Author Topic: CB750 clutch for more torque - clutch OK with 93.1 rwhp, 87.2Nm (64.3 ft lb)  (Read 3967 times)

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Offline PeWe

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I have got clutch slip during break-in period  with bursts of hard accelerations followed by tough decelerations. It slips on 3:rd at quick shift from 2.nd and to 4:th. Sudden slip on 4 and 5 when WOT and slightly less.
Oil today is Motul 3000 mineral 20W-50 (Motorcycle oil, JASO MA), before that Motul 3000 mineral 10W-40

The used clutch (cheap Cruzinimage without metal particels in lining) worked well with 836 and +80rwhp.
1005cc pulls much harder! :) (slip despite the smooth DP315 cam)

I have new EBC CK1145 clutch and new aftermarket metal discs I plan to install.  Barnett springs used today and will be used with EBC
- Anyone tried to glass bead the metal discs just a little for better grip?

Other tricks for better clutch behaviour? Clutch should not drag (glued together over night) and must be smooth when taking off.
« Last Edit: June 16, 2017, 04:31:58 am by PeWe »
CB750 K6-76 1005cc JMR Billet block.
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Offline MessnerMoto

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Re: CB750 clutch for more torque - Break-in broke the clutch
« Reply #1 on: May 05, 2017, 06:52:56 am »
I've combined 2 sets of clutch kits to get 8 clutch kit. I used 4 plates from

http://www.ebay.com/itm/KUPPLUNG-SATZ-HONDA-VERSTARKT-CB750-K-71-78-CB750-F-Heavy-Dutch-Clutch-set-/231282733448?hash=item35d9867188:g:FS0AAOSwMzVTw92N&vxp=mtr

Plates from this kit are 2.7mm thick...

End 4 from CycleX clutch kit. Standard thickness. And because I have f2 engine(later clutch basket) it is important to use 1 plate with bigger ears from CycleX kit.

All new steel plates, 7 of them... Removed the "double" steel plate. When I stack all together height comes to a height of standard clutch set for f2... within of 0.1mm. And I've put standard springs.

But this needs to be tested also ;)

Offline PeWe

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Re: CB750 clutch for more torque - Break-in broke the clutch
« Reply #2 on: May 05, 2017, 07:13:08 am »
I have a complete F2 clutch.... so it can be considered.
CycleX plates too. (But this clutch dragged a lot)
CB750 K6-76 1005cc JMR Billet block.
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Offline Jerry Rxman Griffin aka MuthaF'er

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Re: CB750 clutch for more torque - Break-in broke the clutch
« Reply #3 on: May 05, 2017, 09:29:14 am »
There's been a lot of talk here about going with Honda Brand fibers and stiffer springs?? Only issue is finding the outermost disc. Wish I was at the stage of providing results with my CI clutch too. Check in with Bill Benton and Dragracer Frank. They are pulling some serious power without slip AFAIK anyway.
As of today 3/13/2012 my original owner 75 CB750F has made it through 3 wives, er EX-wives. Free at last.  ;-)

Offline MRieck

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Re: CB750 clutch for more torque - Break-in broke the clutch
« Reply #4 on: May 05, 2017, 09:39:38 am »
 Barnett clutch springs should solve the problem. I have bead blasted the steels too...works well for me.
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Offline bwaller

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Re: CB750 clutch for more torque - Break-in broke the clutch
« Reply #5 on: May 05, 2017, 11:57:12 am »
I've bead blasted mine for the first time this off-season Mike. Curious if it will be harder to modulate slipping off the start line?

Offline PeWe

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Re: CB750 clutch for more torque - Break-in broke the clutch
« Reply #6 on: May 05, 2017, 12:01:51 pm »
Barnett clutch springs should solve the problem. I have bead blasted the steels too...works well for me.
Good news, Mike! I'll bead blast my new steels too. Your bike must pull even harder, right?
My billet block is a success! Cool look and no oil leak or film at all from top or bottom or between cylnders! ;)

I have the Barnet springs in. Before HD springs plus a washer under them too. This made the spring to not seat correctly. It could move around and cause deep marks in the bolt towers.
I thought I could wait with clutch replacement but the 1005cc pulls bike really good and I cannot resist twisting the throttle when the sound is wow!.
 I tried to check how low fuel consumption can become by riding according to the numbers on the signs beside the road. I have not succeeded yet, 900km so far!

