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

G'Day Guys, great forum. It's inspired my to do a hot rod makeover on my 89 model, Scott Bonnar 45.

I just layed my new turf front lawn a few weeks ago and hadn't started my mower in about 3 years......and of course it wouldn't start!!

The fuel had gone way off as I hadn't drained it, so I decided to rebuild the carby. Whilst waiting for the gaskit parts to arrive I painted the engine and associated parts, but as I pulled the clutch off, a huge chunk of crankshaft metal fell off right where the long key sits. Bummer....that was rather terminal. SO after pricing everything up, I ended up buying a brand new Briggs & Stratton 3.5hp engine for only $269.

I only had about 6 months use on the mower after having the reel and bottom blade sharpened the first time, but it had rusted a fair bit and needed redoing. I got ripped off by the local mower place last time, so I decided to strip everything off myself. THANKS FOR THOSE GREAT YOUTUBE VIDS!!

I ended up having to weld up the engine mounts as every mount hole was cracked, so I welded them up and added in some extra steel to beef it up.

Question: I noticed when I tried to pullstart the old engine with the clutch lever disengaged, that the reel cutter would also spin as if engaged. Is this normal? I can't remember.

I striped every nut and bold off the engine and got everything powerder coated. The new green is a tad BRIGHT & LOUD! I was going to get the handle bars rechromed, but fell over at the cost, so I just got them powerder coated silver.

I thought I'd have this thing back together within days of stripping it down, but now it's been almost 2 weeks and putting everything back correctly was a crazy job.

Question 2: How tight or how much movement do I need on the bolt which holds the secondary clutch together? I had to replace the cork too....and all the bearings on the mower. Also, how far should the small c-channel bar at the end of the clutch cable move to drive the engine (freeplay)?

Question 3: I don't think I have setup the clutch fork hand lever correctly? How far do you wind in the adjuster screw on the clutch fork? Seems to bind on the bolt if it's wound in too far.

The local sharpening guy wants to add one of his spec bottom blades. He says it'll cut much better.

I'll get some bling pics up over the next few days.

Hanging out to get my new front putting green looking the part!!

Hi Adrian351, and a warm welcome to the forum. It's always nice to welcome another Scott Bonnar Model 45 owner on board.
I am glad that the videos Joe Carroll (moderator and Victa guru) and I made helped you...I know Joe and I had a lot of fun making them!
Re your questions;
Q1. When the cutter clutch handle is in the disengaged position, the cylinder reel should not rotate.

Q2. Unfortunately, this subject is not covered in the owners' manual and as I have never had to remove the drum clutch, I am unable to answer that one. Scott Bonnar, to my knowledge, have never published a workshop service manual for the Model 45.
However, many of our members here have stripped their machines completely and re-assembled them successfully, and may chime in here and give you some advice.

Q3. The set-up of the cutter clutch is a different matter and in fact quite easy to do, once you set up the location of the clutch assembly on the engine PTO shaft. (ie. the distance between the crankcase of the engine and the inner clutch half) You may glean some good info from the thread HERE which addresses this in some detail.
Re: the bottom blade issue, have a good read of the thread HERE and in particular post number 15497....this mentions the fact that both the reel and bedknife are sharpened to suit one another; in other words you don't replace one without sharpening the other to suit. Plus the fact that the machinist/engineer will supply and fit a new bedknife for you when you get the reel done, if necessary.
Looking forward to seeing your pics...
Once again Adrian, to OutdoorKing.

Thanks Deejay! Those threads you posted up with the pics were great.

I also realised that my sprockets are wearing a fair bit too, but I might do those on Phase II! Just wanna get mowing at the moment.

Your clutch fork adjustment advice was perfect. I don't have the engine back on yet so I was just trying to pluck where it should go. Everytime I moved the lever to the disengaged position, it would spring back, but that was because the adjuster bolt wasn't engaging the lever shaft. All set now.

I noted that my clutch cone was protruding about 5mm from the housing, so that was good advice to pull it apart as the cork looks rather thin.

When I said the cutter was spinning when the clutch lever was disengaged, I think that must have been a lever adjustment issue, ie: the clutch was still half enganged, so now I know what to look for. I wasn't looking to see how far the cone got pushed in.

