Engine Fan Balancing

Glenn C.

Glenn C.

Well-known member
We go through the time and expense of static balancing, or/and dynamic balancing, the rotating elements of the Model A engines. i.e. pistons, connecting rods, counter balanced crank, flywheel, clutch pressure plate.

Question is....How do we ensure the new cast aluminum fan that we might install, or the original two blade fan that we have just repaired is in balance ?

Do we just use a sharp fine edge narrow blade through the shaft hole and be satisfied with a static balance, or is there another prefered method of balancing ?

I talked to a balancing technician about this problem, and he explained to me that it would cost about $280 just to build the fixture device for his balancer......not including the time (cost) to balance the fan blade.

Original two blade fans that may have rust build-up of rust between the two blade metal sections are an accident waiting to happen. Re-inforcing an original fan, with additional re-inforcing metal, or just TIG welding small cracks, is dangerous without re-balancing the fan assembly.

Can a person build his own shaft balancer using a used water pump shaft, or a section, as a mandrel between centers on a lathe ?

Your opinions appreciated.
 
I believe it was Tom W that built a nice one and posted the pics.. It may be in the archives or the Model A homemade tools web site..
 
I have one of Tom's units that I was able to purchase when he was in a 'weak moment':D, and it really works well. Building a static unit requires not only thought, but some work making sure you have the axis bearings aligned, and the counterbalanced shaft balanced beforehand.
 
Hi Glen, Good question, and one I have been trying to answer myself! There are a couple of problems with fan blades. one of them having to do with straight balancing considerations, and the other having to do with the matching of the pitch of the fan blades themselves, both of which can cause imbalance behaviours. So, the fixture for holding the fan must allow for both of these considerations. I'd love to see what Tom came up with on this! Let us know how you solve this one...
 
I check the blades to make sure the leading edges are parallel to each other. Then I check the blade pitch to make sure they are the same. Then I balance the fan using the balancer I made. I'll have to see if I still have any pictures of it. If not I'll have to take some new ones. I had to make a new balancer, because someone talked me out of mine! :)

BTW, I'm using an original fan that I made these checks and did the balance on.
 
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Here are pictures of the first and better second fan balancer I made. The problem with the first thin rail balancer is the rails must be perfectly level and be free of dust and nicks on the top edge. The second design uses 4 very small low friction ball bearings. Just before using it I limber up the bearings with a shot of WD-40 and spin them against the wire wheel on the bench grinder.

I then place the fan to be balanced on the weighted shaft and place it in the crotch of the 4 ball bearings. If it's an aluminum fan and the blades stop in a horizontal position, I know right away the blades aren't parallel to each other and you'll have to return the fan to the seller and hope for a better one. I drill holes in the front of the fan hub, being careful not to drill through the backside, nor into the belt V. I drill a series of holes then drill a small hole at an angle through the side of the larger hole. This will lock the lead in place. Depending on how much the fan seems to be out of balance, it's an educated guess how many holes to drill and fill with lead.

I also grind bumps off the blades and try to make them look better. As mentioned in an earlier post, the blades MUST be parallel to each other, have the same length, pitch and spin in the same plane. Thes checks are easy to make on the ball bearing balancer, but impossible to make on the rail balancer.
 
Thanks Tom for the pictures and proceedure that you use. I am going to build a device of my own from what you have provided. I tried earlier today to send you an note on another thought I had for a balancer for your opinion, but for some reason it would not send. Do you have any ideas for a dynamic balancer
 
When I worked at a large plant near our home, we were able to procur the standard sealed friction ball bearings, but we were also able to order the same size, very precision, ball bearings of higher quality for considerable more dollars.

Does anyone have a line on this type of bearing ?

Tom.....Did you have to dynamic balance the counter weight after maching on the lathe, or was it just static balanced ?

The counter weight must need to be very close to the initial weight of the fan to retain even weight distribution on the four bearings ?
 
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Yes, tell us more about the counter-weight. It looks like it has some balance work done on it. ?????
 
Glenn C. said:
...The counter weight must need to be very close to the initial weight of the fan to retain even weight distribution on the four bearings ?
Click to expand...

Hmmm...put fan on shaft, balance assembly on finger or straight-edge to find approximate CG, put CG centered between bearings? Should be plenty close.

Counterweight then needs only to be in the ballpark, not very critical. Perhaps about halfway between weight of OE fan and aluminum fan, to allow use with either?

Joe
 
"As mentioned in an earlier post, the blades MUST be parallel to each other, have the same length, pitch and spin in the same plane."

We have a Stewart Warner balancer..For doing fans and other things similar, we have an arbor (shaft) about a foot long with a hub in the middle to mount the fan.
Most fans, flywheels, sprockets etc have very little dynamic unbalance in them due to being in a very narrow plane.
Some very large truck fans have to be "masked" in order to spin them fast enough to get up to resonance.
 
As Joe said the counterweight isn't critical. I took a used pump shaft and impellor and stood it on end in a tuna fish can, then poured in melted old wheel weights. I then machined it on my lathe, then static ballanced it on my jig.

The ball bearings came from the AXMAN, which is a local surplus store. They have no seals, so they have very low friction. I keep the balancer covered when not in use to keep dust out of the bearings.

After mounting the bearings to the aluminum channel, go to your local secondhand store (Goodwill, etc) or garage sale and buy a nice brass or wood candlestick holder to use for the stand.

I think after making sure the blades are parallel, run in the same plane, have the same pitch, and are balanced, there is no need to dynamic balace the fan. I'm running a good used original fan on an original rebuilt water pump. I rebuilt the pump exactly as original and haven't touched the brass nut in 3 years and haven't lost one drop of coolant. The next time I rebuild a pump I will use the seal in the rear brass bushing though. It's the best way to keep grease out of the coolant.
 
Pete said:
"As mentioned in an earlier post, the blades MUST be parallel to each other, have the same length, pitch and spin in the same plane."

We have a Stewart Warner balancer..For doing fans and other things similar, we have an arbor (shaft) about a foot long with a hub in the middle to mount the fan.
Most fans, flywheels, sprockets etc have very little dynamic unbalance in them due to being in a very narrow plane.
Some very large truck fans have to be "masked" in order to spin them fast enough to get up to resonance.
Click to expand...

I visited the Horton fan clutch factory in South Dakota about 30 years ago. They make semi and industrial fan clutches. For a smaller factory in a small South Dakota town they had a very impressive operation and a very high tech lab for testing fans and fan clutches. The fan clutches are given many thousands of cycles for testing before the design is approved for production.
 
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