Knowing if your mower’s deck belt is tight enough can be difficult to determine if you don’t have the correct information and the right tools. We’ve all heard of tests like pulling the belt with one finger and measuring how far it extends. However, these methods can’t accurately tell if a belt is tight enough. If you try these tests, you’ll more than likely have too much or too little tension, which will only lead to an unnecessary repair that could have been avoided. So, let me share with you the tools needed and steps you should follow to test your belt while also caring for your mower.
How Tight Should a Mower Deck Belt Be? (The Short Answer)
A mower belt needs to be tested for the energy required to deflect over a set distance. The belt’s deflection is measured between two defined pulleys. The deflection can be measured in ft-lb (foot per pound).
A Quick Test You Can Do to Check If Your Deck Belt is Tight Enough
You are going to need two things to test your belt’s tension. The first is your mower’s technical information specific to its deck and belts. The second is a deflection gauge. Your manual will state which of the two pulley’s deflection needs to be measured and how much you need to move the belt. Then it will go on to tell you how much force is required.
Here’s an example. Apply pressure to the belt between pulley A and pulley B, and deflect the belt ½ inch. The gauge should read 10-15 ft-lb. If the reading on the gauge is higher, it is too tight, and if it is lower, it is too loose.
Why It’s Super Important Belt Tightness is Correct
Having the correct belt tension is super important simply because if it’s too loose, it will damage the belt, and having it too tight will damage the pulleys and the belt. This is why it’s not a good idea to use any form of guesswork and why having a deflection gauge is the only accurate method.
Once you know which pulleys to measure between and the deflection distance, measuring takes seconds, and you’ll be a step ahead of any problem waiting to happen.
Signs Your Deck Belt is Too Loose
There are several symptoms of a loose deck belt that you can look out for when you’re out cutting the lawn. I’m guessing that you have already experienced some of them hence why you’re asking, how tight should a mower deck belt be? Here are some of the common things to look out for.
- Belt Slipping
- Mower Vibrates Really Bad
- High Pitch Noise
- Faster Wearing on Sides
- Belt Keeps Coming Off the Pulleys
Signs Your Deck Belt is Too Tight
Tight belts can be a little more difficult to notice because a tight belt can quickly become damaged and stretched out. But, there are a few symptoms to look out for.
- The Smell of Burning Rubber
- Pulley System Can Struggle to Turn
- Belt Begins to Shred
- Tension Spring Becomes Overstretched
Hi there!
I have an old CastelGarden 98S. The belt keeps coming off when I set the cut level lower. It has 7 levels (7 being the highest cut) and currently I can only use 6 and 7; any lower and off it comes.
What could be causing this?
cheers Al
Hi AL,
It sounds like the belt has become stretched and that it has too much slack. So, when you lower the deck, the slack increases enough that the belt can fall off. Thankfully your lawn mower has the ability to adjust the tension spring to take the slack out of the belt. Therefore, if you tighten the spring, you should be able to increase the belt tension enough to stop the belt from falling off at the lower heights.
I hope this helps.
Tom.
The mower deck belt is very loose when the mower is disengaged and keeps slipping off the engine pulley. When the cutter is engaged the belt seems tight enough and when cutting there are no symptoms of the belt being too loose. What do you think would cause this?
Hi Tom,
Getting the belt tension right can be tricky if you only use guesswork. I used to check my belt tension by pulling it with my hand. But, sometimes, I would get it right, and sometimes, it would just fall off.
Using a belt tension gauge is the only real way to tell if your belt is set correctly. This small tool gives you a specific measurement of how tight your belt is and what adjustments you need to make. These can be picked up at Walmart for about 20 bucks. With the belt setting from your owner’s manual, you should be able to adjust your belt accurately. If the problem persists, you can rule out tension setting and look elsewhere for the problem. But this process will rule out a lot of issues and is definitely an excellent place to start.
Thanks for the question.
Tom.
I just put a new belt on a craftsman ride mower 7400 Pro Series and the belt comes off. It does appear to have a vibration now that it did not have with the old belt. The reason that I replaced the old belt it came off and had a break on the underside.
Hi Gene,
Usually, the vibration from the cutting deck is caused by the belt not having enough tension, and the belt bangs around the cutting deck. Unfortunately, your specific lawn mower (as per the manual) doesn’t allow for any adjustment of the belt tension. So, all you can do is make sure that the tension spring is in good condition. If the spring is stretched, then it won’t create the necessary tension. Also, take a look at the pulleys and check that they are in good condition. If any of them have worn bearings and are baggy, then you could be losing tension.
Finally, try only engaging the blades when they are completely stopped. I have seen issues with this particular lawn mower when you stop/start the blades while they are still moving.
Thanks for the question.
Tom.