Author Topic: Cb750 k6 clutch query (Read 2335 times)

paulreade · « **on:** December 23, 2018, 09:53:48 am »

Hi guys
I have just stripped my clutch. It has 6 friction discs with perpendicular oil grooves and an outer disc with oil grooves at circa 45deg. I have received 7 new discs via David silver which have oil grooves at 45 deg.
The existing set up was such that the 7th disc was installed with the disc shown as fig B. This is when you stand on the right side of the bike ( offside) looking at the clutch in situ. Q is which way should the oil grooves actually go fig A or B. The reason I ask is that I have received mixed feedback and also the attached extract from the sohc forum showing the grooves fitted as fig A which would mean the 7 th existing disc about to be removed was installed wrong ?. Also the steel plates have a rounded edge - again different opinions exist as to whether the round edge should be fitted toward the bike or away , apparently little difference as long as they are all fitted the same direction.
Look forward to your views

??
all very confusing !
Kind regards
Paul

paulreade · « **Reply #1 on:** December 30, 2018, 12:30:52 am »

Hi guys - can anyone assist with this query as I cannot progress the rebuild without a lead on the way the friction discs are put back into the basket. If it helps the question is when you are standing the offside of the bike looking into the clutch basket - should all the friction discs be fitted as A or B ?. Really would appreciate your input to clarify.

Regards
Paul

PeWe · « **Reply #2 on:** December 30, 2018, 01:02:47 am »

OK, I had to remove my clutch in my working bike to find out

There is an old pic about later clutch when a double disc was added. Hub center is deeper to be able to house the higher stack.
My K6 has not the double disc nor the used K6 clutch I bought from USA via eBay. I have an F2 clutch that has it.

Anyway, not the question here, how to set the outer disc. I have used both ways. I have seen one way as allowing more oil to be shoveled in to the clutch.
The pic show the other way as I see it.

pjlogue · « **Reply #3 on:** December 30, 2018, 02:26:02 am »

Under normal rotation of a running engine, the outer edge groves of the disk should be trailing the inner groves. This encourages the oil to be slung to the outside of the basket.

-P.

paulreade · « **Reply #4 on:** December 30, 2018, 02:54:44 am »

Hi guys, the was mention of a ' tech note ' on one of the jpgs. Does anyone have the reference of the tech note ?.
I have an extract of a workshop manual from uk and it shows the opposite whereby the outer edge of the grooves leads the lower edge if that makes sense ?

paulreade · « **Reply #5 on:** December 30, 2018, 08:45:47 am »

One other point my original discs comprised of 6 with perpendicular oil grooves and the 7th with slanted grooves which were fitted as you describe. My replacement discs all have slanted grooves

. The tech note refers to the outer disc being installed to throw out the oil, would the remaining 6 discs be fitted the same direction ( I assume so ).
Regards
Paul

PeWe · « **Reply #6 on:** December 30, 2018, 01:10:49 pm »

All 7 have slanted grooves as the outer one has?
It might work on a stock engine. I have read a post where Hondaman commented that. i do not recall his verdict. I should not use those fibers on a modified engine.
Why not an EBC kit? CK1145
This kit for a K6. Only the outer disc has slanted grooves (and wider tabs on that disc)

pjlogue · « **Reply #7 on:** December 30, 2018, 02:57:28 pm »

If I remember correctly, in reading Hondaman's book, he said that some of the clutch kits were not properly put together and they had all the composite plates had the slanted groves. Only the outer plate should have the slanted groves and the outer edge of the grove trails the inner. This was the way my K6 clutch came from the factory.

-P.

HondaMan · « **Reply #8 on:** December 30, 2018, 07:31:36 pm »

Your original clutch was correct. Slant-cut plates for the CB750 have wider outer fingers, so you can only put one in the top of the stack.
If you install all slant-cut plates in a CB750, the clutch will slip. Here's how they work: when the cork blocks are square-cut, the oil escapes quickly (via centrifugal force) when you release the clutch. The top plate on the post-1975 CB750 was changed to a slant-cut plate along with a dual-sprung steel plate in the stack: this was done to retain a bit of oil in the last (top) plate to reduce the sudden jerk associated with incorrect and too-light oils: this often made the bikes stall with a heavy load aboard unless the owner was judicious with the lever.

