building soon. I have not had anything to do with these before so I seek the advice of those who have.
I am puzzled about how to position them so that they are directly opposite the crank they are to balance. How is this done or do we just take a good guess and then leave it to the balancer to sort out? I realise the shaft will have to be sent for balancing after welding is done.
Is there a possibility of the welds bending the shaft as they cool and contract. I intend giving each layer of weld a few whacks to relieve stresses but....?
Is there anything I have overlooked?

[colin1928]

Hi the 1s I have done were the sweated on and then pinned they come with instructions I will look for instructions later
I remember using a degree wheel and a dial indicator to get them in the correct location

[Synchro909]

Thanks Colin. My weights are just a profile cut chunk of steel not machined anywhere. Not sure we started with the same thing but any info very welcome.
It seems we both live in Melbourne. Pls check your personal messages.

[BRENT in 10-uh-C]

Yes, the crank will likely bend during the welding process however it can be straightened. You can also drill and install them with a bolt and then a weld across each end.

The bigger thing IMO is you really need to build a fixture to ensure you are installing them "square" with the crank. Using a mill and locating off of the crank flange dowels are a good way. Also, check those blanks to see how well they match the crankshaft as I am pretty sure there are two different radii' dimensions on the crank.

[James Rogers]

Brent is correct with the 2 different radii. One is 4.100 and the other is 4.010. Even knowing this, there will be some trimming to get the weights to fit correctly because, these sizes vary. I have a plate drilled to bolt to the crank flange that positions the throws directly up. If you look, you will see the throws are at a right angle to 2 of these bolt holes. I then clamp the cranc to the mill table and use a dial indicator to determine the exact center of each throw and move to the center of the cheek and drill a hole to be tapped for the bolt that holds the weight on. Once done, the pre-drilled, counterbored weight is installed and straightened then welded on each end and the countersunk bolt is welded till the hold is filled. I then put the crank in the lathe and trim all the weights to the same size and to smooth the bolt weld till it is not visible. This is a condensed version but is the gist of the process.

Hope this helps.

[Terry, NJ]

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I was in Bert's, in Denver, one day while their mechanic was was welding a counter weight on a crank. IIRC, he ran a bead all around, using a MIG gun and rather large wire. This was a while ago and I may have the details off a little, maybe alot. I can't recall the guy using any means to locate the weight. But that may be my poor memory.
Terry

[BRENT in 10-uh-C]

Originally Posted by Terry, NJ

I was in Bert's, in Denver, one day while their mechanic was was welding a counter weight on a crank. IIRC, he ran a bead all around, using a MIG gun and rather large wire. This was a while ago and I may have the details off a little, maybe alot. I can't recall the guy using any means to locate the weight. But that may be my poor memory.
Terry

He may not have but think it through, how far out of centerline does a single weight need to be before it becomes a balance issue?

[Synchro909]

Brent and James, Firstly, thanks for the replies.
I asked about locating the counter weights because I realise that they don't have to be out of position by very much to cause a whole new balance issue. I wondered whether any error could be neutralised in the balancing process. Sure, the weights would be lighter but not by much - still better than before they were fitted.
The weights are 5/8" thick slabs of steel in a "C" shape, about 9" OD and 4+" ID. The only place I can see a bolt being of any value is to drill through the 2 3/8" depth of the weight. The hole will weaken the weight but that might not matter once it is welded. What size bolt do you use? What tensile strength? How deep do you drill into the crank? Model A cranks sometimes break (don't ask how I know) and drilling will make it weaker. Does this cause a problem? Are the weights only welded at the ends after the bolt is put in? I imagined grinding the edges of the ID and welding for at least some of the sides too.
Maybe I'm looking for a hair in the egg yolk but I don't like nasty surprises. I know it has all been done before and I'd rather do it the proven way.
Is there a problem if the weights are not dead square to the crankshaft? Intuition says they should be square but if they are off a little, does it matter? I'm not meaning so far off that the con rods foul it - that would be ridiculous. Maybe a square lined up with the main bearing journals by eye would be enough. I have a good "eyeometer". I think I would easily get them within 1/16" and probably half that. I can't see that causing an issue.

[CarlG]

I don't know about you, but this is something I would not consider doing myself, but rather trust someone that does this sort of thing professionally and stands by their work. There's just too many things that I could see that would produce even a worse situation than not having the counterbalances at all. Just MHO.

[James Rogers]

I have done about 25 -50 over the last 10 years and have accumulated a few specialized tools for the job. I clamp the weights with a couple of strong straight edges before welding them. I leave the clamps on till the welds cool and then tighten the bolt as securely as I can, then weld it shut. As for the bolt, I use a 5/16socket head bolt with a grade as high as possible. The ones I use are grade 8 or better and I have never broken one. I have never had a complaint about any crank I have ever done and run one in my own car. Drilling the cheek may weaken it slightly but, when the bolt is inserted in the threads it fills that void and, weakness would be minimal.

[Bill Stipe]

Counter balanced crank pics

[Tanglfoot]

Can anyone tell me how heavy each should be for a 30/31 MA crank, thanks




The older you get the better you were

[Tanglfoot]

That should be--- how heavy each weight should be for a 30/31 MA crank

[colin1928]

100% of total rotating mass + 50 % total reciprocating mass ÷ 4

[Tom Wesenberg]

Originally Posted by Tanglfoot

That should be--- how heavy each weight should be for a 30/31 MA crank

I've never seen the ideal weight published, but I sure like the weights Bill has in his first picture. I like those and the fact that they can be removed for grinding the crank. I bought a set of full circle weights from Dan Price in Ohio, and also feel they have enough weight to do the best job, just like Bill's. However mine won't be as easy to remove for crank grinding.

[Slotblog]

Here's a couple of pics of the Bert's counterweighted cranks, taken about three weeks ago.

crank.jpg

cranks.jpg

Dan Landers is the machinist at Bert's and like everyone there, is a very nice guy.

[SteveB31]

Terry-NJ,

Our weights are indexed with a very accurate fixture prior to installing on the crank shaft. We have done hundreds of them and every one is indexed perfect prior to welding.

Steve Becker
Berts Model A Center

[Kevin in NJ]

Originally Posted by Bill Stipe

Counter balanced crank pics

Show off!!


Just kidding, some cool picts.

[Synchro909]

My counter weights are the same as Slotglog shows in his pics.
It's the indexing of them that is still causing furrows in my brow.

[Tom Wesenberg]

Bill Stipe, in your first picture I see the piston skirts are dark. Is that a teflon coating, or some other coating?