How tight should my starter/generator belt be? That is a very good question, and when I first started working on carts, many years ago, I decided to figure out what a good answer was. So, I studied everything I could get my hands on to come up with the answer. It ended up to be a quite interesting study, and in this article, I will attempt to convey to you what I learned.
Thank goodness, on a gas golf cart we really only have one belt to worry about. I know, there are two belts (the starter/generator and the drive belt) but the drive belt doesn’t require adjustment. As a matter of fact, there are no provisions made for its adjustment. It certainly needs to be the right size and they do wear out eventually, but it is just matter of replacing it when it no longer meets the manufacturer’s specifications.
The starter/generator belt, however, does need to be adjusted to the correct tension when installed. When you look at the starter/generator belt, you will find that it is a standard automotive type V-belt. There are several variations of these, but the most common one (which is what ours is) is called a “Raw Edge Plain Belt”. You will notice that the top of the belt has a “fabric” coating, and usually the bottom does also, but the sides are just rubber (chloroprene rubber to be exact). Inside the belt, if you were to cut one into, you would find a band of polyester cord and the end-view of the belt, where cut, would look something like this:
The thicker lines, indicating the top and bottom of the belt, represent the fabric coating. The little circles represent the ends of the polyester cord, and the rest of it is the rubber material. The strength of the belt is determined by the polyester cords. If it weren’t for these cords, the belt would stretch like a rubber band. The rubber below the cords is just a material to provide traction, by being pushed down into the pulley’s groove edges. It is also important that the bottom of the belt does NOT come in touch with the bottom of the groove. If it did, the rubber on the sides would not provide proper friction on the sides of the groove to provide proper traction. Also, you will notice that the fabric layer on the top of the belt sticks up just above the top of the pulley. That area is called the “Ride-out “area. It doesn’t need to be in the groove, all of the strength and traction happens below it. The angle of the sides of the pulley is generally 40 degrees inclusive.
The first thing to do when adjusting the tension on the starter/generator belt is to check to make sure the belt fits the pulleys as described above. You would be surprised how many times people brought me carts with problems that were being caused by having the wrong belt or a wrong pulley in the mix. What would happen, sometimes, was that someone would replace the starter/generator with a new one that didn’t have a pulley that matched the one that was on the original one. If the belt doesn’t fit the pulleys pretty much just like I have described, you’ll never get the belt adjusted correctly. The pulley on the clutch and the one on the starter/generator need to be the same shape. Obviously, they are very different sizes in diameter, but the belt needs to fit them both as illustrated above. You can get by with some slight differences, but not too much.
So now that we have confirmed that the pullies are similar, and we have the right belt, how tight does the belt need to be. All of the gas carts provide adjusters of some sort. You need to loosen the large bolt that the starter/generator “pivots” on so that it can rock freely back and forth and then make the adjustment and then tighten everything back up.
I’ve studied lots of belt manufacturer’s literature and the general rule that most of them come up with, is that for every inch of “span” there needs to be 1/64 inch of “slack” in the belt.
The span is the distance from the top of one of the pulleys to the top of the other one. The slack is the distance that the belt can be flexed when a reasonable amount of pressure is applied in between the pulleys.
Let’s say that we measure from the top of the starter/generator pulley to the top of the clutch pulley and we get 12 inches. According to the recommendations of literature that I have read, you should allow 1/64 of an inch of slack for each inch of span, so in our case, we multiply 1/64 (.015625) by 12 and we get .1875 (less that a quarter of an inch). Reasonable pressure is generally accepted as about 20 lbs. of pressure for each inch of belt width. Our belt is a lot closer to ½ inch, so we would only apply about 10 lbs. of pressure. So, if we push with 10 lbs. of pressure in the center of the span, we should be able to get the belt to flex a little less than a quarter of an inch. WOW! That seems way to tight to me. From my experience about a half an inch is much more suitable. So, through the years, I’ve learned to leave just about twice the slack that the “1/64 inch rule” would produce. I used to use a small pressure gauge to push on the belt with so that I could be sure that I was pushing with 10 lbs. of pressure, but through the years I’ve pretty much developed a “feel” for how much pressure that is, so I don’t even use the gauge any more. You can go push on your bathroom scale with your hand a few times to learn what applying 10 lbs. feels like.
To go even a step further, since most of the starter/generator belts in gas golf carts are in the ballpark of a foot (give or take a little), I don’t even measure the span anymore. So, in conclusion, I just make sure the belt fits the pulleys correctly (the most important part) and set the slack for about ½ inch and I ‘m usually good to go. If you go much tighter than that, I think you run the risk of putting excessive pressure on the thrust bearing of the generator or even run the risk of breaking the starter/generator pulley, especially if the pulley is one of the newer “cheapies” that are notorious for coming on starter/generators from internet aftermarket (non-OEM) sources now. I’ve had several come into my shop with broken pulleys. Many times, when someone over-tightens the belt, they are trying to compensate for the fact that the belt doesn’t fit one of the pulleys correctly, so they put the increased pressure on the belt to keep it from slipping. There generally isn’t much you can do about the size of the pulley on the clutch assembly (it probably came that way with the cart), but the pulley on the starter/generator can be changed. I used to keep a whole box of used pulleys (and shims for spacing them) around so I could “build” a pulley that would work right.
I hope something in this article might be useful to someone out there. Ron
Ron Staley has published the following books, and you can get more information about them by just clicking on each title below:
Electric Golf Cart Repair 101 (and a half)
Techniques, Tips, Tools and Tales
Gas Golf Cart Repair 101 (and a half)
Techniques, Tips, Tools and Tales
4-Stroke Golf Cart Engines Explored
What Makes Them Tick
By an old Slot Machine Mechanic