Changing drive belt issues on CT151

Hi all,

We brought a second hand Husqvarna CT151 ride-on mower 6 weeks ago, it worked fine. After 10 hours of mowing, the drive belt fell off and it was extremely worn so I decided to replace the belt from this source. I fitted on the new belt, it is rather loose. When I release the brake with the engine off, it picks up some tension but still rather loose, in this state I can easily pull the belt 3-4 inches and when I let go, the tensioner goes to its maximum reach and can't go further. The tensioner spring looks good and it's firm. I don't want to test drive with the belt as-is, worried that the engine will quickly wear out the belt by slipping. I have the manual and the pulley layout shown is different to what the actual layout is, the number of pulleys are different. I've had someone double check the belt route and he confirms that it looks correct. I'm not sure what I should do next - should I return the belt and get a shorter one? Or I'm making a mistake somewhere? Any suggestions would be appreciated.

Many thanks!

Regards - Piers

Because of the rear discharge these mowers have a rather difficult belt routing with a lot of pulleys to keep the belt clear of the discharge chute.
Tripple check the belt routing, missing one pulley will make the belt too loose.
Check carefully the pulleys, if you have less than the book shows, one could have fallen off.
Look for tell tale rubbing / scuff marks under the mower to confirm your belt routing.

Assuming this all checks out look closely at the pulleys themselves.
'Pulleys wear on the side faces which allows the belt to sit deeper in the pulley and so run loose as the effective diameter of the pulley is now smaller.
When I rebelt an old mower I take belts that are 1/2" & 1" shorter than stock to account for this wear.
'Downside is fractional belt lengths are double whole inch prices. a lot cheaper than replacing pulleys but a bit on the pricey side.

If you go for smaller belts, just make sure the belt can actually slip easily in the clutched position or like the great big stem powerd wheel, there will be no way of stopping it.