Sourcing a cost effective cylinder rotor for a B20E commodore

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RatAtco
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Sourcing a cost effective cylinder rotor for a B20E commodore

Good morning all,

I recently acquired a rescue B20E, throttle arm was broken, carb was glued up with 2 stroke oil etc.

I managed to get it running, before I tried the starter (superstitious) gave myself recoil starter elbow. I've recently arrived with a mower that runs relatively well allthough tends to stall on thick grass, get clogged in the blade.

I'm a special purpose machine builder, and I've concocted a blade sharpener with a grinder mounted on a bearing slide.

I realise that my rotor is probably on the small side since the correct size drive belt has a few more teeth than the standard...

Could this loss in rotary inertia be one cause of my stalls? I have another donor B20 but the rotor is also small on this and I was wondering if could acquire a new 20" rotor and machine/ weld the appropriate shafts from the donor...

Don't fancy £300 bill for a commodore rotor off the shelf..

Any suggestions?

wristpin
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Seems a bit strange that you

Seems a bit strange that you should have two badly worn cylinders.

Post a couple of images of your cylinders. In particularly ones showing the amount of blade protruding above the supporting flanges / webs, so that we can determine just how worn they are. While you are about it let’s see the state of the bottom blade; an end on image will be useful.

 

 

RatAtco
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I think I've uploaded

I think I've uploaded correctly.

The mower is used in an orchard, I like the manoeuvrability if it given its cut width but I have to time cuts well well because of the variability of the grass growth.

When getting it going I noticed that there was a worn cap in the internal governor mechanism. I've assumed this wear can be adjusted out in the governor arm/angle setting.

Engine starts and runs well, doesn't seem to have a great deal of rev adjustment with the throttle control.. should I elongate the linkage between the governor and the throttle arm?

All the best

The beast

 

wristpin
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No sign of any images but the

No sign of any images but the word “ orchard “ in your last post may be a clue to your issue. It’s a Lawnmower !  Half an inch is the most that it can be expected to cut off  at a time comfortably .

As for messing with the governor - don't!  Unless, of course, someone has already messed with it and it now needs to be returned to the correct setting.   Not sure what cap you are referring to - again an image will assist.

Images - remember to hit the INSERT button. 

They've just appeared !!

The cylinder looks as though it has enough “ meat” on it but it is blunt and the bottom blade likewise. Power-wise, it has the Mitsubishi engine which just about had enough power for lawn mowing but not enough for rough cutting , particularly with blunt blades.

Don't take offence but it looks unloved, the wrong machine for the job and at the very least in need of professional attention.

 

hortimech
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What Wristpin said, plus it

What Wristpin said, plus it looks like it has been modified, the wrong battery is fitted (in the wrong place) and the handle has been extended with what looks like the upper handles from a rotary mower.

I do not know how long the grass that you are try to cut is, but there is a correlation between the cylinder diameter & number of cylinder blades and length of grass. The longer the grass, the less blades in a larger diameter cylinder, Lloyds Giant gangs had a 15 inch diameter, three blade cylinder and they could cut anything ;-)

Your machine undoubtedly needs professional servicing, the cutters at least.

 

RatAtco
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Thanks hortmech/wristpin,

Thanks hortmech/wristpin,

Good to know I shouldn't bother with a new cylinder. 

In answer to the wrong mower observation I have 2 other mowers: a Quacast B14 with the interchangeable cassette and a large petrol Flymo.

The commodore B20E was actually a donor mower I bought for £5 to get some parts for a £50 project B20 and it came with a long grass kit. The Electronic mower turned into the recipiant since it started  so well.

I was reluctant to break through the £100 boundary until it ran better, which it does now I've got the governor linkage sorted.

Definitely not a purist mower: battery was salvaged from a kawasaki robot, 'Sissy bar' setup because I'm taller than most, key ignition was perished and frankly pretty flimsy anyway.

In terms of sharpening I've got a rig with a bench grinder on a linear bearing, I sit and fix the mower on the rig and cylindrically grind it with the rotor running, then I back lap it against the bottom blade with cutting compound grease... Input appreciated..

That was 3 years ago, 36 months of tinkering has ensued and it seems that the resharpening might get me to the point where I can justify some proper 'love' I'm thinking candy apple red or desert rat beige. However my dti clock is languishing on my work desk and I can't grind / sharpen without it.

Hopefully back to work before the cutting season ends.

If I can find an appropriate blower maybe supercharging it might give the boost I need for 2" grass? Either that or superplus fuel?

hortimech
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When you say 'with the rotor

When you say 'with the rotor running', is this in the normal direction of rotation ? If so, then I have some bad news for you, it needs to be spun backwards, so that material is removed from the back edge of the blade before the actual cutting edge. Also, it is pointless in only grinding the cylinder, you need to reface the bottom blade as well.

Long grass to that machine is probably about one and half inches and then only on an occasional basis, you really need something with a larger cylinder, which will probably mean something commercial, Ransomes Antelope or similar.

RatAtco
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Erm started of running it

Erm started of running it forwards, probably read something online here about the grind direction so used a decent drill to drive it backwards.

Reface the bottom blade: is this the cylindrical surface that faces the outer face (ground edge)  of the cylinder blade or the leading edge that faces the uncut grass?

I guess you're not in favour of a custom paint job... Metallic oak green with cream pinstripes even?

Thanks for your time all.

hortimech
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The 'bottom blade' has

The 'bottom blade' has numerous names, but it is the blade that the cylinder cuts against and both edges need truing.

As for the colour scheme, it is your machine, so you can paint it any colour you wish, but personally, I prefer machines in the original colour ;-)

 

wristpin
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Light reading ! An extract

Light reading ! An extract from the website of Bernhard, one of the leading manufacturers of grinding equipment.

“Spin grinding puts the cutting edge on the leading (front) edge of the cylinder blade and makes the reel cylindrical and even.

Relief from friction between the bedknife and cylinder is also essential. A "no-contact" set up gives relief from this friction, whereas a relief grind (or "blade thinning") removes metal from the back of the cylinder blade so there is less metal to come into contact with the bedknife, also reducing friction.”

Basically by reducing the area of contact between the moving and fixed blades your machine will cut cleaner and make better use of the limited power available from that little Mitsubishi engine.