OutdoorKing Repair Forum Forums Repairs and Maintenance Questions on Walk Behind Lawn Mower Frames Question On Scott Bonnar Cylinder Mowers Scott Bonnar 45 (14") clutch repairs

Hi everyone, just signed up to this forum.

I bought this mower secondhand in 1977, the only mower I've ever had and just for home use. It got a new B&S motor in 1995.




3 years ago I had a major service done, at the time seemed worth spending money on it after so many years plus some sentimental value(quite expensive):
- sharpen and set of reel and bottom blade
- spark plug, air filter, new oil, chains adjusted
- clutch repairs...clutch cable, inner cone, key, engine shaft, thrust bush, thrust race bearing, 2 bearings, half circle cork.

Motor still starts and runs great but a couple of weeks ago I took it in to get the clutch adjusted as the reel was turning sometimes when disengaged and I seemed to be pushing the mower a bit rather than the mower driving. They adjusted it but said the clutch needs some work done on it at some time (quote was $350).
It now drives OK but when disengaged the reel still spins and the cluth assemble/shaft is making crunchy noises....fine when engaged.

I'm concerned if I don't get the repairs done I may damage the engine shaft etc. but I'm a bit over spending a lot of money on it especially after previous exercise. I'm thinking of taking it apart myself and replace damaged/worn parts, but as you can probably tell I'm not overly mechanically minded but have the time and willing to give it a go.

Is there anything in the clutch assembly not replaced last time that could be expensive or could some of those same parts need replacing again after 3 years? Any advice would be appreciated.

Regards
Garry

Clutch disengaged

Clutch engaged


Bottom plate

Hi Garry, and a warm welcome to the forum.
It's great to have another Scott Bonnar Model 45 owner on board!
Thank you for posting the pics, it makes it much easier for us to diagnose any probs you may have. I would like you to post a couple more; please remove the chain case cover and take some shots of all the sprockets especially where not covered by the chains. This will allow us to see the condition of the sprockets.

We, with your help, will have no troubles getting your machine up and running again perfectly as, thanks to your pics....I can see the clutch probs immediately.

If you are willing to have a go yourself, as you have indicated, I will step you through the procedure.
Here are the probs as I see them:

(1) The clutch cone, in the engaged position, seem to be protruding further than it should...indicating possibly that the clutch cork may be worn past its limits (easily and cheaply replaced yourself) See this pic of mine in the engaged position, you can see it doesn't poke out as far as yours....


(2) The clutch operating fork is way out of adjustment, being way over-centre towards the engine side when the clutch is disengaged. It should be almost vertical.
See the pic of mine....


This suggests that the whole clutch assembly needs to be shifted away from the engine slightly. (ie.)the inner clutch half needs to be moved along the Briggs engine shaft slightly when we have the engine off the machine.

Before we start dismantling your machine, do you have a basic toolkit (ie.) sockets, spanners, screwdrivers etc...If not, you will need to get some. We will also need a suitable box roughly about the same height as the engine deck of your 45 to sit the engine on when it is removed from the machine...like a milk crate or similar.
If you could post the pics of the chain case, I will come up with a repair schedule for you.
In the meantime, see my post here, this will explain what we will be doing....Click HERE
Once again Garry, to OutdoorKing!

Hi Deejay and thanks for the response. I did see your video on how to remove engine and dismantle the clutch, that's what inspired me to have a go myself. Although unlike you I wouldn't dare bring a lawnmower inside the house to dismantle, my wife would lynch me up. I do have good sets of spanners sockets etc and good low workbenches as my passionate hobby is woodworking.

I'll have another go at getting the chain cover off. Prior to the last major service I would frequently take the cover off to check things and put a bit of oil in. Unfortunately the mechanic decided to overtighten the 2 holding screws and I've had trouble undoing them. I'll try to get a screwdriver to fit the slot better and have a go tonight.

I have got an old working rotary mower so being without the SB for a period while fixing it won't be a problem.

Regards
Garry

Thanks Garry for the reply. Hoping you get the chain case screws out ok....Looking forward to seeing the pics.

OK..got the screws out (I did have the angle grider out at one stage) Pictures below:

Hi Garry, and thanks for posting the pics.
From what I can see, the engine shaft sprocket (that's the small one at the top of the primary chain) has extremely pointy teeth and is now unserviceable.

The cutter and secondary drive sprocket is also at the end of its working life.
The drum clutch sprocket seems to be in reasonable condition.

When the sprockets are replaced, the chains also would need replacing.
Garry, I'll bet that these are the original sprockets and chains and have done a great job for 30+ years.

I suspected that this may be the case when you said in your original post that the "clutch assembly/shaft is making crunchy noises....fine when engaged" This can be a symptom of worn sprockets, with a SB 45.

Thanks Deejay
Yes you are right, I haven't had the sprockets/chains replaced in the 35 years I have had it.

