Ransomes Marquis 4A Crank Diameter

Unless things have changed, there isn't an engine that will directly replace the sloper. It uses different mount points, so you will have to drill and tap your mowers deck. As you are aware the sloper has a taper crank (which doesn't have the same taper as a generator engine), so you will have to make an adaptor (or find someone to make it for you) between the standard 3/4 inch diameter crankshaft most engines have and the inside of the clutch flywheel. Finally, you will have to obtain a different throttle cable (usually the piano wire type) and fit it to your handles (usually by drilling the handle).

The other option would be to find a flywheel from one of the later Marquis machine fitted with a B&S engine.

Or in other words, I have been there, done that ;-)

When we replacing slopers, the Honda GX120 was a good engine.

After saying all that, do you still want to replace your sloper engine ?

Hortimech has just about said it all : the only thing that I would add is that most modern engines, including the Honda tended to be unhappy ticking over low enough to disengage a sloper centrifugal clutch. When Ransomes switched to the Briggs they introduced stronger clutch springs to allow the clutch remain disengaged at the engine rpm that that would allow it to recover from tickover and not bog down when the throttle was opened. As far as I know, the stronger springs are still available.

PS. Melbourne Oz or Derbyshire?

Re the question of what engine will fit your mower why not get hold of a Sloper engine from a scrap machine that should be a straightforward swap.

Thanks for the replies guys.

Melbourne, Australia. So it's pretty difficult to source parts for this machine. It's the workhorse so I wanted a nice new engine that would run perfectly all the time. It starts okay, but the engine has a very low idle and surges. When I start moving it tends to die out. It's also fairly loud as the muffler has not aged well.

During the 70s & 80s, I used to re-engine these quite frequently using Honda engines, but you can use any engine, provided (as Wristpin pointed out) it will tick over very slowly without stalling when the throttle is opened and you can make an adapter between the crank and Ransomes flywheel. The adapter (which our local Honda dealer supplied) was machined from a piece of round bar, bored out to suit the crankshaft (usually 3/4 inch diameter), internally slotted for the keyway and drilled (above the keyway) and tapped for a securing grubscrew, it was then machined with a taper to match the flywheel, but the taper must not be level with (or protrude from) the inside of the flywheel. This is because of something I missed, the end of the crank must be tapped for a retaining bolt. To assemble the flywheel to the crank, slide the adaptor (with key) onto the crank, apply loctite (or similar) to the taper, place flywheel onto taper and secure with a bolt and thick washer, At this point the flywheel should not move, now fit and tighten the grubscrew into the threaded hole in the apaptor above the key.

I hope you can understand all that, if not just ask.

Sounds as though the fuel/air mix is a bit weak. If you've got the usual Amal 379 carb, raising the needle in the throttle slide should sort it . Providing, of course, that you don't have any manifold leaks. 

https://www.dropbox.com/s/gp20v5w5nkh26h6/Amal%20379%20parts%20and%20ad…

Hey mate,

Not too sure how I will be able to manufacture that piece. By any chance would you have a spare or know where I could potentially purchase one of these adapters. I really just want a reliable machine that parts are readily available and works every time. Cheers

Plenty of  Marquises in regular use with their original F12 Slopers . Properly set up they are perfectly useable and reliable. For extra reliability, do away with the contact breaker points by fitting an electronic trigger module.

Yeah I completely get that, however economically it just doesn't make sense for me. My motor also needs new lines,starter and muffler. By the time I source and pay for shipping to Australia, I could already end up with a new Loncin engine. If it made financial sense, I wouldve just restored it. cheers

All I can suggest is to find someone with a lathe and milling machine and take the Marquis and new engine to them, Explain what is required, a good engineer should understand what is required and be capable of making an adaptor for you. It looks like the Loncin G120F would be a good candidate