Synthetic Oil in my '81 cycle
 

So I got some Mobile 1 0w30 full synthetic oil for our trucks and was wondering if I can use the same stuff in my '81 honda cm400e. The manually suggests 10w30 as long as the ambient temperature is below 90 degrees F, it's air cooled. It's only that hot a couple days a year and I only ride it for short distances (10 miles between cooldowns) anyway, so I'm cool with that. The oil says it meets and exceeds all requirements for 10w30 so I should be good right? Does anyone on here have experience with this?

Another stupid question, I didn't see in the manual anywhere where it mentioned tranmission fluid. Is the transmission just cooled by the enging oil in the motor?

Lots of bikes share the oil between the engine and transmission. In fact you have to be a little careful if you have a wet clutch, a buddy of mine put some fancy oil in his magna and the clutch started slipping.

As long as the oil does not say energy conserving on the ratings label it can be used. Energy conserving oil will not work well with the clutches.

To be safe i would make sure you get a motorcycle specific oil. They typically have different additives to help with the wet clutch, and the heat issue with air cooled bikes. I wouldn't use normal car oil. Amsoil makes motorcycle specific synthetic oil that is very good( i use it in my scooters) and i'm sure other companies make it as well. Just get an oil that says motorcycle 4-stroke synthetic and you will be good.

you will destroy your clutch unless you use an oil that is wet clutch compatible, I've changed a number of motorcycle clutches for this reason this mistake will cost you about $100 in parts and about 2 hours of your time.
I've had great luck with amsoil synthetic in my bikes, gained 1mph top speed in my honda cb100 when I switched (judged with a digital speedometer).

Like coyote said, you don't want anything that says "energy conserving" or that has friction modifiers in it.

You don't have to pass your wallet through your nose for "special " motorcycle oil, which is probably plain oil without friction additives in it and the word "motorcycle" printed on the side.

This guy uses Mobil 1 red cap and Rotella:
Honda Motorcycle - Anyone using full synthetic oil in their Goldwing

I have used mobil 1 20w50 non energy conserving synthetic in all my bikes always. Over 40k miles without ever having clutch problems :) If you have your manuals for the bike they all pretty much say the same thing. Use their brand or an equivalent non energy conserving 20w50 but they don't say you have to use a motorcycle specific oil since they are normally the same as regular oil just more expensive.

I dunno, i've been told motorcycle oil has special additives to help with the wet clutch( you may say it's bs) but normal car oil has additives to stay cleaner and reduce wear(you don't seem to question "special car oil"). If you thought there was no difference in any oil besides bottle why aren't u using cheapy non-detergent oil?(yes it will run on it, but how well and for how long?) Which by the way, my bike manual says in an emergency you can use non detergent oil, but it should be swichted asap. I dunno, i think if the manual says to use motorcycle oil, there is probably a reason, because air cooled wet-clutch compact motorcycle engines are not aircooled large displacement fuel-injected computer controlled car engines(i know some are, but normally they aren't.) so it only makes sense they need a different kind of oil. Imho oil additives that you can buy are "snake oil" and that's the reason manufacturers do not recommend them. If motorcycle oil wasn't different then why would they recommend it?

I dunno, I'm just skeptical of all the lubrication offerings. I run total crud in my engines without fear, usually whatever it came with, and it gets changed very rarely and with regular castrol, for no particular reason.

If by regular castrol you mean regular car castrol you find in the aisle at megamart stores, then you mean a detergent oil that is name brand and designed specifically for cars and has additives meant for such an application. Non-detergent oil is the stuff you find that says non-detergent and is typically only used in lawnmowers and such. It costs like 0.80 a quart and will ruin your car.

Ok, here is the quote from the manual and you guys tell me what it means.

"Engine Oil Recommendation
USE HONDA 4-STROKE OIL OR AN EQUIVALENT.
Use only high detergent, premium quality motor oil certified to meet or exceed US automobile manufacturers' requirements for Service Classification SE.
Motor oils intended for Service SE will show this designation on the container.
The use of special oil additives is unnecessary and will only increase operating expenses.

CAUTION: Engine oil is a major factor affecting the performance and service life of the engine. Non-detergent, vegetable, or castor based racing oils, are not recommended."

Then it has a chart showing SAE 10W-30 is good for when the average temperature in my riding area is between -5F and 90F and SAE 10W-40 is good for -5F and up.

So I get the detergent thing, but what is 4-stroke oil or an equivalent? Cars are 4-stroke. What should I put in this thing for the best mileage without spending $50 on oil? The 0W-30 I got from Wal-Mart is about $30/5 quarts, so using that would cost me about $15.

stay away from "efficiency" or friction modifiers. Look at the bottle for an sf or an sg.

From:
Honda Nighthawk Specs

Recommended Oil Honda 4-stroke oil or equivalent.
API SF or SG, SAE 10W-40

5 � F to 110 � F SAE 10W-40



5 � F to 90 � F SAE 10W-30

Typically if it says 4-stroke it means motorcycle/powersports oil. Honda 4-stroke is used for honda motorcycles and powersports and is made for use with wet-clutches. If it just says motor oil it's typically for a car. Amsoil synthetic was only about 8 bucks a quart for me, how much oil does your bike take? You can try normal oil, but i have a feeling you will feel your clutch start to slip.