So working on rough prices for parts from this website for 2 chains, clutch cork, cutter sprocket and engine shaft sprocket...maybe $160? I'm assuming these parts are all readily available?

I guess my best plan of attack is to remove the clutch to make sure there are no extra surprises before I commit to replacing the sprockets etc.

What do you think?

Hi Garry, yes mate, I agree that would be the best plan of attack....you now know what is required for the sprockets and chains....let's proceed and remove the engine and clutch and see what is required there.

We will start a little differently than in the video (because I knew my whole clutch assy would come off in one piece).

I would like you to remove the 3 screws that hold the 2 clutch halves together first; this will allow you remove the engine with the inner clutch half still attached.... (this will also make it easier when reassembling and adjustment of the clutch)
Then proceed as in the video and remove the engine.
Please take pics as you go along....

Hi Deejay....well that was all easy and painless, maybe because it's been apart a few years ago. All looks reasonable to my untrained eye, no obvious cracks, worn metal. One thing is the bearing in the first picture...once I pulled it off the shaft, it doest spin as freely as I imagine it should and sounds a bit dry. Not sure how much clutch cork is serviceable. Please let me know what you think.

I took the liberty of adjusting the clutch operating fork to the vertical position as you indicated earlier, it seemed easier while all exposed

Regards
Garry

Hi Garry, glad it all went well for you....good work mate!
I need a good close-up of the cork lining, but from what I can see, it looks glazed....perhaps it will need replacing.
I will give you more advice tomorrow...

Thanks Deejay....While I'm not sure what the cork lining should look like, I tend to agree that it does have a glazed and hard compressed look. That might explain why the cone was protruding so much disengaged and why the fork was overadjusted towards the engine.

I think for under $10 it is probably worth replacing anyway. Is it easy to get the old one off and a new one on? I guess it's glued on right? I'll try to get one early next week.

Regards
Garry

So I bought a cone clutch cork today, only $5.50. On comparing the new one to what is currently on the housing it doesn't seem overly worn. Anyway I may as well put a new one on just in case the condition of the exising one isn't right.
'New compared with old cork'

'Ready for new cork'

'glued and clamped'

Notice in this last picture how the cone protrudes much the same as before I pulled it apart (see picture in post#1), guess that's just how it is. Maybe because it was a new cone 3 years ago and wasn't machined the same as the original housing.

The contact glue was touch dry within a couple of minutes, I suppose because it is really hot and humid here today. I found it quite difficult to insert the new cork exactly in place as it grabs really quickly and the cone shape made it awkward. I should have done a dry run first to find out the best way. Anyway it's in now and hopefully with the cone clamped in place it will take care of any slight misalignment.

Regards
Garry

Good work Garry, and at least you you now know the history of the clutch internals....and I agree, that cone will do the job and the fact that it protrudes does not indicate a worn clutch cork, as I suspected.
Re: the thrust bearing, from some research, they don't seem to be greased, however, I did push some grease through the small opening in my bearing with my thumb...and it definitely runs quieter and smoother.

Thanks Deejay,
I checked this morning and the cork glued on fine. I'll put a bit of grease on that bearing and put it back together.

As far as lateral positioning of the clutch housing on the engine shaft....now that the clutch fork assembly is in the vertical position when engaged, do I just slide the whole clutch housing along until it touches the thrust pad while disengaged and then tighten the engine shaft captive pin? Does it matter if the gap between the clutch housing and the engine body (i.e. exposed engine shaft) is significantly bigger than before. I imagine it will be after I adjusted the fork outwards. What would be the maximum gap you would have?

Hope all this makes sense.

Regards
Garry

Well she's back together now and I'm absolutely stoked. The clutch operates really smoothly, better than I can ever remember.

I'm now pretty sure it was because the clutch housing was too close to the engine and hence the fork was adjusted way too far over and so the cone wasn't clearing the cork enough and probably shining up the cork.

Is it possible that this unbalanced the shaft etc.? Just that the whole machine runs so much smoother with no vibrations whatsoever. The only thing I did to the engine was clean the air filter and clean up the spark plug a bit, but they were both quite new and in really good condition anyway. I'll probably take that metal strap off connected to the grass deflector...because the mower vibrated, the rattling of the grass deflector was really annoying.

I ran the mower over a very spongy area of the lawn and it purred through on half revs, whereas before I would have it almost full throttle and it would struggle. A few pictures below:



Deejay, I can't thank you enough. I would never have tried taking the engine off or attempt to take the clutch apart without your guidance and the confidence you gave me by making it all look simple, especially your videos. They really are not that complicated bits of machinery from what I've seen (bit overconfident maybe). There is no way I'll ever take it to a mower shop again except for maybe the engine....although maybe I could give that a crack too.

Regards
Garry

Hi Garry, and on getting all back together and running sweetly....I has been my pleasure in helping you achieve this milestone; well done mate.
Any probs in future, you now know where to post your questions
As this thread is now complete, I will now close it. If any member wishes to add to it, please PM a moderator.