SOHC.co.uk Forums > CB350/400
Acceptable / normal oil consumption
Cappodimonte:
Motorcycle engines which are unit construction and use the same oil for moving engine parts AND the gearbox have a really tough life with the result they will get broken down quickly hence Hondas short service intervals of the 70/80s
Hope that changing to a thicker oil viscosity helps you out, bear in mind your bike is an old lady and should be treated like a lady.
I’ve seen and heard so called modern bikers scream the engine till it hits the Rev limiter, a sure fire way of drastically reducing engine life.
The oil being very black and thin to me points to it being modern synthetic 0-30 oil which is unsuitable for classic bike engines.
Good luck with your ongoing biking.
K2-K6:
"No idea what oil was in it but it came out very very black and thin so I suspect it was breaking down which wouldn't help."
Usually associated with running too rich, either from carbs being altered to excess or more normally far too much running with engine cold/choked to allow excess fuelling past the piston rings into the oil. The giveaway is oil smell (compare old to new) as it will generally stink of unburnt fuel.
The gearbox doesn't colour or dilute the oil in use but often it's pointed to as culprit in these scenario. Honda service interval is an acknowledgement of overall fuelling strategy which ultimately comes from the necessity to run slide carbs too rich ideally for a decent longer oil term, essentially it will dilute the oil and reduce viscosity.
Sensible to start with new oil and monitor condition, see what it looks like at 500 and 1000 miles etc.
With short runs and often on choke though you'd expect the oil to be knackered by about 500 and well short of Honda service specification.
350Simon:
--- Quote from: K2-K6 on September 19, 2022, 08:40:34 AM ---"No idea what oil was in it but it came out very very black and thin so I suspect it was breaking down which wouldn't help."
Usually associated with running too rich, either from carbs being altered to excess or more normally far too much running with engine cold/choked to allow excess fuelling past the piston rings into the oil. The giveaway is oil smell (compare old to new) as it will generally stink of unburnt fuel.
The gearbox doesn't colour or dilute the oil in use but often it's pointed to as culprit in these scenario. Honda service interval is an acknowledgement of overall fuelling strategy which ultimately comes from the necessity to run slide carbs too rich ideally for a decent longer oil term, essentially it will dilute the oil and reduce viscosity.
Sensible to start with new oil and monitor condition, see what it looks like at 500 and 1000 miles etc.
With short runs and often on choke though you'd expect the oil to be knackered by about 500 and well short of Honda service specification.
--- End quote ---
Thanks for this really useful information K2-K6.
I couldn't believe how black the oil was considering its only done 500 miles. I'm used to only seeing that on diesel engines.
Have been starting the bike with a small amount of choke and running for 2 to 3 mins on the drive at a high idle of about 2-2.5k rpm.
After this I can knock the choke off and the bike will idle perfectly at 1200 rpm. Then I set off.
Is this excessive? I'm not one for constantly adjusting the idle speed screw, I like to set it when the bike is hot and leave it alone.
I'm pretty sure mixture when on throttle is spot on but I might whip the plugs out in a layby after a full throttle run to check.
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Nurse Julie:
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.
350Simon:
--- 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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