Honda-SOHC
SOHC.co.uk Forums => CB750 => Topic started by: StevieWonder on March 14, 2020, 01:21:01 PM
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Hi All,
It is usually very difficult if not impossible to select neutral on my 1970 CB750 K0 when hot or properly up to temperature. No problem when cold or warming up. Clutch seems fine, correct play before de-engaging, no drag when fully depressed. Could this be a selector problem or am I looking at a gearbox overhaul?
All advice appreciated.
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Sounds like a cable adjustment problem more than anything else. Some of my SOHC/4' are a bit tight to get into neutral when hot but obviously not impossible, but I consider this normal on these old bikes, metals expand when they're hot so things do get tight.
Edit.. Should also have asked if you're trying to get into neutral when stationary when the engine is hot? That can be almost an impossibility at times, just rock the bike backwards and forwards and it should find neutral with no problem if everything is in order.
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Yes Julie is right about that, trying to get into neutral on mine when stationary is a trial so I normally snick it into neutral before stopping, or when stopped cut the engine and put it in then.
Cheers
Dennis
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Thanks both. I have tried rocking the bike when stopped, but it rarely helps. I'll try snicking it in when coming to a stop, but would like it to be able to select it when stopped. Was never this bad on previous bikes.
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I may be thinking of someone else but if I remember correctly, your bike has only done a few thousand miles in the whole of its life, therefore it would be almost impossible for parts to wear out, go beyond spec, break etc in such a few miles, unless someone in its past life had a bad habit of stamping or standing on the gear change lever with all their weighet and causing internal damage. I would still be looking at cable adjustment at this stage personally.
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Are you completely confident the clutch isn't slipping, at all?
If it does, then it'll heat the clutch pack and prevent you fully opening the clutch when hot.
If it works when cold, it suggests the mechanical components of the gearbox are OK and wouldn't need looking at.
Most of these are very concise regarding clutch operation setup, can you post a picture of the engine end of clutch cable looking straight onto it? To see if we can spot anything.
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Yes Julie, only completed some 750 miles since top end overhaul, but no idea what the total mileage is or if the clutch has ever been changed.
K2-K6, Haven't ever notice any clutch slip, not as smooth as it might be and range from first bite to fully engaged could be wider. Am yet to give it a handful of throttle or pass 5,000 revs. Attached photo shows clutch level, with handle bar lever untouched. Would have liked to see it more in a 7 o'clock position.
All comments appreciated.
Steve
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To me the lever is too far rotated anti-clockwise.
To set it, remove cable from arm, undo locknut, and then adjust screw until you can just feel it has no movement on the arm. This tells you that you've taken all of the clearance out of the clutch thrust mechanism. Now back the screw out slightly until you get 2 to 3 degrees of arm movement, this demonstrates you've now got running clearance.
Only now fit and adjust the clutch cable. The cable should have enough slack (just) in it to avoid you loosing the rotating play in the arm, with the spring able to hold the play in clockwise direction.
Then try it like that :)
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Thanks K2-K6, I have quite recently set the clutch in a similar manner to how you described, by using the procedure in the Owners Manual. I will do again using your description and in the hope that I can get it closer to 7 o'clock.
Gave it a run out today, before any adjustment, only about 10-miles, with air temp much cooler than I usually ride it. Interestingly, selecting neutral was noticeably easier. :-\ :-\
Will update when I had a chance to make adjustments as you describe.
Regards
Steve
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Thanks K2-K6, I have quite recently set the clutch in a similar manner to how you described, by using the procedure in the Owners Manual. I will do again using your description and in the hope that I can get it closer to 7 o'clock.
Gave it a run out today, before any adjustment, only about 10-miles, with air temp much cooler than I usually ride it. Interestingly, selecting neutral was noticeably easier. :-\ :-\
Will update when I had a chance to make adjustments as you describe.
Regards
Steve
Just a thought Stevie Wonder.... If I remember correctly the handbook has an error in it in relation to the setting up. I think it says words along the lines of 'turn it in until it touches and then turn ½ a turn clockwise' or words to that effect. It should read 'turn it in until it touches and turn ANTI CLOCKWISE ½ a turn'. You may well have sussed this yourself but I thought I would mention it just in case.
