SOHC.co.uk Forums > CB350/400

Acceptable / normal oil consumption

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Nurse Julie:

--- Quote from: 350Simon on September 19, 2022, 09:09:51 AM ---
--- Quote from: Nurse Julie on September 19, 2022, 09:00:41 AM ---Not sure what work your engine had done prior to you getting the bike but if Graphogen had been used during the build, the oil will come out black at the 1st oil change.

--- End quote ---
Hmmmm indeed a possibility.

I hate the stuff but that's another topic entirely.

I had strip and clean a freshly rebuilt engine with no oil pressure once because the oilways in the crank were blocked with graphogen.

Ever since at work we only use the oil the engine will be run on as assembly lube. Then build up oil pressure before cranking.



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--- End quote ---
Yes, some people slather the Graphogen on like buttering bread 😂😂😂. Graham (Trigger) has always used Graphogen on new mating parts fitted in the engines but he's never had restrictor jets blocked due to excessive use.

Cappodimonte:
When rebuilding any engine gearbox or axle I only ever used the oil that was going to be used in the workpiece, as I stated earlier with motorcycle engines that are untitary construction with oil being used for gearbox and engine the oil has a much harder time in that it goes through compression forces in the cam,crank pistons  rockers etc but very high shearing forces in the gearbox as gears mesh together under load..
The oil used has therefore a rough life with the result oil changes were a lot more frequent than they are now. This is due in no small measure by synthetic oils being far more resistant to breakdown and shearing forces but the clearances now are in microns, thousands of a millimetre not thousands of an inch which allow modern machines to use 0-30 oils whereas our classics need 10-40 oil which is thicker due to larger ( in comparison) clearances.
In days of old where cars had engine, gearbox and back axle the oils used were 20/50 for engine, 75/80 for gearbox and 90/110 for back axle due to the different forces exerted on the oils, in a motorcycle like Honda the oil is expected to combat all the forces in one.

taysidedragon:
Cappo, I don't disagree with what you posted, but a major reason for thinner oils now is the push to get better and better fuel consumption.  Thinner the oil, less drag and resistance.

Also, nearly all vehicles now are watercooled, which allows for better temperature control and therefore closer tolerances.

My Triumph Tiger 500cc is unit construction but still has separate engine and gearbox oils. All the unit Triumphs before the reborn Hinckleys are like that. I believe the other old Brit bikes were built the same way, but I'm not familiar with them.

Cappodimonte:
You are correct in that modern oils are thinner along with a host of other engine management systems aiding fuel consumption to increase mileage per gallon. The major difference is that modern engines are using clearances in microns (thousands of a millimetre ) not thousands of an inch as per 70/80s Hondas and especially Triumphs/BSAs etc. use modern oils in a classic bike engine and it will go straight past pistons and down valve stems which will cause you problems with burning oil
Classic bikes use classic thicker oils, simple as.

McCabe-Thiele (Ted):
On the subject of modern fully synthetic oils most owners of modern cars rarely need to top up the oil between services - they falsely think that they are not burning any oil at all.

To combat the sulphur impurities in petrol that would combine with moisture to form corrosive acids they add special ingredients to synthetic oils (micronised chalk is one) to neutralise the acids - over time these neutralised products build up in the oil replacing what oil has been used /burnt off making the oil level appear stable.

If you happen to be close to a scheduled oil service then make a long Motorway trip you can suddenly find your oil level drop dramatically (up to a litre in a couple of hundred miles) as these products are burnt off. This can help explain sudden unusual amounts of oil being used on a motorway journey. It also emphasises the need to change oil regularly especially on short journey work.

This is based mainly on my own anecdotal experience with oil consumption in cars.

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