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

[Ilja]

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 

Wow nice power, well done!

I have an ebc clutch with HD (or super HD) springs and it withstands at least 111hp and 110nm dyno confirmed. And my bike makes more power and boost now so its even more in reality.

With the stock plates and springs it started slipping 0.5sec after the turbo kicks in.. no way in hell it would hold. 😄

[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 

Wow nice power, well done!

I have an ebc clutch with HD (or super HD) springs and it withstands at least 111hp and 110nm dyno confirmed. And my bike makes more power and boost now so its even more in reality.

With the stock plates and springs it started slipping 0.5sec after the turbo kicks in.. no way in hell it would hold. 😄

The sudden high torque increase the turbo create needs a good clutch.

My car has modified program and the two piece flywheel vibrates  a lot if flooring too early on gear 3-6.  The torque increase is too much for the drive train if driving careless.

[Nose736]

Honda 305 hawk springs should solve this I should think ,Run them in 970cc  100rwhp  at Mosport without any issues.

[PeWe]

Honda 305 hawk springs should solve this I should think ,Run them in 970cc  100rwhp  at Mosport without any issues.

I guess that I have those springs in now.
Barnett 501-66-04010 that have a long list of matching bikes, CB550 and 1970-1980 Honda 305 Hawk/Scrambler among others.
I have got slip again. Prepared 6 metal discs today with sand blast and heavy grit paper making radial scratches.
- Which clutch do you use?

I'll swap the discs tomorrow and put washers under the springs as I had in the 80's with a 8 disc kit. Back than only 836, not the strong torque the 1005cc kit gives today with DP315 cam. Torque arrives early, pulls really fine before 3000rpm, max torque at 6600.

I have thoughts about Dynoman +2 disc clutch.

I think the clutch grip can live longer if I shift gear up, wait a little before max throttle so clutch have time to land and grip. Or avoid using the clutch as Sam Green wrote earlier. OK when gearing down.

I'll change oil too, from Motul 7100 10W-50 today to Red Line 20W-50, both full synth and give a nice working gearbox finding neutral when warm too.

[MRieck]

I have used a OEM clutch pack (maximum height) with Barnett springs for years. My old 915 made a little over 97HP and it held no problem. Holds with over 1000cc

[dragracer]

Do you have the correct, matching clutch basket and hub in your bike?? The F2/3 parts cannot be mixed and matched with K clutch parts. Also, did you double check the splines on the hub?? If there is any wear from the plates eating into the aluminum, it could have an impact on the clutch locking up. I drag racer my bike with stock OEM plates and stock springs. I've had low 1.30, sixty foot times and run as quick as 10.36. I experienced no clutch slippage that was evident. During race day, we make many passes with relative consistency. A slipping clutch would not net repetitive ET's. Personally, I would start with a matching basket, hub, lifter plate and  pressure plate using OEM clutches and Barnett springs.  Buy a new clutch cable and properly adjust it with the correct free play at the lever. Too little play at the lever could be causing the clutch to remain partially engaged leading to slippage under heavy load.

[PeWe]

Do you have the correct, matching clutch basket and hub in your bike?? The F2/3 parts cannot be mixed and matched with K clutch parts. Also, did you double check the splines on the hub?? If there is any wear from the plates eating into the aluminum, it could have an impact on the clutch locking up. I drag racer my bike with stock OEM plates and stock springs. I've had low 1.30, sixty foot times and run as quick as 10.36. I experienced no clutch slippage that was evident. During race day, we make many passes with relative consistency. A slipping clutch would not net repetitive ET's. Personally, I would start with a matching basket, hub, lifter plate and  pressure plate using OEM clutches and Barnett springs.  Buy a new clutch cable and properly adjust it with the correct free play at the lever. Too little play at the lever could be causing the clutch to remain partially engaged leading to slippage under heavy load.

Thanks for sharing your experiences guys!

Yes, the clutch has matching parts. I replaced my old K6 clutch with a fresher K6 found on eBay, basket and both hub parts (hub + plate with towers for springs) + primary hub that I sent to germany for new cush rubbers + new needle bearings).
Not the longer hub the later clutch got. Splines are OK. My old had small dents after the metals

I'll swap metal discs today + adding washers under springs. I'll also increase the play of the clutch lever since I have seen that play will change rather much if engine is cold or warm. I usually adjust that on the adjuster when riding.

