503 CHT rings???

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David L. Downey

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Joined
Aug 7, 2019
Messages
147
Location
Harleysville, PA
Can someone point me to an authoritative source for how to use BR8ES plugs with CHT ring terminals on the Rotax 503 DCSI fan cooled points engine? The plug comes with a crush washer but if it is retained when using the CHT ring I would think the seal washer would be installed between the ring and head surface (ring between the plug seat land and the seal washer).
I have the current and historic user and maintenance documents but must be reading past it?
Thanks for any advice here.
 

challenger_II

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Joined
Jul 15, 2009
Messages
546
Location
Fisher County, Tx. USA
Back in the Dark Old Days, when I purchased my first two-stroke aero engine (coincidently, a 503), the rule-of-thumb from the Big Boys at the Pool Room was to remove the seal gasket when using the CHT ring.
On another, related note, some folks have had good luck replacing the 14mm ring with a ring that would fit an 8mm bolt, and placing the CHT under a head bolt close to the spark plug.
 

n3puppy

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Joined
Jun 25, 2019
Messages
259
I don't remember seeing official Rotax guidance on the crush washer BUT

The CHT sensor manufacturers typically say to remove the crush washer and the CHT ring replaces it. They like the ring in contact with the head for best temp readings.

With both the washer and CHT - the plug will sit higher in the head and could allow carbon build-up on the now exposed threads in the plug hole

BFC3BD0D-AE63-42A3-8F66-628CB2438C50.jpeg
 
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