SOHC.co.uk Forums > CB750
Clutch plates
McCabe-Thiele (Ted):
Essentially yes but viscosity is not quite the same as thickness the term iirc only applies to fluids.
Thickness is an easy visualisation if you compared water with treacle.
The visual comparison starts to fall apart when you see how much thinner oil is when draining from a hot sump.
I think of the higher figure being a measurement of the oils ability to perform as a lubricating film at high engine temperatures - the lower figure being the performance at lower temperatures.
Johnwebley:
Thanks Ted,so for an old worn motor, like a 1960s Mini,a 50 grade is OK
For a modern tight clearance motor, a 5 is OK for cold starts
So,would a 5 x 40 be ideal for our sohc motors?
If no,why?
Sent from my SM-A546E using Tapatalk
Martin6:
I think for 500s it's the same as 750s, the lowest viscosity recommended by Honda, is 10W40. So you risk the oil being too thin as the motor warms up, particularly during warm weather.
I take the view, oil is cheaper than a re-build.
Trigger:
Honda recommend 10/40 or 20/50 on the CB750 ;)
As your decal states >>> https://www.ebay.co.uk/itm/193883042558?hash=item2d245472fe:g:iVIAAOSwBLlU-OiF
McCabe-Thiele (Ted):
--- Quote from: Johnwebley on July 27, 2023, 01:35:58 PM ---Thanks Ted,so for an old worn motor, like a 1960s Mini,a 50 grade is OK
For a modern tight clearance motor, a 5 is OK for cold starts
So,would a 5 x 40 be ideal for our sohc motors?
If no,why?
Sent from my SM-A546E using Tapatalk
--- End quote ---
In old Minis we used the old spec oils like Duckhams 20/50 as the engines like a motor cycle have to lubricate the engine, gearbox & diff so an oil that worked at high temperatures was essential.
It was a common thing that if you drove a Mini on long motorway distances like I did from Derby to Bradford they would sometimes become stuck in top gear - even on models with oil coolers - the problem would go away if you had a cuppa at the services.
When Vauxhall built the first of the FWD Cavaliers & Astras gearbox layshaft rattles were an issue that were solved by using ATF in the gearbox instead of the normal gear oil. I understand that they did modify the gearboxes in later builds but the fix did work.
Many modern cars use 0W/30 engine oils. With ATF's it is pretty much accepted that the modern ATF oils are backward convertible so a gearbox designed to use Dexron 2 can now use Dexron 3 or 4 even. With ATF's vehicle manufacturers were very specific about using the manufacturers brand e.g. in a Nissan model use AT-Matic J only stating that deviation would invalidate any warranty. Happily this sort of Pseudoscience is a thing of the past with a bit more honesty about the ingredients with multi use fluids by well regarded manufacturers.
For some reason acceptance of a modern synthetic diesel engine oil being suitable for a diesel engine designed back in 1985 is met with scepticism.
I do not have enough knowledge & long term experience of sohc engines to advise you if a 5W/40 oil would be suitable - I suspect that grade would be fully synthetic so probably no one has done the testing & research to find a true answer based on rigorous testing.
In reality my experience on different oil brands/grades is anecdotal - we read the adverts & technical specifications and are swayed with a term like contains Zinc or PTFE etc we make choices that suit our wallet and personal preference's. As has been said before any oil is better than none.
Reverting back to original Honda engine oils as per old handbooks etc is based on technology that is now 50 or more years old but no one I suspect has explored if a more modern oils are better or backwards convertible across the range.
The idea that a modern synthetic engine oil is worse for your engine than one designed on synthetic technology I find very hard to accept.
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