OutdoorKing Repair Forum Forums Repairs and Maintenance Questions on Walk Behind Lawn Mower Frames Question On Scott Bonnar Cylinder Mowers Grinding noise after reassembly

Heyas,

Just rebuilt the engine on my SB 45 17" on the weekend.

The woodruff key on the drive shaft (not the output shaft on the engine) had broken at some point long in the past and had badly flogged out the grove it sits in on the shaft.

We fabricated a new key and built the keyway back up with a mig and ground it back into shape.

Since reassembling everything, when pulling the clutch lever on the bars to engage forward drive, there is a moment grind and clunk as the mower starts moving forward.

Is this just fine tuning needed in terms of the clutch housing's positing on the drive shaft or something else?

The mower actually cuts really well and the blades hum nicely...it is just this noise as you move of each time from a standing start.

Ben.

There is a possibility that when you built up and filed the shaft, you ended up with it running eccentrically. I suggest you check for runout.

I have resolved the issue! The cause was a combination of two problems...

The cork clutch lining for the 'cone' (in the flywheel on the output shaft) was totally shagged - nearly as thin as paper. Took a whole 5mins to replace it.

The other thing I noticed when putting the engine back on after replacing the clutch lining was that, with the engine bolts partially in, the engine could be twisted in posistion ~5-10mm. This in turn affected the alignment of the output and drive shafts. By leaving the engine bolts loose and doing up the clutch housing fully, the shaft alignment was assured and it in turn determined the pisitioning of the engine and then the bolts could be tightened.

End result - everything runs beautifully now.


Ben.

Hi morphias, great to see that you got a good result and your machine should give you hours of mowing pleasure.
As this is all complete, I'll close the thread.

Glad you sorted it out morphias. I've had that problem with veteran cars that had huge cone clutches and shaft-driven gearboxes: it was necessary to shim all of four engine mounts in the vertical direction, and move the engine sideways both front and back, using a dial indicator between the flywheel and the gearbox input shaft, to get the alignment right. With those cars, once you get them aligned, you usually dowel them in position and stamp the shim stacks.