OutdoorKing Repair Forum Forums Repairs and Maintenance Questions on Walk Behind Lawn Mower Frames Question On Scott Bonnar Cylinder Mowers Height Range for a SB 45

Hi Guys,

I wanted to see what the typical mowing height range is for the Scott Bonnar 45 - I've downloaded the manual - but aside from how to adjust the height, cant seem to find the actual range...

Cheers

Jeff

Hi Jeff, and a warm welcome to the forum.
It's always great to have another Scott Bonnar owner onboard.

Re your question, I can't answer that....with my Model 45 I just set it to the height that I wanted for my lawn ( I have kikuyu) and locked it up at that and have never changed it.....It all depends on the front roller which travels in an arc...you can lower it to the extent that the bedknife blade will almost touch the ground, which is not good, to the other extreme where it is at an incorrect angle for cutting.
It all depends on your personal preference I guess.
Once again Jeff,

Thanks Darryl,

Looks like the good ol' trial and more trial. The previous owner setup the reel and bed knife for me when I picked the mower up, but I'm thinking it might be a little tight as it materially slows the engine when I engage the clutch. Obviously I'm still coming to terms with the feel of the throttle etc but once I've got it to a good (reasonably high) rev and warmed up, to my mind engaging the clutch shouldn't stall the mower.. So some study for me to do on the forums I think...

Thanks again for the warm welcome, this seems like an incredible resource and inspired me to venture down the SB track vs getting a 'normal' mower...

Cheers

Jeff

Jeff, with the engine not running (that is extemely important, for your safety) and the clutch disengaged, just turn the reel with your fingers and see how easily it turns. If you flip it with your fingers, it should continue for at least half a turn. If it doesn't, either the reel bearings have failed or the reel is contacting the bedknife. In either case, stop using it immediately and correct the bedknife clearance or replace the bearings, whichever is the problem.

Hi again Jeff, grumpy is spot on there, if the reel spins freely and is not actually touching the bedknife (there is approx 1/1000" clearance) there could be a bearing prob, but I tend to believe through your input that is an adjustment issue.

If this is the case and the previous owner has continually adjusted the reel/bedknife clearances incorrectly, the reel and the bedknife could be "out of true" due to wear.
This causes extra strain on the drive train as well.
The remedy, if this is the case, is to have the reel and bedknife professionally reground and replacing the bearings (as they are not expensive) and after re-installation, adjust it correctly.

We can step you through the process if you require any assistance.
Could you please post some pics of your machine, and especially the reel and bedknife area, so as we can see the condition of both.

Righto, applying Grumpy's 'spin to win' test, it is definitely contacting the bed knife. I'll get some close up shots tomorrow and post them. One other thing it was doing in my quick experimental mow(tm) was the ignition seemed to randomly cut out then it would either die or pull itself together again. Let's save that for once we've got the reel/bed knife issue resolved (as it may be (as you say Darryl) just the strain on the drive train caused by reel/bed knife)...

Cheers Guys (and thanks!)

Jeff

Hi Jeff, I thought that might be the prob...Looking forward to seeing the pics

The cyclic engine speed variation sounds like it may be hunting, which is usually caused by lean mixture. Of course it also may be that there is an electrical fault in the ignition circuit. Engines seldom actually stop from hunting. Anyway, when you are ready to address that problem, we can walk you through some diagnostic steps and talk about how to put it right. It isn't likely to be anything significant.

OK - here are the pics of the BedKnife and blade...

After tinkering today I think the issue may be the throttle cable linkage - there seems to be quite a bit of play in it (when I move the throttle handle it doesn't seem to move the throttle linkage by the full range of movement).

Looking at the blade and knife contact - it is definitely contacting 'too much' is my guess..

Any who - feedback welcomed

Jeff

If the reel is touching the bedknife, it needs to be adjusted immediately. There are a couple of SB threads here that will tell you how to do that.

The Briggs and Stratton engine has a governor, so there is no throttle control that the operator handles. The control you have adjusts the engine's speed setting, then the governor adjusts the throttle to maintain that speed, regardless of load (unless you get to maximum throttle and that isn't enough to pull the load you've imposed on it). You will notice that when you turn the mower upward on a slope, you can hear the exhaust get louder without the engine speed changing.

You need to ensure that the speed control covers the full range of the governor lever that it connects to at the engine-end of the cable, on top of the carburetor. If it does not, you may not be getting full engine speed from the governor. There should be a little tin-pot clamp that holds the bottom end of the cable outer stationary. It is held to the cooling air cowl with an even more tin-pot self-tapper. Often the self-tapper self-transports itself out of the hole and onto the ground, leaving the cable outer loose, so it slides back and forth when you adjust the speed control. Check for this. If the clamp is missing, you need to get or make one - it's a sixpenny part. If the self-tapper has stripped the thread in the air cowl, just use a bigger self-tapper, and don't over-tighten it like the last guy did.

