SOHC.co.uk Forums > CB750

Oil, oil pumps and primary chains

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the-chauffeur:

My experience is that moving from motorcycle oil to car oil isn't really that much of a problem.  Moving from mineral to synthetic, however, is more problematic.

Having said that, the problem isn't lubrication; K2's right - it's all about clutch slip potential.  As far as I can tell, the best way to care for the engine is to decide early on in the life of the bike what type of oil you're going to use - car, bike, mineral, semi-synth and so on.  Once you've decided, stick with the same type, remembering the frequency of oil changes will be infinitely more important than which particular type oil you chose.  Like K2, I tend to use car oil on the older bikes but for financial reasons; I change the oil far more regularly in my old bikes than I do in the modern ones (every 1,000-1,500 miles or so as opposed to every 3,000 odd) and if I was keeping to that sort of schedule exclusively with bike oil, I'd be bankrupt by now.  I don't race, and don't put the bikes under any unusual loads, so that suits me fine.
 
If you decide to switch between oils, I've found the best way to reduce/minimise/eliminate clutch problems is to strip out the clutch when you switch and either replace the fibre plates (not cheap) and/or clean all the plates with thinners and let them dry.  In both cases, soak the plates in the new style oil before putting them back into the pack.  At least that way you've got more of a chance of them responding properly when you flush the engine with new oil.

The fun thing about oil is that you'll find pages and pages of stuff of the interweb, either in articles or across forums, and as many different opinions as there are drivers . . .

UKROBK7:
Everyone has a favourite oil!  I have used Castrol Power 1 10W-40 4T (motorcycle) oil in my bikes.  This is what my local dealer uses when they service customers bikes.  It's semi-synthetic and I've never had problems with wet clutches with it.  They said never use fully synthetic or the clutch will slip

Rob

K2-K6:
A lot of the internet comment seems to ASSUME that synthetic and derivatives is mythically more slippery and I don't know if that statement is true.

My understanding of synthetic is that the long chain molecules (these are apparently the bits that keep your pristine metal bits from touching each other and hence prevent wear) are more stable, stay intact longer and under wider conditions i.e. heat contaminant etc still manage to perform the job over and above the ability of non-synth type oils, all the stuff by the oil companies seem not to claim it's more slippery.

The clutch is specifically designed to expel oil from between the plates (that's what all the little detail gaps in friction plates are for, to break the oil film when they come into contact with the metal plates)when you let go of the lever and, the materials are matched to that environment to operate effectively. I guess if you had any specific effect it would be in the time the clutch took to bite fully as the oil cleared.

If you take the demand of an air cooled four stoke engine into account I would say that the benefits for using  synthetic are definitely there i.e. localised hot spots that are better managed with water cooling are potentially offered improved operation with a synthetic. Also things like the F2 cam area, and any of the later SOHC engines that run wth lean carbs and probably higher temps.

ST1100:

--- Quote from: K2-K6 on June 29, 2011, 07:04:10 PM ---...long chain molecules are more stable, stay intact longer and under wider conditions i.e. heat contaminant etc still manage to perform the job over and above the ability of non-synth type oils...
--- End quote ---

Exactly the arguments why I'm successfully running 5W60 fully-synth (MC17/EXS) in my 1100cc w/cooled touring rig since many years/miles now...
plus the points about better suspending abilities, friction additives, lower decomposition rate, chemical stability, etc...

So what are the opinions of using a 5W60 in a fully rebuild, air-cooled SOHC?

K2-K6:
I think that if I were in that position certainly it would be worth trying.

Couple of things give me a benchmark to go on.

1, car use. We owned an audi 5cyl petrol bought second hand direct from owner at 48000 miles which had been run from new on shell synthetic. We changed it to Mobil1 and ran it to 150000 miles (then sold) but you could look into the cam cover and still see the clean aluminium of the head plus the original grind pattern on the base circle of the cam lobes. the oil was always changed at 6000 miles intervals and came out a pale fairly clear golden brown i.e. similar to when it went in. It had no work other than service items during this time and ran fualtlessly, also revved to 7200rpm so not far off some of these old SOHC but longer stroke so could even have a higher linear piston speed than these.

2, Friend worked on military aviation jets and explained to me that as the oil used was not subjected to fuel contamination then there was much more detailed examination of oil performance as it virtually looked new although it would be at the end of it's performance life. This really showed me how dirty four-stroke motors make their oil from combustion by-products and degrade the oil.

From these I formed some opinions of my own about oil use. First is that combustion polutants get into the oil by going past the piston rings (specifically the top compression ring) and can be general blow by from poor sealing in normal use and much more blatant with extended use of the choke during warm-up.
The audi showed me that a well designed and good materials used engine, when run on synthetics had easliy almost nil wear over it's 150000 miles so a testemant to synthetics I think and certainly agrees with your use ST1100.

If you can get low wear from the start of your engine's life you will simply have less oil contamination anyway as you have not worn the piston rings/bores in the first place and so long term oil performance would always be less compromised. You'd probably have less need to change the oil any way.

IF there was an issue with the clutch, some sensible investigation (maybe use a stronger clutch  spring to raise the clamping pressure) could deal with it.

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