Motorcycle Repair/Oil


What oil brand should we be using on our 305's?  I can't find a straight 30w that is JASOMA compatible.   I could only find Castrol Activo Semi Synthetic 10w 30 JASOMA/Motorcycle approved, are there any issues with this oil in our old bikes?  I am in a hot climate (S Florida)

David, Honda specified non-detergent oils originally, but oil quality has changed a lot since then. I have been using Honda 10-40 m/c oils and it seems to be fine. You aren't too much hotter than SoCal can be. We had a CB77 out in 105 degrees a few weeks back and it did fine. Detergent oils keep the grit in suspension, so the filter can screen it all out as it moves through the system. If you tear down an original motor, you will find lots of gunk/dirt/additives lying in the bottom of the lower engine case, mostly due to non-detergent oils being used in the past.

Keeping these bikes fine-tuned and fed premium gasoline is the best defense against premature failures and wear. Honda has 20-50 oil as well, for use in sustained heat and hard riding conditions. There are very few hard friction points inside the 305s. Just the cams/rocker arms, pistons/rings and low gear bushing for the most part. Everything else is on ball bearing, needle bearing, roller bearings, which just need nice clean oil to be happy. There really is no oil pressure to speak of in these bikes.

Bill Silver

Motorcycle Repair

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Bill Silver


Need help with vintage Hondas from the 1960s? I am an expert with 250-305cc bikes in particular and most all of the other pre-91 models, in general. I do NOT claim to have a great deal of experience on Gold Wings, Cruisers, ATC/ATVs and dirt bikes.


I have owned/ridden/maintained Honda motorcycles for 35 years. I have written five books on Honda repairs and collecting. I was a service manager for two Honda shops back in the 1980s.

VJMC (Vintage Japanese Motorcycle Club) of North America

VJMC newsletter, as editor for two years and as contributing editor currently.

3 years auto shop in high school, teacher's aide in Automotive Technology in Jr. College, Diesel mechanic course in college, self-taught mechanic and automotive writer.

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