Small Engines (Lawn Mowers, etc.): older 3 hp briggs, piston check, oversized pistons

Question
excessive oil in the piston, easily pull's ,start's fairly easily, doesn't seem to have alot of compression and run's low speed w/o opening the choke or it dies, excessive carbon on the vavle faces, took the piston out, how do you tell if the ring's are bad or the piston also need's replacing, older engine, is it safer to just replace everything and not take the chance or does replacing the ring's usually take care of the oil problem, thx mjz

Answer
Hi Mark,

Piston check is done by measuring the bottom of skirt 90 degrees from piston pin hole with a micrometer.  Check the ring side clearance use a feeler gauge with new ring.  Make certain that you've removed all carbon in the piston top and ringed grooves before you measure. Look to see that there are not any scratches  or scoring from grit or dirt being sucked in mistakenly. If there are too deep marks showing then replace the piston. If the piston needs to be replaced then an oversize piston will be necessary.  Oversized pistons are stamped with an imprinted decimal size on the top of the piston.

After you do the cylinder bore diameter for the rebuild, then you can check measure the gap using a feeler gauge.

Hope this helps you out.

Howard