OutdoorKing Repair Forum Forums Repairs and Maintenance Questions on Walk Behind Lawn Mower Frames Question On Scott Bonnar Cylinder Mowers Model 45 - PTO Shaft Allignment

I am new to the forum, I have been doing plenty of reading regarding the model 45. I have owned a Rover 45 from new and apart from a few little problems it has been a great mower for many years ( it was probably blow up next time I use it now).

I was reading an old thread regarding pto shaft alignment, the view was that the shaft had no real support on the engine side. I am pretty sure when I changed the engine clutch housing on my mower many years ago that the end of the shaft fitted in to the bore of the thrust bearing. I realize that the thrust bearing is pretty average but it would still help to locate the shaft. Interested to hear peoples thoughts as I am in the process of repairing a couple of old SB 45s and I am wondering what is correct, shaft in or shaft out.

Thanks

A bit more research and I think I have answered my own question.

The shaft I am referring to is the shaft that has the 12 tooth sprocket on the end. There is a discussion in the technical section about a model 45 clutch balance device where the issue of alignment is raised. I may be wrong (generally am) but I am pretty sure that the shaft is supported at the clutch end as it fits in the bore of the thrust gearing. I realise this bearing has some radial play but it still holds the shaft captive while also allowing a little movement so that minor misalignment would not be too much of a problem.

I believe that if the clutch is in good condition and adjusted correctly around 8-10 mm of the shaft will supported by the inner race of the thrust bearing.

In an attempt to try and align the engine I now do the following. Firstly I totally agree that the bearing adjacent to the sprocket should be self aligning, Prior to fitting any of the clutch components I sit the engine on the frame (engine pto shaft needs to be 3/4", 5/8" engine shafts would need a temporary 3/4" OD bush fitted) I loosely fit the engine mounting bolts and then clamp a vee block to both shafts. If the engine is happy to sit flat on the frame when the shafts are clamped in the vee block the alignment should be pretty good, I then tighten the bolts.

I fabricated a simple 90 degree jig that clamps to the frame that has screws that are adjusted until they locate on two faces of the crankcase near the mounting bolts. I then remove the engine, fit the clutch , locate the engine in the jig and hopefully it should be aligned fairly closely.

Hello Gino

Great research there. I admire that you could resolve the issue yourself
by listening to what others say in the context of your own knowledge
and experience. You clearly have mechanical aptitude.

Yep, totally agree. The shaft is clearly supported by a thrust bearing
designed for the job. The thrust bearing, itself, was chosen because it
would take some acceptable factory-set misalignment.

For it to work, it does also require a self-aligning bearing in the bearing
housing next to the frame. Any cheapening of that is a compromise.

Rover did cheapen the design. The issue, for me, is whether they compromised
the design as well. They did discard the cotter arrangement in favour of
off-the-shelf square head screws. I'm more interested to know whether your
machine has a self-aligning bearing in the side frame housing. Also, could
you also tell us whether the housing for that bearing is plastic?

It could be argued that the mysterious 'balance weight' had noting to do
with the balancing of the clutch assembly, but was some sort of micro-
balance for the motor. That's just speculation on my part.

Cheers
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JACK