How long will a brand new lawnmower engine run without oil?

I guess you put the oil in the right tank., had you put it in the fuel tank you would have noticed the smoke as the oil burned. Now it is not unknown for lawnmowers to be manufactured with faults, even the odd Rolls Royce had from new faults. Tell the shop to either replace the mower or have it sent back to the manufacturer for inspection. The shop most likely never ran the mower so cannot possibly know if it was ok when they sold it to you. They are incorrectly surmising that it was manufactured correctly. That is a decision for the manufacturer and the manufacturer only.

Jjf

The only way to prove that there was oil in your engine would be to tear down the engine. It is possible that when you overflowed the oil filler, you didn't get enough oil into the engine. I have had bad experiences with lawn mower shops who try to blame your abuse of the equipment so that it isn't a warranty issue. They will make more money from you than the manufacturer.

I think you must have had some oil in the engine if it ran for 40 minutes. You should try using a wire or thin wood stick to measure the level of the oil if it doesn't show on the dip stick. Think like a lawyer - you have to prove to the repair shop that there is some oil in the engine before you take it home.

If there was no oil in the engine I would expect serious engine failure in the first hour or less which is what you seem to have got. Engines don't like to run without lubrication especially those like air cooled lawn mower engines.

So which is it? if you put oil in it there isn't a problem if you didn't then you broke it as simple as that.

You can tell if there is oil in the engine by looking at the dip stick.

There are usually big warning labels on the lawn mower saying put oil in before use.

Well you couldn't possibly lose all of that oil without it making a total oily mess all over your lawn. Please don't think I'm insulting your intelligence but did you put the oil in the oil tank? That seems to be the only way you could put oil in, only to find that there isn't any AND there's no trace of it on the grass.

And 'Yes' the engine will definitely seize up if you run it with no oil.

It seems as though the engine seized. This means the metal parts of the engine were damaged enough by a lack of lubrication to create a condition that prevents the motor (pistons, crankshaft, camshaft) from turning. At least have someone (a friend/coworker) who is familiar with the operating principals of an internal combustion motor evaluate your motor's status, if you don't know anyone like that, then you are stuck having a mechanic do this, which will cost money.

There is no way a brand new lawn mower would be sold with no oil in the engine. If you buy a new car do you have to fill with oil before you drive it????

your mower will run with-out oil as for the shaft turning it will if its a riding style mower as the blades are belt driven if its a push type you could still have damage bad not as bad if blade still turns but might still have scored cylinder walls not a cheap repair.. also you may have used oil but wrong type that too can cause damage