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Discussion Starter #1
Hey, guys. The rebirth of the 82 CB450SC is going well and I had a question. I came across a company who manufactures synthetic motor oil and I needed to find out if there are any 5W oil viscosities which will suit the Nighthawk? The manual says 10W40, but I'm not sure there were a lot of 5W oils around, that long ago. Does anyone have experience with other weight of oils in these bikes? Thank you very much.
 

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My question to you is, why do you want to change the oil viscosity? Factory recommended 10w40 oil is readily available. Are you hoping for faster revs or better fuel economy from a lighter oil? These are high-revving flat-tappet motors that will need a thicker oil to protect fast moving parts. A lighter viscosity oil brings the risk of engine damage from oil that could be too fluid and might not maintain pressure on critical areas like main bearings and camshaft.
Compare with the current 2020 models of Honda motorcycles, owners manuals here, which specify 10w30 and 10w40 oils. See Honda Oils & Chemicals which lists HP4, HP4S (synthetic) and HP4M (mineral).
 

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Discussion Starter #3
Hey, Scramblr. Thanks for responding. I was playing with the idea of using a corn based synthetic oil I've run into through work. The oil seems to be much less likely to break down and cover the engine components with sludge. Of course, sometimes that sludge can be useful to protect engine parts from wear... I spoke with the manufacturer and they had mentioned that none of their oils were certified for motorcycle engines, but I am from the "more information is always better" school and wanted to talk to y'all, since there is tons of experience here. It sounds like I'm best off going with old school 10w40. Thank you for your help.
 

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Discussion Starter #5
Yeah. I had thought about the wet clutch. Thanks for mentioning that part. I'll read those guides and see what they suggest.
 

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If you're still looking, any oil with a top grade of 40-50w and meets JASO MA (or later MA2, MB), which is the wet sump clutch part. The lower "Winter" end all depends on what temps you'll start the bike. Shell Rotella T3/4/5 are all popular because of the low cost and JASO rating, they one I use is 15w-40, which is fine as I don't start it around Zero F.
 

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Discussion Starter #7
If you're still looking, any oil with a top grade of 40-50w and meets JASO MA (or later MA2, MB), which is the wet sump clutch part. The lower "Winter" end all depends on what temps you'll start the bike. Shell Rotella T3/4/5 are all popular because of the low cost and JASO rating, they one I use is 15w-40, which is fine as I don't start it around Zero F.
Thank you, Kmarsh.

The oils I am looking at are 5W, which would not be suitable for the wet clutch, I don't think. Thanks for your explanation. That helped a lot.

D
 

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I run Rotella T6 5-40 in my CB350's, CB175, BMW RT1150. It is a full synthetic diesel oil.
Oil at start up either being pumped quickly or having stayed on the parts when not running is critical to engine longevity.

The W stands for Winter tested and goes beyond the pour point of the oil.

Given the operating temperature of an engine it is always a cold initial start even if you are living in a hot climate.
 

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Discussion Starter #9
And I'm not gonna be in a hot climate. I'm going to be taking the bike to MI. Thank you for your input. Diesel oil isn't something I thought about.
 
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