Which oil for cb750k2

[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"    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)]

We had "a bit of a chat"    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.

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

[Johnny4428]

Worthwhile info there Ken! Not long since I watched a video with a wrecked engine due to the spring placed between filter and engine!

[Laverdaroo]

Just my two 'penneth but whilst service manager at hed offic for MotorcycleCity amillion years ago we would never put fully synthetic oil in anything that didnt have a dry clutch as it simply made the clutch slip as previously mentioned. Even if the customer requested it. Its too thin and semi was always the best as stipulated by the manufacturers. TheDucatis loved the fully synthetic but dont rely on it for the clutch plates as you know hence the choice but try a early 2000's fireblade with standard clutch springs and fully synthetic oil and it doesnt want to drive out of the corners with the throttle pinned or hit max speed in top, the clutches simply let go and used to be noticably loose all over the place.

The folk that used to ask for it were the same guys who used to balk at the cost of tyres asking why they could get a set for cheaper for their car. When asked if their car would go over 170mph and or change direction from one side of the tyre to the other in less than a second, the answer was always, "EErrr, no.......I see what you mean".

Always soldiers with everything on tick from accross the road at the Aldershot barracks, they always asked for the most expensive and didnt know why. Cannon fodder (pardon the pun) for a new bike salesman in the show room after which they were always introduced to the race leather salesman who always managed a suit, new lid, gloves and boots out of them at the same time beforee thay left

Getting back on track, leave really expensive oils for really expensive engines, these motors arent that fancy and simply dont need it. AND, save yer brass

More expensive is often, still no the best.............

[SeanFD]

On the road in Africa, and Europe for that matter, the choice of oil is limited, if there is a choice at all. In temperatures ranging from low single figures to the high 30ºC, these are the oils I used:

Motul 3000 4T 20W50 ;       Motul 7100 4T 10W40 ;              Total 4T Special  Hi-Perf 20W50 ;
Castrol GTX Diesel 15/40 ;            Total 4T Special  Hi-Perf  20W50 ;    Fuchs Titan Truck Plus 15W40 ;
Castrol Actevo 20W50 4T ;    Moto Quip 4T Street 20W50 ;            Ipone R4000 RS 20W50 ;    
Liqui Moly 4T 10W40 ;       Liqui Moly 4T 20W50 ;               Liqui Moly 4T 20W50

The only one that gave me bother was the Motul 7100, a 100% synthetic, MA2 rated oil. While using this, a weep started at the cylinder head gasket and this plagued me throughout the rest of the trip - quite spoiled my new riding jeans.

On the US site, I read a post, by Hondaman I think, that it was not unknown for synthetic oils to seep through the head gasket in this fashion. Needless to say I never used it again. I also read that low detergent oils are better for our bikes.

Now I'm certainly not an expert, but the lesson I took from the experience is that any high quality oil will do the job, if it is changed frequently enough.

I now use the Liqui Moly 4T 20W50 or 10W40 when I can get hold of it.