Acceptable / normal oil consumption

[K2-K6]

"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."

This is far more involved a topic than generally appreciated and often projected via internet wisdom.

These Honda engine are, and always have been a 30 viscosity (hot running conditions) engine, with tolerances to match. They've always been far ahead of general motor manufacturer engineering in materials specification and production targets. It's new engines that have caught up with this type of engineering.
Running in ambient temperature below 60degree it's actually a 20 viscosity design because of the clearances of crankshaft main etc and only goes to 30 viscosity because air cooling doesn't have an effect thermostat as does a water cooled engine.
To summarise, it's designed built and produced to a specification that matches modern low viscosity specified modern engines.

Oil life has changed the most not from oil chemistry but accurate fuelling that doesn't dilute the lubricant by passing excess unburnt fuel and combustion byproduct past the piston rings. This is always the reason for change intervals in reality.

Viscosity is not protection in absolute terms, it's just resistance within the system it's being squeezed through by the oil pump pressure. Viscosity is exactly the same in either mineral or synthetic oil when measured against the same criteria, it doesn't differentiate one from the other.

Of those two examples of oil grade above, one does have a higher base oil viscosity than the other. Anyone know which way round that is ?

[Lobo]

…you are a mine of information K2-K6; always enjoy / appreciate what you write. Ta.

[Cappodimonte]

K2-K6, I don’t intend to get into ‘Oil Wars’ but simply put old engines use thicker oil, if you wish to use synthetics designed for modern engines in old classics, it’s your call.

[McCabe-Thiele (Ted)]

I have had similar discussions on the Nissan Terrano  4x4 site about the same issues.

The compromise might be the semi-synthetics that are available in similar grades to mineral oils. It's due to the wet clutch that I stay with mineral.
Come back good old Duckhams.

[Cappodimonte]

If you want Duckhams Ted, contact Fuzz Townsends Classic oils at Bicester Heritage
They sell all the oils you can think of along with other additives for all sorts of mechanical items.
Been in there a number of times and they are very willing to assist. The whole site is a classic car owners dream, they do have a few motorcycle interests in there too.

[Johnwebley]

  Just to put another idea,

  if the oil was a modern synthetic,maybe the rings haven't bedded in?

  have you ridden it to gently?

  I believe you have to get pressure behind the rings ,to force them against the cylinder wall to bed them in,

 ideally firm acceleration to 6k revs,then shut the throttle,

 I think the idea is to pressure the rings on acceleration,then with a shut throttle it sucks oil mist up the bores to lubricate them,.

I have heard of modern engines using lots of oil because the new owner drives them to sedately to run them in.

you have well over 500 miles on the clock,with the mineral oil,start to work it?

 try running it up to 8k in 3rd then slamming the throttle shut,

  it can't hurt

 

 

[Cappodimonte]

Words fail me!

[Nurse Julie]

  Just to put another idea,

  if the oil was a modern synthetic,maybe the rings haven't bedded in?

  have you ridden it to gently?

  I believe you have to get pressure behind the rings ,to force them against the cylinder wall to bed them in,

 ideally firm acceleration to 6k revs,then shut the throttle,

 I think the idea is to pressure the rings on acceleration,then with a shut throttle it sucks oil mist up the bores to lubricate them,.

I have heard of modern engines using lots of oil because the new owner drives them to sedately to run them in.

you have well over 500 miles on the clock,with the mineral oil,start to work it?

 try running it up to 8k in 3rd then slamming the throttle shut,

  it can't hurt

 

 

Totally correct there John. At over 500 miles there should be no pussy footing around at that mileage. You stand more chance of polishing the bores, which will make it smoke, if the engine isn't put under load.

[Lobo]

An interesting thread to me as just beginning to break in a comprehensively rebuilt CB750 K2 engine… red line fyi 8000RPM.

But… despite all the varying advices here, I’ll be going with what the owners manual recommends - why wouldn’t you?

If interested, the relevant pages attached.

[350Simon]

  Just to put another idea,

  if the oil was a modern synthetic,maybe the rings haven't bedded in?

  have you ridden it to gently?

  I believe you have to get pressure behind the rings ,to force them against the cylinder wall to bed them in,

 ideally firm acceleration to 6k revs,then shut the throttle,

 I think the idea is to pressure the rings on acceleration,then with a shut throttle it sucks oil mist up the bores to lubricate them,.

I have heard of modern engines using lots of oil because the new owner drives them to sedately to run them in.

you have well over 500 miles on the clock,with the mineral oil,start to work it?

 try running it up to 8k in 3rd then slamming the throttle shut,

  it can't hurt

 

 

Totally correct there John. At over 500 miles there should be no pussy footing around at that mileage. You stand more chance of polishing the bores, which will make it smoke, if the engine isn't put under load.

How I rode it was keeping between 5 and 6k preventing the engine labouring at all, up to 60mph in top and let off the throttle back on throttle etc so as not to have extended periods at constant rpm.

Then as I neared 500 miles I started going to 7 and 8k through the gears riding quickly and again not staying at a constant speed for too long which is pretty much where I'm at now except I'm changing up around 8 or 9k, haven't gone to the 10k red line yet.

Interestingly when I'm riding at 60mph or below 6000rpm the mirrors are clear. However get to 70 or 80mph 6500 to 8000rpm and I can see a fog lingering behind me on the road. 

So it's not burning any perceptible amount of oil below 6500rpm but above that it's really quite evident!