EDIT: Could not wait for bead blasting the discs. That is a tool I need in my garage that should have triple floor size
I made cross hatch pattern with grit 50 paper. Grinded each side lightly sideways and up-down. Surface not that slick now and no hard edges/scratches grinding the clutch.
I hope I'll install the clutch and change oil tomorrow and have time for a test ride. Full throttle, 2-3-4-5.... ???   :o

If I'll get a slip, glass bead is next to do. (Winter project)
« Last Edit: May 06, 2017, 10:41:27 am by PeWe »
CB750 K6-76 1005cc JMR Billet block.
CB750 K2-75 stock looking project started 2017

Offline dragracer

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Re: CB750 clutch for more torque - Break-in broke the clutch
« Reply #7 on: May 06, 2017, 07:12:11 pm »
I've never had a problem with stock Honda fibers and steels slipping on my bike. I won't use anything else until the OEM parts can no longer be found. As to longevity of aftermarket clutches, ask Wilbur. You couldn't twist his arm to make that mistake again. I've got an F2/3 clutch set up by the way. Although the double steel and odd outer plate are discontinued, they pop up on various sites from time to time. I've got 2 of each left. 😞. Barnett springs are fine but do not use the discs.

Online madmtnmotors

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Re: CB750 clutch for more torque - Break-in broke the clutch
« Reply #8 on: May 06, 2017, 08:41:57 pm »
As to longevity of aftermarket clutches, ask Wilbur.

LOL... I have indeed had similar results with generic friction plates. I managed to strip the friction material off the two innermost disks with a low compression flat top piston 836 build. Like Frank says, Honda friction disks for me until they can't be had or something better comes along.  8)
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Offline MRieck

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Re: CB750 clutch for more torque - Break-in broke the clutch
« Reply #9 on: May 06, 2017, 09:34:54 pm »
As to longevity of aftermarket clutches, ask Wilbur.

LOL... I have indeed had similar results with generic friction plates. I managed to strip the friction material off the two innermost disks with a low compression flat top piston 836 build. Like Frank says, Honda friction disks for me until they can't be had or something better comes along.  8)
Yes
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Offline PeWe

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Re: CB750 clutch for more torque - Break-in broke the clutch
« Reply #10 on: May 06, 2017, 11:41:02 pm »
Thanks guys for sharing your experiences!

How to be sure about real Honda discs? They must have had more than one manufacturer of discs?
All Honda labeled discs are good?
Anyone that had compared EBC with Honda OEM?
CB750 K6-76 1005cc JMR Billet block.
CB750 K2-75 stock looking project started 2017

Offline Big Jay

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Re: CB750 clutch for more torque - Break-in broke the clutch
« Reply #11 on: May 07, 2017, 12:20:31 am »
Put our extra plate clutch in it. You can't make enough power to slop it.

Offline PeWe

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Re: CB750 clutch for more torque - Break-in broke the clutch
« Reply #12 on: May 07, 2017, 12:34:18 am »
 I'll replace the clutch today. This summer will show if more discs is needed ;)
Jay, 1 detail, though. Is there a kit for later clutch? K6-F2.  The outer disc must have the wider ears.

