Honda-SOHC
SOHC.co.uk Forums => CB350/400 => Topic started by: 350Simon on September 14, 2022, 11:10:37 AM
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What would be considered normal for a 350/400 sohc?
I've done 500 miles of running in new pistons and rings, the bores were properly machined and honed and I know that my valve guides are on the upper end of the serviceable limit.
Oil level is just above the min mark on dipstick after 500 miles. Is this acceptable or should I really get the head reconditioned?
I'll be honest I can't detect any smoke from the exhausts in my mirrors while riding or at idle but my friend said the other day there's a faint haze when I'm giving it the beans.
Cheers
Simon
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My ex CB400F never burned oil, inc after a full rebuild. In fact no vehicle of mine burns any oil, inc a 50yo Kombi. If you’re using Max-Min quantity over a mere 500 miles there’s surely something wrong?
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Try topping up the oil to the mark and see how it goes over the next 500 miles.
It might bed in and oil consumption reduce. If not, I would overhaul the valves and guides.
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What would be considered normal for a 350/400 sohc?
I've done 500 miles of running in new pistons and rings, the bores were properly machined and honed and I know that my valve guides are on the upper end of the serviceable limit.
Oil level is just above the min mark on dipstick after 500 miles. Is this acceptable or should I really get the head reconditioned?
I'll be honest I can't detect any smoke from the exhausts in my mirrors while riding or at idle but my friend said the other day there's a faint haze when I'm giving it the beans.
Cheers
Simon
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Did you replace the 4 valve stem seals?
It has been my experience that when valve stem seals need replacing on a car engine then you tend to get visible smoke if the engine stands for a while from hot and you then restart it 5 mins later - the smoke is often just for the first 5-10 seconds then all is good. Again on cars I have found giving it the beans also burns oil & produces smoke at high engine rpm.
I would not be too concerned until you carry out your first oil & filter change then see how it goes on the next 500 miles making sure you check the oil on level ground etc.
I would also check if there a lot of excess pressure from the crankcase vent pipe system.
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With valve guides at the upper end there was always going to be a good chance to burn oil as the valves are likely to wobble and the seals will let by.
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What would be considered normal for a 350/400 sohc?
I've done 500 miles of running in new pistons and rings, the bores were properly machined and honed and I know that my valve guides are on the upper end of the serviceable limit.
Oil level is just above the min mark on dipstick after 500 miles. Is this acceptable or should I really get the head reconditioned?
I'll be honest I can't detect any smoke from the exhausts in my mirrors while riding or at idle but my friend said the other day there's a faint haze when I'm giving it the beans.
Cheers
Simon
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Did you replace the 4 valve stem seals?
It has been my experience that when valve stem seals need replacing on a car engine then you tend to get visible smoke if the engine stands for a while from hot and you then restart it 5 mins later - the smoke is often just for the first 5-10 seconds then all is good. Again on cars I have found giving it the beans also burns oil & produces smoke at high engine rpm.
I would not be too concerned until you carry out your first oil & filter change then see how it goes on the next 500 miles making sure you check the oil on level ground etc.
I would also check if there a lot of excess pressure from the crankcase vent pipe system.
I didn't do any of the work I bought the bike as is. It's this one that was featured in this you tube video where the guy had real issues identifying the cause of smoke that turned out to be a loose guide in the head. He said the offending guide was replaced but the other 3 remain. All the stem seals were replaced. All 4 exhaust valves were replaced which brought the stem to guide clearance just within the serviceable limit.
https://youtu.be/YM15Gijr6Ag
It seems like a lot of oil to use in 500 miles, through the guides..... especially when I can't see any smoke at all! There's also no oil leaks anywhere.
Perhaps it isn't actually bedded in yet as someone said above.
Next question would be who could properly sort the head out for me?
Cheers
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Guide replacement generally means refacing the valve seats and that's not a skill most people have and does require special tools. Graham (Trigger) has the tools, isn't too far away from you BUT I have heard he's sort of semi retired these days so whether he will still be interested is another matter. No harm in asking.
