Government durability ratings are for emission compliance only. They may offer some insight as to the overall quality (durability) of the engine but not necessarily so. At least not in a linear relationship.

Most smaller engines are splash lubricated. Some rely on a "dipper" (think of a spoon) than hangs down from the rod on a horizontal crankshaft engineand smacks into the oil laying in the botton of the crankcase. Oil splashes willy-nilly and the bearings get sprayed as does the clyinder. Some engines may have a gear driven "squirter" which is a small piston inside a tiny clyinder that sucks in then squirts out oil in the general direction of the moving parts. Ball bearings last longer with willy-nilly lubrication, plain bearings last longer with pressurized oil being fed into them. Major bearings in your car are pressure fed whereas the roller cam followers in the valve train are willy-nilly splashed.

Glow engines are 2 cycle just like most trimmer engines. The ball bearings last longer than plain bearings when lubrication is dependent upon 50 parts of gas vaporizing and leaving behind the 1 part of oil.

Why not rebuild a small engine? Doesn't take a lot of time, can be done sitting down and is more efficient than recycling in the smelter. Iron sleaved engine may just need rings and a hone. Aluminum clyinder may have to be bored oversize, with an oversized piston and now approaches the not worth doing stage.

Small trimmer engines have "chromed" clyinders. Although the coating is very thin it is very hard.

Yungman, I can tell right now what you need is a 2 cycle Lawn-boy.

Others agree?

Hi Weed Cutter
Thanks for replying. Why a 2 cycle Lawn-boy? Are they that good?
Sounds like bearing and cylinder wall make monor difference depend on the way lub method. I am sure the manufacturer choose the best way for that particular engine. I also think the manufacturer will not intensionally make the engine last not as long so they can rate it down.

I bought a Troy Bilt TB836 which is the top of their line, electric start, variable speed and rear drive mower and is very disheartening to see that it only rated for moderate durability. The engine is B & S 126T05-0475-E1 which is no cylinder lining, no bearing engine. Do you know the way this engine lub? splash or squirt? I paid $370 for the mower and I thought I got a better one. I learn about the durability rating and how to read the engine after that....too damn late. If I were to do it again, I think I will buy a Honda comercial one. Hey, I am a gagithead, I want to buy the best and do a little!!!!

Anyone know how does the goverment justify the durability rating? Only on the smog, not on how long it last. Even when I email to B & S people, they said the rating has not much relation with how long it last.

Thanks

Take care of the engine and it'll outlast the rest of the mower.

Yeah as already stated the durability ratings are an emission rating. Its the hours that a well maintained engine will go before having a need to repair or replace some components to maintain emission standards.

Think of it this way. In Japan, car engines have to be replaced with new engines after I believe it is 50,000 miles. Someone knowing the actual figure may want to jump in and correct me on mileage. But its something like that and as we know Japanese car engines will last 3 or 4 times that long. But it's an emission standard the Japanese government imposes on car owners in that country. So in a way we really have nothing to complain about reagrding the regs we have to follow. We drive far more miles in a year then the Japanese, can you imagine the cost we would have if we had to install new engines that frequently?

Hi Navada Walrus
Good hearing from you on this one. I guess emmision durability has really nothing to do with how long the engine last. Unless we "people's republic of Kalifornia" start impose smog test on lawn equipments!!!!!!!....just a joke!!!!
That is the reason why I don't quite understand the rating. I don't think any manufacturer will design engine that last 1/3 of what it can be just to save a little cost.
About the restriction in Japan. If Japan is like in Hong Kong where I came from, being big city, you don't drive long distance at all. The engine spend most of the time stuck in trafic idling. In Hong Kong, 30,000 miles car is a very old car. You think everyone else in this world is lucky like us, having open land, drive everywhere. They really stuck in one small place. I heard people in the older days in Hong Kong said that their first and second gear are all worn out and the others are still new.
Have a nice day.

You can roughly correlate a product's durability rating to price and longevity. A better built machine will cost more to build but will also withstand wear better, thus maintaining the tolerances necessary to meet emissions standards.