Topic: Oil circulation problem?...getting hung up in neutral

[ron.cieri.313]

Hi all...this is ron again and my '76 Honda CB750 K...after all those WOT test my tranny decided to give me headaches.

The problem is hard shifting down into first (clunk!) or up into second which takes to kicks up from first; the first kick just moves it into neutral - yes, I kicking up very firmly - and the second kick up puts into it gear with normal sound (sometimes I get chatter).  It also takes two kicks to go down into first from second and usually clunks with chatter sometimes. So, basically its getting hung up in neutral. Shifting between 3rd, 4th and 5th is no problem/no bad sounds.

So, thought to change the oil...noticed that the oil in the resovoir looked very clean and then oil from the bottom of engine looked really bad.  Is it possible my engine oil is not circulating?  I mean, I know its possible but how do I check for that?  I changed the oil and my symptoms still exist...I've also double check my clutch adjustment and starting to think the worst.  I guess I'm hoping that if its an oil circulation problem this may still be a lubrication issue...thoughts?

..thanks, ron.

[Inkscars]

I'm tagging along as my bike does something similar. Mines Intermit though....

[IAmCitizenMe]

Maybe this will help

http://forums.sohc4.net/index.php?topic=52973.0

[Inkscars]

Not my condition. Mine clunks from neutral to 1st SOMETIMES mainly from a dead stop.
SOMETIMES mine takes 2 clicks to go to second. ( 1 out of 10 tries.)

[ron.cieri.313]

Thanks Citizen...Lloyd's post are always informative.

I'm trying to figure out next steps..ignore the oil issue (if there even is one)?...head straight to the plates (as in order new one and replace them)?...check under the rear left side crankcase, understand there might be pins and such that can go bad?

[Spanner 1]

Not to alarm but how could the oil in the reservoir tank be clean and the oil in the engine be dirty/used looking unless no circulation between them ?

[ron.cieri.313]

Dunno...I was originally thinking that is the main clue to my problem.

Should they look same?...my thought was "yes" and consequently, maybe my gears and such are not being lubricated properly and therefore they stick in neutral.

...any thoughts?

[TwoTired]

The 750 is a dry sump system.
A scavenge pump fills the oil tank.
An oil pump drains the tank and distributes the oil about the engine.

If it is not circulating how would you still have oil pressure and no oil light?

On to the shifting issue...

Ok, I am NOT the expert on CB750s.  Particularly the lower end mechanical stuff.   I have never opened one of these up.  So, stop reading if you wish. 
But, I have looked into the Shop manual and studied the trans parts pictures.  It doesn't seem too different from the 550.  With that in mind...

All my 750s clunk much more than my 550s.  But, they do go straight through neutral to the next gear, unless I short stroke the shifter lever.  They don't "find" the next gear on their own with a quick nudge, you have to mean it. This is true for the 550 as well.  Certainly finding 1st from neutral makes a small clunk on the 750, but there is no lunge or lurch from the bike.  On the 550, an RPM blip with the clutch disengaged helps the clutch disc overcome any lock up tendency if the bike has been sitting for a while.  Then going into first is pretty much noiseless if you wait a few seconds for the trans parts to spin down.

A dragging clutch leaves pressure on the gear train which resists any change of position.  The shifting components then take extra wear in order to overcome this pressure on the gear dogs from the dragging clutch.  This accelerates wear of the shift drum, shift drum pins, shift forks and engagement slots for the shift forks.  If you are grinding "gears" you are wearing off the engagement dogs rather than the gear teeth themselves.  Anyway, when all these parts wear down enough the play increases so that gear dogs aren't fully engaged while trying to shift cause the lever cannot impart full travel due to worn components.

Slipping clutches are usually attended to straightaway.  Dragging clutches are often ignored as they are only annoying during stopped motion of the bike or when neutral is encountered.  However, dragging clutches advance transmission and shift component wear, which the next bike owner has to seal with.

Towards Ron's complaint;
Hanging in neutral says dragging clutch to me.  Chartering during engagement say the same thing.
Taking two tries to the get past neutral in either direction says to me that the clutch has been dragging a good long while, and probably worn out trans shifting components.

IMO

[ron.cieri.313]

Appreciate the response as always Lloyd...So I could be seriously s.o.l.?

Any alternatives, before a major teardown to the transmission gears?

