Skip to main content
Collection, Preservation and Display of Old Lawn Mowers

Ransomes Marquis Mk4 - Backlapping tips ?

Enter a word or two to search the forum section and click the Search Forum button.

 

I'm trying to backlap the cylinder on my Marquis. I have managed to jam a tapered dowel into the central hole in the cylinder drive sprocket and with a socket hammered on to the end of this I can turn turn the cylinder. It seems to me that this would be easier if I could disconnect the drive chain as there would be less resistance. However, there is a lot of tension on the chain; it's really tight. I think that even if I was successful in getting the split link out I would never be able to reassemble the chain. There must be a way of adjusting the tension on this chain but I don't know where it is. Is it anything to do with those two bolts lurking behind the cylinder drive chain ?

Has anyone got any ideas or tips on how to do this or on backlapping this mower ?

Thanks in advance. 

Forums

hortimech Sun, 20/12/2015

Hi, if you look closely at the clutch, you will see two holes and if you turn the clutch slowly, you will see that they line up with two other holes inside the clutch. There is a specific Ransomes  tool that fits these holes, but you probably don't have it, but you should be able to use a couple of dowels instead. Fit a dowel into each hole, place a lever between the dowels and turn in an anti-clockwise direction. This will loosen the nut that holds the clutch on, once the nut is loosened, you will find that you can move the clutch about, this is how you adjust the chains.

If you cannot adjust both chains satisfactorily, so that neither is too tight or too slack, then you will probably have to replace one and/or the other.

The chain has probably become tight because the cylinder has been adjusted down as the cylinder and/or bottom blade became worn.

I would also like to point out that backlapping is a maintenance thing, it will not sharpen a blunt cylinder and/or bottom blade. If there is any trace of rounding to the blades, you can attempt to backlap until next Christmas and you will not get an edge on your blades.

 

 

 

wristpin Sun, 20/12/2015

This is the tool for slackening the clutch holding "nut" - easily made but also still available as a Ransomes part - at a price!

As Hortimech says, if your cylinder is blunt, back lapping is a waste of time. Bite the bullet and have the cylinder ground and the bottom blade refaced. For back lapping to work as a maintenance operation the cylinder blades need to be single blade relief ground so that the relief acts as a reservoir for the back lapping paste. A Marquis will cut perfectly well with a properly ground cylinder and bottom blade without the need for back lapping.

 

hortimech Mon, 21/12/2015

You don't have to relief grind the cylinder, the cylinder just has to be fairly sharp to begin with. It is the sort of thing a golf club does on a weekly basis, before the cylinder has a chance to get blunt.

 

wristpin Mon, 21/12/2015

I beg to differ regarding needing relief. If there's no relief there's nowhere to retain the grinding paste and the blades just wipe most of  it straight off which is why so many attempts at back lapping are pretty ineffective.

The following is the  relevant section from an interesting article written by the then MD of Hunter Grinders (now part of Lloyds) one of the UK's leading manufacturers of cylinder grinding equipment.

"To B or not to B (Back lap that is)? Back lapping is one of those contentious areas where some people champion its merits and some bemoan. Like spin grinding it can be a quick, albeit temporary, fix! However one point that should be made is that if you do back lap as part of your cylinder maintenance programme then your units must have a relief angle. The relief angle is essential to force the cutting paste to the cutting edge; without it you will only succeed in sharpening the back of your cylinder blade, in other words its non-cutting edge. "  

hortimech Tue, 22/12/2015

Please tell me you didn't believe everything that Eric told you, Eric Hunter was a salesman and you should never believe anything a salesman tells you, without checking it.

You do not need to relief grind most cylinders, it is only really required if the individual cylinder blades are very thick. I would also love to see you relief grind a cylinder from the early Toro single greensmower, you know, the one with an 11 blade 3 inch (approx) diameter cylinder.

The Jacobsen greensking came with the facility to backlap the units without removing them and you didn't need to relief grind them.

Hayter LT's (now Toro machines) could also be backlapped without removing the units and Hayter recommended spin grinding.

Toro's SPA greens units could only be spun ground to get the accuracy required so you could set them up correctly, these units were that finicky, special training courses had to be run for the golf club greenstaff.

 

wristpin Tue, 22/12/2015

Looks like we will have to agree to disagree , which may also be a reflection of industry disagreement on the subject.

This is what John Deere say"

John Deere recommends backlapping after spin grinding to remove burrs and rough edges
left from the spin grinding procedure. John Deere machines also have “on board backlapping”.
“This allows the technician to regularly backlap the cutting units to ‘maintain’ the cutting edges.
But to maintain cylinders with backlapping the blade must have relief. Backlapping does NOT
replace grinding and should never be used to sharpen extremely dull or out of shape cylinders,
 
At least we all seem to be in agreement that backlapping is no substitute for the correct grinding of blunt blades!

hedgelayer Wed, 23/12/2015

Many thanks gentlemen. Clearly a contentious issue ! I have only had this machine for a couple of months so I don't actually know how well it cuts. To date all I have done is clean up the blades on the cylinder and test to see if they can cut paper, which they can in the centre of the blade but not towards the edges. I would not commit to a regrind until after I have see how well they actually cut - which won't be until the spring at the earliest.

Many thanks also for the information about the clutch. I would never have guessed.

Regards

 

Jon Thu, 24/12/2015

I have backlapped several mowers successfully to the point where they will cut paper cleanly along the length when before they would not. However the cylinders were in pretty good shape with little or no deformation from hitting stones or similar. I have tried to backlap cylinders that were deformed and the results are minor improvement but not satisfactory. I would be interested to know what 'spin grinding' is? Basically I can't afford to take my cylinders to an engineer for sharpening.

wristpin Thu, 24/12/2015

Spin grinding may be done either with the cylinder still in the machine or cutter unit  - in-situ grinding - or on a "between centres" grinder. In either case the cylinder id rotated and a grinding wheel moved along it .  Modern grinders offer the facility for both   in-situ single blade (relief) grinding and spin grinding to a high degree of accuracy and cost serious money  - hence the charges for doing the job.

My 50+ year old grinder can do both spin and single blade grinding but only with the cylinder removed from the machine or cutter unit but in the right hands produces excellent results!

Guarding removed for photo!!!!

Not sure whether this will work on the forum

https://www.dropbox.com/s/59kl0yn10sgf3ra/Video.MOV?dl=0

gtc Fri, 25/12/2015

Not sure whether this will work on the forum

Works fine! Many thanks for that video clip.