Topic: Dry Clutch Problems - why ??

[750goes]

Can someone enlighten me as to why my clutch basket is DRY.....
no hint of oil on the plates or discs.....

I have oil in the oil tank,
no leaks via the sump  (a few around the head - a few drops only)
no other oil leaks I can see...
oil pressure light goes away on startup...
oil gets hot in the tank...

My thoughts are I have a blockage somewhere.. so where is the best place to start

all suggestions appreciated

[nteek754]

hey there  wow this is a wild one been a collector of the 750 for 30+ years never heard of this but any way I remember a buddy years ago talked about doing a mod on the 750 clutch by replacing the bearing in behind the basket with a 305 bearing and drilling matched holes in the basket  im saying this because the differant bearing was a solid one and oil wouldnt go through there like the stock one hnce the drilling of holes in the basket (I didnt go that route)  and not sugesting it  but just trying to give you an idea where to look for the oil entrance to the clutch basket  let me sugest checking the breather tube from the valve cover and the oil tank vent  that could possibly cause a vacum and stop oil from getting to all places not much help but good luck and keep us posted Craig in Maine

[Jonesy]

The shaft that the clutch center spins on is hollow. From what I can interpret from the lubrication diagram, oil flows through the shaft, out the end at the clutch center and is distributed via the spinning clutch assembly.





Hope this helps...

[750goes]

Thanks for the replies so far -  more ideas needed.

Jonesy I will look at the shaft tomorrow (and I hope it is blocked) - if it is hollow I will poke a piece of wire along its length to see if there is some obstruction.....I will also take some pictures tomorrow of the dry clutch..

So Far.....
drained sump   -about 1 litre of oil
drained oil filter (bloody bolt siezed up real good) - less than 1/2 litre and new bolt required..
emptied oil tank - about 2 litres in there
took off sump  - bit of debris (wait for photos)
took oil tank off bike and checked the oil lines - all clear and free
turned over the oil pump by hand and oil comes out the forward hole.....
oil pump was very easy to turn  - worn out ?? or degree of difficulty if you have done this

oil is thin and smells of fuel - I do not leave the petcock turned on, and bike is on centrestand...

oil is pretty clean - but a bit of sludge in the oil filter housing and the bottom of the sump
(pictures to follow)

probably done 20km since the motor has been back in the frame (out for cleaning, paint  and degrease only)
compression checked OK..


any thoughts  ?

thanks guys - tell me good news - or bad -

[mark]

From looking at the pix above, it looks like the trans/clutch get oil from the scavenge side of the oil pump (gray oil in diagram). Not clear to me whether that valve at bottom right controls/limits oil flow to tank/trans. Keeping the tank full may be more of a priority than wetting the clutch.

The oil light switch gets pressure from the delivery pump(black oil) and wouldn't appear to be related.

Thin, contaminated oil probably isn't helping matters any.

As the sump is already off, I would pull the pump and make sure the valve isn't stuck. Then I would probably take my squirty oilcan and pump some clean oil in thru that hole in the end of the shaft - see where it runs out.


Good luck.

[750goes]

thanks mark - another good suggestion - the pump will be off tomorrow - and then I get to see where it goes from there......more concerned the clutch is getting no lubrication at all...and it seems the discs are all quite meaty.....

got to measure springs as well

got to find my little squirty oil can and buy some more oil and a filter........

the reason I took the clutch out was to check it, as I was losing all ability to put into first gear without crunching badly...and no more adjustment left after fully adjusting it....then when I got it in gear it did slip a fair bit.......probably because it is bone dry.........

hopefully my camera skills will be good enough to show all the right angles and exposure...

thanks again 

[scunny]

any updates
this is a side note from a drunk kiwi but wouldn't a clutch that is dry bind(as in not work) thus your clunking into gear but if it then slipped I would expect to see glazing

[Jonesy]

You may also check for blockage in the gear shaft holder (under the shifter assembly cover on the left side of the engine- shown below), as per the diagram it looks like the oil travels up to the shaft through this cover.

