Correct link belt for Model A

alexiskai

alexiskai

Well-known member
This discussion started elsewhere but I don't want it to hijack the thread.

For those who may not know, the Horne harmonic balancers are thicker than the stock pulley (same diameter but "taller"), so they take up more of the hollow in the front crossmember. This makes it impossible to remove a conventional fan belt without jacking up the engine. However, a link belt or segmented belt can be used instead. This type of belt uses a series of urethane links, like links in a chain. It can be resized and detached easily, so the belt can simply be pulled off.

This means we need to ask what sort of link belt to use. To do this, we need to measure the dimensions of the channel in the pulley sheave. I didn't have access to an original pulley but I took some measurements of a few two-piece aftermarket pulleys. The width at the top of the channel was .60-.62 inches. The Horne pulley is .625" at the top. The depth of the channels was at least .625" on all.

Best-practice with a V belt is that the belt should ride at or slightly above the top of the pulley, meaning that the belt must be at least as wide as the pulley. This causes it to grip the sides of the pulley.

Looking at an explainer page on V-belt sections, the correct one for the crank pulley would seem to be a Type 5V belt. This type is .62" wide at the top and .54" deep. However, the pulley on the aluminum two-blade fan is only .50" deep, so a 5V belt would not fit properly. Instead we need a Type B belt, which is .66" wide and .41" deep.

Some belts that appear suitable include:
Power Twist 5/8 x 5 B type industrial transmission V Belt
Jason Industrial Accu-Link B-Link-4 or B-link-6
BDH DuroDrive B Size, 6.5 Ft. Sleeve

The BDH DuroDrive belts are made in the USA and consequently are 2x the price of the others. Supposedly they are very high quality.
 
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I have the Murray Horne Harmonic Balancer on my Pickup. I tried a link belt but could never get it tight enough. It would work for a while then became loose. Remove a link, drive a bit more & it became loose again. After several episodes of this, I gave up and went back to a standard belt. True, it's a little more difficult but not impossible. Certainly less effort than removing those pesky links.
 
The discussion does not mention a generator or an alternator when figuring the end length. A metric belt with an alternator fits very well Don't ask me the size tonight, the snow is 6" and the temp. is 15. As I remember it is 62".
 
The stock belt is 43" long, so any link belt 4' or longer will work because you can remove segments until you get the proper fit for either a generator or alternator. I just ordered 2m of Power Twist belt for $42 shipped. Cheapest belt I've seen was $36 for 5'.

BDH told me they could do an order of US-made belts, in any color I wanted, but the minimum order size is 45' at $8.25/ft. That means I'd need to round up 11 buddies to buy the same color belt from me at roughly $40 shipped. Didn't think I could guarantee that much interest.
 
Some belts are marked FHP, which stands for fractional horse power. You don't want to use one of those.
 
katy said:
Some belts are marked FHP, which stands for fractional horse power. You don't want to use one of those.
Click to expand...

FHP belts are sized using L, as in 5L. If you search FordBarn for members using a 5L430 belt you will find at least a dozen instances. All of them seem to work fine. Remember that the fan belt is not transmitting the full power of the engine - only enough force to turn the water pump and generator. So in fact it is a fractional horsepower application.

Having said that, size B belts fit better. Many belts are labeled with both a B and a 5L designation, those should work fine as well.
 
I don't know why Carl was having problems with his linked belt but i thought i should mention that linked belts are directional. I'm not suggesting Carl had his belt on incorrectly, just thought I should mention it.

Just ensure the tangs point away from rotation.

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As a side note, we once had a guy have his water pump brearing giving up on a tour. We were not far from home. We were able to shorten the linked belt so he could just turn the generator and limp home, allowing the cooling system to thermosyphon. Not ideal but it got him home.
 
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Y-B, would you mind explaining what "tang" refers to and how your explanation of proper installation applies in the photo in your last post? Thanks!
 
Thanks, both of you. Perhaps the essential point here is understanding that the tabs (tangs) are the parts extending through the links at each joint. And that having them trail the direction of travel is the goal. I got it.
 
I have the harmonic dampener pulley. I use the cogged V belt, see https://www.mcmaster.com/6057K117/. This belt has cogs on the inside that allows it to bend easier and is slightly larger than 5/8 width which helps with worn pulleys and it lasts longer before getting too narrow. It is thin enough so that twisting it 90 degrees allows it to slip between the frame cross member and the pulley so that I don't have to jack up the engine to change belts. Since it bends easier it works better on the small pulleys on alternators. I think cogged belts may have been used originally, but not sure if that is the case.
 
nkaminar said:
I think cogged belts may have been used originally, but not sure if that is the case.
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The JS has photos of original belts and they’re regular V-belts. Any BX40 cogged belt will work in this application. The cogs reduce the surface area that touches the pulley but for the low power needed here it probably doesn’t matter.
 
Alexiskai, Thanks for the information about the original belts not being cogged.

The cogs will not reduce the amount of power that can be transmitted.

F = Fn X Cf. F is the force that is driving the pulley, Fn is the normal force which is supplied by the belt tension, and Cf is the coefficient of friction which is determined by the belt material and the pulley surface. Area does not enter into the equation.
 
I looked into the belt issue a little. It appears that cogged belts actually have higher friction than V-belts because of the way they're made. However, most guidance says that in applications where there may be a torque spike, i.e. the speed of the drive pulley may change suddenly, V-belts are preferred over cogged belts because the V-belt will slip a little when the spike occurs, which damps the torque applied to the other pulleys. Seems like that would be advantageous in the Model A application, because sudden changes in crank rpm would be moderated by the slippage of the standard belt and wouldn't put as much stress on the generator.

If you have an alternator, that benefit may be outweighed by the cogged belt's better ability to wrap the small alternator pulleys. Hard to say without testing.
 
I run an alternator so that pulley is smaller than a generator uses. That means the belt must grip on the small pulley. I use a notched belt for that reason but some of them fit too low in the water pump pulley and make one heck of a racket as the teeth touch the bottom of the vee. To over come that, I turn the belt inside out and use the bench grinder to remove some rubber from the ends of the teeth. Fitting the belt pst the harmonic balancer is now easier (and quieter)
 
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