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Towable digger, excavator and backhoe website. Features Fleming Micron, Powerfab, Mantis, Benford, Roughneck, Gopher, Smalley, Tow-hoe, Standard Muscleman, Termite, Mitchell Cotts, Mini Gigant, Baromix, Euromach, Bronco, JPB, Digger 50, homemade and other small diggers. Links to current manufacturers such as Groupe-FCM and suppliers of plans for the Ground Hawg Homebuilt Backhoe and CDP Excavator. Includes other plant and mechanical information, Digger Bucket Page, Plant Photo Gallery, Dumper Restoration Project and useful links for Digger Spares and Repairs. Extra information and pictures to add to the site always appreciated. Also includes a section dedicated to preserving information about Johnson Machinery Limited.

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Fleming Micron Digger - changing the Honda engine

My digger came with a Honda GX140 engine. As with most Honda's (my favourite small engine) this started and ran well. At about 20 years old it was burning a small amount of oil and the thin metal casing around the flywheel was pretty rusty. A friend of a friend had bought a Honda GX160 to replace the engine on his generator. Before he had chance to fit it some little charmer pinched the generator. So I ended up buying the engine for my digger.

The GX160 is 5.5 horsepower as opposed to the original engine's 5. Apart from that the shaft and mounting bolt holes are all identical so no problems there.

The first job was to remove the old engine from the digger. To get to it easily it is best to remove the tin box that the seat is on top of. This is held on by 4 x 17mm bolts underneath the digger. With that removed, you can undo the hydraulic pipes from the pump. Then I undid the 4 bolts that hold the engine to the digger and took the engine and hydraulic pump to the garage for easy working on the bench. The digger lives in my firewood shed when not in use and this is not exactly the best place to work.

Honda engine and hydraulic pump

Here's the old engine and hydraulic pump sitting amongst the usual collection of detritus on my workbench.

Honda engine, flexible coupling and pump

The hydraulic pump is fixed to the engine with a crude box metal bell housing. There were four Allen key bolts into the standard holes on the engine. These were very rusty.

Once I had undone the four bolts, the bell housing could be removed (it has a large hole which will pass over the half of the flexible coupling which is fixed to the engine). There was no need to unbolt the hydraulic pump from the housing. It never pays to create more work than necessary. Then I just undid the grub screw which locates the engine half of the coupling on the engine shaft. I then pulled this half off with a gear puller and fitted it to the new engine with the key in the shaft.

Pulling off the flexible coupling

Once the hydraulic pump and bell housing were removed I pulled the flexible coupling off using a gear puller.

New Honda engine

Here's the new engine with the hydraulic pump mounted on.

The flexible coupling is basically two opposing sets of jaws with a star shaped piece of nylon (or rubber) sandwiched in between. These can be sourced from one or two of the suppliers on the Spares and Repairs page. If the coupling is seized onto the engine shaft they can be warmed up a bit which is usually enough to free them. If you are tempted to use a blow lamp be careful not to melt the aluminium or to blow yourself to bits as the petrol tank is only inches away. The alternative method is to wrap a rag around the coupling and carefully pour boiling water onto it. This is arguably safer as long as you don't scald yourself.

When I refitted the coupling to the new engine I put some grease on it to hopefully make sure it's easy to remove in future should the need arise.

Honda Engine, flexible coupling, hydraulic pump

When re-fitting the bell housing to the engine I used some new bolts as the original Allen key bolts were in poor condition. It's important to make sure there is clearance between the two metal parts of the the flexible coupling. Make a note of the clearance before removing the coupling from the old engine.

Honda engine, back on digger

Here's the new engine and pump back on the digger with all the hydraulic pipes reconnected

Whilst I had the hydraulic pump off the digger I could see the gears inside through the pipe unions. The pump appears to be in good order. Hopefully with the new engine there are years of reliable operation ahead!