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Difficulty finding neutral when stationary with a fully hot engine has been a problem for me most of the eight years I've had my K2. Basically, everything works perfectly when engine is cold / warming up but becomes next to impossible when the oil temp is above about 60C.
Type and age of oil makes a difference but the biggest improvement came after trying various options and finally changing to smooth rather than dimpled steels.
Current setup uses only five rather than seven square cut friction plates with stronger springs to reduce the tendency for slip when accelerating hard.
Finding neutral can still be a little hit and miss in hot weather but at least doesn't require so much effort it feels something might break!
We're not the only ones btw, there are several threads about this problem on the US forum with no real consensus on the cause(s)...
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Many thanks to all for helping me move this forward. I have re-adjusted the clutch (yes Julie, the Owner's Manual has a small error! See later.) with the help of description from K2-K6, the lever is now in a more like 7 o'clock position and cable slack almost completely taken out. Thought we'd fixed it, as on the centre stand when hot, gears and neutral selected easily, but noted rear wheel still turning when in-gear with clutch disengaged (clutch lever pulled), which could be stopped with a boot. However when off the stand, couldn't get neutral :-\ :-\
gp_st3 has described my very similar issue perfectly. Has clearly gone to some lengths with fewer and non-dimpled steel plates. Be grateful for a lead to the source of these. CMS site picture looks smooth. DSS doesn't have picture but can order them in.
So for what it's worth, the way I see it: There is a clutch issue, not a slip problem but drag or not fully disengaging. This puts torque into the gearbox, not enough to drive the bike forward, but places cogs under tension, resulting in difficulty pulling them apart and finding neutral.
With a wet (running in oil) clutch one might expect more drag when cold (I use mineral oil - synthetic should be smoother?). So I need to inspect the clutch, maybe some of the clutch plates are buckled or perhaps the lifting mechanism has inadequate range and can be improved? Whilst it's out might as well do a full service and include friction plates and springs.
Owner's Manual Page 58. "Loosen the clutch lifter adjusting screw lock nut '2', turn the clutch adjusting screw in the counterclockwise direction 'B' (correct so far) until a slight resistance is felt (wrong: until it loosens). From this position, turn the adjusting screw in the clockwise direction 'A' 1/4~1/2 turn. Tighten the lock nut '2'." Correct.
What fun!
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Try a different make of oil next time see if that improves as I had the same problem when using Motul 5000. In one of my bikes ,
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I was quite surprised to read that so many SOHC owners are using 20w50 motor oil. I can't remember this weight being recommended for any Honda motorcycle since the introduction of 10w40 grades at the start of the 70's. In fact all the workshop manuals I have covering singles, twins and fours name Castrol GTX (at the time a 10w40 weight) as the prefered oil. Duckhams 20w50, also one of Castrol group brands doesn't get a mention as an option anywhere I have seen. I accept others may have a different opinion but I have never used 20w50 oil in any Honda engine; and there you are for what it's worth. ;)
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Its in the owners manual for warmer conditions
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Also stated on the decal on the side panel of the 750 SOHC ;)
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That maybe so but this is on the Castrol website.
https://applications.castrol.com/oilselector/en_gb/c/recommendation?vehicleType=motorcycles-scooters-mopeds-quads-(atv)&manufacturer=honda&model=cb-(1969-)&modelType=cb-750-four-(1969-1978)
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And the W (as in 10w 40 for example) doesn't stand for 'weight' the W stands for 'Winter'
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smooth steels - Lucas/TRW, made in Germany - bought on ebay.uk for about £40 (set of six) about a year ago ... why these work better for me is a mystery, so best try all other suggestions before shelling out for new plates that may not improve things for you.
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That's right. Alexander Duckham were the first UK oil blenders to produce a multigrade oil which meant there was no longer any need to use one oil weight for summer and another for winter. The 20w50 signified the oil would maintain a viscocity sufficient to provide engine protection for both summer and winter temperatures. Its introduction also reduced the constant need for engine decokes due to the use of various additives. A blue/green hue to oils signifies high quality and that is why Duckams used a green dye in their multigrade.