[754]

The clucth does not  actually  run submerged in oil as far as I know, and although it gets some oil, it is also flinging it off centrifigally..

I would take a real good look at the cluth parts and adjustment, before removing the sump and pulling the pump..

[TwoTired]

Speculation here:
Would a wet clutch that is run dry overheat and warp plates?  That would explain the drag (incomplete disengagement) and difficult gear finding, and perhaps slippage, as well.  Oil would make it slip even more, unless the frictions expand with the oil absorbed and increase the clutch pack stack height, thus increasing the spring tension/plate pressure.

Food for thought....

[Tower]

I've only seen this once before: where worn main bearings or a bent main shaft have effected oil passage enough to starve the clutch.

Excessive clearance at the main shaft bearing allows excessive oil to be passed through the bearing.  This has the effect of lowering the oil pressure at this point enough so that almost no oil continues into the clutch drum.  Instead, most of the oil drips down the engine case inside the clutch housing.  The outside of the clutch outer drum is oily, but the inside drum is relatively dry.

If you have experienced a lot of noise from the transmission, especially at higher speeds, this would indicate worn bearings or possibly a bent main shaft.  Other symptoms which apparently you have experienced, include hard to change gears, and perhaps slipping out of gear.

In very short order, the slipping clutch will mask this problem.  Lack of oil in the clutch assembly may first be perceived as a nasty smell, then as slippage.   Plates would be glazed and a thick sludge should be adhering to the cluch housing.

If you've tried fixing any of the early symptioms by using thicker oil, that would actually have made the clutch problem worse.

[754]

My BARNETT clutch always is hard to get into first when cold, part of having a racing clutch.. better warmed up.

Do you know if your plates are stock or not??

I would not crack the sump.. I would first inspect clutch and look for improper assembly.. there are oil holes in one of the main parts check for blockage. Now if it is not a stocker, there are extra plate clutches.. now this leads to the possibility of , a missing or extra plate being in there changing things.

Go through all that before taking the rest of the bike apart...

[750goes]

I have lots of replies to give, and lots of pictures to supply....it's 8:00am Sunday here - so I have to get to the shop and take some photos............

I don't like to hear the possibility of a bent main shaft - that one hurts.....all the rest I can probably live with................

Sump is already off...........

breakfast, then shop, then photos, then back here.....

[CB750F2]

There is an oil passage that branches off the scavange pump outlet. This oil passage runs across to the LH side of the motor and is blanked off by a rubber plug. In behind this rubber plug another oil passage branches off to supply oil down the center of the main and counter shafts via the gear shaft holder - see the picture in Jonesy's message. There is also an "O" ring in behind this holder. I suggest that you check that the oil passages are not blocked, the rubber plug has been installed and not punched in so far as to block off the branch oil passage, and the "O" ring is in place and providing a good seal. A good check would be to blow some air from the scavange pump outlet - you should feel some air coming out of the centre hole in the main shaft. Once you are satisfied that everything is OK re-assemble everything except the clutch, fill the oil tank with oil and pump oil around with the starter motor. Oil should eventually come out through the hole in the end of the main shaft. This may take some time because the oil comes from the scavange pump and initially the sump will be dry - you could probably start the motor to quicken this process but be ready to cut the motor if oil starts squirting everywhere.Hope this helps, Pat

[CB750F2]

I forgot to add the following. If oil is still not getting to the clutch it may be that the scavange pump is just not good enough to lift the oil to the the main shaft. Please keep us posted. I find this problem interesting. Pat

[750goes]

Well, I will start with the photos as that will take me the longest to put up...

Main shaft is hollow and no blockage at all to the depth of 9-10" . I stuck a plastic cable tie up the hole and it came out clean.....also ran compressed air through it and could hear it coming out in the bottom end........

I will start answering the queries raised after I print it all out, and then answer them as best I can.........

No - I haven't pulled the pump off yet - have to be tomorrow........