SO.....the only unknown bit now is the drum clutch adjustment. I'm picking up the engine tomorrow, so I'll ask the mower mechanics there.

As mentioned in that other thread too.....my clutch bearing feels really rough. They look a bit trickier to pull out. Do you punch them out with a screw driver etc from the inside?

Thanks again!! Adrian

Hi Adrian, yes mate, just tap it out gently from the inside....just a tip...if you have some penetrating oil, let some soak around the circumference of the bearing, just in case it has some corrosion it being metal and the clutch half alloy.
Also, make note of the way it sits in the clutch half, as you will see, the backside of the bearing has a rounded shoulder.

Thanks. I'll soak it overnight.

Well, here's some pics of the rebuild so far. It's been a ground up resto which got out of control! I'll blame you guys for that

I had to pull the engine off to weld up the cracks on the engine frame. All 4 holes had cracks, so I welded them up and also welded some extra reinforcement bars on top and underneath to stiffen things up.





Whilst I had everything stripped off the frame, I got all the big parts powdercoated. I stripped the drive drum apart and lubed up the insides and replaced the bearings too which were a bit rough.









Got to replace those horrible rusty bolts tomorrow! They are wrecking the new 2013 makeover look. I was going to get the handlebars etc chrome plates, but I fell over when I got a quote....they wanted to slug me over $300, so I got the bars powdercoated silver.




Got some cool retro Scott Bonnar decals from ebay!!

Got the clutch handle adjustment sorted. Fork nicely vertical and ready for fine tuning.





From those other threads you posted, I figured my cork clutch clutch lining was worn out, seeing that my newly painted red cone stuck out over 5mm.



All glazed up and quite thin.




New cork clutch lining ready to glue in. Just used a small tube of Selleys Kwik Grip adhesive. Same stuff I used to replace the new drum drive clutch lining. Fully set in 24hrs. It gets quite tacky quickly, but for the cone lining, you don't want to wait too long as you need to slide the cork into position. Popped the cone back in to hold it in place overnight.






Now the clutch cone sits further in with the thick new cork lining.

Pick up the new engine tomorrow!!.....and newly sharpened cylinder and bedknife. That was all powdercoated red.

along with a heap of small bits - new clutch cable, handle grips, woodruff keys.

....oh, and a new stainless steel front roller!!!

Sprockets are worn, mainly the other small ones, but I'll do those later.



Here's the drum drive clutch bolt which holts the lever on the other side for the clutch cable. This is the bolt which I wasn't sure how tight it should be, obviously real tight will hold the drive clutch on all the time, so I'll do it just loose enough not to glaze the clutch when it's stationary.

Hi Adrian, and on your ground up restoration thus far. All looking good mate...and thanks for posting the pics.
Just one question, did you paint/powdercoat the whole clutch cone? If you did, you will have to remove the paint from the inner section where it contacts the cork, to engage correctly. Can you please post a pic of just the cone?. Thanks mate.

Re-assembly Tip: Please install the complete rear and front roller assemblies, before installing the soleplate with its bedknife, as the rollers maintain frame integrity (keep everything nice and square. ;))

Thanks!

I picked up that hot tip in your youtube clutch video - NOT to paint the actual clutch cone surface. I just painted the outside of the whole body which got about the last 5mm of cone, but after fitting the new cork lining, the clutch cone now sits further in.....so you'll see in the last clutch pic above, I took a razor and got rid of all the paint on the cone.....so the whole surface is bare metal.

Thanks for the tips on assembly.....I was almost going to put the bednkife on first.....but rollers it is!!

Cheers

man. nice job

Hi Adrian, looking forward to seeing the finished pics mate, she looks a real treat!

It's ALIIIIIIIIIIIIIIIIVE!! Runs like a Rolls Royce!

I'll post up some pics from the assembly today and share a few lessons learned.

Clutch bearing removal and relacement.

Like you said, you can tap it out with a thin screwdriver from the inside (input shaft hole). This doesn't seem to be a sealed bearing, so I packed it with grease before refitting. Taps in nicely with a socket. You need to use a socket that is the same diameter as the bearing. Too small and it will cave in this bearing body.