Since about 2012 we are seeing the parts supply get these mixed-up plates. You can get the correct square-cut ones at PartsNmore: I have worked with them on several occasions to help them keep their inventory straight. You can also get a square-cut top plate (with the wider fingers) from them, which is useful if you want a stiffer clutch and will use the correct oils (with zinc, in 20w50 weight) for this engine.

paulreade · « **Reply #9 on:** December 31, 2018, 12:37:20 am »

Cheers guys, this has been an interesting debate on both sides of the pond, with varying thoughts. I will look into the issues of the double sprung plate also before I rebuild.
Once again many thanks
Regards
Paul

paulreade · « **Reply #10 on:** January 02, 2019, 01:19:05 pm »

Hi guys
One final query I have ( I am a very novice DIY mechanic) - when standing on the offside of the bike ( right side) looking into the clutch assembly. If the engine was running which way does the actual clutch basket spin ? Anti-clockwise or clockwise?

. To confirm does it spin in the direction of B or A ?
Regards
Paul

HondaMan · « **Reply #11 on:** January 02, 2019, 05:22:03 pm »

It spins CW (to your right) as you look at it. PeWe above is holding the plates in the direction they should be installed. You'll know right away if they are in backward: the clutch will slip like it's broken, hooking up after about 10 seconds (or more!) after you let it out.

paulreade · « **Reply #12 on:** January 03, 2019, 12:50:29 am »

Thanks 'hondaman' for that clarification. It's been an eye opener seeing the various replies on both sides of the water on this, and still there seems to be opposing thoughts. In pewe's pic the slant grooves are installed with the out edge trailing the inner which is exactly what mine looked like on strip down.
However one of the U.K. Experts states he installs the outer plate the other way round as the attached pic. It may have marginal difference I don't know but I think when I get the right plates I will review all threads again.
I have emailed the supplier 'David silver spares 'in the uk who have initially advised the pack of 7 discs with slant grooves is correct, I have however passed over everyone's comments re clutch slip etc and will see if they exchange. I have also asked them to comment on why they sell 7 discs with slant grooves and not the 'correct' kit (ebc CK 1145).
Good feedback and appreciated. Happy new yr to all.
Paul

PeWe · « **Reply #13 on:** January 03, 2019, 02:53:20 am »

Crusinimage on eBay sell a working K6 clutch, cheap too. Shop closed due to holiday.
Mine worked fine with 836 +80whp. EBC went in when 1005cc caused slips.

The Crusinimage clutch now in a stock K2 engine.
I added one new CycleX fiber I had extra since K2 has 7 of same type, no outer with slanted grooves and wider tabs.
It will hopefully work fine.

HondaMan · « **Reply #14 on:** January 04, 2019, 06:26:02 pm »

Quote from: paulreade on January 03, 2019, 12:50:29 am

Thanks 'hondaman' for that clarification. It's been an eye opener seeing the various replies on both sides of the water on this, and still there seems to be opposing thoughts. In pewe's pic the slant grooves are installed with the out edge trailing the inner which is exactly what mine looked like on strip down.
However one of the U.K. Experts states he installs the outer plate the other way round as the attached pic. It may have marginal difference I don't know but I think when I get the right plates I will review all threads again.
I have emailed the supplier 'David silver spares 'in the uk who have initially advised the pack of 7 discs with slant grooves is correct, I have however passed over everyone's comments re clutch slip etc and will see if they exchange. I have also asked them to comment on why they sell 7 discs with slant grooves and not the 'correct' kit (ebc CK 1145).
Good feedback and appreciated. Happy new yr to all.
Paul

There's often confusion about the cork angles because some of these bikes are gear-driven from the crankshaft, spinning the clutch the other direction. The smaller Fours come to mind, and many twins, too...

PeWe · « **Reply #15 on:** January 05, 2019, 07:53:16 am »

Good that this is ventilated here. I have assembled the slanted disc wrong some times.
Last time I was thinking about to not let the slanted disc pump oil into clutch via the grooves when rotating causing more lubrication (slip).

paulreade · « **Reply #16 on:** January 09, 2019, 12:51:11 am »

