OutdoorKing Repair Forum Forums Repairs and Maintenance Questions on Walk Behind Lawn Mower Frames Question On Scott Bonnar Cylinder Mowers Clutch not staying dis-engaged on Scott Bonnar 45

Gday this would be my first post here so hi to everybody here .I just bought a second hand 14" 3hp briggs scott bonnar 45 on ebay, all is good except for when I engage the clutch handle to stop the blades spinning as soon as I let go of the handle the blades start spinning again ,the clutch wont engage proply.Any ideas what could be causeing this before I pull it apart. thanks

Hello gavin351!

A warm welcome to the ODK forums. I'm sure we can help here.

The Model 45 is, arguably, the best residential reel mower machine of its time.
It easily holds ground with many of the best made today.

You have identified a problem with the primary clutch on your 14 inch machine.
There are a number of possibilities here, some simple; some less so.

The causes could include maladjustment or misalignment , clutch pad failure, or
clutch thrust pad or bearing failures.

If you could take a close-up photo looking down at the clutch assembly that would help the
SB experts to ascertain the problem for you.

How to upload photos may be found HERE.
When you return to the site, a good place to start is 'Active Topics' from the menu bar.

Hope this helps.
----------------------------
JACK.

Hi gavin351 and CJ,

The other main issue that causes this problem is a rail failure which misaligns the two halves of the clutch.

I must admit that it's rather strange to have a 3Hp motor on the 14 inch model, chances are it's not the originally fitted engine that's on it. I also suspect that it's a twin rail chassis and not the earlier solid deck machine that you've got.

My fears are if correct, that a clutch issue has arisen and that has induced vibration into the driveline, this has either unevenly worn the thrust pad which in turn would affect the alignment or even worse induced fatigue fractures into either the front or rear rail which is causing the engine not to sit perfectly solid, thus giving the clutch the opportunity to grab every so many revolutions.

As CJ suggested some good close up shots of clutch area and also the rails where the engines bolts down on the clutch side. Also a good shot showing how straight both the front and rear chassis rails are.

Without a doubt we'll nut it all out. Poetry in motion there LOL !


Cheers,
BB

BTW shouldn't this topic be called "Clutch not staying disengaged"

Hi to gavin351, and a warm welcome to the forum.
It is always great to have another Scott Bonnar owner on board as we all like to learn new things and tinker here.

Many thanks to CyberJack and Bonnar Bloke for their replies. I have taken BB's idea on board and have renamed the topic to better reflect the problem at hand.

I tend to think that this could be an adjustment problem in as much that the clutch handle and associated clutch fork need adjusting at the clutch fork.
The dis-engaging of the cutter clutch works by pressure being applied to the plastic thrust pad by the clutch fork.
This in turn pushes the clutch cone inwards and away from the outer clutch cork lining thus dis-engaging the clutch and stops the cylinder reel from spinning.
If this adjustment is out of wack, the reel will spin sporadically or all the time, creating a dangerous condition.
Looking forward to seeing your pics....
Once again, to ODK

A big thanks to CJ ,BB ,and DEEJAY . The original owner informed me the engine was replaced with a new one a few years back that would explain the 3hp on a 14" as BB thought . ive checked the rail they are straight/flat with no signs of fatigue .The problem is now fixed as I adjusted the fork as DEEJAY suggested the lock nut was loose . Again a big thanks to all you guys and il post some more photos when I finish restoring the SB .

Hi All,

Great to see that it was only the adjustment that required tweaking and nothing more serious like many of the 17's suffer from due to a flogged out clutch. I notice that your clutch is still all original and never been tampered with. One thing to keep an eye on is the captive cotter that locks the clutch half against the PTO shaft of the engine, ensure that the nut stays nice and tight as they do work loose and that's when the trouble really starts.

BTW This would be one of the very last 14 inch machines made as it sports the apple / alpine green colour which was the last variant of green that Scott Bonnar used prior to the Rover take over. Shortly after this colour was introduced the 14 inch machine was discontinued leaving only the 17 and 20 inch models as the line up. The 20 inch was then discontinued leaving only the 17 inch machine left standing until it's eventual demise.

If I'm correct your original engine would have been a 2.5 Hp Orange Briggs & Stratton powerplant.

Also while I'm at it, looking at your photos shows that there is a lack of lubrication in the thrust pad area and I'm sure that the rest of the machine will then be suffering the same. Lubrication is one of the most essential issues with all the chains and friction producing parts of the machine.

Cheers,
BB

Hi to All,
I am so glad that my thoughts were correct and an adjustment was all that was required to see it back working as it should.
I strongly agree with BB re lubrication, a couple of drops of oil in the thrust pad hole, plus the same in the hole in the clutch cone, will see the shaft well lubricated.

BTW, I love your dog in the pic, he/she looks a real beauty!
Well done with your repair, plus you just saved considerable $$ doing the job yourself rather than taking it to a repair shop.
Good stuff!