counterbalanced crank welds

oldspert

oldspert

Senior Member
I bought a Model A engine that has a counterbalanced crank. Was inspecting the crank and found it only has what I consider tack welds on each end of the weights. It has the safety bolts holding the weights to the crank, but very little weld. I'm not sure that is sufficient to keep everything from coming apart. I can weld more area to the crank, but should I have it rebalanced? After V'ing out the area and adding weld, it might be a wash on weight. The crank was done many years ago by a place called Ron's in Ohio. Still in business?
 
I have one that way as well. It was run, I think in a Pietenpol aircraft. The welds are short as you say on the ends of the weights but are clearly clean, well-penetrated tig welds.
I'd run it.
D
 
spert - if it would make you feel more assured, by all means have the weights rewelded by a GOOD welder. But you will definitely need to rebalance after that. Take the opportunity to balance with the flywheel and pressure plate installed.
 
I cannot say this with any authority but I think this is the way the weights were intended to be added. I think full-pen welds all around the weights would bend the crank. In fact, I'm pretty sure it would. Not that such things aren't done on larger cranks(think welding and regrinding damaged journals), but these are kinda light and having to have the thing completely reworked may not be worth it. Your call but I'd look into the mod. Yours and mine are not the first I've heard of this.
D
 
There are a lot of crankshafts that were done that way back in the day. Never really heard of it being a problem. It should also have a small weld on the bolt heads to keep them coming loose. More welding WILL bend the crank as said above and then need even more work to straighten it out and then regrinding
My vote....run it as is and dont worry about it
 
JayJay said:
spert - if it would make you feel more assured, by all means have the weights rewelded by a GOOD welder. But you will definitely need to rebalance after that. Take the opportunity to balance with the flywheel and pressure plate installed.
Click to expand...

While I'm not a Model A expert; on other equipment I've always had the crank, flywheel, and pressure plate balanced individually.
 
rich b said:
While I'm not a Model A expert; on other equipment I've always had the crank, flywheel, and pressure plate balanced individually.
Click to expand...

My thoughts as well. What if you ever need to change the pressure plate or flywheel. Are you going to disassemble the engine to re-balance the crank/flywheel/pressure plate togeter? Much easier to just balance the new parts.
 
oldspert said:
I bought a Model A engine that has a counterbalanced crank. Was inspecting the crank and found it only has what I consider tack welds on each end of the weights. It has the safety bolts holding the weights to the crank, but very little weld. I'm not sure that is sufficient to keep everything from coming apart. I can weld more area to the crank, but should I have it rebalanced? After V'ing out the area and adding weld, it might be a wash on weight. The crank was done many years ago by a place called Ron's in Ohio. Still in business?
Click to expand...

Yes, while Ron Miller passed away last year, his son BJ and their crew are still building many A & T engines. There was/is a video on YouTube by Hagerty that featured the Hagerty crew filming their Model-A engine being rebuilt by the same Ron's Machine in Shandon, OH.

As for the counterweights you mentioned on your engine, that is the same basic process they have been doing for years, ...and pretty similar to the way I do it. Think about this. Ron's guys machined the counterweight where the radius of the weight exactly matches the OD of the crankshaft web. There is a Grade 8 bolt that holds the weight tightly to the web. The tac-welds are there to keep the weight from rotating on the bolt however it is the bolt that is keeping the weight stationary. This bolt is in constant tension unlike the connecting rod cap stud & nuts that are in constant compression and then tension in each revolution. Because the crankshaft has been dynamically balanced, the weights remain 'friendly' with the crankshaft as it is spinning.

If you still have concerns regarding the tack welds, then TIG weld across the width of the weight on both ends and then re-balance. Likely if the weight is actually fuse-welded to the web (-without using any filler rod), then you may not even need to re-balance it.
 
