Old petrol engine spares (for Honda G40 general purpose motor)

[profp]

I want to rejuvenate a piece of equipment (a small tractor) which is based on a Honda G40 four-stroke. Honda ceased manufacture in 1969, and I'm struggling to find anywhere that sells parts - I thought the folk here might well have similar experiences and be able to point me in the right direction. The engine runs - very noisily - but lacks power. I'm after at least new points (and plug, which is trivial), as well as ideally a replacement air intake and exhaust -- it seems a shame to be considering a replacement without at least trying to perk it up (or am I most likely wasting my time? It seems to have a good reputation for reliability). All suggestions gratefully received...

[danny stardust]

At 1969, that is an old engine. It may well be that the spark plug, points, and condenser are pretty standard across a range of Honda engines. I presume you have enquired at various garden machinery sales and repair shops. Possibly cross referencing or superseding the part numbers will produce compatible parts.
The lack of performance may well be down to the damaged or corroded exhaust and intake system. The pressure pulses caused by the engine running are dampened down by them, and if missing or compromised, this will have an affect on the engine running.

[Ivan]

I'd use a performance car air filter  - very cheap on ebay. and for my old and noisy petrol concrete mixer, I used a Kawasaki ZX6R standard motorbike exhaust, to which I welded up an adaptor to go around the old exhaust outlet pipe. This had a double advantage 1)it made it quieter, not only because the exhaust was a lot bigger and more sound-deadening, but because it discharged above the height of people, straight up, so most of the sound went upwards rather than all over. 2)It was a lot less smelly. In normal operation, I'd end up breathing fumes as I shovelled into the mixer, but with the extended exhaust, fumes were discharged above me rather than under my nose.

[camillitech]

Hi Profp,

if it's starting easy enough and running the points and condenser may well be OK. I'm not familiar with the G40 but have had quite a few of the later G125s and G200s on diving compressors etc and I think they're pretty similar apart from electronic ignition. If the noise is not just the exhaust and is a mechanical noise then it's probably shot as they have no bearings as such on the con rod and just rely on a splash feed via a little prong on the big end cap. Still, it would be worth removing the cylinder head and having a look at the valves and head gasket as they are prone to blowing and making a noise, being a side valve it's pretty straight forward and the valves may well benefit from a lap. Not sure if you can adjust them on the G40 but you can't on the later models, so basically you throw the engine away when it's done 

Having said that, they do just keep going and going and are probably the best wee stationary petrol engine on the market.

Good luck, Paul

[profp]

Thanks for the informed comments, Danny - very helpful.

I'd use a performance car air filter  - very cheap on ebay. and for my old and noisy petrol concrete mixer, I used a Kawasaki ZX6R standard motorbike exhaust, to which I welded up an adaptor to go around the old exhaust outlet pipe.

Thanks Ivan - I don't have welding equipment (or experience!), but I expect I could find a fabricators locally who might oblige. Definitely worth pursuing. I'd like to avoid cutting up the body work if I can, but it should be workable.

if it's starting easy enough and running the points and condenser may well be OK.

Hi Paul! It starts brilliantly - but tends to run out of puff when going up hill. It also has a tendency to stall when up to temperature/hot (after 10-15mins of labour)

I'm not familiar with the G40 but have had quite a few of the later G125s and G200s on diving compressors etc and I think they're pretty similar apart from electronic ignition.

Yes, the internets seem to agree! It may be worth a punt on some G125/200 spares to see if they fit

If the noise is not just the exhaust and is a mechanical noise then it's probably shot as they have no bearings as such on the con rod and just rely on a splash feed via a little prong on the big end cap. Still, it would be worth removing the cylinder head and having a look at the valves and head gasket as they are prone to blowing and making a noise, being a side valve it's pretty straight forward and the valves may well benefit from a lap. Not sure if you can adjust them on the G40 but you can't on the later models, so basically you throw the engine away when it's done 

It's hard to say (I'm deaf). I'm told that in addition to being noisy (and the noise may just be down to poor exhaust & poor mounting - it's mounted on two wooden blocks onto the metal chassis!) there is also a 'hissing' noise.

Having said that, they do just keep going and going and are probably the best wee stationary petrol engine on the market.

If I can get it going properly, I will!