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2003 Tiger Cub (48" cutter deck) which still has the long belt unfortunately.
Previous owner fitted a genuine Scag belt just before I bought it. That one lasted about 15 hours before snapping.
I then fitted a Continental PowerSpan belt (SPB3750) - this one reverted and got caught in the clutch after 10 hours.
Bought another Continental and this one is 5 hours in but looks like it isn't going to last much longer.

All pulleys and idler pulleys are new and in line. All I can think of is the belt size.
Scag list the belt as 482529 - quick search says this is 148" ? The Continental is 147"
Would the extra tension cause premature failure ?

What is the model and serial number of your Tiger Cub?

Hi MM
Model STC48A-20CV
Serial from memory begins with 841

Hi jetty,
Overheating of a V belt is the cause of the failure.
I suggest that you inspect each V pulley for wear in the V groove. As V pulleys wear, the sides of the V groove loose their shape and will grip the sides of the V belt as it travels around a V pulley. This causes excessive heat which in turn overheats the V belt causing premature failure. This includes the clutch pulley.
I also suggest that you loosen the tension and pull the V belt away from each pulley and deck spindle, turn each pulley and spindle checking for ease of turning.
A slipping clutch can also overheat. The clutch is actually a clutch/brake and if the airgap for the brake part of the clutch is out of adjustment, the brake will drag on the clutch engagement surface the friction from which will cause overheating of the clutch pulley and in turn overheat the V belt.
I would also check the clutch for internal resistance and possible shorting to ground. To do this, you need to find and disconnect the clutch electrical connector and with an ohmmeter, check the resistance between the two terminals and then from each to ground. The resistance of the clutch coil should be no less than 2.5 Ohms and there should be an open circuit from each terminal to ground.
As the machine electrical grounds all connect to one of the engine mounting bolts, I suggest that you inspect these connections. A poor ground particularly for the clutch, can cause it to not fully engage during machine operation. A worn PTO switch can also cause the clutch to not fully engage causing it to slip.
Also check for oil leaking onto the V belt as oil will cause a V belt to slip.
A few thoughts!

Thanks for the tips - some troubleshooting over the weekend required.
It is probably the clutch end as all the spindles, pulleys and idler pulleys have been replaced on the deck.

When the belt snapped - I tried turning the clutch pulley and there was quite a bit of resistance. Is this normal ?

The clutch is a clutch/brake. when the power to the clutch is off, the brake engages.
Go to ganos.com, a power equipment dealer in CT.
Click on service, click on service tips, there you will find info about clutches.
I haven't learned how to cut and paste with Windows 10!!!
Ganos is not far from me and my Scag dealer.

Thanks good info there!
Just put another 2 hours on the belt - looks really bad. Photos attached - doubt it will cope with another start!
Ordered a new spindle pulley as I noticed a bit of damage along the edge - whether that has anything to do with it, no idea.

The clutch has two dodgy connections at the plug end. The wires just before the plug have been exposed and taped up - on my list of things to fix.

Also forgot to mention - when you turn the key to start it rarely starts. Instead you hear a "click" - takes several turns of the ignition before the motor fires up. Worth replacing the PTO switch ?

Under the panel that has the key switch and PTO switch is the cranking relay. When all the safe starting parameters have been met, the electronic control module will ground the relay so that when the key switch is turned to the start position, the contacts inside the relay will close allowing voltage to the engine starter solenoid.
The click that you hear is the fuel shutoff valve operating in the carb.
Your V belt is really tore up. You need to inspect each V groove pulley to see what is hanging up the V belt as it travels around the pulleys.
I also recommend that you disconnect each electrical connector, inspect, clean and reconnect if OK. This includes the battery cable connections. Disconnect the battery before doing the connectors. There are three just under the control panel, PTO switch, key switch and the cranking relay. If you replace the cranking relay, make sure that you get a Scag one as it has a blocking diode inside of it.
I also recommend that you inspect the deck V belt travel as sometimes there are brackets that are positioned to help prevent the V belt from flying off a pulley. Sometimes the V belt can get routed incorrectly and drag on these brackets if not installed correctly. Most of these brackets are removable/adjustable.

