The amount of engine hours that is too much depends on the engine type and whether it's a tractor engine, lawnmower engine etc.
For example tractor engines that are diesel are often good for 5,000 hours to 20,000 hours depending on the engine and some heavy duty truck diesel engines may last 400,000 miles to 500,000 miles.
Lawn mowers that are of lower quality may last only 450 hours to 500 hours and higher quality lawn mower engines may last 1,000 hours to 1,500 hours and any hours over these hours would be considered too much.
Anything over 1,500 hours to 2,000 hours is often considered too much for gasoline engines depending on the engine and anything over 5,000 hours to 10,000 hours for diesel engines is too much depending on the type of diesel engine and how well it is maintained.
Between 500 hours to 1,000 hours or more is considered to be a lot of hours for a small engine.
Although it can vary on the type of small engine as some commercial small engines may last longer and residential small engines often have a shorter lifespan.
Some commercial grade small engines with better build quality can last 2,000 to 3,000 or more hours.
Gas powered lawn mowers will often last for 7 to 10 years or around 1,000 hours to 2,000 hours although some lawn mowers may last longer depending on the quality of the mower and how well maintained it is.
Often 1,000 hours is considered to be a high number of hours for a residential lawn mower engine even if it's well maintained.
And some commercial lawn mowers and especially lawn mowers that have stronger engines and better construction can often go for 2,000 hours or more.
A lawn mower typically lasts 7 to 10 years when properly maintained although some lawn mowers that are not properly maintained or see a lot of use may only last 5 to 6 years and some lawn mowers can even go 15 to 20 years.