OutdoorKing Repair Forum Forums Repairs and Maintenance Questions on Walk Behind Lawn Mower Frames Question On Scott Bonnar Cylinder Mowers SB Model 45 Engine & Clutch Removal Guide

Hi to All,
Whilst carrying out some routine maintenance recently, I discovered the captive cotter pin (clamping pin), that secures the inner cutter clutch half to the free end of the engine crank-shaft, was protruding from its captive position by almost 1/2" (12.5mm).

Alarmed that it might leave the cutter clutch completely at engine high speed (3600 RPM) and injuring me (a captive cotter with washer and nut attached striking me in the groin at speed would be extremely painful, to say the least ) or damage the machine, an investigation needed to be carried out to ascertain the cause.

This means removing the engine and cutter clutch from the chassis. I spoke to Joe Carroll and we decided to do another SB video of the removal process, so that our members can see how relatively easy it is to accomplish and so that SB owners can see the internals of the cutter clutch assembly.

I will post some still pics tomorrow of what we found when the cutter clutch was disassembled.
Many thanks again Joe!


[video][/video]

Hi to All,
Here are some still pics of what we found;

This is the inside of the inner clutch half....It is a little hard to see, but the innermost side of the key-way is slightly flared.

Below is the 1 1/2" x 3/16" engine shaft key....you can see the damage to the very tip.

Below is the captive cotter pin (crank pin)... You can easily see the damage to the right hand end....this allowed it to protrude from the inner clutch half...which alerted me to the problem...

Below is one of the outer clutch half showing the cork clutch lining....all good here.

Below is one of the clutch cone with the return spring installed in what would be the normal disengaged position.
Below is one of the Honda crankshaft free end....thankfully no damage here....

Finally, this one is the clutch cone in the 'engaged' position viewed from inside the clutch...

Thanks for looking,

Yes great Pics Deejay
Can I ask what is the best glue to use for cork lining Im just about to do both the engine clutch and drive clutch on my mower

Hi Jason, here is the method one of our members Steve (deviosi) uses and is the best glue for the purpose on both clutch corks....Click HERE
Please let us know how it goes.

Hi to All,
Here are some pics of the new parts...
The new inner cutter clutch half....inside view, below


Below is the outside view of the new inner cutter clutch half; showing the orientation of the grub screw (tapped hole) with the key-way.


Below is the outside view of the new inner cutter clutch half; showing the orientation of the second grub screw (tapped hole) at 90degrees to the key-way.

Below is the cutter clutch thrust bearing.If you look into the small circumferential slit, it is possible to see a double row of ball bearings.

Below are the new end caps, Honda engine shaft key and cutter clutch thrust bearing.

Below is the inner clutch half primed ready for painting after a trial fit for shaft and clutch half alignment checks...All good.

Below, just painted in "Delicious Red"....now leave to dry for 24 hours.

All good to go back together soon a paint hardens...will post a pic or two on completion.

Hi to All, happy to report that all went well with the re-installation....the clutch was much easier to adjust with the grub-screws rather than the captive cotter (clamping pin) and the spacer washers are no longer required.
Here it is, in its new clutch colour scheme, all back together and complete.

That's looking good, Deejay: it is now a better design. Can you let us know whether there is any reduction in vibration when you mow with it? I know the vibration was low anyway, I just thought it might improve from Briggs-like to Honda-like, if that damaged bore in the clutch-half was making the clutch run out of true.

Hi grumpy and Dave,
Grumpy, I will post once I get it out on the lawn and give it a try...I assume it will be much better...especially with a well greased thrust bearing and better mounting of the inner clutch half...Unfortunately, it is raining here today, like cats and dogs...
Dave, thanks for the kind comments.

Hi to All,
Been raining on and off... however, it fined up today so finally got the Scotty out and gave it a run....absolutely fabulous, no vibration...in fact better that ever. The clutch engages smoothly and dis-engages without a hitch. I am very happy with the result.

Hi to All,
Re: the new front roller end-caps, I drilled a hole through the end of the cap to allow oiling of the shaft where most of the wear would occur...I had done this some years ago to the original caps and very minimal shaft wear has occurred. All the wear and slop seemed to be in the end-cap itself. The front roller is rolling freely and will do its job without any slackness at the end-caps.
Cheap solution to a common problem. All good now.