HP vs Cu-In Question

[StarTech]

This is just question out curiosity. The customer has complained about it, it just me and what I am accustom to.

I have a Yard Machines mower in the shop that simply seems to be way under powered. It has Briggs 21B series on it. If I understand the decoding correct that makes it a 21 cu in engine. It rated at 13.5 Gross HP. To me this seem very over rated when compared to the 280000 series with 28 cu-in engine. Am I just thinking wrong or there is it sales play with the numbers?

When I get deck belt tight enough prevent slippage then whenever I engage the deck I have almost no power with heavy vibrations from the engine until blades come to speed.

Just some enlightenment on this.

[bgsengine]

It rated at 13.5 Gross HP.

http://www.briggsandstratton.com/us/en/ ... que-rating


As to your question, it may very well be under-powered equipment - is the engine original to the equipment spec? Is everything in proper operating condition ? correct original blades? (heavier blades make for greater load) all pulleys and belts in excellent , free running condition? Could be engine needs a little tune-up , maybe a slightly sheared key (timing) , maybe the spark plug, maybe just the fuel itself.. maybe engine is a little worn out .. or a combination of any or all of those factors and others..

You don't provide enough info for a diagnostic.

CI no longer has that much of a bearing on the rated HP of an engine. A 20 HP single cylinder may have less power than an 18HP Twin.. then it could be a carburetor or governor droop issue.. (governor spring original, new?)

[KE4AVB]

Star meant to say the customer hasn't complained about the problem. He actually has the mower over at my shop so we could do some tech training.

I can see why twin will have more power and torque as they have a power stroke on every rev vs a single cylinder. I have seen the same engines down to the type number be rated at different HP which can be a little confusing.

Everything original except I have change the deck belt and the spark plug (known good plug) since the last time was in the shop in 2011. The mower well taken care of; looks like a new one. Under power issue is same as it was the last time. Personally I think that it is under power issue too when compare to my personal Bolens with the same chassis design of it is using 15.5 hp 28C series on it and cuts just about everything thrown at it; of course, it is rate 2 more HP.

The customer's mower is a Yard Machines 13AC762F052 with 38" deck. Engine is a Briggs 21B807-0453-B2 2009 model. Engine has steel key that is not sheared (thought of that). No carburetor issues other than it was loose on the intake when came in. Engine does have some wear (cylinder still has some the honing marks) but well with specs. Changed head gasket due possible oil disappearance related issue plus it was only way I could get a good look at the cylinder. When I was checking the carburetor notice a little extra oil in the breather vent tube. I know the head design is a known issue on these engines. Head is not warped checked straight edge while I was checking the cylinder.