Replacement Time for New Rotax Spark Plugs

According to the Rotax 912ULS Line Maintenance Manual (Edition 04 / July 01, 2021), specifically in Section 05–20–00, Page 10 (available at this link: https://www.rotax-owner.com/pdf/MML_912-Series_Ed4-Rev1.pdf 

The spark plugs should be replaced in the following circumstances:

• If leaded fuel is used for more than 30% of the engine's operation, replacement is required after 200 hours.

Additionally, it is recommended to perform the following maintenance tasks:

• Every 100 hours (or the first 25 hours on a new engine), remove all spark plugs and inspect them for defects such as deposits or melting. If any defects are found, the spark plugs should be replaced.

It is worth noting that the manual does not provide instructions for cleaning the spark plugs. For inspection instructions, please refer to LMM Section 12–20–00, Page 57.

The electrode gap specifications are as follows:

• New: 0.8 - 0.9 mm (0.031 - 0.035 in)
• Wear limit: 1.1 mm (0.043 in)

Furthermore, the information contained in the Line Maintenance Manual supersedes the information provided in the following documents: SI-912 i-013, SI-912-027, and SI-914-028, which were released on 2017-03-01.

NOTE: All work has to be performed in accordance with the relevant Maintenance Manual.

Subjective opinion:

Your plugs look okay for continued use.

Cleaning: I have never had access to one, however I think  a sand/bead  blasting cabinet, would likely give the best result, followed by using a solvent (eg carburettor cleaner) and a wire brush. I don't clean my plugs (don't use leaded fuel) just replace at 200 hrs. 

Is there a benefit to using the Rotax plug at $20 versus an NGK plug at $7?

In essence, the issue boils down to NGK's unwillingness to allow their plugs to be utilized in aircraft engines, which compelled Rotax to cease their sales and provision of NGK plugs with their engines. As a result, Rotax had to pursue an alternative path by introducing its own branded spark plugs to avoid encountering a similar situation in the future. Due to the relatively low demand for these plugs, Rotax has been left with little choice but to set higher prices. It is worth noting that NGK spark plugs had been used in Rotax engines since the early 80s, and they would likely have continued to do so if NGK had not intervened.

Additionally, it is worth mentioning that the NGK plug caps are not compatible with the new style spark plugs. To use the new style ROTAX spark plugs, it is necessary to switch to the corresponding new style plug caps. This is an important consideration for anyone using or planning to use the new spark plugs in their Rotax engines.

Furthermore, this issue extends beyond just spark plugs and encompasses other branded components used in Rotax engines. Carburetors, specifically those from BING, are also a subject of discussion regarding the rising prices of parts. Rotax not only had to develop its own brand of carburetors but the entire industry itself is transitioning away from carburetors, resulting in lower production volumes and increased prices for components. This trend has contributed to the challenges faced by Rotax and the overall pricing situation in the market.

Look at the MML the replacement for the double electrod spark is normally every 400h and half if you use 100LL you just need to clean them by soda blaster. Whil do you use this ? It’s bad for the engine and your bank account so…