A plain-English guide from Saber Manufacturing. This is a summary, not a replacement for the official document. Always work from the latest revision on Lycoming’s website.
What is SI 1098Q?
Service Instruction 1098 is Lycoming’s reference for propeller flange bushing location, meaning which drive bushings (the lugs pressed into the crankshaft flange) go in which holes. Revision Q is dated April 2020 and replaced revision P. It applies to all certified Lycoming direct-drive engines, and Lycoming lists compliance as at the owner’s discretion.
Why it matters
On many Lycoming flanges, the bushings aren’t all the same size, and they have to be in specific positions so the propeller indexes (clocks) correctly on the crankshaft. A bushing in the wrong spot can mean a prop that won’t seat properly or sits at the wrong position relative to the crank. If you’re replacing bushings, swapping props, or adding an extension, this is the document that tells you what belongs where.
What’s inside
- Bushing location tables by engine model, including flange thickness, flange type and which figure to use
- Flange diagrams showing each bushing position
- Bushing part numbers and dimensions (outside diameter and height) so you can identify what you have
- A measurement checklist to record your flange and bushing measurements
- References to related Lycoming documents for re-indexed bushings and flange markings
How to use it
- Find your exact engine model (from the data plate) in the tables.
- Measure your bolt circle to confirm which flange type you have. A 4-3/4″ bolt circle indicates Lycoming’s Type 2 flange.
- Measure and record your flange thickness and bushing sizes on the checklist.
- Match your bushings and their locations against the tables and figures for your model.
- When in doubt, stop and ask an A&P, Lycoming technical support, or us.
How it relates to Saber parts
Our prop extensions reproduce the engine’s flange pattern and drive lugs on the propeller end. That’s why we ask for your engine model and propeller with every extension order, so we can set up the bolt pattern and lugs correctly for your combination. Flange thickness also affects your prop bolt length. Our prop bolt calculator includes standard and heavy-duty Lycoming flanges.
Questions about your setup? Call or text (817) 326-6293 or request a quote.