Honda-SOHC
SOHC.co.uk Forums => CB750 => Topic started by: Pauarc on November 19, 2023, 08:39:54 AM
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Just run bike with the clutch cover off I don’t think it’s getting any oil to clutch the clutch is quite dry is there anyway I could check the oil feed pump seems to return oil to tank ok
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Just fitted a test oil gauge and idle pressure seems to be about 35psi and at about 3000 to 4000 it is about 60psi this is with the engine hot just can’t understand why clutch drags so much (help me)
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Does anyone know what the hole in clutch centre is for
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Do these links help?
https://www.cb750.com/threads/clutch-and-lack-of-oil.7221/
.http://forums.sohc4.net/index.php?topic=55051.0
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Took clutch apart again no oil in central hole bike is a cb750k2
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Second link looks like it could be the solution Ted. First link isn't very informative.
There is a mod to increase the oil flow to the clutch plates but if there's no oil in the first place it's kinda redundant.
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I have changed the oil seal under bearings plate not sure if this is the plug
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It almost sounds like you have a blockage in the oilway to the clutch 🤔🤔.
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I have changed the oil seal under bearings plate not sure if this is the plug
No, that's a bolt hole, I've circled the plug in red. But some of them didn't have the rubber bung, the gasket covered the oilway. Your bung looks like it's got a hole in it for some reason 🤔🤔🤔🤔
[attachimg=1]
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The plug may be worth a look if the plug is removed I could see if oil is there if I spin on starter motor
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The plug may be worth a look if the plug is removed I could see if oil is there if I spin on starter motor
Yes, if you're not getting any oil out of that chanel, that could suggest a blockage somewhere.
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There is a good return to oil tank so hopefully may be that?? Keep fingers crossed 🤞
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There is a good return to oil tank so hopefully may be that?? Keep fingers crossed 🤞
Yes, fingers crossed, if you've got enough pressure for the oil to return to the tank, you should get oil out of that hole once the bung is removed. When you've removed the bung, take a photo of it so I can see if its a proper bung or something that someone has made at home.
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Looks like sealant not a bung to me
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Hopefully l have time at weekend to look at it I will keep you updated thanks for help
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Just had a Quick Look at plug came straight out with no problem. No damage just had a little bit of sealer on the end turned over on start motor oil comes straight out see picture will have a proper look at the weekend and check the bearing outlet through to the clutch
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Looks good. Is the plug rubber and has it got a groove around it?
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Yes it’s rubber and still pliable, and it has a groove round it Like a top hat
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So I'd imagine the rubber bung is to plug up the oil gallery where it's been drilled to force oil to go up the 2 towers that look to be connected to that gallery, these towers look to be feeds for oil into the centre of the gearbox shafts, the longer tower I'd say is the feed for the clutch shaft, if there is oil at the bung and not at the clutch then it must be that one or both of these tower galleries are blocked, most likely with a blob of sealant. I'd try some compressed air down them to see if it blows it out, failing that you may have to dismantle the engine and really get in there to get whatever is blocking that feed out.
Try compressed air down from the clutch side first to see if you can feel it around the bung area.
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Yes that was my thought too so clutch cover coming off again and remove bearing holder select end and clutch so I can poke something through and blow it through with the air compressor looks like my weekend is gonna be taken up on the bike hopefully I find something blocking passage way
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I have a nice selection of guitar strings of various guages, if you are looking for something to clear the oil passage. 👍
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Thanks Martin I will bear that in mind how The bike going
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Picked up the frame and brackets today. Nice and shiny :) So, the putting it back together, begins.
Tried to fit the centre stand. Needs some serious muscle on the spring. Will try again tomorrow.
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If the frame is bare Martin try fitting the pivot bar and lifting the stand up inside the frame and you will find the spring just falls on when you do that. Works on the 500/550 so in theory it should also work on the 750.
Oh and really grease up that pivot bar before fitting
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All cleaned and blown through and clears found nothing which would be blocking it
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Do you think it’s would be ok to run with cover off to see if oil comes out of the hole in centre of clutch after fitting gear shaft bearing and plug
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You tried to see if there is anything inside the gearbox shaft itself?
