OutdoorKing Repair Forum Forums Repairs and Maintenance Questions on Walk Behind Lawn Mower Frames Question On Scott Bonnar Cylinder Mowers Scott Bonnar 40

I want to get the blades sharpened and need to remove reel but can't get the cog driver off. Any suggestions ? Gus

Hi Gus, and a warm welcome to the forum. Its good to have another Scott Bonnar owner on board.

Gus, we need you to post some pictures of the sprocket and chain case so we can help you. In any case, you will have to remove the cylinder reel and the sole-plate complete with the bed-knife blade attached, and take both to the engineer for sharpening.

We need the pics to identify how the cutter sprocket is attached to the cylinder reel.
In the meantime, have a look at the video....Click HERE
Once again Gus, to OutdoorKing.

Hi Gus, as you can see, on your mower the reel sprocket's retaining nut is welded to the sprocket. That means the sprocket has to screw onto the reel - it can't be keyed to the reel's axle. Note that the engine output shaft, which attaches to the top sprocket, rotates anticlockwise viewed from the chaincase end. Therefore the reel also rotates anticlockwise. If the reel sprocket's thread were a normal right hand one, it would unscrew itself when the reel was under load cutting grass, so it has to be a left hand thread.

To remove the reel sprocket, remove the chain, and put a piece of steel bar of the right diameter through the holes in the collar behind the sprocket, to keep the reel from rotating. (On most mowers you have to put a wide piece of wood through the reel to prevent it rotating, but yours seems to be a more luxurious version.) Unscrew the sprocket retaining nut by using a socket spanner and rotating it clockwise, as if you were tightening a normal right hand thread. The sprocket and nut will screw off together.

As a point of good workshop practice, the collar under the reel sprocket seems to be designed to be held by a C spanner when unscrewing the sprocket. The C spanner would presumably have been a special tool available from Scott Bonnar. I tend to make special C spanners when I expect to use them more than once, not least because if you just use a steel bar, it mashes the initially-round hole in the collar and makes it look like the tenants have been playing with it.

Hi Gus, unfortunately, NO it won't! There have been a few 'tenants' improvements that I can see here inside the chain case. grumpy is on the right track with it being a left hand thread, but if you follow his method, you will be fighting yourself, as the red collar has the thread inside it, behind the hole. If you look carefully at your pic, you will see nothing is inside the threaded hole in the nut.
This is a 'tenants improvement' to assist in sprocket removal, as originally a steel rod was placed through the hole in the collar, and struck with a hammer to loosen and the opposite direction to tighten....the welded nut now makes this procedure a breeze!

Put a wide piece of wood through the reel to prevent it rotating, and unscrew the welded sprocket retaining nut by using a socket spanner and rotating it clockwise, as if you were tightening a normal right hand thread. The sprocket and the red collar will screw off together.

Thanks Deejay, sorry about that. So that beautiful factory-like weld holding the nut to the collar is a tenant's improvement. I wish all the tenants did nice work like that.

The white plastic pad on the chain tension adjuster does not look original. Some SBs had a hard plastic pad to do that, and others had a ballrace to do it. I suspect the previous tenant has replaced a hard plastic pad with a soft one which is shredding. The shredded garbage in the chaincase might be from that source.

Gus, on looking at the set-up of the 'tenants' chain tension adjuster, I think a Model 45 unit could be easily retrofitted here which would alleviate the shredding problems you are having now......it is made of very hard plastic...on my 45, it has done well over 20 years of work with virtually no signs of wear. They are available in the OutdoorKing online store...Click HERE

Thankyou all for your suggestions, have finally got it off, now can get the blades sharpened, hope not too much of a problem putting it altogether again. Gus

No worries Gus, glad we could be of help. If you have any probs with re-assembly, just post some pics and we will give you some help.
Don't forget to check the serviceability of the cylinder reel bearings, as, if they are worn, you will not achieve satisfactory adjustment. Also, don't forget to take the soleplate (complete with the bottom blade still attached) to the engineer as it will need attention as well.

If you need further help, can you please post in "Repairs and Maintenance > Questions on Lawn Mower Frames > Questions on Scott Bonnar" Thanks Gus.
I will now close this thread, If any member has anything to add, please PM a Moderator.