[750goes]

I have a total of 7 friction discs -the photos show the state of the discs to be pretty similar....I have not wiped them over...or cleaned them up...
plate1 - through to disc 6 are the same style......


plate7 - is angled differently than all the others.........

I have a total of 6 steel discs
disc1 & disc 2 the same
disc3 is double thickness and riveted together
disc4,5 &6 all the same

all oil holes in the clutch basket are clean - inner & outer

[750goes]

more photos

[750goes]

just a few more

[750goes]

Answers for everyone - sorry if i forget some..

nteek754 - standard bearing in behind basket -
- breather tube is vented to an open pipe (no filter or blockage here)
- oil tank vent pipe is/was connected to the rear of the transmission vent pipe

Jonesy - main shaft is hollow and definitely not blocked

madmark73 - going to get that pump off tomorrow......oil level has not dropped, or been an issue so far as I know from looking in the oil tank.....contaminated oil is a bit of a concern.....not sure about that at the moment....ran compressed air through the hole in the end of the shaft - no blockage apparent

scunny - drunk kiwi - never heard or seen one before - binding clutch - the last 10 minutes or so I was riding round the car park - it was a bugger to get in gear, and had a tendency to grab really quick - I stalled several times in gently ,gently releasing the clutch lever....
glazing - is as per the photos - not really shiny - but the whole assembly is dry as a desert...

754 - I agree with you - have a look at the photos - no oil anywhere.........the whole clutch does not show a great deal of wear.....

TwoTired - good thinking - I thought that if the plates got that dry they may have thinned out enough to make the clutch slip - I can measure the stacked height as I have the clutch basket assembly with me at the moment..

Tower - the outside of the outer clutch basket was hardly even wet....I am worried that it may be a main shaft  - that means motor out - split cases - rebuild - damn.......
transmission is a little bit noisy when on the centrestand and running through the gears - but I think this was mainly chain and sprockets, and no load on the running bike...riding it around the carpark up to 4th gear - no real noises from transmission...no jumping out of gear or hard gear selection either...  have thick sludge on the inside of the clutch basket
......have not used thicker oil........

754 - plates are as per the photos - first time I have pulled the clutch...I did notice the last friction disk is different and there is a double thick plate in there....

cb750f2 - Pat , thanks mate....I will check all that tomorrow...had enough for the moment,,,,going to investigate all the oil flow diagrams I can find...and think some more on this bugger of a problem.....

as before - any and all suggestions welcome...

three cheers to all responders 

[754]

All your plates should have same type of groove on the fibers.. someone clearly has mixed something in there..

 Start from scratch and make sure the right number and type of plates is in there..

 I stand corrected.. have not even thought of running a stock clutch since the 70,s..

[eurban]

Actually the later clutches have the spiral cut type outer friction disc as stock.  This disc also should have a wider tang to mate into the wider area on the outermost part of the clutch basket fingers. You can see this area if you look carefully at the clutch basket 1 jpg. He also has the riveted double thick plate that goes in center of the clutch sandwhich.  This is another feature of the later (I think 76 and later or so) upgraded clutch.  Looks like stock parts to me but clearly missing that important oil stuff!

[Jonesy]

All your plates should have same type of groove on the fibers.. someone clearly has mixed something in there..

I beg to differ...

I don't know what year bike you have, but the riveted plate in the middle of the pack is a 1975-later clutch assembly. The last plate is supposed to have angled slots in it.



I remember Hondaman saying something about turning it around to encourage more oil to stay in the clutch assembly for drag racing.  

BTW- I wonder how everything got so rusty in there?

[750goes]

Hi guys,

754  - the plates are as per jonesys diagram - I have a 75 750F but I think I have a k5/6 engine -
the last spiral cut plate is starting to disintegrate - that is, part of the plates are peeling off the backing steel - so its definitely got to go.....I haven't measured them yet...need to borrow some verniers........

eurban - thanks

jonesy - thanks again for that, when and if I get to go drag racing I will let you know   

[mark]

BTW- I wonder how everything got so rusty in there?

dang..... beat me to that one.