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1960's Honda G40 170cc Engine #5380907 03/20/20 06:04 AM
Joined: Mar 2017
Posts: 476
Bailes1992 Offline OP
OP Offline
Joined: Mar 2017
Posts: 476
Trying to build myself a petrol powered air compressor as cheap as I can.

I picked up a very old generator yesterday for £30. It was fully operational, although I probably wouldn't have wanted to use it. LOL

The engine is a Honda G40, I've seen it start and run, it ran surprisingly well. The person I bought it off recently found it clearing out some storage containers belonging to his Father who died several years ago. Apparently he topped up the fuel tank, pulled the cord and it fired into life.

There is a tap that comes off the fuel tank which is leaking a small amount of fuel and the boot and HT lead going to the spark plug is cracked and fatigued. I'd also like to re-string the pull cord as the existing item is badly worn and frayed.

I'm struggling to find a workshop manual or replacement parts. The Honda G42 seems to be based heavily on the G40, I suspect it was an emissions update. Are parts interchangeable?

I will probably be looking to quieten the exhaust down somewhat. Are small engine exhaust flanges usually the same? The current exhaust has a small mount of rot on the bottom.

My plan is to run a centrifugal clutch on the back of this with a V-Belt running a compressor pump around 10-15cfm. I will then control the engine speed by grafting on a compressor throttle control onto the governor. I.e. at 9-10bar the engine will be at idle and the clutch open, at 8bar I'd want the clutch starting to close and drive the compressor and by 6bar I'd expect the engine to be at max speed.

And obviously... why we are all here... oil! My plan is to run a 15w40 A3/B4 oil in this and change every 100 hours or so. The oil I drained out last night was a little sludgey, thick and some shiny filings. I expect it's been in there for 10-20 years so it's no surprise really. Anyone have any other suggestions for oils in this? Obviously i would love to drop some Valvoline Blue Restore into it but £150 for 3.78litres of oil is just unjustifiable.


19 Volvo V40 D3 - 19 Jeep Renegade eTorq - 03 Ford Mondeo 3.0 V6 - 96 LR Defender 90 300TDi
Castrol Edge 5w30 LL
Valvoline Maxlife ATF
Fuchs Sintofluid 75w80
Fuchs Sintopoid 75w90
Re: 1960's Honda G40 170cc Engine [Re: Bailes1992] #5381432 03/20/20 04:47 PM
Joined: Aug 2003
Posts: 12,444
JTK Offline
Joined: Aug 2003
Posts: 12,444
Very cool! I've only see a handfull of Honda flat-head OPE engines.

2019 Nissan Pathfinder SV
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