I am getting close to doing my final fall service on my HRX. I know Honda oil... = $11.70 a qt!
Side questions: What is the replacement interval of the spark plug? Do any of you just dust off / clean the air filter? I plan on putting in a new air filter at the end of the season (so I start fresh in the spring) but have "cleaned" the filter mid season.
Honda is indeed a bit spendy, no doubt. Honda says to use (any) SAE 10W-30 oil is okay. Synthetic or petroleum are fine, although Honda uses petroleum-type in the engine when it is being certified for emissions. The key factor is to change it every six months or 50 hours, whichever comes first.
The spark plug should be checked every 100 hours or each year. You can clean it and re-use if okay. At 150 hours, it should be replaced.
You can use gentle amounts of compressed air to backwash the air filter to clear it of foreign materials, dirt, dust, etc. Tap it on a hard surface to knock loose larger bits. When the filter becomes torn, worn, or shows any damage, cracks, etc., it should be replaced. The maintenance schedule says to replace at 150 hours or two years, but sooner if used in dusty or dirty environments.
Spark plug part number is 98079-55846, $2.98, set gap to 0.7~0.8mm (0.028~0.031 in.)
Air filter part number is 17211-ZL8-023, $5.66.
Hot Rod Tip: You can update any Honda GCV mower engine (HRR, HRX) to the better 2-stage air cleaner and filters used on the Honda HRC215, which uses the commercial-grade GSV160 engine. You need to two filters, and the screen grid, and the deeper air filter cover. The extra foam element acts like a pre-cleaner and can be easily cleaned and re-oiled:
Parts:
Cover, air cleaner dual: 17231-Z2B-020, $3.36
Filter, outer (foam): 17218-Z2A-000, $4.08
Grid, air cleaner: 17212-Z2A-000, $1.80
Element, air cleaner paper: 17211-ZL8-023, $5.66
The shop manual says to use regular 10W-30 engine oil on the foam element, but Honda offers a MOTUL oil just for this application. It is more sticky and water-repellant than just engine oil: 4 ounce bottle is part number 08207-MTL-100, $7.56.