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Which oil for cb750k2

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Nurse Julie:
The problem with the oil debate is that the likes of Trig and myself that own and ride 750's regularly, know what oil the engine needs and feels best running on. I tried semi synthetic on my 400/4 and it was shite, serious clutch slip whilst riding the bike hard, so I went back to mineral and the bike was happy on that. If you've not ridden 750's recently, or ever for that matter, you won't know what is best as far as oil is concerned. You can read the manufacturers blurb but it really means nothing, they are just trying to sell their product.
The most important thing I find personally, is regular oil changes not the type of oil you use.

McCabe-Thiele (Ted):
Similar discussions have been posted both here and on other forums on the mineral v semi-synthetic discussion usually without a consensus on a definitive answer. Not doubting anyone's personal experiences on the subject.

Our experiences with mineral v semi-synthetic oils are anecdotal at best so there is never going to be complete  agreement on this topic.

I doubt any oil company would want to finance a definitive  scientific  test  using independent labs to test their products on bikes that are over 40 years old.

Just handy that you can still buy mineral oil that was the mainstay of oils when these bikes were built.

Regular oil changes is never in dispute.

K2-K6:
We had "a bit of a chat"  ;D  about this, with some interesting interaction with a 450 type engine Ted. I like looking through this topic and trying to be more objective in discussion to simply find out more about it.

http://www.sohc.co.uk/index.php/topic,14515.0.html brought up some alternative views certainly. 

Oddjob:
A small contribution.

Back in the 70s I used to run my 500s on 20/50w Castrol GTX most times, it ran ok. I even used to dump some STP oil additive in there and never at any time did I experience clutch slip.

As the 80s drew near I changed oil to what is still my favourite oil, BP VF7, it was 5/30w IRCC. It had so much detergent in it that any internal engine work was a lot easier as the inside of the engine was almost gleaming.

As my 500 is still not back on the road I'm not sure what I'll run that on but I did find 25 litres of Mobil mineral oil in the garage where it was stored so I'll most likely use that for a while.

One thing to mention that may be worthwhile to note, whilst cleaning the oil filter bolt the other day I decided I'd zinc plate it, so I first of all checked the oil pressure relief valve which is inside it, I was surprised to find it jammed solid, when I eventually did get it to move it stuck wherever it was left. Thinking it may be just because it hadn't moved for a while I checked some others I had in storage, out of 5 oil filter bolts only 1 worked as it should, one was solid, 1 worked and 3 were sticking. Which makes me wonder, has anyone ever tested theirs? In all my years of removing these bolts this was the first time I ever thought of doing it.

In case your wondering how to test it (not you Nige) you get a right angled piece of metal and slide it through the upper most holes in the bolt, right under the head, the pressure valve is essentially just a metal cup with a spring underneath holding it up. The bolt itself is ridged so the cap stops just below the top holes, pressing down on the cap with the right angled metal piece should move the cap downward exposing the next line of holes, it should move back in place when you release the pressure on the cap. Try testing yours next time you change the oil. Another thing to note, and all mechanics know this one but the filter bolt should have a large metal spring fitted along with a large diameter metal washer, the filter goes on next. The washer is there to stop the spring from piercing the rubber seal on the filter, most don't notice the washer, which has a tendency to stick to the rubber seal on the filter and it then gets thrown away with the old filter. Check any previous owners haven't already disposed of this washer, it's the one part mechanics always find missing whenever we'd service an engine the owner had also been servicing. Apologies if this sounds condescending, it's just information you may not know. 

McCabe-Thiele (Ted):

--- Quote from: K2-K6 on May 22, 2023, 02:05:22 PM ---We had "a bit of a chat"  ;D  about this, with some interesting interaction with a 450 type engine Ted. I like looking through this topic and trying to be more objective in discussion to simply find out more about it.

http://www.sohc.co.uk/index.php/topic,14515.0.html brought up some alternative views certainly.

--- End quote ---
Very interesting link plus the link in the link - I will spend some time doing a thorough read - thanks K2-K6.👍👍👍

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