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

[754]

I had good luck with them.. Both the standard and the extra plate.. They can withstand huge amount of clutch slipping abuse off the line.
 Today, I would try Jays APE clutch, before anything else.

 Btw if anyone has an old Barnett catalog , I would like to get the part numbers for 750 cables. They no longer make them, but do special orders. I bet if you had the number, they would pull a card out of an old RolloDex, and be able to make it. Their nylon lined were the treat.. Perhaps we could get a group bulk order made.

[MRieck]

Motion Pro will make anything you want Frank. Modern cables.

[Bill/BentON Racing]

Not in my opinion. They had some issues, best to adjust when hot. Spring pressure at lever more than some like. OEM plates work well. I've used APE and CycleX all with success. The engine that the Carrillo rod broke,  not its fault,  had a NOS copper coated steels and Barnett springs and discs.  Was RC top of the line kit, 9 plates. Going clean it all and reuse....Bill

[PeWe]

Not in my opinion. They had some issues, best to adjust when hot. Spring pressure at lever more than some like. OEM plates work well. I've used APE and CycleX all with success. The engine that the Carrillo rod broke,  not its fault,  had a NOS copper coated steels and Barnett springs and discs.  Was RC top of the line kit, 9 plates. Going clean it all and reuse....Bill

Bill, which Barnett springs did/do you use? 56  or 66 Lb?  (Standard Barnett deliver with their kit is the 56 Lb)
The std Barnett CB750 spring feels softer than the other HD springs I used in the 80's with an 8-disc kit. Those springs had washers under too.

As mentioned earlier:
Barnett  HD Spring set (This is the std for CB750 Barnett deliver)
(recommended for street to hot street)
501-56-04015

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

[754]

I remember that clutch, Bill. The Barnet was pretty graunchy cold but I did not mind because the abuse it took.
Mike i have a new set of Motion pros on a bike, but never rode with them, have seen the odd complaint though.
I just liked Barnetts service and product, I was a dealer for them..my nylon lined throttle tied in a 5 inch coil, still glides very smoothly with very little effort and I bought it in the early eighties..

[PeWe]

I think I got a clutch slip with EBC plates today. I advanced the ignition and got more power. Got a sudden slip when twisting throttle on 3:rd gear when I tested the advanced ignition.

The tougher springs need to arrive soon. I'll replace the clutch hub too. I have a better one. No additional oiling holes in next. The clutch mod for smoother take offs.

Let's see if my engine demands even more clutch.

[PeWe]

Got the springs and replaced them today. They feel harder when pressing them between thumb and index finger. Very scientific!!
The new do not feel too hard when driving. Feels more like my old HD springs I used in the 80's.

The std Barnett CB750 springs (501-56-04015) are clearly too soft! Maybe OK for 836cc. Better to use the stiffer 501-66-04010 from the very beginning. No pain in clutch hand!

The new  stiffer are not that hard when driving. I replaced the clutch hub too since the old had smooth start mod with additional holes. Used std hub complete with less miles. Did not glass bead the metals, no time to find someone doing it. It will hopefully work as is.

I also flipped the outer slanted disc with grooves showling oil into the clutch. The grooves will hopefully  not showel oil inside the clutch as before when flipped. Clutch feels fine.  Honda introduced the slanted disc to make smoother take off, outer disc sliding a little if I have understood Hondaman's clutch posts correctly

Once I have heard and felt a slipping clutch I'll "hear and feel" slipping clutch when not slipping. Like getting a flat rear tire in 100-130kmh. That feeling will remain later on when tire is fixed. Imagination...

The advance of the ignition gave more power that needed more clutch. Now need of larger main jets (again) and more fuel screws. Let's see what the clutch will say about that 

[Jerry Rxman Griffin aka MuthaF'er]

Progress!

So, no double metal in the middle of the pack. That would make me assume you have a pre-77 basket!?

[PeWe]

Progress!

So, no double metal in the middle of the pack. That would make me assume you have a pre-77 basket!?

No double metal, K6 -76.
I have an F2 clutch on the shelf with double metal disc.
- Maybe possible to replace the double metal with 1 fiber + 1 std metal to get an 8 disc setup? I'll use a disc from a CycleX clutch I have together with the EBC I have in now.
The F2 clutch is complete with the outer basket and clutch cover. The black surface need some grinding, polishing to become alu.

I'll play around with the F2 clutch when I have time. The CycleX clutch came with 8 discs so I can check the clutch pack height and hope it will fit the wiider F2 clutch.

Photos when I stacked 8 discs to the K6 clutch a few years ago. I have to verify this with F2 clutch.

[PeWe]

Update:
F2 clutch will not house 8 std thickness discs. I guess there is not enough splines left for the mating clutch part that might jump out of the splines when using the clutch.

Photo F2 clutch with double metal replaced by std metal + 1 fiber + 1 metal at top

Clutch pack height, std F2 w double metal in the middle, used discs: 39.0mm
8discs no double metal 7 used discs + 1 new:                                    41.8mm

[Jerry Rxman Griffin aka MuthaF'er]

I was curious that you had not used a F2 basket with earlier discs pack installed. That would have created too much 'play'. I haven't done that but 'I know a guy' that installed a K8/F2 clutch pack in a F0/K6 inadvertantly basket and there wasn't enough room. The lever just wouldn't do much, it squealed and the kick lever was doing erratic movements  HE had to replace the basket with the later one.

