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 dramapig,
OK, what we need now is some pics of the cutter clutch cone, one with the clutch is fully engaged (ie. in the position it would be when cutting grass) and one with the cutter clutch disengaged....I want to see particularly how far the clutch cone extends past the outer ring when it is engaged, and how far it is pushed in when disengaged. Thanks mate.

Instructions for posting pics using our forum Inline Uploader can be found HERE
Looking forward to seeing the pics,

Hi Deejay, photos are attached.

Clutch engaged

Clutch disengaged

Thanks for your help and let me know if you need more info or photos.

Hi DeeJay and dramapig,

Just my observations and that is the engaged picture shows (just) that the clutch fork may still have the slightest pressure applied to the thrust washer clutch thus allowing the clutch to slip under load. I've always adjusted the clutch fork so that there is ever the very slightest amount of play between the fork and the black plastic thrust washer, thus from there you have total clutch contact, but I'll leave it to DeeJay to make the final call on this.

BTW just an observation and it looks like there hasn't been much lubrication applied around the thust washer area for some time.

Cheers,
BB

Hi to dramapig, and BB,
And my thanks for posting the pics, and for BB's observations, regarding the thrust-pad.

They say pictures say a thousand words...and there is no exception in this case....The problem is with the clutch cork that is glued to the inside of the outer clutch-half...or should I say lack of it!

I believe that would explain all your symptoms, as the cork has most probably worn well past its used-by-date.

I have come to this conclusion because of the excessive protrusion of the inner clutch cone when it is engaged, and not depressed far enough when it is dis-engaged.

Here's your pic of the excessive protrusion:

Clutch engaged....

Here's mine....
Clutch engaged....

Here's your pic of the clutch cone not depressed far enough to dis-engage:

Clutch disengaged

And here's mine...
Clutch dis-engaged....

You will need to follow my "Engine and Clutch Removal Guide" HERE and remove the cutter clutch assembly and examine the clutch cork....and replace it. You will have to remove all of the old cork carefully and all traces of the old glue...Eucalyptus oil may help with the glue removal, then you have to remove all trace of the oil....'Prepsol' (wax and grease remover) is excellent for that!

The replacement cork can be found HERE

This is the method of gluing the new cork in place and the recommended glue for the purpose...


Here is a pic of a used cork in place, with heaps of life left in it....for comparison with yours, after removal....

Good luck, and please keep the pics coming....

Hi Guys,

Well I guess I'm going to say that "2" pictures are worth even more ! Well spotted DeeJay.

I must admit that I initially thought that the cone was out too far but the the wife distracted me about going out and being rushed I overlooked it. From looking at the A~B comparison shots dramapig's clutch must make some horrific noises when activating the lever as there is probably no cork left on it at all and she's metal to metal with that amount of protrusion.

If there's one thing I've learnt and that is that when you don't have the item right in front of you to operate and look at constructively then sometimes one overlooks things that are just so plain and obvious while looking for something much more sinister and hidden.

Again well spotted DeeJay and that's why you're the "old Master" on here !

Hi BB, and Dramapig,
There is an old saying that goes something like..."At times you can't see the wood for the trees"....Don't belt yourself up too much BB, we've all done it at ODK and the best part is, this is how we learn new things....

You will often hear me say to new members..."We all like to learn new things and tinker here"...You have imparted your great Scott Bonnar knowledge, that you have gleaned from your experience with the marque, to many a 'newbie', but sometimes occasionally, it takes a fresh pair of eyes to spot the problem....

This is what ODK is all about...helping our members sort their probs....in a friendly, professional manner...You do that all the time, and is much appreciated by all concerned....

To Dramapig, let the adventure continue....

Hi Deejay & BB

Thank-you both heaps for your time and expertise. The cork makes a lot of sense; I will order some today and post pics as I go.

BB I will definitely get onto lubrication after I have sorted the clutch out.

I might take a video of what I am doing just in case. Thanks again guys

Hi Deejay, I watched your video again...very thorough

One problem, I cannot budge the captive cotter pin. It is difficult to tap as the cutter clutch is hard up against the motor. I don't want to hit it any harder as I am scared I will damage the engine shaft. I have already flattened the head of the nyloc nut.

Any suggestions?

Update...the captive cotter pin moves upward but won't drop down at all. I've disassembled the clutch and as suspected the clutch cork was destroyed. It wasn't attached and it had broken into pieces. The spring still has plenty of tension and the and the inner clutch cone looks ok, but I'll let the experts make that call. I'll post some photos later once I manage to get the main clutch body off the engine shaft. Damn that captive cotter!

Hello Dramapig, Administrator Deejay, Technician BB and others

I interrupt here because this is turning into a great topic for the "101" of SB45 primary clutch removals.
Dramapig (what a great name!), the captive cotter will not "drop down" because it can't.
It's just like the cotter on a bicycle crank. You tap the pin to "release" it.

Once 'released', you need to tap the engine side of the clutch housing to move it off the crankshaft.
In most cases it will move freely and easily. It is only then that the cotter can be removed.
It is no longer 'captive'.

All very interesting.
------------------------------------
JACK.

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.