New bling stainless front roller!





The left side of the drive drum has slotted holes in the bearing cup which allows for level adjustment of the drum so you can get it parallel with the front roller. ie: with the bolts loose, you can move it up and down as required.



What helps a LOT is to do all this refitting an on exact level surface. I just used an old bench top.

The rear drum flat, but the front roller is lifting up on the right side front. With the bolts loose on the rear left side of drum, you can lift the frame as required to get the mower level, then tighten all bolts.

Now this is where the fun begins....

I refitted the drum sprocket and the differential would not engage. ie: I'd rotate the sprocket in the forward direction and it would simply spin without driving the drum. BUGGER! It's only supposed to rotate free in the reverse direction.

Thinking cap on.....I had the whole lot stripped down last week and greased up the diff lock pins. I realised then that they are not supposed to be greased as the grease holds them in place so they can't drop under gravity and engage the drum.

SO.....after assembling everything perfect as above, I had to strip everything down again. Most annoying! But that's one lesson learned!!

There are 3 locking pins on each side which drive the left and right drums together, but they allow one drum to rotate slower around corners or free rotate backwards. The pointy end of those pins normally fall under gravity and grab one of those 6 locking tabs on that red hub. But the grease was holding them in towards the centre and they weren't engaging.



Who the hell put all that grease in there!!



Bit of dry graphite powder to the rescue! All degreased and ready to assemble....AGAIN!







Once the drums are together, these locking collars hold them together on the drive shaft. It's easiest to mount the drums by sliding them DOWN onto the VERTICAL shaft, so the pins stay in place.

New bedknife blade.







New bearings on the cutter. Freshly powder coated and sharpened. As per the video, fit the concave end of the washers towards the cutter.



New bearing end sponge fitted. I was going to fit the old one, but my local mower shop guy had one sitting on the shelf!





Refitting procedure followed as per the awesome youtube vid!!

I fitted a washer to one of the bedknife bolts, BUT, it makes the nut stick out about 2mm too far and it hits the chain. So had to remove it. Just something to check on your assembly as it's hidden behind there.



Brand new 3.5hp Briggs and Stratton engine!! Wooooohooooo!! Took a bit of massaging to get the 4 bolt holes to line up. Easy to fit the clutch first and slide the whole thing on to the clutch drive shaft.



Then to fit the new clutch cable. What a pain in the backside! I was lacking some cable length at the start and I had wongly assumed that because my mower was a bit old, that I should be using the other clutch cable mount hold on the handlebar clutch lever. But you can't fit the retaining shaft in the handle, so I made some room with a grinder!





BUT..after all that farting around, that was totally unecessary and WRONG. The correct hole was the original one on the handle.

Back to my original question in my first post regarding the drum clutch bolt adjustment......with the clutch cable fitted, I tightened the bolt just to the point of grabbing and backed it off a smidge. It's a nyloc not so will hold the adjustment.

The lever has excellent response.....not loose and rattly.

All done.....ready for a trial!

Exit the workshop!



Just gotta make sure I don't turn my back on the old girl when I leave it out the front!!....someone might take a liking to it

Thanks again deejay for you help, advice and great videos. It seriously made the whole rebuild a lot easier.

When I took my Scott Bonnar into the shop a few years ago to get sharpened, they said it requires a very high level of expertise to set these mowers up and should not be attempted at home Certainly proved them wrong!!

I had the laptop in the shed with wifi watching youtube as I went along!! Certainly a novel way to get the job done.

The new engine is a treat. Nothing like having something that starts first pull.

I'm worried about the two clutch retainer bolts that holds it onto the engine output shaft. They are exactly lined up with my head and I keep thinking they are going to fly off and take me out!! I'm gonna have to whip up a guard cover.

Thanks again!

Adrian, What a beaut!

That really came up good.. And I'm sure it will last you for ages now!

Kori

Good job Adrian, I have often thought about those locking screws myself, could cause a nasty injury if they let go. You can get the black guards which fit to the Rover 45 however not sure if they will fit the Scott Bonnar 45's. may just need to modify it a little & drill a couple of holes?

Cheers - Ross