Clutch plates

[Trigger]

Yes trigger should have listened
the putoline 10w40 was no good for my CB750k
Just now I like to get tikover down to about 1000 steady?mainjet 120 slow 40

1000 rpm is too low and why have you got 120 main jets in ?

[Athame57]

No good in a 400 engine. You need to use 10w/40 or 15w/40 mineral oil 

Thanks for this Graham. Next time I'll get that instead, surely nothing will go bang using it in one change though? 

[Trigger]

No good in a 400 engine. You need to use 10w/40 or 15w/40 mineral oil 

Thanks for this Graham. Next time I'll get that instead, surely nothing will go bang using it in one change though? 

Too thick for a 400 gear box pump 

[Athame57]

Too thick for a 400 gear box pump 

I'd best go on hold a couple of days until I get some then! BTW I've been using any old four stroke M/C oil these past five years, hope I haven't done any harm. 

[Martin6]

Yes trigger should have listened
the putoline 10w40 was no good for my CB750k
Just now I like to get tikover down to about 1000 steady?mainjet 120 slow 40

1000 rpm is too low and why have you got 120 main jets in ?

Trigger,

This is an interesting post and got me searching through the Honda workshop manual. 120 jets were on the 750s K0 to K4. K5 no mention of a change, but K6 are specified as 105 main jets. Are the carbs different on a K6? Do you know how they differ?

I have my idle set higher on my old bikes. I don't have any justification. It just feels kinder to avoid chugging and get a bit more oil pressure. My CB750K6 is set at between 1200 and 1400rpm. But the Honda manual does say 850 to 1,000rpm. Could you explain why you would avoid 1,000rpm?

Thank you.

[Trigger]

The Main jets on a 750K started out at 125 and then Honda dropped them to 120 on the early 750K0's. I have lost count on how many different carb numbers that were fitted to the 750's over the 10 year period.

The early 750's had 300 exhausts which have less back pressure than the 341's so, the jet range was 125 down to 120 but, some had 110 in the K1. Then the 341's were fitted to the K2 onwards that had 110 as standard in the UK. And the K2 was sold in the UK from August 1972 to 1975. Don't know about the K3, K4, K5 as these were USA bikes.

And then the K6 came out in the UK with 110 or 105 jets.

I have also lost count on how many different needle numbers across the 750 range and can be a struggle to find the sweet spot sometimes. My own K6 runs sweet with 110 with a little discolour on the plugs, pulls well and gets a little scary over 110 mph.

I always set the RPM at 1150 rpm as this puts less strain on the engine. Never had a 750 that was happy at under 900 rpm.
 

[Martin6]

Thanks for explaining Trigger.

I recently replaced 2 of my K6's carbs with better condition ones, bought as a bank off ebay, complete with gantry. I replaced the brassware, so all 4 were consistent with 105 mains. Relived the jetting is the only difference on the later bikes.

[Trigger]

Thanks for explaining Trigger.

I recently replaced 2 of my K6's carbs with better condition ones, bought as a bank off ebay, complete with gantry. I replaced the brassware, so all 4 were consistent with 105 mains. Relived the jetting is the only difference on the later bikes.

Are the carbs all the same number stamps ? No need to replace the brass, just used the original brassware once cleaned .

[K2-K6]

No good in a 400 engine. You need to use 10w/40 or 15w/40 mineral oil 

Thanks for this Graham. Next time I'll get that instead, surely nothing will go bang using it in one change though? 

Too thick for a 400 gear box pump 

Ultimately detrimental to hi-vo type drive chain primary too.

Natural development state of 5 viscosity oil, survive in these engines at outer limits with thicker oils with functioning and compromised lifing because of this.

Related to flushing of internal bearing surfaces via oil throughput to replenish oil film, take away heat and not fail the shear properties of the oil.  Used in much higher torque installation with ATF oil in plsce, will easily reach 200,000 miles or more, but lucky to see 50,000 in these engine for practical service life.

No suggestion to use ATF  but you can see the balance being struck with the specified engine oil they ask for.

[Johnwebley]

Interesting comments about multi grade oil

I always thought the lowest number was for cold viscosity,

And as such would get pumped around a cold engine easier to get oil to bearing during initial start,

The larger number is the hot running thickness,

But, am I correct??



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[McCabe-Thiele (Ted)]

Essentially yes but viscosity is not quite the same as thickness the term iirc only applies to fluids.

Thickness is an easy visualisation if you compared water with treacle.
The visual  comparison starts to fall apart when you see how much thinner oil is when draining from a hot sump.

I think of the higher figure being a measurement of the oils ability to perform as a lubricating film at high engine temperatures - the lower figure being the performance at lower temperatures.

[Johnwebley]

Thanks Ted,so for an old worn motor, like a 1960s Mini,a 50 grade is OK

For a modern tight clearance motor, a 5 is OK for cold starts

So,would a 5 x 40 be ideal for our sohc motors?

If no,why?


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[Martin6]

I think for 500s it's the same as 750s, the lowest viscosity recommended by Honda, is 10W40. So you risk the oil being too thin as the motor warms up, particularly during warm weather.

I take the view, oil is cheaper than a re-build.

[Trigger]

Honda recommend 10/40 or 20/50 on the CB750 

As your decal states >>> https://www.ebay.co.uk/itm/193883042558?hash=item2d245472fe:g:iVIAAOSwBLlU-OiF

[McCabe-Thiele (Ted)]

Thanks Ted,so for an old worn motor, like a 1960s Mini,a 50 grade is OK

For a modern tight clearance motor, a 5 is OK for cold starts

So,would a 5 x 40 be ideal for our sohc motors?

If no,why?


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In old Minis we used the old spec oils like Duckhams 20/50 as the engines like a motor cycle have to lubricate the engine, gearbox & diff so an oil that worked at high temperatures was essential.
It was a common thing that if you drove a Mini on long motorway distances like I did from Derby to Bradford they would sometimes become stuck in top gear - even on models with oil coolers - the problem would go away if you had a cuppa at the services.

When Vauxhall built the first of the FWD Cavaliers & Astras gearbox layshaft rattles were an issue that were solved by using ATF in the gearbox instead of the normal gear oil. I understand that they did modify the gearboxes in later builds but the fix did work.

Many modern cars  use 0W/30 engine oils. With ATF's it is pretty much accepted that the modern ATF oils are backward convertible so a gearbox designed to use Dexron 2 can now use Dexron 3 or 4 even. With ATF's vehicle manufacturers were very specific about using the manufacturers brand e.g. in a Nissan model use AT-Matic J only stating that deviation would invalidate any warranty. Happily this sort of Pseudoscience is a thing of the past with a bit more honesty about the ingredients with multi use fluids by well regarded manufacturers.

For some reason acceptance of a modern synthetic diesel engine oil being suitable for a diesel engine designed back in 1985 is met with scepticism.

I do not have enough knowledge & long term experience  of sohc engines to advise you if a 5W/40 oil would be suitable - I suspect that grade would be fully synthetic so probably no one has done the testing & research to find a true answer based on rigorous testing.

In reality my experience on different oil brands/grades  is anecdotal - we read the adverts & technical specifications and are swayed with a term like contains Zinc or PTFE etc we make  choices that suit our wallet and personal preference's. As has been said before any oil is better than none.

Reverting back to original Honda engine oils as per old handbooks etc  is based on technology that is now 50 or more years old but no one I suspect has explored if a more modern oils are better or backwards convertible across the range.

The idea that a modern synthetic engine oil is worse for your engine than one designed on synthetic technology I find very  hard to accept.