I used 8 disc clutch in the 80's, all discs looked the same, even the outer that broke. That happened twice since the outer disc had too much play in the basket. The last one below, photo taken during the restore 2010-2013

I see now that the pieces are not positioned correctly  ;D
EDIT: This is a 8 disc HD clutch kit. I do not recall the brand.  NOT APE or Barnett

EDIT again: Had a 160km ride. EBC clutch feels smooth at take off as needed. I did not drive hard, first time for a long period of time I could avoid twisting the throttle a lot. Clutch had a chance to break-in.
« Last Edit: May 07, 2017, 11:06:24 am by PeWe »
CB750 K6-76 1005cc JMR Billet block.
CB750 K2-75 stock looking project started 2017

Offline Sam Green Racing

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Re: CB750 clutch for more torque - Break-in broke the clutch
« Reply #13 on: May 07, 2017, 11:23:21 am »
I have to agree with Frank that OEM plates and springs are quite OK in a tuned 836 motor.
The one I built made 86bhp and 60flb torque. No problems in 5 seasons drag racing and I don't even remember it having to be adjusted.
 I fitted a set of EBC fibres in my VFR400R and it caused it to vibrate like hell, I swapped to Honda plates and the vibration stopped.
C95 sprint bike.
CB95 hybrid race bike
CB95 race bike
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Offline cbr954

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Re: CB750 clutch for more torque - Break-in broke the clutch
« Reply #14 on: May 07, 2017, 11:40:09 am »
I have been running the cycle x extreme clutch kit w/stock springs in my 970 street motor for a couple of years now, seems to be holding up well. 
03 CBR954RR, 72 750 chopper(970cc
F2 head), 2017 CRF450R, 2001 CR250R, 72 CB500, 79 XR250, 04 CRF50,70's soon to be rebuilt cb750 drag bike.

Offline dragracer

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Re: CB750 clutch for more torque - Break-in broke the clutch
« Reply #15 on: May 07, 2017, 01:17:41 pm »
PeWe, I'm not sure if you carefully inspected your clutch hub but over time, the steels will eat into the aluminum and not allow the plates to move freely. This not only affects disengagement but engagement as well as can cause slippage. Its more prevalent in my experience with high horsepower engines. Pull all the plates out and rub your hand along the lines to feel for indentations. Replace that hub if its not smooth.

Offline PeWe

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Re: CB750 clutch for more torque - Break-in broke the clutch
« Reply #16 on: May 07, 2017, 02:10:22 pm »
Thanks for your inputs guys!

The hub has marks after the steel plates, but not that it willl make the plates to move less freely and fall into a notch. I'll have this in mind. I have another K6 clutch with less marks I can use if needed. Complete F2 clutch too...

The clutch operate easier now, maybe due to the new metal discs that have tighter fit in the alu splines less wiggle and lock-up?

There is a huge difference torque wise with 1005cc, JE pistons 10.5:1 compared with my earlier 836cc, similar CR. 80 rwhp. The power is much rougher. I need to think how I shift gear and apply power. A small wait time between a shift and twist so the clutch get time to grip is OK for me, no clock in the end of the road showing my time!

1005cc kit bother less about HM300 4-4 without diffusers than the 836 that preferred a rather open 4-1 to deliver power.
I guess that a 4-1 will unchain even more. But the 4-4 has so good sound.

Setup today:
1005cc JE 71.25mm pistons  customized by Dynoman to give CR 10.5:1 with 24.4cc chambers
JMR Billet block
Ported K head, 34mm in valves, 28mm ex  Kibblewhite 5mm valve kit
DP315 cam
Ape Ultra crank plus lightened alternator
Undercutted trans 2,3,4
Carbs: Mikuni TMR32
Exhaust: 4-4 HM300 replica from Yamiya
No oil leaks!  ;D
CB750 K6-76 1005cc JMR Billet block.
CB750 K2-75 stock looking project started 2017

Offline cbr954

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Re: CB750 clutch for more torque - Break-in broke the clutch
« Reply #17 on: May 07, 2017, 03:14:09 pm »
Nothing compares to the sound of open HM300.  My dad has a oem set on his stock 74.  I like to follow him when we would ride so I could hear the sound.
03 CBR954RR, 72 750 chopper(970cc
F2 head), 2017 CRF450R, 2001 CR250R, 72 CB500, 79 XR250, 04 CRF50,70's soon to be rebuilt cb750 drag bike.

