OutdoorKing Repair Forum Forums Repairs and Maintenance Questions on Walk Behind Lawn Mower Frames Question On Scott Bonnar Cylinder Mowers Scott Bonnar 45 clutch slipping under load

Hi CyberJack, that makes perfect sense as I was just looking through the parts list and could not make sense of how it could drop down. I assume it just frees up with no tension. I'll take another shot at the clutch housing now. Thanks for your help

Hi Deejay, CyberJack, BB, Firstly, thanks again for all your help so far...it is truly appreciated. I tapped the cotter and freed it up and had to use a rubber mallet to get the clutch housing off. It took a bit of effort to remove.
I have cleaned all the parts up as per attached photos.

Engine Shaft (from a few angles) has some wear marks but doesn't look too bad from my nube standpoint.




Clutch main housing. Has a previous ding mark on the outside (NOT ME) but looks OK inside. The paint on the cutter clutch melted off as soon as I got some petrol on it so I removed it all and I will repaint it later. There are a few bur marks on the inside edge (hope you can make it out in the photos)




The inner cone has cleaned up pretty well.





The outer cone looks Ok...but once again, up to the experts



Spring and clutch key look ok although the key has a small ridge worn into the end.

Not-so-captive Cotter pin is a bit rubbed and bruised. It does have some thread stripped so I will get a new one anyway and keep this one for spares.



Lastly, the main culprit...the cork had completely detached and was shredded aside from being worn down. I wonder how I was getting any traction at all.


Hope the photos come out Ok as the lighting in my garage is a bit poor.

Hi Dramapig, CyberJack and DeeJay,

As far as the removal of the clutch body is concerned, sometimes you will need a 3 jaw gear puller as you only need the slightest amount of fouling with the key steel and you'll have a hard time getting it off the engine's PTO shaft manually. Please don't use a steel hammer as this will only get you into more strife.

3 Jaw pullers are cheap enough from the Asian import shops and you'll use it again and again. Just ensure that the threaded screw is narrow enough to be able to fit inside the thrust bearing and come in direct contact with the PTO shaft.

I'll post a picture up tomorrow of the one that I use for all of my SB 45 work with a ruler next to it so you know exactly what size to get.

Cheers,
BB

UPDATE :

I wrote the above while Dramapig was posting up his previous post with pictures, as such my post is now out of sync.

Meanwhile a gear puller is still a good tool to have for removing the various gears and sprockets in the drive system.

Great to see you used the rubber mallet as both cast iron and the later alloy based clutch bodies don't respond well to harsh blows from steel hammers.

So far a good result from yourself.

Thanks BB, It looks as though someone has had a go at it before with a steel hammer as it is dented on the outer lip. I'll be sure to buy a the gear puller as I might renovate the entire machine later this year. I have a bit of a taste for it now

Not sure how to get the thrust bearing out. Might need a hand here

Right now, looks like I'm buying the following

1 x Captive Cotter Pin
1 x Clutch Body Key
1 x Cork lining


Any other comments on the clutch assembly? It looks OK to me but I am a nube so happy to take advice from those more experienced.

Hi dramapig, CyberJack, BB,
Well done mate, you've got it all apart and my suspicions re the clutch cork were proven correct.

I'm of two minds here, one part of me is saying keep the machine original and replace the captive cotter and retain that inner clutch-half....the other part is being more rational and asking you to consider purchasing a new inner clutch-half with the 2 grub-screws which is a much improved attachment method....

You can see (in your pics) where the end of the engine shaft key is chewed, this is because with the captive cotter retention method the key can move in its keyway, but with the grub-screw retention method, it can't, as it is held in position firmly by one of the grub-screws.

The grub-screw retention method is much better in that it allows you to loosen the grub-screws and move the whole clutch assembly to facilitate cutter clutch adjustment much more easily.
There is also the thought that this improvement helps reduce vibration and thus reduces the chance of cracking of the engine deck.