[Spanner 1]

TT, here's how I understand it about the oil pump.....the tell-tale sign is the clean oil in the tank and dirty oil in the engine...first off the CB750's being a dry sump is a bit of a mis-nomer as oil having passed thru' the oilways under pump pressure is collected in the sump and sucked-up thru' a filter for return to the oil tank....however if the filter becomes clogged a by-pass valve will open to maintain oil pressure and feed to the motor ( no oil light on ). In by-pass condition oil is not cycled thru' the tank...bike could run for a long time like this except small amount of oil circulating is way overstressed and could cause the clutch/transmission problems as described.......

[Spanner 1]

Ron, here's what I would do....un-do the oil pan under the motor, I think its 10 bolts and the pump filter is revealed...fingers crossed, the screen just needs to be cleaned....also 'whack' the pump a few times in case the by-pass valve is too used to being in by-passed mode !!

[Patrick]

This is a long shot, but much easier to check than a teardown of the engine.

The neutral light switch engages when a ball shape in the end of the neutral light switch pops into a depression on the shift drum. The switch usually rides around the drum except when that ball pops out and engages the drum in neutral. If the neutral light switch is freezing up because crud got into it, or just age, it then it would be harder to depress that ball. It would engage with the shift drum more readily and be more difficult to dislodge. I can see how this might grab the shift drum when you are trying to shift from first to second or second to first.

I have never had this happen, but it could be easily checked by removing the neutral light switch from the bottom of the engine (one screw) and see if it depresses normally. It shoudl depress very easily.

Like I said, a long shot but much easier to check than tearing down the engine.

Patrick

[ron.cieri.313]

Lol...I get to whack something?!...that's a way better option...j/k.

I was just going to ask you how I can check/reset the bypass valve...thanks for reading my mind.

Its funny that this shifting issue started after my WOT runs to set my main jet size (damn pods!)...which could have a made a deteriorating problem alot worse if the condition existed prior to them and I'm pretty sure it did...of course, I could be dangerously close to hearing what i want to hear cuz I would stand in the park and recite shakespeare in a duck suit before wantiing to tear apart a transmission.

And yes, my neutral light is frozen on and have a new one waiting to be installed on the shelf...sounds like it worth putting in a seeing what happens?!...maybe the longshot is a little shorter

Well, stay tuned...I go on vacation this week but will be back at it next Thursday.

[TwoTired]

Appreciate the response as always Lloyd...So I could be seriously s.o.l.?

Any alternatives, before a major teardown to the transmission gears?

I would address the clutch drag issue first.  You can do that with the engine in the frame. With some luck, the trans issues might be minimized.   If not, then it's tear down time. 

[ron.cieri.313]

Hi Lloyd...what should I do to help the clutch drag issue?  Ive tried adjusting the clutch but not much luck yet.

[TwoTired]

TT, here's how I understand it about the oil pump.....the tell-tale sign is the clean oil in the tank and dirty oil in the engine...first off the CB750's being a dry sump is a bit of a mis-nomer as oil having passed thru' the oilways under pump pressure is collected in the sump and sucked-up thru' a filter for return to the oil tank....however if the filter becomes clogged a by-pass valve will open to maintain oil pressure and feed to the motor ( no oil light on ). In by-pass condition oil is not cycled thru' the tank...bike could run for a long time like this except small amount of oil circulating is way overstressed and could cause the clutch/transmission problems as described.......

Dry sump systems are defined by having the major oil storage outside the engine.  I don't see any mis-nomer here.  See:
http://en.wikipedia.org/wiki/Dry_sump

"A dry sump is a lubricating oil management method for four-stroke and large two-stroke piston internal combustion engines that uses a secondary external reservoir for oil, as compared to a conventional wet sump system."

The CB750 oil system has two valves; an anti-drainback valve from the tank and and the overpressure relief valve.  There is no bypass valve between the scavenge pump and the pressure pump depicted in the shop manual.  (See pg 27.)  The only oil supply for the pressure pump comes through the anti-drainback valve which is fed solely from the oil tank.  If no oil comes from the oil tank, no oil gets to the pressure pump, it will run dry, leaving no oil pressure.  The oil light should come on in that case, assuming it is working.

Really, I'm not just picking on you, Spanner.  It's just that what you say just doesn't agree with what Honda printed.

Cheers,

[TwoTired]

Hi Lloyd...what should I do to help the clutch drag issue?  Ive tried adjusting the clutch but not much luck yet.

If you can't adjust out the clutch drag (See pg 183 Fig 19-13), you're going to have to take the clutch apart and look for warped/damaged steels and/or frictions.  Then check the spline drum for notches as well as the basket tangs for straight slot edges.  Either the disks aren't flat or they aren't free to separate cleanly.  Or, there isn't enough cam action on the disengagement mechanism.