I'm going to check the level a day or two as I'm nearing 700 miles and see where it's at.



Sent from my SM-G780G using Tapatalk

[K2-K6]

Just watched the whole video posted early in thread, quite a few concerns he has there  obviously experienced at assessment but didn't come to a conclusion in that one. Is there another ?

Clearly there's oil getting to combustion chamber/ports somewhere, statement of the bleedin-obvious there. Can only really be head or barrels/rings/pistons etc.
There's nothing to judge the tolerances used for rebore, just an assumption that he's familiar with just how concise they have to be. No indication of rings (may have been prudent when he took head off to quantify these for failures etc) but certainly a question mark over them. Very often machine shops don't, or unwilling to, get the tolerances where they need to be. Have you compression checked it warm with throttle wide open ?
Head, not that confident with that guide fit if they can be pulled out like that, what was outcome of refit on these?

While head was open, that bearing for camshaft next to #3 looked shagged  !   Another thread on here had a crack into exhaust port with the the same oil burning as you're experiencing on one of these engine, It may be worthwhile trying for another head to work on as a way forward.

Odd thing to try. Glass of engine oil, place breather from cases into it and run for decent period of time to see if it sucks up any oil (mark the glass) ordinarily you'd get outflow very gently, but if it's slurping the oil fast enough may show as vacuum here.

Certainly it's an elusive problem, you know where it is, but exactly what's causing it yet to be found.

[K2-K6]

K2-K6, I don’t intend to get into ‘Oil Wars’ but simply put old engines use thicker oil, if you wish to use synthetics designed for modern engines in old classics, it’s your call.

I think you've missed what I've written there. There's no recommendation from me for others to use any specific type of oil, old or new. Understanding how viscosity interacts with any mechanical device is valid in best lubricating them with some of the currently available oils helping to understand why certain choices are made. It is a technical forum which entails discussion at various levels which if clearly written the people present here can then form an opinion of and contribute/question the ongoing scenario. That's what a forum is about surely......

If anyone is curious about the viscosity question, the thicker oil is the OW30 product. But probably for another thread in reality that doesn't get it mixed in here with the very real problem the OP is experiencing.

[Oddjob]

Was following a Triumph 900 the other week coming back from an oil meet. It started to smoke, I could smell oil being burnt. I signaled him to pull over and his left leg up to the knee was saturated in oil, it was pouring out of the engine and forming a pool on the floor. He'd only had the bike a month so he was understandably a little upset. Turns out one of the half moon shaped rubbers sealing the camcover to the head, where the cams would be, had popped out. We managed to force it back in enough that he could get home.

The next week he turns up and explains the breather pipe had been fitted wrong by the PO and instead of being fed to the bottom of the airbox they'd fitted it to a blank on the airbox. This compressed the cases so much the seal popped out.

This got me wondering, could the engine be forcing oil back into the airfilter via the recycling system fitted to the 400, this causes the smoke from the exhaust. Which leads you to think it must be head related when in fact it could be something else, like a failed ring allowing compression into the crankcase.

Have you checked the airfilter to see if it looks really wet with oil?

[400 Cafe Racer]

Was following a Triumph 900 the other week coming back from an oil meet. It started to smoke, I could smell oil being burnt. I signaled him to pull over and his left leg up to the knee was saturated in oil, it was pouring out of the engine and forming a pool on the floor. He'd only had the bike a month so he was understandably a little upset. Turns out one of the half moon shaped rubbers sealing the camcover to the head, where the cams would be, had popped out. We managed to force it back in enough that he could get home.

The next week he turns up and explains the breather pipe had been fitted wrong by the PO and instead of being fed to the bottom of the airbox they'd fitted it to a blank on the airbox. This compressed the cases so much the seal popped out.

This got me wondering, could the engine be forcing oil back into the airfilter via the recycling system fitted to the 400, this causes the smoke from the exhaust. Which leads you to think it must be head related when in fact it could be something else, like a failed ring allowing compression into the crankcase.

Have you checked the airfilter to see if it looks really wet with oil?

Also check the accuracy of the breather pipe inner diameter to ensure fully unrestricted breathing over the full length. Some of these breather pipes can Kink or partly deform which could lead to choked breathing, crankcase pressure build up and force thin hot oil past the valve stems and piston rings.

[Laverda Dave]

Just to add my bit for what it's worth.....
This sounds like the same issue I had with my rebuilt CB250RSA just before it seized on the M40!
The oil consumption was very high yet I couldn't see any smoke whilst I was riding it. I got the wife to ride it whilst I rode behind on my VFR. It was only then I could see it smoking, 30 miles later it went bang. It was only when I stripped the motor I noticed the excessive piston to bore clearance and this was on a freshly rebored barrel with new piston. When I asked the engineer who bored the barrel if he had used the Honda spec clearance he said no, he thought it was too tight so he bored it to a bigger clearance that HE thought was correct! Result was it drank oil. The individual has now gone out of business (I wonder why?).
About 30 years ago I had my 400/4 rebored by a m/cycle engineering company and it also drank oil. Turned out they hadn't rebored the barrel square!
Reboring motorcycle engines and especially modern close clearance motors is a very specialised field and you have to trust who is doing the work. If it were my engine I think I'd be stripping it down by now for further investigation to check the bores for clearance and straightness and especially if someone else has rebuilt the engine before you got it. If Trigger is still working I would take it to him.