Small Engines (Lawn Mowers, etc.)/Craftsman Piston Rings


QUESTION: I used regular gas in my Craftsman snow blower by accident and it scored the piston and froze it up.  Got new Craftsman rings but they are slightly different sizes.  Does it matter which order they go on the re-ground piston?   Thank you for any insight you can provide!

ANSWER: Possibley.  What is the model number?  You will find the model number on a sticker, about the size of a business card.

What do you mean by re-ground piston?  Did a machine shop polish or grind the piston?  

Is the cylinder scored or scratched?


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QUESTION: The model# is 536.885214. The piston had small scratches/grooves and was polished by a machine shop. I ordered OEM rings from Sears. The Rings now slide freely in their indentions. Just not sure if the rings have a top or bottom?   Thanks

The engine model should be 143.045071 which is a Tecumseh HSK850-8335E...hang on to the Tecumseh model and spec number.

From the repair manual:

The piston and ring sets on some 840-850's are of a standard type construction. Either ring may be placed in either ring groove of the piston.

Some 840-850 models use a half keystone upper ring.  The ring groove in the piston and on the ring have a distinctive taper to them. The ring must be placed in the top ring groove with the long beveled side towards the dome of the piston as shown.

NOTE: Piston ring end gaps should be staggered upon installation.

If you copy/paste this in Google you can find the service manual:

Should be the 9th URL/link...should take you to the service manual.


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Eric A. Jones


Lawnmower Repair . Certified Master Service Technician from B&S. Have 23 years experience on B&S, Lawn Chief, Weed Eater, Echo, Peerless, Wheel Horse, Snapper, Atlas, MTD, McCulloch, Homelite and many other numerous brands. Specialize in electrical repair.


Born and raised in the midwest. Started tinkering with engines when I was about 14 on my Suzuki RM-80. I began lawn mower repair at a small hardware store. I knew absolutely nothing. I read lots of repair manuals and met an older fellow who taught me many lessons. I continued working on small engines through high school and paid my way through college working on mowers at the same hardware store. Decided to get away from the midwest and mower repair so I joined the Air Force. I repaired air traffic control electronic equipment and ended up in Hawaii where I got a part time job at Small Engine Clinic. I gained a lot of experience from the Small Engine Clinic and had a blast repairing small engines. I then took the Briggs and Stratton Master Service Technician test and earned my MST. I then traveled to Wisconsin where I attended the factory update training seminar and received formal training. Continued working on mowers part time as I completed 20 years of military. Retired from the military on a Friday and continued in the lawn and garden industry the next Monday.

MAS Aerospace Operations BA Mathematics AAS Electronic Communications AAS Electronic Technology

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