[kmb69]

.....
I haven't done that but 'I know a guy' that installed a K8/F2 clutch pack in a F0/K6 inadvertantly basket and there wasn't enough room. The lever just wouldn't do much, it squealed and the kick lever was doing erratic movements  HE had to replace the basket with the later one.

Yeah, I bet you brush his teeth each morning!     

[PeWe]

I'll not mix them The F2 complete clutch must have the F2 clutch cover too?
The later with double metal can not run without it, to much play, right?

K6 clutch use same discs as F2 except for the extra thick double metal F2 use.

It would be nice if the F2 clutch could have been 2.5mm deeper so 8 discs could have been used.

Dynoman 8 or 9 disc clutches are made for early and later clutches.
Separate part numbers so the outer disc must be correct for the later with wider tabs.
I do not know if APE has with wider outer disc.

I hope clutch will keep together now. If still slipping, good sign of engine creating power. I'm convinced that I have to switch gear and twist the throttle with correct timing, avoid causing slip, OR do not use clutch at all when gearing up which work fine too.

Lat slip with softer springs was with not completely warm engine, might be one factor too.

[dragracer]

I'm a little confused about clutch slippage. Glad my stock clutch isn't a problem.

[PeWe]

I'm a little confused about clutch slippage. Glad my stock clutch isn't a problem.

Which springs do ypu use?
Glass beaded metals?

[Jerry Rxman Griffin aka MuthaF'er]

Yes, you need the later clutch cover unless you modify the older one by grinding down the ribs.

I don't know how a later clutch without the double would go together and work. It seems it would sit farther back in the basket and not out to the edge?? Perhaps the whole UNIT would have play within the basket and the adjuster would not be long enough to wedge it in??  Any other takers on this question?? KMB69 has the largest stash of parts west of the Mississippi River. Maybe he can piece one together like this and provide an answer?!

Unsure about the 9 plate APE kit. I had directed that basic question, will his kit work with early AND late clutches, to Jay but there was not a response?? Never mind about the first part of my answer - just found one LOL. All the discs have the same size tabs.

[754]

The RC extra plate that went to Billy Bling had copper plated steels, I believe it worked well.
On my Barnett xtra plate, I believe fibers were thinner and I added a stock steel plate.
 One thing not sure PeWe did is orient the steels in same direction...  Examine edge and look for slight curve on edge.

[PeWe]

All metals oriented in same way, sharp edge facing inwards.
Photo above show how. See where the slanted disc is shown together with all metals.  I assembled the package direct after flipping the outer one

- Anyone that has tried Dynoman 8 disc setup?   9 disc not for street, too much on-off ?

[754]

The on or two times, I got the steels glass beaded they gripped better. Not sure about the copper plating, but I think Bill said it worked.

[NitroHunter]

I agree Frank, to me the glass beading made a grip difference. I blasted mine every time they were out, which at one point was quite often.
By far the biggest improvement I ever did was smoothing out ANY gouges in the hub grooves and basket, it made a huge difference I could really feel at the lever. Diligent hand filing worked for me, I'd dress the sharp edge of the floaters tabs too. After getting an expensive thin plate 9 disc hung up in a rough set up and fried it quickly, that got me massaging things and using a good 7 disc with stout springs. The engagement tabs were thicker and didn't gouge the basket slots.

[PeWe]

Thats's a good point, thinner discs dig easier into the basket making marks. My basket look OK, clutch ran smooth with the previous springs, still not that hard with the stiffer.

I have not found any wear limit for the metals, only warpage. I'll can reuse my old ones that got a light blast in the 80's. Glass bead them and have for quick use.
I hope my metals got some additional friction with the cross hatch pattern I grinded with grit 50 paper.

- Which springs do/did you use with bigger bores, guys?

[754]

Keep in mind Nitro,s bike ran 10.0*
If it was me at this point I would be getting one from Jay...he says they will work.

[PeWe]

I'll see what needed. I still have one ace in my sleeve, glass bead the metals. I hope clutch will do the job. Rwhp is hopefully over 90, or even better >95 as the parts should make
Huge difference compared with 836 and 80 or 83rwhp (cams). Soon time for a dyno runs and see the graphs.

[PeWe]

Clutch work fine now
I had a nice ride on country roads today together with a friend that rode a Honda CBR1100XX Super Blackbird -1997, 133rwhp on dyno recently. It has no fairings, Streetfighter look that reduce the top speed and desire to go beyond 220kmh.

He had to gear down several times and really twist the throttle to hang on when I let my CB750 get all from 3:rd gear, from around 80-190 kmh.
He did not need to gear down before when I had 836cc/80rwhp.. I'm positive about an eventual dyno and the graphs.

The recipe now is flipped outer slanted disc (disc B) and the stiffer Barnett springs that do not make clutch lever too hard.... Metals still not glass beaded, only some cross scratches by 50 grit.

No slipping yet and my rear tire is really flat causing cobra movement of the rear in the corners and when passing white lines in the middle of the road.
Ok if there is a cobra like power pushing the bike forward 

[PeWe]

Clutch Ok, no slip.  It withstand 93.1 rwhp@8300rpm / 87.2Nm (64.3 ft lb)@6630rpm
Early torque feels fine in da butt!      

4-4 exhaust (HM300 replicas) restrict some. 7hp more must be possible with more open pipes. More dB for more hp