Hi Jeff,
Looking at the reel itself, I doubt that it has ever been sharpened in its life.
The same could be said of the bottom blade, I guess..
A good spin-grind of the reel and a grind and lap of the knife blade could do wonders for the cut....makes it easier to adjust as well, as everything is "true".
The cylinder reel, having constant contact with the bedknife, would have caused un-even wear of both over time....
If you plan to adjust it, please read my sticky on Scott Bonnar routine maintenance, I have shown the spanner I have modified to make the task easier. You may consider making one yourself.

Awesome, thanks guys, I think i'll get the reel and blade professionally sharpened. Is there a 'best' place to do that in Sydney ? I may also get them to check governor connection as part of an overall 'first professional' service which wil at least give novice me a 'known good' state to work from...

I will make some inquiries first thing this morning for you and will post the results...

Hi hakkonslash, I have some info for you:
These guys have been recommended by OutdoorKing.
J & C Mowers
214 15th Avenue
West Hoxton 2171
Telephone: (02) 98260188
Please let us know how you get on.

Legend, thanks will do....

Jeff

Hi Deejay, not sure if this is the correct topic to ask but will ask anyway as I am sure its relative.
Appears depending on what you read or who you ask there are differing opinions/ advice on how to adjust the reel properly. My question is should the reel actually touch the bedknife or should there be a gap between the reel & bedknife. I know with my set up I find it difficult to cut paper the entire length of the blades unless the reel ever so slightly comes into contact with the bedknife.
What do you suggest?
Cheers Ross

Hi rossf, in my opinion, there should be no contact between the cylinder reel and the bedknife. The clearance that we are discussing here is .001 of an inch...so it is minute, but it doesn't contact.... This is the reason we discuss replacing the reel bearings after sharpening to keep everything running "true".

Here is some interesting info for you to read....

Myth: You must have contact between cylinder and bedknife.

Fact: �You do not need contact between the reel and bedknife to cut turf grass. Contact between the reel and bedknife will generate heat which will have many effects on not only the turf grass, but also on the traction unit. The heat generated between the reel and bedknife will tinge the leaf blade. Also that heat can cause the bedknife to expand which will tighten the cutting unit up even more. The tighter the reel - bedknife contact, the more strain this puts on the traction unit which can cause hydraulic hose failure and premature failure of the hydraulic system�.

Contact between cylinder and bedknife causes drag requiring greater effort to turn the reel and in turn this greater effort has an adverse effect on drivelines and engines. This drag also leads to rapid wear and loss of sharp edges, as well as a poor quality of cut. With contact you have the undesirable �scissor� action instead of the desired �scything� action. It is the scissor action which damages the turf plant and can prolong the healing process.

Myth: New bedknives are �true� and don�t require grinding.

Fact: �New bedknives are certainly not true coming from the factory. Every bedknife that gets installed on a bed bar needs to be ground properly in order to achieve a consistent quality of cut. The bedknife is the single most important factor in achieving a great quality of cut. The bedknife�s job is to position the grass before the reel blade cuts it. Depending on where the position is will depend on how clean and consistent your turfs after cut appearance will look.

Bedknives will take the shape of the existing bed bar once tightened. By grinding the bed knife properly it will give you a smooth surface that you will then align to a reel that has been ground to a true cylinder. Once this is complete you will have 2 perfectly aligned surfaces that can achieve the quality of cut that everyone is looking for. It is very important that the bed knife is ground to its proper angle (manufacturer�s recommendations) in order to maintain high quality turf grass.

Hoping this information helps clear up any ambiguity.

Ross, if you need contact at one or more points to achieve a perfect, full length cut of a sheet of paper, either your bedknife is not precisely straight or your reel is not precisely cylindrical, along its full length. If the problem is very slight, it can probably be cured by back-lapping rather than a full resharpen, but I personally do not approve of backlapping to deal with a problem of more than a few ten-thousandths of an inch. However we have some greenkeepers here who disagree with me quite vehemently, so I won't claim that I'm right.

Hi grumpy, there appears to be different schools of thought on backlapping between grinds...I am in agreement with you...

Most greenkeepers I know have professional machines that are hydraulically driven and have a 'reverse' feature that send the reel spinning backwards at a given speed.
They use 120 grit emery and oil paste to achieve the desired result and judicious use of the 'bedknife buddy'
They have explained that is just for 'touch-up' only for (as you have said) very small tolerances.

Deejay, the reason I don't like the practice of backlapping is that it removes metal from both the reel and the bedknife without checking which one was wrong. It is therefore "unstable" in terms of the straightness of the line produced. It is just as likely to make the straight component wavy, as it is to make the wavy one straight: all it achieves is to make them match each other. So long as the amount of metal removed is minuscule, it doesn't really matter provided you have both components professionally ground straight from time to time. However if you backlap repeatedly without ever truing up the components, you will probably eventually have big enough waves in both parts to require a greater amount of metal to be removed when you eventually admit defeat and have the parts spin-ground. The cost of new reels being what it is, this can be an expensive mistake to make.

Realistically the amount home mowers are used may not be sufficient for the odd backlap to shorten the life of the reel and bedknife to any important degree. I think the main problem home reel mowers face is occasionally mowing a bolt, rather than becoming wavy over the course of say 20 successive backlaps. To regrind a bolt-bitten reel uses up an awful lot of reel-meat.