Routine Decarboning of the Rotax 503

The maintenance schedule for the Rotax 503 calls for inspection of the pistons, rings, and cylinder heads at 50 hours to determine the extent of carbon build up in those areas. If excessive deposits are found, the engine is to be disassembled for cleaning. The following pages describe that procedure as experienced by a builder with some mechanical experience but who is relatively new to this engine. As with all the pages on this site, I welcome comments, corrections, opinions, and constructive criticism. I'd also like to take this opportunity to publicly express my gratitude to Tom Olenik and Bob Robertson for their generosity, advice, and the valuable feedback they have given me on this project.

For the first 50 hours of operation I was unable to locate a source for Pennzoil Air-Cooled two-cycle oil which is the factory-recommended lubricant for the Challenger engine. I used an oil marketed by a large retail chain which was described as appropriate for air-cooled engines at a 50-1 ratio and which, I had reason to believe, was a Pennzoil product marketed under their own brand name. When I performed the 50 hour inspection on my engine, however, I found significant carbon build-up. Although there was some movement in three of the rings, this movement was restricted compared to when new, and one ring showed little to no movement. The piston crown and combustion chamber were seen to have substantial deposits. This photo is taken from an article in The Experimenter which described a series of oil comparison tests done by Lockwood Aviation and Pennzoil/Quaker State. The pistons were taken from new 503's run for 280 hours with various pre-mix oils. The piston labeled 'purple,' which was from an engine burning an unspecified generic brand of oil, bears a striking resemblance to the condition of the pistons in my engine after only fifty hours of operation. Needless to say, I've found a source for the recommended oil. At the next 50 hour inspection, I'll update these pages with a comparison.


To read the entire article on the oil comparison test, click here. A link to the article is at the bottom of the page.

Here is a chart of torque values for Rotax engines. You'll need Acrobat Reader to view the document. If you don't have it, it's a free download HERE.

Additional information on this and other maintenance procedures is available in the California Power Systems catalogue or on their website.

Please read the following disclaimer before following the link below to the pages describing the procedure:

WARNING: The author of the following pages is not a professional or certified aircraft engine mechanic. The information contained herein constitutes a description of the writer's experience only and should not be construed or interpreted by the reader as instructions or guidance for the successful completion of any repair or maintenance procedure . Use of any information contained herein is at the user's own risk. This information has not been reviewed, evaluated, or approved by the manufacturer of the engine. Following any link on these pages constitutes acknowledgment of and agreement with this disclaimer.

Enough with the lawyer talk already. Show me what you did.

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