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I'm using 10W40 Rock oil, Gamma. It a mineral oil that are apparently better for 'running in' an engine after rebuild - as my top end was.
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Finding neutral when engine is hot is one way for me to verify the oil to be OK for the engine.
All 10W-40 oils I have used cause very hard an mechanical gear shifting. I used those for break in only.
CB750 should use 20W-50. I think that 10W-40 was for colder temperature, max 15C.
I have tested Motul 5100 15W-50 semi. Better than Motul 20W-50 mineral and much better gearbox feeling than Motul 10W-40 mineral. Castrol 10W-40 mineral also very hard gearbox.
Motul 7100 10W-50, even better.
Red Line 20W-50, best so far.
This in my K6.
Spectro Heavy Duty 20W-50 mineral caused sticky clutch. Out with 1L and in with Q8 SBK racing 10W-50 (cheap synth) made it really good. Gears shift very smooth!
In my K2.
Both Red Line and Spectro have high amounts of zinc and phosporous.
I have ordered Eurol Harley Davidson 20W-50 oil that is very cheap. It cannot be high quality synth as Motul 7100/300 or Red Line (esthers) but well worth to be tested. The gearbox when hit will tell! ;)
I have done my own semi by mixing 2 Spectro 20W-50 mineral, 2 SBK racing and 1 Red Line 20W-60 to be used in My K2 stock spec.
The latter for my K6 summer 2018 where we had over 30C during a long period of time. I ordered a box of 20W-60 to my hotter running K6 with 1000cc Billet block.
I'm convinced that CB750 run well on V-Twin 20W-50 JASO MA oils.
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In the UK 10w 40 or 15w 40 mineral or semi is perfectly adequate. We don't have the high temperatures you have Pewe so don't need anything ending in 50. 10W-40 is for Temps up to 40°. Thats plenty high enough for us in UK. Any 50 will be like treacle trying to go around the engine.
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Then you'll get the harder gearbox, problems finding neutral while bike is standing still.
Check the other forum where Hondaman explains 10W-40 history for CB750, why it is mentioned on the sticker.
I'm sure you have higher temp than I have in Sweden ;)
Yesterday was OK riding weather!
The old UK bikes runs with straight 50, right?
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Only ever used 10 40 in dealerships never 20 50 and no problems except the known fact of neutral, even Honda said select neutral as stopping not when stopped
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The old UK bikes runs with straight 50, right?
I do remember in the dim and distant past I may have use 50 on some of my pre unit Brit bikes but that was a totally different design and engineering tolerances. The thicker oil also helped it from pouring out of the all the joins in the cases.... But it didn't help much.
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"The old UK bikes runs with straight 50, right?"
Not since the 1950s! ::) Interesting you should be experimenting with mixing the blends from various manufacturers. You must have a lot of free time on your hands as all motor lubricants whatever their SAE rating are basically formulated to the same standards. The only differences are the oil companies making minor changes to the additives to imply a USP that makes their product better than others. A 10W40 from company "X" will not be substantially different to company "Y"s product for the simple reason they have to be compatable and not cause damage when mixed. Oil blends have to differ across the world simply due to the different climatic operating temperatures. What works in a tractor unit in Iceland probably wouldn't be much use in the Sahara. 8)
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Only ever used 10 40 in dealerships never 20 50 and no problems except the known fact of neutral, even Honda said select neutral as stopping not when stopped
Both my Hondas and Guzzi have to be rolling to select neutral. Both are air cooled the Hondas run on 10W 40 and the Guzzi on 10w 60
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Oil threads in car and bike forums are to be avoided like religion and politics - they can go on forever and, being more faith based than scientific, no one ever changes their mind.
I ran both CB750s I have owned on 10-40, and however well I had my clutch adjusted, just like any other bike from that era I have ever ridden, neutral was something best found before you rolled to a stop. At lights that I knew were going to be ages, such as roadworks, if I hadn't pre-selected neutral I'd switch off for a second, get neutral and restart. At least we have luxuries like electric start and a neutral light - not so easy on a Brit twin.