OutdoorKing Repair Forum Forums Repairs and Maintenance Questions on Walk Behind Lawn Mower Frames Question On Scott Bonnar Cylinder Mowers SB45 won't drive

Hi,

I have just finished restoring my sb45 17" and it won't drive. I removed the rear drum from the chassis but did not pull it apart. The cork on the friction plate is good. I have tried adjusting the clutch but when I have the clutch too loose it does not drive and when it is adjusted enough to gain friction it stalls the engine. before I restored the mower it was driving fine.

any suggestions out there?

cheers

also just to add the mower will free wheel forward but not backwards. the drum locks up when I pull it backwards

I'd say your main cutter chain is way to tight after you adjusted your reel downwards.

Cheers,
BB.

thanks BB do you have any guide as too how tight/loose it should be? I have loosened the chain right off and doesn't seam to have fixed it.

Is the chain between the land roll clutch and the cutter tight as well or loose ? meanwhile also check the short chain behind the land roll clutch feeding the rear roller.



Cheers,
BB.

i think the small chain may be tight... so should all the chains be relatively loose? the bolt that goes through the land roll clutch to the clutch cable with he nyloc nut, how tight is that usually?

cheers

I would adjust that small drive chain so that it has the tight tension removed from it and thus a small amount of play in it and then see how it goes.

Now to re-tension that chain is rather critical as there are two bolts to loosen to slide the the land roll clutch assembly downwards, but take note that the bottom bolt also allows lateral movement of the slide assembly that way both land roll chains can be adjusted in one action. How I do it is not to loosen those two bolts much at all thus you can use a drift and lightly tap the slide downwards but only a millimetre at a time. Don't loosen it so that it drops down by itself, that's the trick to doing this operation without frustration.

Cheers,
BB.

Ok I have checked all chain tensions and we're all backed off and are no longer tight. I attempted to adjust the clutch again and still have no drive whatsoever. I decided to check the pawls in the rear roller and everything in there seams fine.. im at a complete loss now

I'm gonna sound petty here but have you removed the chain case and had the machine running to watch the chains actually turn ?

Cheers,
BB.

Yes the chains turn expect the small rear drum chain obviously otherwise it would drive. Whilst I was attempting to adjust the clutch I noticed that the large outside sprocket that the clutch cork runs on was getting hot due to the amount of friction on it but it still won't drive the bloody thing!

Well that all sounds good.

Now I need to know when you pull the clutch lever does that small chain turn the drum sprocket and if it does and the roller doesn't turn then you've lost the woodruff key that locks that small sprocket to the shaft.

Cheers,
BB.

No the chain does not turn when clutch lever is pulled in

Then your problem is either you have no cork on the land roll clutch sprocket which will give slippage or you land roll is poorly adjusted (loose) and applying no pressure on the pressure plate which drives the chain to the roller.

Cheers,
BB.

Update..

I have replaced the clutch cork with a brand new one, checked all chain tensions again and have adjust the land roll. Still does not drive. The clutch is definitely adjusted correctly so that when lever is depressed there is no pressure on the inner sprocket and when it is applied there is definite pressure on the sprocket and the engine begins to load up and does not drive.

I did note in one of my earlier posts that the mower does not freewheel backwards, is that normal?

Cheers

Hello coxman82

The mower should freewheel backwards when the clutch trigger released.
I suggest a simple test - given what you have said.

Remove the final drive chain.
With hand on landroll sprocket do the following.
The sprocket should turn freely clockwise (and you should be
able to hear the 6 pawls 'ticking' in their housings.

The sprocket should lock anti-clockwise, signifying the engagement
of the pawls for driving the landroll forward.

Also, the rear rollers should be free to turn in any direction
when the engine is stopped and the trigger is free.

Your initial post said the engine was stalling on trigger engagement.
I suspect a seized landroll or pawl system. This would be unusual.

Hope this helps.
----------------------
Jack

Hi Coxman,Maybe your chains were to tight at first causing the locking.When you dismantled rear roller to check pawls did you make sure each section of roller was in correct position on reassembly i:e pawls must be facing forward in the drive position

I think you would only get then wrong way around if you removed the pawl holders and then re installed them backwards