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I have had a bright spot light shining through from clutch side and it shines through onto a piece of paper and also a long pipe brush down the centre to other side and a air line as well
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I fail to see how oil isn't coming out of the shaft and onto the clutch plates, IF oil is at the bung, the transfer towers are free and clear and the shaft itself is free and clear why no oil ? Only answer I can think of is that the bung is blocking the gallery somehow. When the transfer tower part is removed and the bung is in place does oil come out of the hole where the bung is forcing it to go?
Another possibility, when you removed the transfer tower plate was there an oring around the hole where the oil would come out? if that was missing it's possible all the oil being pushed through would just leak into the gear area close by, especially if the plate isn't exactly flat, should be one of these fitted around that hole https://www.cmsnl.com/honda-cb750k2-four-england_model14363/o-ring-5x24_91301283000/
Might be my imagination but there does seem to be a very clear track leading to that gear area from the oil exit hole.
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Do you think it’s would be ok to run with cover off to see if oil comes out of the hole in centre of clutch after fitting gear shaft bearing and plug
With ONLY that clutch cover off, it should be ok to run it like that.
All left hand side bearing plate, cover and gasket to be installed fully though.
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I have already fitted a new oil ring and left hand bearings plate I was going to try spinning bike over with the bung out (kill switch off) to see if oil comes out where bung goes then put bung in and see if it get to bearing if it does I will fit gear change and cover and try running the bike and see if it gets to clutch
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Update I have oil getting to clutch also pic of bang just waiting for gasket hopefully it made a difference in gear change
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Well done. What was the cause of the problem?
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I don’t know I just wish I found something just cleaned out galleries with bottle brushes but until I get clutch cover gasket I won’t know finally if it’s sorted it
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Fingers crossed, let us know how you get on.
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I don’t know I just wish I found something just cleaned out galleries with bottle brushes but until I get clutch cover gasket I won’t know finally if it’s sorted it
Fingers crossed. That's been my experience with carbs!
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Update all back together still clunky between gears goes into neutral okay I found a note in the Honda manual about viscosity of the oil given drag on the clutch so now going to try some Castrol GTX 10w40 classic for classic bikes, and cars also going to check the oil pump strainer in sump. Would it be a good idea to change the O-rings where the pump meets The engine
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Needs to be an MA2 spec oil.
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Ahh! Castrol GTX was there any other oil in the 70’s? 😂😂
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Castrol GTX 10w40 mineral That the oil I used in the 70s and 80s on all my bikes
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I just emailed Castrol about ma spec oil and they replied I don’t know if the info is any help
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Interesting stuff there Paul.
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Interesting information in there pauarc.
Jaso Ma2 would appear to (going by convention) have a reduction zinc element to reduce the affect on post combustion exhaust gas treatment equipment, not helpful in these engines we talk about.
The point about Jaso labelled oils, is not the absolute std and the oils that are classified as such, but that perfectly good oils we could use are never going to be subjected to testing for that std as it's not necessarily their target market.
The point is made though, that this oil is a match for that previously used in these engines when contemporary. Making it realistic to use it currently without any particular concern.
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Was horrified to discover the PO had cut grooves round the friction surface of the steel clutch pressure plates of my CB750F1.
But as the clutch had been previously working OK I just re-assembled it as is.
Seemed like a severe botch to me, and probably done to help prevent clutch drag perhaps?
Anyhow I'm not advocating this as a cure for clutch drag.
Be good to find out what the proper cure is tho...
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There is this mod to the 750 clutch, done in order to get more oil onto the friction plates etc in order to make the action smoother and thus gearchanges.
http://forums.sohc4.net/index.php/topic,7190.0.html
I've done this mod to a CB1300 and whilst the difference wasn't pronounced it was a bad change before but as they say "Every little helps"
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I have done the clutch mod I have changed oil need a nice day to try it out will have to see if any better will keep you posted
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I just emailed Castrol about ma spec oil and they replied I don’t know if the info is any help
Learned something new.