Just adding to CyberJacks post above, here is how the captive cotter works...



At this time also I would consider purchasing a new thrust bearing also, as yours, (most probably) is past its used-by date.

Hi Deejay, BB and CyberJack,

Thanks for getting back to me, I was having that same dilemma last night after reading your clutch rebuild Deejay. The grub screw option makes a lot more sense I think except that after reading so many great restoration posts on the forum, I now want to fully restore this SB45. So I a might buy another cotter and cork lining now to get her up and running and then buy the new clutch as part of the full restore which I can start at the end of summer. that will give me plenty of time to get the turf in order and do enough research to do the restoration job properly. I am considering replacing the B&S motor with the Honda GX120...any other engine suggestions?

One other question...can I use the existing inner clutch cone on the new outer cone Nd main body or do I need to replace it as well?

Hi dramapig, all you need to rebuild your clutch is the grub-screw inner clutch half, and the grub-screws to suit and perhaps a new thrust bearing, the engine clutch key, and cork, glue etc. for the repair.
Easy peasy!

Hi Deejay,

Already ordered the new parts as suggested.

Since the parts are getting harder to come buy, I ordered another captive cotter pin so that I have a spare clutch housing.
But I took your advice and ordered a new thrust bearing also.
Can't wait to get the clutch sorted.
I'll post some pics etc as soon as i get time to work on it.

Excellent mate! Looking forward to seeing the pics.

Lucky I bought a new thrust bearing as the one that was in there took a beating to get it out.

Hi Dramapig,

There's a tool designed to remove internal bearings, it's called a slide hammer with an expandable shank (collar) on the end of it to grip inside the bearing hole and remove it without doing any physical damage to both bearing or clutch body.

Anyway you've got a new one on the way so just ensure it is lubed up well with grease before inserting it and it will last forever.

Honestly most of them survive rather well especially if they have grease in them and they really don't do much as they aren't really being loaded up apart from when the cutter clutch is disengaged. I've pulled many of them out re-greased them and away they go for the next umpteen years.

Cheers,
BB

Hi Deejay, BB,
I got the new parts today (I have been away for a few days). Already glued and clamped. Can't wait to grease up the thrust bearing and put her back together tomorrow when the Kwik Grip has dried. Selleys appear to have changed their product line and I used the Contact Grip (Vertical). Thank-you to you both for your help so far.

Here she is glued and clamped

BB, meant to say thank-you for your input re the thrust bearing also...really appreciate you guys sharing your experience. I am definitely going to invest in a slide hammer and cog pullers.

Hi dramapig,

That's exactly the best way of how to do the job. You're going to find that your machine runs somewhat smoother resulting from this repair job you've done and saved quite a bit of money in the process I'd say.

If you have any other questions no matter how trivial you might think they are I will only be too happy to help you from here onwards as DeeJay won't be available for a little while.

Cheers,
BB

Hi BB,

I have greased and inserted the new thrust bearing into the new clutch housing



Replaced the cork lining


Reassembled the clutch


Engine back on


Readjusted the clutch fork as per Deejay's advice in a previous thread HERE



What is the best way to reset and adjust the clutch lever assembly?

Hi dramapig,

The way of adjusting the clutch fork is to adjust the set screw that pushes against the clutch lever until the fork is just making the thrust pad touch the clutch cone with no play (as you already have preload on the cone via the internal spring) and then just back it off until there is the smallest amount of visible clearance between the pad and cone. This way you have full pressure contact within the clutch (via the internal spring) when the lever is released and full non engagement clearance within the clutch body and cone when the clutch is disengaged.

Ensure that the lock nut on the set screw adjuster is done up firmly to avoid any movement of the screw due to vibration and recheck the clearances.

You've done a great job all round from where I see it.

Cheers
BB

PS. Just one small thing and that is I would've painted the cone assembly so as to avoid it rusting as it's made of cast iron which will rust up straight away when exposed to the elements.