Thanks once again MM - I'm going to strip the machine in a few months and rebuild from the ground up. It has been a waste of time this season, spent more time in bits rather than cutting grass.
Forgot to mention - measured the clutch resistance - 3.6 Ohms

Hopefully the new V pulley on order will help.

The damage on that belt is typical of pulley damage.
Now this can be a nick in the pulley or a rock stuck in the pulley.
Look closely and you will see the cover is cut at regular intervals and these intervals will be the circumference of the damaged pulley.
Once the cover is cut the belt tends to split due to the action of the tensioning pulleys which bend the belt backwards.
If the tensioning pulley is badly adjusted or not rotating freely then it accelerates the deterioation of your belt.
Whenever you replace a broken belt, every pulley should be checked for free rotation & damage as should all of the pivot points of tensioning pulleys.
One inch either way on a 147" belt will make a difference to the belt life but we are talking around 5% to 10% not 90%.
Too tight will also substantially shorten the life on the various bearings and I have had cases where spindle bearings failed each season due to the belt being too small but that was 3" too short on a 90" belt.
A belt that has rolled over is toast.
Belt rolling happens when the pulleys are out of alignment and the belt is too loose.
Or you get a bit of debris like a stick stuck in a pulley that is not sharp enough to cut the belt but causes a local stretching or in really bad cases tearing of the chords.

jetty said:

Thanks for the tips - some troubleshooting over the weekend required.
It is probably the clutch end as all the spindles, pulleys and idler pulleys have been replaced on the deck.

When the belt snapped - I tried turning the clutch pulley and there was quite a bit of resistance. Is this normal ?

Click to expand...

You sound like you are disregarding the possibilility that it is spindles, pulleys and idler pulleys because they have been replaced.

There could be one installed wrong...I would recheck them.

What about belt routing?

I have spent the past day replacing all spindles and pulleys and replaced an idler pulley.
Brand new belt as well for good luck!
Same problem - 40 minutes in and this is the belt.



I'm at a complete loss now - new pulleys, spindles, belts, adjusted the PTO, checked the PTO. Belt runs great along the spindles and pulleys.
Either I'm hitting a limit on these Continental belts or the belt is the wrong size. Continental measure their belts by datum which is 147.6" - wondering if Scag measure the inside length instead ?

SPB wedge V Belt
Datum length is 147.6"
Inside length is 145"
Outside length is 148.5"

Any further suggestions before I push the thing off a cliff?

V belts have 4 dimensions.
Length
Width
depth
angle
The original part number is for a 148.375" x 21/32" 40 deg belt 6 strand kevlar chord with cotton cover.
That is USA measurements which are outside length.
A belt 1" shorter over that length would cause it to be a little tight and knock a small amount of time ~ 10% off its service life.

Your pickies are nice but there is no refference point so it is impossible to work out which side we are looking at.
The cover has a definate cut look to it on 2 images and unraveling on the first with no signs of wear unless we are looking at the back of the belt.
There is no signs of abrasion adjacent to the cut which rules out rubbing against something like a steel edge or a bolt.

Did this one roll over and invert as well ?

Sorry those are cuts to the inside of the belt.
Just had it running - checked all over just in case it was catching something.....nothing, all clear.

I'm going to run it now for a couple hours and see how the belt holds up.

This belt hasn't rolled - runs nice and smooth, just seems to be disintegrating at a rapid pace!

All I can think of is that these Continental belts aren't up to the job. Which manufacturer do you guys use ?

Looking everywhere I could for info on the belt you have purchased. It is metric not SAE. IT is not wide enough and the angle is not correct. I would bet that this is a belt only problem and your first problem has been fixed with you buying everything new. Find a belt that is (quoting bert) "148.375" x 21/32" 40 deg belt 6 strand kevlar chord with cotton cover.". 21/32" 40 deg is the most important part of the equation.