OutdoorKing Repair Forum Forums Repairs and Maintenance Questions on Walk Behind Lawn Mower Frames Question On Scott Bonnar Cylinder Mowers Please help re scotty590

Hi can someone please help. Ive got a sb 590 diplomat which doesnt want to stop. As soon as i start the engine it wants to take off. Doesnt matter if the clutch lever is in or out. Ive tried adjusting the clutch cable but no real success.
Please help a novice.
Regards
Daniel

BTW its a 2.5hp B&S engine.

bruce and deejay are the guys on SBs, but the mower can't be driven forward unless the clutch is engaged, so it appears your clutch is not disengaging: there is no other connection between the engine and the drive chain. Have you looked at the clutch while operating the lever, to see what is happening?

daniel_l have you checked the belt to see if it is the correct one?

The belt has just been replaced. So if its wrong this could cause it to constantly drive? What could the difference in belts be?

Also another thing ive noticed is that i cant roll it backwards. It seems to lock up. It has rolled back before but now doesnt. This thing is driving me mad. It cuts terrific but is a pain in the bum.

daniel_l if it is not the correct belt then you will have these problems because the belt length is critical.

The belt part number is 3601080 according to the parts list in the parts list and manuals area of the forum.

What is the size of the belt that is on the mower?

The SB590 has a belt drive in what would be the chaincase on other SBs that I am (very vaguely) familiar with. This was a complete surprise to me, I thought they were all poor-man's ATCOs (right Darryl?) The clutch lever moves the idler at the left side, making it press against the V-belt. This tightens the belt. When the clutch lever is not being pulled, the belt should be loose enough to slip. Pulling the lever tightens the belt, making the engine pulley drive the cutter and roller pulleys. If the belt is too short, or the idler pulley is wrongly adjusted so it presses against the belt even when the lever is not being pulled, the mower will want to work: it will take off without you intending it to.
If you have just replaced the belt without adjusting the idler pulley, it sounds like the new belt is too short. If someone adjusted the idler pulley, that could just as easily be the problem. Is the idler touching the belt when the clutch lever is not being pulled?

Took it back today as it was the belt that was too short. They put a new belt on only as they dont make the exact ones this one is slighly larger. To fix this they adjust the idler pulley to take some of the slack of the belt. But still leave it so its loose enough to slip.
Thanks for the help.
regards
Daniel

daniel_l It looks like I was correct again.

Bruce, if the correct belt is no longer available there will probably be other people having this same problem. There seems to be plenty of room in the SB590 side compartment between the upper and lower pulleys, so using a slightly longer belt and having the idler adjusted to be permanently in contact with the back of the V belt shouldn't do much harm. The idler seems to consist of a sealed ballrace, so it should last many hours even running all the time (which it will be now, but wasn't intended to be). Even if the ballrace had to be replaced eventually they should be readily available (unless it is another discontinued part, like the original belt).

grumpy,

You can get after market belts for just about any machine and most of the time they can be fitted. As I posted in my first reply to daniel_l question. Did he have the correct belt fitted because common sense was part of the assessment.

When repairing equipment is not really that hard when you apply common sense and a little bit of knowledge.

The idler pulley needs to ride on the back of the belt in order to create a small loop over the pulley and when it is pushed into the belt it tensions the belt onto the pulley which then engages them all.

It is great when people post pictures here with the problem area in question, because most of the time when you see it, the diagnosis in most cases is usually fairly easy.

Thanks again grumpy for adding information to the topic because we all appreciate members like yourself helping others.

You cheeky devil!!

Hi to All,

This is great advice Bruce, as it makes it much easier to understand the prob in question

Hi I recently replaced the belt on my Scotty 590 and the belt that seemed to fit ok was an A38 Vee Belt which is readily available

Cheers Wonka

daniel_l,

If you asked what size belt I would have told you but you said that it was just replaced but you did not quote the size of the belt that was used.

If it was a mower shop that replaced it then they should have known the size in the first place but you did not quote who did the work so we can only guess who did.

As I said in my first post was is it the correct size belt.

The more information you can supply when asking questions the quicker the answers come.

Hi Bruce, I think you might be on the wrong train, mate, as the member with the belt problem was daniel_I, not Wonka....he was just advising what belt he used on his SB 590.

Thanks Darryl I have now directed to the correct person. Too many late nights I think.

No probs Bruce, I too, have had a few lately.....Party, party...