Offline Jerry Rxman Griffin aka MuthaF'er

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Re: CB750 clutch for more torque - Break-in broke the clutch
« Reply #18 on: May 07, 2017, 07:26:21 pm »
Put our extra plate clutch in it. You can't make enough power to slop it.

Jay, is your kit a direct replacement for the early clutch and/or the wider 77/78 clutch basket?
As of today 3/13/2012 my original owner 75 CB750F has made it through 3 wives, er EX-wives. Free at last.  ;-)

Offline dragracer

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Re: CB750 clutch for more torque - Break-in broke the clutch
« Reply #19 on: May 07, 2017, 08:42:16 pm »
Put our extra plate clutch in it. You can't make enough power to slop it.

Jay, is your kit a direct replacement for the early clutch and/or the wider 77/78 clutch basket?

Great question Jerry. Curious what the actual stack height might be myself.

I have one for the rest of the group; does anyone know the exact stack height measurement of an OEM set of F/2/3 steels and fibers versus the stack height for the early K???

Offline Sam Green Racing

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Re: CB750 clutch for more torque - Break-in broke the clutch
« Reply #20 on: May 08, 2017, 10:14:25 am »
Another thing we are overlooking here, most Honda gearboxes don't require the use of the clutch when changing up, why not give it a try PeWe.
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Offline PeWe

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Re: CB750 clutch for more torque - Break-in broke the clutch
« Reply #21 on: May 08, 2017, 10:50:08 am »
When I changing up I do not press the lever that much. But still lift the plates from each other.

I just release throttle and shift as when the clutch cable is snapped? :) In the land between,  acceleration turns to decelaration and trans has no press in any direction.

I have found an old thread about APE clutch. If I shold use an 8-9 clutch variant, the outer discs must fit my basket for wider tabs. Honda call this disc for disc B.
http://forums.sohc4.net/index.php/topic,69523.0.html

Thanks for the driving hints! :)
« Last Edit: May 08, 2017, 10:54:11 am by PeWe »
CB750 K6-76 1005cc JMR Billet block.
CB750 K2-75 stock looking project started 2017

Offline PeWe

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Re: CB750 clutch for more torque - Break-in broke the clutch
« Reply #22 on: May 08, 2017, 12:41:48 pm »
One more thing... Springs. Barnett is often recommended so I ordered a set a few years ago and they feel good.
- Now I see that there are 2 versions according to Dynoman
http://www.dynoman.net/engine/clutch/barnett.html

Barnett  HD Spring set
(recommended for street to hot street)
501-56-04015

Barnett  Drag Racing Spring set
(recommended for 1000cc or larger motors)
501-66-04010

I have these in, 501-56-04015.

Anyone tried 501-66-04010.  Much harder? Barnett specify them for CB550 and other models, not CB750.

The part no seems to refer to the spring rate, 56 Lb vs 66 Lb. I found another thread where these springs were mentioned http://forums.sohc4.net/index.php/topic,157284.msg1802235.html#msg1802235
« Last Edit: May 08, 2017, 02:03:34 pm by PeWe »
CB750 K6-76 1005cc JMR Billet block.
CB750 K2-75 stock looking project started 2017

Offline PeWe

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Re: CB750 clutch for more torque - Break-in broke the clutch
« Reply #23 on: May 08, 2017, 09:58:26 pm »
I hope my left hand will accept the harder clutch springs ::)
I'll test the harder springs. I found a seller that provides cheap shipping to me. No meaning order stuff for 15-25 and pay additional 20-70 for shipping that will trigger the customs with another +30%. (under 50 is usually no customs+vat)

Here FREE shipping and only $15US for the springs
http://www.ebay.com/itm/231391835515
« Last Edit: May 09, 2017, 10:45:36 am by PeWe »
CB750 K6-76 1005cc JMR Billet block.
CB750 K2-75 stock looking project started 2017

Offline BPellerine

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Re: CB750 clutch for more torque - Break-in broke the clutch
« Reply #24 on: May 09, 2017, 09:05:24 am »
just wondering is there a problem with Barnett clutch kits?I have one kicking around.bill
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