Is there such a thing as a lawnmower, or indeed any internal combustion engine, that runs on a mixture of oil and petrol?

My landlady swears blind that the mower in our garage needs said mixture of fuel and lubricant, but I’m slightly more sceptical.

Yes. Old skool two strokes. there is no sump and no oil in the engine – the oil is suspended in the fuel and lubes the main bearings in a mist. chainsaws and the like as well.

http://en.wikipedia.org/wiki/Two-stroke#Lubrication

Cheers TJ. This is a brand spanking new one though, so perhaps she has got the wrong end of the stick.

Could still be a simple two stroke. They are still made especially for mowers and chainsaws. It will probably ( but not always) say “petroil mix 50:1 or something on the fuel cap.

Basic two strokes will require a oil/petrol mixture.

Just like my old lovely Vespas and Lambretta.

Cheers TJ. This is a brand spanking new one though

RTFM then dumbass.

just bought a petrol strimmer last week, that runs two stroke at a 40:1 mix.

Modern 4strokes can use oil in another section.

2 Strokes need the combo. But I haven’t seen 2 Strokes for years.

It’s interesting how the 2 stroke works – I believe it was invented after the 4 stroke, and initially as a diesel engine… the oil in the fuel is required as the crankcase is used to force the mixture into the cylinder, so there can be no sump oil lubrication for the main bearings. Some 2 strokes use direct oil injection instead.

Cheers all. Especially Kingtut, you little ray of sunshine. 😛

I was disappointed to find this wasn’t about insane lawnmowers.
So here’s one for you….

Lots of current modern small engined thingys use a 2-stroke with a pre-mix (i.e. DIY) fuel system. Generators, pressure washers, strimmers, hedge trimmers, and indeed lawnmowers.

Run them on petrol without the oil, and you’ll only do it once. Run a 4-stroke on oily petrol, and it will smoke a bit and run crap, but it’ll be OK afterwards.

Samuri, that’s off topic. It’s a 4 stroke!

I’ve got a brand new petrol hedge trimmer and a brush cutter, both of which are 2 stroke and require mixes of 25:1 and 50:1. My 10 year old mower is also 2 stroke and requires 50:1. There’s nothing odd about it. Most small petrol powered garden equipment requires a mixture. Dads sit on top has a fancy 4 stroke and electric start but that’s a bloody garden tractor.

As dave_aber says above, DO NOT RUN A 2 STROKE WITHOUT OIL! You’ll seize the engine which will be either an expensive repair or a new engine.

This reminds me of a friend from school who rode a borrowed 2 stroke scooter to go on a trip which resulted in an accident and serious permanent injuries…

As written by someone else:

It was a Saturday in July, the weather was very hot and dry and Steve had been invited to join several of his friends on a run down to Brighton. I think most of his friends were on Scooters and, one friend had recently brought a second hand Vespa px200 and, this was the Scooter that had been lent to Steve for the ride to Brighton.

During the ride, the Scooter’s engine seized causing the rear wheel to lock up and swing violently from side to side until control was lost and throwing Steve into the road. The vehicle, which was following Steve, a car, braked immediately pulling up quickly, but from behind the car emerged a motorcycle. The motor cycle, a Suzuki GSX 600R, it is assumed to avoid the braking car, veered to the right and overtook the car, rode towards Steve who was positioned in the path of the motorcycle. The motorcycle made contact with Steve’s head and, the rider was thrown into the road also.

What caused the engine to seize?

I think most Vespa scooter engines are of Two-stroke configuration, which mean they rely on an oil/fuel mix ratio for lubrication of moving engine parts and don’t have an independent oil sump to draw oil from for lubrication. If the ratio is incorrect, for example insufficient oil to fuel, then those moving Engine parts will be deficient in lubricating oil deposits. Together with an incorrect oil/fuel mixture and a hot day, the potential for an engine seizure is possible!

Two stroke refers to the fact that it takes 2 strokes of the piston to complete one full ‘cycle’. It has no valves but relies on ports which are effectively slots cut in the side of cylinder, which get opened and sealed off as the piston passes

A 4 stroke takes 4 strokes of the piston. Suck. Squeeze. Bang. Blow. They have valves which control the inlet of fuel and removal of fumes. The valves are opearted by the engine by a camshaft, camchain or pushrod etc etc. Most (if not all) 4 strokes are now overhead valves (OHV) but in the old days were side valves.

…sorry wnet off on one. I like little engines me!

I know naff all about engines so this is all very useful stuff.

Samuri, funnily enough I was just reading the Guy Martin interview in Dirt this morning, where he was enthusing about lawnmower racing. Apparently some of those things will do 60 mph. 😯

Is there a generic weight or type of oil, or is it a case of RTFM again?

I thought 2 strokes had been banned from sale in new machines by EU legislation because they are too noisy and too polluting. I have a 2 stroke brushcutter and have noticed a thin film of oil on the pond every time I use it in the vicinity

2 strokes are still on sale all over the show even in new items, AFAIK there is no legislation against them in small applications. My R/C boat runs on one too 😀
Oil mix is critical.

There are no 2 stroke mowers sold, at least in B&Q, as they are all 4 stroke. Only two strokes you can get are petrol strimmers and chainsaws, but that might not have enough power for you.