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Guide replacement generally means refacing the valve seats and that's not a skill most people have and does require special tools. Graham (Trigger) has the tools, isn't too far away from you BUT I have heard he's sort of semi retired these days so whether he will still be interested is another matter. No harm in asking.
Great I'll ask him if he's interested. Cheers
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..... especially when I can't see any smoke at all!
[/quote]
The old Mini A series 1275 S engine could burn a quart of oil in 200 miles without a trace of blue smoke!
I would definitely wait & see how much oil you use in the next 200 miles before doing anything hasty.
Another factor is warm weather ups apparent oil consumption for complicated reasons connected with oil additatives.
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..... especially when I can't see any smoke at all!
The old Mini A series 1275 S engine could burn a quart of oil in 200 miles without a trace of blue smoke!
I would definitely wait & see how much oil you use in the next 200 miles before doing antything hasty.
[/quote]Yep will put some more miles on it and then see where I'm at.
Thanks chaps
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Another quickie sorry guys, are the sohc seats 3 angle
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Another quickie sorry guys, are the sohc seats 3 angle
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Yes
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Yes, it requires 3 separate seat cutters.
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So having just giving it a good thrashing home and got it nice and hot, unfortunately I can see now that it is smoking a bit looks like cylinders 3 and four.
I'm going to look at just the head first, assuming that the bottom end has actually been done properly as I'm told it has.
Hey ho the joys of old machines!
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Yes, it requires 3 separate seat cutters.
Cheers. I'm a machinist by trade so feel i could do the job myself but as is often the way with these things by the time I've invested in the tooling it's probably not worth it.
I'll message Graham and hopefully he will agree to the job.
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Surprised Julie didn't say yes or no for Graham or maybe that would be a bit cheeky, I hate it when my missus volunteers me for jobs.
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Surprised Julie didn't say yes or no for Graham or maybe that would be a bit cheeky, I hate it when my missus volunteers me for jobs.
Yep I know that feeling!
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What would be considered normal for a 350/400 sohc?
I've done 500 miles of running in new pistons and rings, the bores were properly machined and honed and I know that my valve guides are on the upper end of the serviceable limit.
Oil level is just above the min mark on dipstick after 500 miles. Is this acceptable or should I really get the head reconditioned?
I'll be honest I can't detect any smoke from the exhausts in my mirrors while riding or at idle but my friend said the other day there's a faint haze when I'm giving it the beans.
Having seen your missives and having worked on Hondas whilst in the trade I never came across any Honda car or bike that had a 500 mile per pint consumption. There is something seriously wrong and with the data you provided I’d have walked away from that one as it appears to have been done on the cheap.
No way would I have taken it down to piston rings and honing without doing work on the whole head with complete strip down, that’s a recipe for problems that you seem to have incurred. If one valve stem has loosened then the whole shebang needs doing. Another fault could be the piston rings being put in the wrong piston step or even upside down in the right one and yes I came across that but not on a Honda.
500 mile run in and giving it ‘The Beans ‘ is not conducive to running an engine in even a Honda. I wish you all the best with it but I suspect you have inherited a moving money pit.
Cheers
Simon
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As a thought, what oil have you used?
If you use modern 0-30 oils then that will go up past th e pistons and down the valve stems.
You should use a 10-40 mineral oil or equivalent, Hondas clearances we’re close but not to todays micron standards.
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As a thought, what oil have you used?
If you use modern 0-30 oils then that will go up past th e pistons and down the valve stems.
You should use a 10-40 mineral oil or equivalent, Hondas clearances we’re close but not to todays micron standards.
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.
I've filled her up with 10W40 mineral oil and done another 100 miles so far, I'm now not getting any smoke that I can see while riding, a small amount if I blip throttle hard on the drive.
Just going to put some more miles on it this week and if it uses a load then I'll replace the guides.
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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.
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"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.
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"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.
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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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.
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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.
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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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.
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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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.
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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.
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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.
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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.
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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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"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 ?
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…you are a mine of information K2-K6; always enjoy / appreciate what you write. Ta.
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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.
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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.
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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.
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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
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Words fail me!
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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.
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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.
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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.
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Just watched the whole video posted early in thread, quite a few concerns he has there :o 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.
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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.
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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?
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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.
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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.