Question re Mountfield S421

[dregsy]

Hi all,

I know virtually nothing about lawnmowers, however I own a Mountfield S421 petrol mower and I've recently astonished myself by managing to replace the drive cable on it, however there is a but!
I find myself with a spring left over!
The mower does now drive. I thought it felt slightly slower than it used to, but my wife is adamant that it's the same.
I've tried taking some photos of the underneath of the mower, but I can't get my phone close enough take any.
I was just wondering if anyone had any idea what purpose this spring serves please?

Thanks.

[Mick]

Hi dregsy, and welcome to TGMForum.

I suspect the spring is the belt tension spring, hence why your drive is slow.  It sits on the front of the gearbox and hooks up on the chassis. It tilts the gearbox backwards to put tension on the belt..

[dregsy]

Hi Mick, thanks for your reply. A fortnight ago that would have meant absolutely nothing to me, but having spent a couple of days with my head inside the underneath of the mower I think I actually understand what you're saying!!
I've just had another look and I think I can see where it would clip onto the chassis so I've just now got to work out the same for the gearbox.
Thanks again for your advice.

[Mick]

I was only guessing, as it's quite normal for the spring to come off when messing about with belt or cable etc.  I actually wasn't sure from your image what size the spring was.

The very end of the spring hook (if it is the one I'm thinking), just literally hooks into a hole in the lower front of the gearbox and up to the chassis if that helps. 

[dregsy]

Thanks Mick, I suspect you're right as there is a bit of play in the gearbox which does make the belt a bit slack. My difficulty is being able to see the gearbox clearly but I'm sure I'll get there with it.
It's very satisfying being able to fixing without having to send it off to the repair man. I was like Tom Hanks in Castaway when he made fire 🤣

[Mick]

It's sometimes easier to fit the spring while the belt is off because you can tilt the gearbox, then slip the belt on while making sure the spring stays in place.

[dregsy]

Thanks Mick that's above and beyond 🫡