By way of an update, I have ordered a replacement clutch pack - CK 1145 to ensure I fit what everyone both sides of the pond has suggested.
I have new springs etc and on measuring those that I removed they are different lengths. The k6 springs ( new) are circa 31mm as suggested in the manual however those that I have just removed are circa 35mm - a suggestion has been made that I may not have a k6 basket installed ( no more info at this stage). The bike is definatly a k6 - as this is the first clutch I have seen and removed from any engine I have no idea how one would identify the differences in the baskets ?. I am at this stage tempted to re assemble with the new springs to see if it goes back together and works ok - can anyone advise why I might have longer springs fitted in the first place and what effect slightly shorter springs may have once running ?.
Also is there any tech info available to try and Id the different baskets fitted to these bikes

??
Any advice welcome
Regards
Paul

HondaMan · « **Reply #17 on:** January 11, 2019, 08:16:26 pm »

Quote from: paulreade on January 09, 2019, 12:51:11 am

By way of an update, I have ordered a replacement clutch pack - CK 1145 to ensure I fit what everyone both sides of the pond has suggested.
I have new springs etc and on measuring those that I removed they are different lengths. The k6 springs ( new) are circa 31mm as suggested in the manual however those that I have just removed are circa 35mm - a suggestion has been made that I may not have a k6 basket installed ( no more info at this stage). The bike is definatly a k6 - as this is the first clutch I have seen and removed from any engine I have no idea how one would identify the differences in the baskets ?. I am at this stage tempted to re assemble with the new springs to see if it goes back together and works ok - can anyone advise why I might have longer springs fitted in the first place and what effect slightly shorter springs may have once running ?.
Also is there any tech info available to try and Id the different baskets fitted to these bikes ??
Any advice welcome
Regards
Paul

Be wary of installing too-long springs: this can break the clutch hub!
If you have my book: check the length of the clutch springs per my chapter on bottom-end reassembly.
There are some clutch hubs, notably the F2/3 hubs, that have longer recesses and springs. They are NOT interchangeable, and our vendors are very confused about this issue. Keep in mind: the original OEM springs are good for holding up to 80 HP with square-cut cork plates of 0.135: thickness, which is a long way from where your engine is running.

PeWe · « **Reply #18 on:** January 12, 2019, 12:25:07 am »

I noticed that the shorter springs are much harder than the longer
I ordered from VintageCB750
High Performance Clutch Spring Set (4pc).
Fits: Honda CB750K (1976-78),
CB750F (1975-76) Supersport
Part #: 39-1047

They were stiff for my clutch hand. This was together with sticky CycleX fibers that gripped a little bit too well replaced by Cruzinimage fibers later replaced by EBC with bigger bore and more torque.
I changed to Barnett springs for CB750, longer but not that stiff. The total spring force is probably similar when compressed.
I got slipping clutch (at around 90 whp) so Barnett springs for CB550 went in. Same lenght as CB750 version but are a little bit stiffer according to Dynoman that also sell them.
I added a washer under as extra preload of the springs. Not hard for clutch hand.

The clutch will get a billet pressure plate when I have time to mount it.
http://forums.sohc4.net/index.php/topic,165531.msg2029452.html#msg2029452

Strange that the clutch keep together. The alu parts that hold the pack together look fragile, the 4 towers from the bolts inside springs included.

paulreade · « **Reply #19 on:** January 19, 2019, 01:32:20 am »

Cheers guys for all your assistance here. Everything back together and running fine. The ck1145 kit works well with the replacement standard springs. Slightly stiffer clutch lever but no slippage. Transformed the bike.
I now need to look at the tuning aspects of the bike so I guess I'm going to need the 'my cb750 book' - can someone advise which version is the latest, is there an update due, and best place to secure a copy ?
Once again many thanks - it's going to be a pleasure seeing this bike out on the roads again in spring !

PeWe · « **Reply #20 on:** January 19, 2019, 12:20:17 pm »

Hondamans book available from Lulu books
http://www.lulu.com/shop/mark-paris/my-cb750-book-hardcover-edition/hardcover/product-22322967.html
They have special deals time to time. Maybe still possible to get 15% off
http://forums.sohc4.net/index.php/topic,65293.0.html

Maybe soon again.

paulreade · « **Reply #21 on:** January 22, 2019, 04:49:38 am »

Copy ordered, 15% off. Looking forward to a good read.

paulreade · « **Reply #22 on:** March 09, 2019, 08:58:44 am »

Book arrived and a very informative read - highly recommended. Cannot believe how poor the Haynes manual is !!

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Author Topic: Cb750 k6 clutch query (Read 2335 times)