I would be concerned that your cylinder is worn out, there was one of this little motors that was notorious for that, but do not remember which one.

Link to Dongya

Rings are broken in with running on 2X the normal oil mixture…

http://www.richardsoutboardtools.com

I have an 18 Johnson that had (actually still HAS) worn cylinders. New, standard rings still had way to much end gap. I happened on to some .020″ over-size rings. I figured it was worth a try; so I spent a little time with a file and made them fit the worn cylinder properly, making sure the ends didn’t actual touch at the bottom of the stroke. It now runs like the wind, with very good compression, power and no unusual noises that I can hear……Maybe something similar can be done with a little engine?

Long live American manufacturing!

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Keep in mind that pistons rings need to seal in two places. The cylinder wall is the obvious place, but they also need to seal against the bottom of the ring land. Be sure the ring lands are free of carbon and corrosion. Don’t use anything sharp to clean the lands, scratches and gouges are to be avoided.

I’ve taken an old ring and sanded the top and bottom surfaces with 220 grit wet and dry paper on a surface plate to get them smooth. Then loaded up a piston groove with polishing compound. With that done, load the piston and ring into its cylinder. Move the piston up and down in the bore while twisting the piston back and forth. This does a pretty good job of polishing the lands, but you have to thoroughly clean the piston lands and cylinder when you’re done.

T

Did you mean 1.5hp mate, or is this engine actually .5hp? I am guessing you are dealing with one of the 68-70 versions of this little OMC engine.
If so, these engines are pretty simple and reliable, they run pretty well also for being just a single cylinder. But, when they are mechanically “worn out”, they exhibit some common symptoms. They are hard to start, have a very poor idle, and a lack of WOT power output. Unlike many OMC outboards, these little engines are not very forgiving when it comes to a worn cylinder or piston skirt. I don’t know why, but have experienced enough of them with these symptoms, and wasted too many hours trying to “tune up” or rebuilding carburetors trying to overcome a worn out powerhead.
I don’t understand what you mean by “…a smaller free gap as the new rings”…. I do think that ring design changed over the years of this powerhead, so newer rings might have different end gap specs than the original specs. You mention low compression, what readings are you getting? Did the engine run OK before you tore it down, or is the engine new to you and you just went ahead with rebuilding without running it?
In any event, if the powerhead is apart, I would spend the time measuring the piston skirt and cylinder wall very carefully….New rings might raise compression readings, but they won’t compensate for a loss of primary compression due to worn piston skirt/cylinder wall…..

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How to choose the right wear ring for your application

Author admin When it comes to choosing the right wear ring, the devil is in the details. Slot design, fixing groove depth and width, and material all play an important role in the performance and lifetime of the component. In this blog post, we'll fill you in on what you should consider when selecting the right wear ring for your application.

Mechanical requirements for wear rings: pressure, speed and lubrication

The most important factor in the selection of wear rings is the pressure (force per area), which acts on the rings in the application. But frequency and speed of movement also play a major role. The type of lubrication and the coefficient of friction should be taken into account too. But why are these values so important? Wear rings that are exposed to high pressure should be made of the most resistant material possible. Self-lubricating fiber-reinforced plastics or steels are commonly used here; however, they have the disadvantage of being heavier and requiring constant lubrication. Speed of movement also plays a role. Depending on the material used, if the product of speed and pressure is too great, the resulting frictional heat cannot be sufficiently dissipated without additional lubrication. The type of lubrication depends on application requirements and the technical characteristics of the wear rings in question. Wear rings made of plastic or plastic fabric are often self-lubricating. Solid lubricants such as PTFE or molybdenum sulphide (MoS2) minimize coefficients of friction and protect the rod or cylinder from wear.

Wear ring shape and dimensions

Wear rings can be mounted in two ways. They can either be fitted on shafts or rods or installed as guides in cylinders. This is why guide rings are slotted -- to provide the necessary clamping force and flexibility. Wear rings also serve as a sealing function or are designed to let lubricating or hydraulic oil through (depending on the shape of the slot). There are also angled and straight slots or form-fitting variants with a Z or tooth profile. Wear rings made of plastic offer the advantage of less complex shaping since plastics can be processed and machined relatively easily and cost-effectively.

Material variety for wear rings

The world of plastics has an especially wide range of materials. Not all of them are suitable for wear rings though. Additives are also required to specifically optimize the material properties for use in wear rings. In addition to improved properties such as elasticity, coefficients of friction, and mechanical stability, the materials differ primarily in their temperature resistance, thermal expansion, and chemical resistance. The properties mentioned above, mechanical strength and elasticity, maximum PV values, and thermal properties can be compared especially well by means of data sheets. But what do they say about component durability and service life? Here the comparison is often difficult. Design programs and formulas, like our plastic bearing service life calculator, can help here. For assistance choosing the right high-performance plastic wear ring for your application, contact us here or call us at (800) 521-. You can also learn more about our maintenance-free iglide bearing materials here.