All good advice. The bolts that hold the weights are in tension and depending on the bolt size, the tensile strength far exceeds the amount of weight being exerted on the bolt. Never thought about the weld only being to keep the weight from moving. As far as rebalancing the crank, the engine is currently apart doing a complete clean up and resurfacing the valve seats, and reworking the one guide that came out. I am now inclined to take the advice on here and reassemble the engine as it is. Do not want to go through the expense of a balance job.
Ed
 
Ruth said:
My thoughts as well. What if you ever need to change the pressure plate or flywheel. Are you going to disassemble the engine to re-balance the crank/flywheel/pressure plate togeter? Much easier to just balance the new parts.
Click to expand...
Balancing as an assembly avoids the potential pitfall that tolerances may add to each other rather than cancelling each other out.

The way my tech does it, you start with individually balanced components (like Terry Burtz sells for the Burtz engine - balanced crankshaft and balanced flywheel - or balance the components separately). You then balance the crank plus flywheel to double check that you are still OK, , and come back to spec (if necessary) by flipping the flywheel or (if necessary) drilling the flywheel. You then add the pressure plate, and come back to spec by rotating the pressure plate on the flywheel, and if necessary add weld to the pressure plate. Naturally you mark all components for reassembly. That way you end up with the final product as close as possible. If you change the pressure plate without rebalancing in the future you are no worse off than if you had not gone through the assembly process originally, since the flywheel and crank assembly was balanced previously.

In reality, given the low rpms we operate our Model A engines (for the most part, I'm not talking hill climbers here), balancing each component separately and then assembling them without further ado has served many quite well, and is a way way improvement over stock.

It's sort of the same concept as we use in balancing reciprocating elements. We usually start by getting the rod small ends as close as possible, then mix and match pistons, pins and small end rod weights to get as close as possible, then tweak (usually the pistons) at the end to get balanced assemblies.

Truth be told, I have only done this on motorcycle engines. Have not done this on a Model A engine yet, but will do so when I finally get around to building my Burtz. I figure that I have so much invested in the engine that it's worth taking the extra step.
 
The strength of the crankshaft material and its fatigue life are effected by welding, especially if the crankshaft is not heat treated to relieve thermal stresses after welding. Use the crankshaft as is without any additional welding.

The bolt is the primary reactant of tension from the centrifugal forces due to the counterweight. Although the tack welds do react some of the centrifugal forces, their primary purpose is to retain the alignment of the counterweight by preventing the weight from pivoting about the bolt.
 
JayJay said:
Balancing as an assembly avoids the potential pitfall that tolerances may add to each other rather than cancelling each other out.

You then add the pressure plate, and come back to spec by rotating the pressure plate on the flywheel, and if necessary add weld to the pressure plate.
Click to expand...

NO!!!!!! YOU NEVER WELD ANYWHERE ON A PRESSURE PLATE!!!!
People that permit and do such things should have to clean up and repair the inside of a car with a pulverized leg splattered all over it.

You drill the spring posts for balancing.
 
I did not know that Ron Miller passed away. More than 20 years ago he rebuilt 2 engines for me with counter balanced cranks. He did a good job and they still run.


Vic
 
Thanks Brent,
I didn't know. It's a great shop and they do great work.
I've been using them for babbitting rods for 30+ years.
 
BRENT in 10-uh-C said:
As for the counterweights you mentioned on your engine, that is the same basic process they have been doing for years, ...and pretty similar to the way I do it. Think about this. Ron's guys machined the counterweight where the radius of the weight exactly matches the OD of the crankshaft web. There is a Grade 8 bolt that holds the weight tightly to the web. The tac-welds are there to keep the weight from rotating on the bolt however it is the bolt that is keeping the weight stationary
Click to expand...
This pic is from your comment on the oil pressure to the center main that you state is the way you do the tube. The picture shows a lot more weld than tack to keep the weight from moving. I still believe the bolt should be strong enough to keep the weight from slinging off into the pan, but this crank has a lot more weld than just a tack.
Ed
 

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