NotTaR of small Gasoline Engines and Rotary Lawn Mowers : Should you even bother?                 
 Copyright © 1994-2007, Samuel M. Goldwasser. All Rights Reserved. Reproduction of this document in whole or in part is permitted if both of the following conditions are satisfied: 1. This notice is included in its entirety at the beginning. 2. There is no charge except to cover the costs of copying. I may be contacted via the Sci.Electronics.Repair FAQ (www.repairfaq.org) Email Links Page.

                   << Compression testing |  Index  | Special tools >>

Should you even bother?

Only you can decide if the time and effort will be worth it. If you enjoy a challenge, then engine overhaul may be for you. However, this is probably not going to be your idea of fun. Doing something like this for the first time WILL result in scraped knuckles and the liberal use of 4 letter expletives. If the mower was a Hechinger's $100 special and has seen several seasons of use, then it may be time for a new one.

If you are not the detail oriented meticulous type, you may be better off leaving this sort of overhaul to a professional or buying a new engine or mower. Most parts must go back in exactly the same orientation as they were originally - including matching of timing marks on the crankshaft and cam gears. Even the piston is not symmetrical - though this is not obvious except by taking detailed measurements. Nonetheless, it will not work well if at all, or will wear quickly if rotated 180 degrees upon reassembly.

Furthermore, once a wear pattern has developed, it is generally a good idea to replace parts in exactly the same position - the direction of the piston (wrist) pin or location of the intake and exhaust valve lifters. Violating this rule won't result in immediate failure but could lead to excessive wear and reduced life

What this means is that you cannot assume anything about the parts you remove. Even if they look identical at first glance, they may have a definite right and wrong orientation and/or may want to be replaced in exactly the same location. Even lowly head bolts may be of different lengths. Make notes and diagrams. Most of these will be pretty simple but they will save your hide in the end!

Bearing surfaces are very finely ground and polished - just dinging the crank pin journal surface against a steel part will put a nick in the relatively soft bearing which will need to be carefully removed as best you can - affecting as little else as possible - with very fine emery cloth.

In addition, if you don't like to get your hands dirty and oily, forget it. You will have disgusting black crud under any surviving fingernails for days. This is a messy operation! The outside of the engine will be coated with decayed grass clippings, dust, and dirt. The inside of the crankcase will have the remnants of old used motor oil (also a carcinogen) and the combustion chamber will be coated with filthy carbon deposits.

At the same time, cleanliness is critical when reassembling as any particles of dirt or metal will find their way between rotating parts resulting in excessive wear or worse.

Having said all that, overhauling a small engine is not like overhauling an automobile engine. In the words of a colleague: "It's just a frick'n lawn mower". What this means is that you can get away with tolerances, imperfections, and mistakes in dealing with a small engine that would be unacceptable for the health of your Chevy or Porsch.

 <<Compression testing | ToC | Special tools>>