Just checked the 10w40 Motul 3000 mineral oil (not synthetic, nor semi) I bought from David Silver. Says it's MA2 spec. Also checked my Nortons 20W50, I use Royal Purple mineral oil, also states MA2. Odd?
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I no it’s odd the gtx oil is the last thing to try this is a page from Honda workshop manual from the 70s if this doesn’t sort it looks like I will have to take engine out and look at gearbox I don’t know what else it could be
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I no it’s odd the gtx oil is the last thing to try this is a page from Honda workshop manual from the 70s if this doesn’t sort it looks like I will have to take engine out and look at gearbox I don’t know what else it could be
👍
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When for a short run gear change seems to be working better will have to see how it is on longer run
Running on empty
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Hopeful. Well done. Let me know if you fancy meeting for a coffee locally in the new year :).
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Will do Martin
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I have been given a complete k2 gearbox from late 1975 bike which my mate was braking I am going to clean it up for a spare incase I decide to change my bikes gearbox at a later date need to get out for a good run any one no if it’s ok to put the bearings in a ultrasonic cleaner
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Shouldn't hurt them, alternatively steam them with something like a nozzle on a wallpaper stripper to remove existing oil based products.
Either way, soak them in engine oil after to make sure they are completely lubricated for storage.
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Yes that’s what I thought I was going to soak in oil and bag the hole gearbox up for storage thanks
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With the GTX in the bike definitely better when for a long run about 70 miles yesterday
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Good old GTX. Glad to hear your getting some trouble free miles in with no hassle from gearbox. The development of oils undoubtedly have come on in leaps and bounds but these machines were developed to run on the oil technology available 60 years ago!
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I just emailed Castrol about ma spec oil and they replied I don’t know if the info is any help
Very interesting. I've never heard of this before.
I looked it up on online and all the 4L metal cans it comes in are slightly different. Is there any rogue stuff out there, or is it all good?
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Got mine from GTX site GTX classic 10w40
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Excluding fully synthetics I'm sceptical that new oils are not backwards convertable for bikes.
When I owned a diesel Terrano a lot on the 4x4 sites said mineral was best. I used modern Synthetic Diesel oils in mine for over 60k miles - it ran quietest on Total.
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On my 750, I used synthetic once because I couldn't get anything else. It started to leak at the rocker cover.
Subsequently, in the absence of any MA2 graded oil, I use various things, including long distance diesel oil. This apparently has less of something or more of something - memory like a sieve - that makes it more suitable than modern oil for cars.
I'm looking at 20W50, and the cans are all green with different descriptions on the front.
Castrol do produce a data sheet, but only on the US website, and then show it only in 1L plastic bottles.
https://www.ebay.co.uk/itm/155143601025?epid=22032787237&itmmeta=01HSV0Z4R41K9G4JQCY7RG7TZF&hash=item241f477b81:g:Yt4AAOSwNMdjpICv&itmprp=enc%3AAQAJAAAA8G8noC9WWL%2BZnL95TCzuiicFGveRWXCORGcA13MdNYA7HNE1gZpZbt1V3%2Bdr9WJi2m0ipxglgTLoYzluOm2MwUW2Y%2FvVI0FdtkfXwHYfFc9c3hKbVMsnt9T4uLWwfDMJcmlo4y8NdAF71W36bAYj09NUKdv%2B0ztEuveWnJ0Et060Dl2Zg8aW7WAbI07f594iQK3%2BTV9ia6XT7Y0QAtD4tkJ7YOWJEr9S7ds98jYOMDxJ3mZe4g%2Fo0s79eWqDte23XCBPECsMEJKokjb1BqViBP4GwD4NI%2B9t%2FmIDmVnBW2eyTSM5dz85n902D6sPNhPp%2FA%3D%3D%7Ctkp%3ABk9SR5bM_ODOYw
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Try hear https://classicoilsshop.co.uk/gtx-classic-10w40
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Found it! Thanks