SOHC.co.uk Forums > CB750
Clutch plates
Martin6:
--- Quote from: McCabe-Thiele (Ted) on July 27, 2023, 02:47:15 PM ---
--- 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?
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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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Ted, I'm a member of the Access Norton forum. Some research was done on oils. See the link: https://www.accessnorton.com/Oil-Tests/NortonOil.php
Even if you only look at the first table, half way down, you can see the difference between Royal Purple HPS 20W50 and their HPS 10W40, is an increase in friction and heat, as tested. Just makes me wary of using oil outside the original spec.
I'm not a scientist, nor engineer, so I tend to play it safe. The key thing I find persuasive is, motors manufactured in the '70s used the design, materials and mass manufacturing technologies of their day. Modern oils may well be better manufactured and have superior additives, but the 1970s engines (even before allowing for 50 years of wear) have run for their lives happily using oils in the ranges specified by the manufacturer and were designed using materials, oil pressures, temperature ranges and moving parts tolerances specifically for those oils.
Only my view, I wouldn't be anti synthetic or semi-synth oil use in a freshly (properly) rebuilt motor, provided it is the right spec (viscosity and for use in wet / semi wet clutches), e.g. 10W40 MA01. I'd personally, be a bit more wary of using synthetic in an unknown / high mileage motor (sadly, mine is in that category!). My concern would be whether there's any risk the detergents pull out a few decades of sludge and do damage, before being filtered out. I wouldn't use 5Wxx.
So, I play it safe, stick to the Honda recommendation and listen to the corroborated, long term experience of other owners. But, I'm not knowledgeable or rich enough to experiment myself. :)
Martin6:
--- Quote from: Pauarc on July 27, 2023, 07:03:39 PM ---Yes cold and no oil
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👍
So will be higher, especially once run in. Did you do the engine work yourself or use someone? I may need someone this winter.
Pauarc:
Yes I have always worked on all my bike since the 70s away Honda (cb250,cb360,cb400,cb550 cb750 k7 cb750f2n and now CB750k2)
Martin6:
👍
Pauarc:
In the 70s and 80s I used Duckham 20/50 or Castrol GTX20/50 and had no problems
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