OutdoorKing Repair Forum Forums Repairs and Maintenance Questions on Walk Behind Lawn Mower Frames Question On Scott Bonnar Cylinder Mowers SB 45 Clutch Modification and Repair

G'day,

I'm having some dramas with my clutch on my Scotty 45. It doesn't appear to be the type with the two grub screws, but it also doesn't appear to be the type with a captive cotter. I say this as the bolt hole that goes all the way through the clutch, does now expose the drive shaft of the engine which the cotter pin would line up on. Hopefully you can see this fro the pics. However I'm guessing a bit there as I'm assuming that is how the cotter pin works. Additionally, of the two bolts that came out, neither was a captive cotter (seee pics below).




Thoughts?

Salty

Your engine-side clutch-half has unfortunately been adulterated, Salty. It was once a captive-cotter type, but it has been "improved" by a previous tenant. If you remove it from the shaft and post a picture of it from in line with its axis, from the engine side, I think Deejay will explain what has happened, and discuss your options.

Hi Salty, Sorry I had to move your post, but the previous post to yours is still an on-going repair and it affects the archival value of Jeremy's thread.

Now to your prob; Grumpy is quite correct, someone has had a prob with the captive cotter in the inner clutch half and removed it....and then in error, drilled the hole right through and thought this will fix the prob. Unfortunately, it will not.
That inner clutch half has now run its race and kissed its chips; it needs to be replaced with a new one which will have the grub screws placed (one over the engine PTO key) and one 90 degrees opposed to it. Don't forget also that the cutter clutch should be in balance; otherwise vibration will cause further damage.
This is a better fixing method than the captive cotter....and will allow you to adjust the cutter clutch perfectly.

If you agree, I will step you through the procedure to remove the engine, separate the clutch halves and repair it.

Deejay,

Thanks for the advice, I knew it didn't look quite right.

I'm happy with the removal process (thanks to a good vid on youtube :)) however another question if I may:

The larger woodruff key on the Engine shaft that sits inside the clutch is not a tight fit....it sits quite loose with the recess. Is this normal?

Cheers,

Salty

Hopefully you can see what I mean by the pic below. There is probably a good 1-2mm of room in the recess.

Nice picture Salty, but can you remove the Woodruff key and take another picture from directly above, so we can see the Woodruff keyway in the shaft? If the keyway is damaged, you need a new shaft. The key needs to be a good slide-in fit, no slack at all.

Hi Salty, and I'm glad that the video that we did, helped you to remove the engine and clutch assembly successfully.
Mate, I'm sorry to be the bearer of sad tidings, but taking extra pics won't help; I can see the problem immediately, the cutter shaft and woodruff key have also kissed their chips, and need to be replaced before going any further.

To that end; I now would like to see pics of the chain case after removing the cover, and in particular the engine sprocket and the cutter sprocket (the one that attaches to the cylinder reel, where the sprocket is not covered by the primary chain. This will allow me to assess the condition of the sprockets...I suspect that there might be some secondary wear or damage there as well, because of the extra stresses and strain.

Looking forward to seeing the pics mate.

I suspected as much. Oh well, them's the breaks. Thanks for the diagnosis.

As for the sprockets, I asked the question about their viability a little while ago here: New Sprockets?

The plan is to now replace the clutch housing, 12 tooth top sprocket, and engine shaft.

Appreciate the info, thanks guys.

Salty

Hi Salty, thanks for that, and with your purchases installed, you will have a really nice machine there. Don't forget to measure the PTO shaft of your engine so as to make sure you purchase the correct size clutch half.
Happy Easter mate.

Salty has sent me a PM and requested that I post the further question and re-open the thread....
Deejay,

You mentioned in a early post in this thread that:

"Don't forget also that the cutter clutch should be in balance; otherwise vibration will cause further damage"

Could you please elaborate how to check this, and adjust if necessary?
Thanks.
What I am advising there is that any modifications to the clutch halves or attachment screws may cause a slight out of balance problem.
When you purchase the replacement clutch half, it will be fitted with the two grub screws and no hole for the captive cotter....this, when attached to its opposite half, will be in balance. I also suggest that you source three high tensile countersunk screws and three nyloc nuts to replace the attachment screws you now have...as they are too long.

Salty, if you have a piece of shaft about 9-12" long and the same diameter as the crankshaft extension (or PTO), you can slide it right through your old clutch half and rest the protruding part of the shaft on both sides on two pieces of flat steel that are exactly level. When you let go of the clutch half, it will rotate until its heaviest part is at the bottom. When it is balanced, it won't have a heaviest part, and will not rotate by itself - it will stay where you put it. You should also do this test on the new clutch half, with the other half of the clutch bolted to it. You will soon find out how well it is balanced. You'll find that the three screws holding the clutch-halves together need to be identical. You may also find that the grub screws disturb the balance just slightly, because unlike the short Allen type (hexagonal recess) grub screws, they stick out above the clutch boss. However the grub screws are close to the axis, and have less effect than those three bolts holding the clutch halves together.

It is a good idea to get into the habit of checking the balance of any largish object on your mower that rotates at full engine speed, like that clutch. A well-balanced mower is nicer to use than a rough-and-shaking one.

Hi grumpy, I think that when Salty bolts the assembly all together with the new clutch half and identical screws and nuts, that it will be reasonably well balanced....if not, there is no method of balancing it other than removing some of the cast alloy which I would not advise, as this could weaken it....I would not like to be around it if it fractured at full engine rpm, as it has no cover.

Deejay, if a new clutch-half is out of balance, it would be time to take it back to where you got it, and exchange unpleasant remarks with the supplier. However if that doesn't work (either because they are all out of balance, or because it is the other, output shaft half that is out, not the new engine shaft one), it is traditional to correct the unbalance by putting one or even two extra washers under one of the three bolts that hold the two clutch-halves together.

I suspect that the dummy bolt that replaced the captive cotter in Salty's clutch was put there in order to bring it roughly into balance.