I have a 1981 honda cb750c motorcycle and need to know what the best oil would be?

Answer 1

As the King of Run On Sentences has already stated synthetics will leak right through the gaskets on that old thing.

For the last few years I've been using Pennzoil 15-40 diesel oil in all of our old bikes - two old dirt bikes, three 1970's street bikes (including a 1979 DOHC CB 750), and a 1970 SOHC CB 750 race bike. The 15-40 diesel oils are certified for wet clutches. And they cost about 8 bucks a gallon at Wal-Mart.

I've got the 1970 CB 750 race bike's engine apart right now for a top end rebuild. All the wear surfaces in the head look great. No metal shavings in the oil pan. The clutch hooks up very nicely.

I found the bike after it had been sitting for 18 years. I took it racing without ever going inside the engine. I did 8 races and at least 6 track days a year for two years on that bike using diesel motor oil and the internals look great.

Answer 2

Motorcycle engines can run much hotter than auto engines because they depend on moving air to keep them cool. Therefore auto oils do not need the protection against high temps like motorcycles do. Stick with an oil designed to resist breakdown in high temps. Synthetic oils do protect better but they "CLEAN" away deposits left from the petroleum oils and may cause leaks at gaskets that were sealed by the gunk. That doesn't mean the synthetic is bad, it means the petrol oils have impurities that break down and help seal leaks as the gaskets dry out and shrink.

Ask the Honda dealer what rating should be on the oil and use any good quality petroleum oil with that rating. I would start with 10w40 for cool weather and switch to 20w50 for summer.

Answer 3

1981 Honda Cb750 Custom

Answer 4

bike engines can run lots warmer than vehicle engines via fact they remember on shifting air to maintain them cool. as a result vehicle oils do no longer choose the safety against severe temps like motorcycles do. follow an oil designed to withstand breakdown in severe temps. guy made oils do shield extra ideal yet they "clean" away deposits left from the petroleum oils and can reason leaks at gaskets that have been sealed with the aid of the gunk. that does no longer mean the synthetic is undesirable, it means the petrol oils have impurities that wreck down and help seal leaks via fact the gaskets dry out and shrink. Ask the Honda broker what score could be on the oil and use any solid high quality petroleum oil with that score. i might initiate with 10w40 for cool climate and turn to 20w50 for summer.

Answer 5

synthetics have a tendency to make leaks in old bikes worse as for the 20/50 castrol i used it for years with no prblem except for when it got really cold the bike turned over very hard. I would use 20/50 any brand except those that use a parafine base as they tend to create a wax build up on your clutch plates castrol is fine but steer clear of the eastern oils as they have this problem the purist will insist you use only motorsickle oils and if I could afford new bikes I might beleive them but my old hondas 550 750 650 and 750 twin cam all do just fine on automotive oil as long as I stay away from wax based oils

Answer 6

Don't use GTX, its automotive oil and has friction modifiers which can cause clutch to slip. Use a motorcycle specific oil , even though it costs more. Car oils tend to break down pretty quick (around 1000miles or less) when used in wet sump motorcycles, they use same oil for transmission lubrication, which breaks down the polymers. cars use hypoid oils or ATF for automatics due to the pressures involved between gear teeth.
Its correct about the 15W/40 diesel oils, they contain zinc compounds which are 'good' for older engines

Answer 7

I called a long time and very reputable Honda dealer in my area and the service department recommended Honda GN4, 10-40 weight. At this particular dealer it sells for $3.89 per quart. As I thought, synthetic is not a good idea for your bike.

Answer 8

This engine calls for 10W40. Says so right on or next to the filler cap/dipstick. You will get no benefit from synthetic. If you insist on using 20W50 do it only in summer.

Had a CL360,CM400A,CB650andCB750. From '74 to '86. They all called for 10W40 right on the bike (and in the manual).

Answer 9

I highly recommend Castrol 20W-50. This oil is design for high rpm engines and works well in most motorcycle engine designs.

Answer 10

A 10/40 semi synthetic will be best for an older engine like that.