OutdoorKing Repair Forum Forums Repairs and Maintenance Questions on Walk Behind Lawn Mower Frames Question On Scott Bonnar Cylinder Mowers SB Drive Assembly

I'm working my way through restoration of an old SB.
How do I remove the drive assembly from the crankshaft? The attached pic shows a locking nut that is now loose.
On later SB's it looks like they have a cotter pin but this is either screwed or pressed on.

Thanks
Ian

I haven't see one like that before, but I agree it seems to be screwed on. The locknut would have no purpose if it were pressed on.

it looks to me as if you need to unscrew the locknut until it contacts the shoulder on the crankshaft, so you can use a spanner on the nut to hold the crankshaft while you screw off the clutch. However I can't be certain, so I suggest you proceed reasonably gently. There does not seem to be rust on the crankshaft thread, so hopefully the clutch will just unscrew from it easily.

Hi Jimmer, and a warm welcome to the forum. It's great to have another Scott Bonnar owner on board.

Firstly, it would help if we had the Model number/ Serial number of the machine, I suspect it may be a Model 33, 14" cut.
Seeing as you have separated the cutter clutch half, what I would do is remove the throttle assembly from the handle, undo the four bolts that attach the engine to the motor deck, and slide the engine off the clutch shaft, with the existing clutch half in place. You could then inspect the inside of this clutch half, to see if there is a circlip or some other method that is retaining this half in place.
Please let us know how you get on.
Once again,

It's a model 33 serial# 10819 17". I've disassembled the whole machine and newer pic's are attached.

Looking from the inside, it would appear the assembly is on a keyway so I don't think it will unscrew. But from the back it looks like it's screwed on???

After loosening the locknut and jamming the magneto from turning, I gave them clutch a good firm twist (probably harder than I should have) but it wouldn't budge.

Thanks for the forum and your help.




Cheers
Ian

The whole thing is unfamiliar - I had no idea Briggs and Stratton offered a threaded crankshaft as an option. I suppose it is possible that the purpose of the nut is to locate the clutch axially (keep it from moving toward the engine). You might try holding the flywheel so it can't rotate and tightening the nut against the clutch: that might push it off the crankshaft. It might be a sort of built-in puller.

Thanks Grumpy, it's a kirby engine. I don't think that will work as the nut was already very tight.

I wondered if the key could be tapped through to the nut so the clutch could be spun off... something else to try.

I thought spinning it off was the first thing you tried?

I should have noticed the red and silver model identification plate, which was characteristic of Tecumseh/Kirby-Lauson.

I thought you would have spied the Kirby-Lauson immediately, grumpy...seeing as you love them so much!

Jimmer, the method of removal is easy; just unscrew that nut as far as it will go...(ie.)towards the engine so that it is loose; grab yourself a three leg gear puller and carefully pull the clutch half off the engine shaft...be careful not to lose the key.
Please let us know how you get on.

If the clutch is just tight on the crankshaft, and the nut was done up really tight against the clutch, the clutch may be very tight on the crankshaft rather than slightly tight. You may find you need such a serious puller that you won't want to buy it just for this one job. You may prefer to take the engine to the local garage and have the mechanic pull it off for you.

The end of the crankshaft does not have a center-drill impression, and most pullers have a point on the pulling screw which requires this impression. If you do this job yourself, put a small piece of aluminium in the recess first, so you don't damage the point on your puller. There is an interesting mark on the end of the crankshaft as if somebody has done this before.

Grumpy, the nut that was done up tight against the clutch half, according to advice I have received, is part of the locking system as you have intimated. Once undone the clutch half should (and I stress should) come off with the puller fairly easily.

But, using Murphy's Law, I agree with you, a trip to the local mechanic is the way to go, as it could be very well seized on the engine shaft and a bugger to get off...and the mechanic will have the tools and know-how to get it off successfully without damaging it, hopefully.

Got it! As you thought, it was a press fit with the lock nut to secure it.

I didn't have a puller but I managed to jig something up with a lathe faceplate, a few clamps and an old bike axle.

Thanks for your help.

I'll post some pics of the finished Scotty when she's done

Cheers
Ian

Glad it worked out, Jimmer. I don't think you could have achieved much force that way, due to the strength limitations of the G clamps, so it must have been at most a very light press fit as Deejay indicated. It looks to me as if that threaded part was not part of the crankshaft, but a tapered thread on a sleeve which was locked onto the crankshaft by the nut. Hence tightening the nut against the clutch pulled the tapered sleeve through the tapered bore of the clutch and locked it to the shaft. If I'm right there would not have been a key in the tapered sleeve - the longitudinal slot would have been there to allow the sleeve to contract when it was pulled through. The right way to get the clutch off would be to loosen the nut, then give the clutch a smack with a mallet, toward the engine/nut, so it moved down the taper and released itself from the crankshaft. This would be easily done without any tools other than a spanner and a mallet.