SOHC.co.uk Forums > CB750
Which oil for cb750k2
McCabe-Thiele (Ted):
--- Quote from: Nurse Julie on May 18, 2023, 11:47:08 PM ---No Ted, mineral oil. And if you can get hold of it 20w50 with zinc is the best for a 750K.
--- End quote ---
The reality is semi-synthetics perform close to mineral oils - I don't know if the clutch might be an issue as I've not used it. Many sites list semi-synthetics for motor cycles even though they have wet clutches.
https://www.westwayoils.co.uk/products/10w40-semi-synthetic-motorcycle-oil?_pos=5&_sid=c0fba5ec0&_ss=r
The advantage of a semi might be the improved flow properties over just mineral. There is no regulation on the percentage of synthetic oil in the semi type it is my suspicion that the cheaper semis will have a greater mineral content to save money as mineral oil is much cheaper to make. It appears that as modern engine design has moved to fully synthetic so the mineral market has lost its large volume demand so oil companies are just profiteering as mineral oil should be as cheap as chips.
Many brands of Semi oils already contain high levels of zinc, Phosphorous & Sulphur.
https://www.westwayoils.co.uk/products/20w50-classic-oil-high-zinc-semi-synthetic-zddp
Update or https://www.westwayoils.co.uk/products/10w40-semi-synthetic-motorcycle-oil?_pos=5&_sid=c0fba5ec0&_ss=r
K2-K6:
Technically 20w50 is too thick viscosity for the specification needed.
It will, unless always heated to correct range, mean reduced flow volume through any of the flow restrictions in these engine.
Ultimately they are a true 30 viscosity design.
Running 20w50 at below realistic hot temperatures will result in the oil pump output being dumped through its pressure release valve as too much pressure accumulation in system distribution, resulting in stalling volumes throughout the engine under these circumstances.
royhall:
I tried Mineral 20W50 in my CB750F2 and it appeared to have no negative effect on the engine, but it did make the rattly clutch somewhat quieter. This is the oil I used Millers Oils Classic 4T 20w-50 Mineral Motorcycle Engine Oil - 4 Litres 5024081844747 | eBay
davidcumbria:
--- Quote from: Nurse Julie on May 18, 2023, 10:08:08 PM ---10w40 or 20w50 mineral on a 750 sohc. Synthetic will give you clutch slip.
--- End quote ---
Is that also the same for a 550 k1?
Bryanj:
Yep, 10w40 or 15w40. 20w50 is a bit thick for UK normal temps but ok for 40 deg summers
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