Alternately, the oil has lost lubricity.
You could search for a mod done to the clutch drum where oil holes are added, leading to better oiling of the clutch.  I remember reading about this.  I just don't know exactly where.

I've seen some clutch friction discs that have spiral groves and it matters which directions the spiral groves face.  I don't know if stock 750 discs have spiral or radial grooves to shed excess oil during engagement.  Radial grooves don't have a spin direction, spiral ones do.  Can't recall, off hand, which way they have to face.

[Spanner 1]

TT,P27 of my Shop Manual shows exploded view of the motor with heading 3-3 Camshaft Drive...
See P.22 , 3-2 Lubrication System, Paragraph 2, 'By- Pass Valve...
TT, don't always be  so dismissive of other posters, or just continue...it's all good....

That's Honda Shop Manual, Green cover, c Honda Motor Company.,Ltd. 1971. Honda CB 750.

[TwoTired]

TT,P27 of my Shop Manual shows exploded view of the motor with heading 3-3 Camshaft Drive...
See P.22 , 3-2 Lubrication System, Paragraph 2, 'By- Pass Valve...
TT, don't always be  so dismissive of other posters, or just continue...it's all good....

That's Honda Shop Manual, Green cover, c Honda Motor Company.,Ltd. 1971. Honda CB 750.

My manual is the 1977 version so the page numbers are different.  Could be added info in this one somewhere, as the camshaft drive Fig 3-3 doesn't appear until pg 33.  Paragraph 2 of the Lube system is about the oil filter. There is a by-pass valve, but it is in the oil filter bolt, in the event the oil filter becomes clogged.  The filter is supplied oil by the oil pump, which won't get oil unless the oil pump is supplied oil from the oil tank.  Even if the oil filter IS bypassed, it doesn't change oil routing to the oil tank.  There is no bypass between scavenge pump and oil pressure pump depicted or described.  If the oil isn't circulating through the oil tank, there won't be oil pressure, and the engine isn't going to run very long without severe damage.

[WHALEMAN]

The bypass is in the oil filter housing bolt. Dan

[CB750F2]

Loyd's explanation of how the oil pump operates is correct. I would like to add that the scavange pump has two purposes. One is to return the oil that has accumulated in the sump back to the oil tank and the other is to provide low pressure lubrication to the transmission via a passage that allows oil from the outlet of the scavange pump to travel to the LH side of the transmission and return through the centre of the main and counter shafts. Passages in the main and counter shafts allow oil to be thrown on to the gears. This is illustrated in the oil flow diagram in the Honda service manual. On the LH side there is a rubber plug - Part No. 11209-300-000. This plug plugs the oil passage coming across from the scavange pump. If this plug is missing or has been pushed in too far the main and counter shafts will be starved of oil. This plug is held in place by the transmission cover. There is also an "O" ring that is held in place by the counter shaft bearing holder. If this "O" ring is damaged or missing oil meant for the counter shaft may leak directly to the sump.
To check that the transmission is getting oil disassemble the clutch enough so that you can see the end of the main shaft, start the bike and see if oil flows from the end of the shaft - this may take a few seconds.
I hope that this helps to understand the operation of the scavange pump. Pat

[ron.cieri.313]

I'm printing all this out and taking it on vacation so I can read on the beach (if its not raining) and catch up with all these great ideas!!!

...can't wait till I can get back and start doing this stuff...thanks all...many more questions to come as I proceed...ron

[Spanner 1]

I read it as the OIL PUMP has the by-pass valve, not the OIL FILTER, so I stand corrected...is there any explanation for the seemingly clean oil in the tank vs. dirty oil in the motor ?, or is the poster wrong about that?

I understand that the oil pump is a two part pump, both scavenge ( low pressure to tank and transmission) and high pressure to crank, valvetrain etc.,but if the tank can't supply oil to the pump, blocked tube for instance, can the pump circulate the 'scavenge' oil or is it a closed circuit, i.e. fed by the tank only ?

[bryanj]

The pump has to suck from the tank to work

[CB750F2]

Spanner 1. The pump has two rotors. One for the high pressure circuit which is fed from the tank and the other for the low pressure/scavange circuit which sucks up oil from the sump through the stariner. The high pressure circuit supplies oil to the the crankshaft bearings and the top end of the motor. So, the answer to your question is no. If there was a blockage to the input to the high pressure pump the crankshaft and top end would be starved of oil resulting in serious damage.
I cannot explain why the oil in the tank is clean and from the sump is dirty. Pat