The clutch has worked fine for around 3000km. A few gearing mistakes with slow clutch hand - quick throttle hand will polish the metals.

- Anyone here that tried the Dynoman +2 clutch?

I have EBC fibers in now. I have not much used CycleX plates that were prone to stick together really quick. Dragging clutch better then slipping

I'll do an oil change too. Use the oil leftovers I have. Motul 5100 semi + Motul 3000 mineral 20W-50. This to rinse the engine before change oil again to Red Line 20W-50.

Full synth specified to be OK with wet clutch must be OK, right?

[PeWe]

Update:
Last slip can be my fault alone
- First thing I checked before doing the clutch was to check clutch lever play. NO play at all! (I had play before but not much)
- Out with the clutch, in with the fresh metals I sand blasted and scratched some extra with rough paper.
- 3mm 2mm washers under the springs. (Same washers I got with a 8 disc heavy duty clutch kit in the 80's)

Clutch work much better now. I have good play at the handle clutch lever but still better working range than before where clutch engaged in the outer end.

Root cause: Clutch lever arm on clutch cover had no play. Today tightened to stop, then opened almost 1/2 turn. Before too little, max 1/4 turn without recheck after. I'll check soon again that it has play.

[livefast_dieold]

Update:
Last slip can be my fault alone
- First thing I checked before doing the clutch was to check clutch lever play. NO play at all! (I had play before but not much)
- Out with the clutch, in with the fresh metals I sand blasted and scratched some extra with rough paper.
- 3mm washers under the springs. (Same washers I got with a 8 disc heavy duty clutch kit in the 80's)

Clutch work much better now. I have good play at the handle clutch lever but still better working range than before where clutch engaged in the outer end.

Root cause: Clutch lever arm on clutch cover had no play. Today tightened to stop, then opened almost 1/2 turn. Before too little, max 1/4 turn without recheck after. I'll check soon again that it has play.

Hey PeWe,

I?m thinking to change my barnett clutch as well. It sticks a lot and it's a pain everytime I have to start the bike. Not to mention race starts: it closes when it wants and it's quite unpredictable. I can easily get an EBC clutch, is it what you are using. If so with normal or HD duty springs?

Thanks!
Riccardo

[PeWe]

Hi Riccardo,

I use Barnett springs  501-66-04010 slightly harder than the Barnett CB750 with the EBC clutch plates. Metal plates sand blasted and added 3mm washers under them last time.

The negative thing with this is the indent for the springs are filled by the washers. The sping can come in contact with the alu tower for the pressure plate screw and make marks.

I used washers in the 80's when added a HD 8 disc clutch where the washers were included.

//Per

[livefast_dieold]

Hi Riccardo,

I use Barnett springs  501-66-04010 slightly harder than the Barnett CB750 with the EBC clutch plates. Metal plates sand blasted and added 3mm washers under them last time.

The negative thing with this is the indent for the springs are filled by the washers. The sping can come in contact with the alu tower for the pressure plate screw and make marks.

I used washers in the 80's when added a HD 8 disc clutch where the washers were included.

//Per

Thanks! Just to avoid confusion, you add 3mm washers to the springs right?

[PeWe]

Hi Riccardo,

I use Barnett springs  501-66-04010 slightly harder than the Barnett CB750 with the EBC clutch plates. Metal plates sand blasted and added 3mm 2mm washers under them last time.

The negative thing with this is the indent for the springs are filled by the washers. The sping can come in contact with the alu tower for the pressure plate screw and make marks.

I used washers in the 80's when added a HD 8 disc clutch where the washers were included.

//Per

Thanks! Just to avoid confusion, you add 3mm washers to the springs right?

Sorry, 2mm thick washers.
Important to document with a camera so I can check afterwards what I have done!!
Photo shows the reality 

[livefast_dieold]

Great thanks!

[PeWe]

I could not resist to order billet stuff for the clutch. Can be a good idea with more power and harder springs.
http://www.good-bits.co.uk/product/cb750-sohc-clutch-actuating-hub/
https://www.ebay.co.uk/itm/263157686207?ul_noapp=true&shqty=1#shId

[kmb69]

I could not resist to order billet stuff for the clutch. Can be a good idea with more power and harder springs.
http://www.good-bits.co.uk/product/cb750-sohc-clutch-actuating-hub/
https://www.ebay.co.uk/itm/263157686207?ul_noapp=true&shqty=1#shId

Their eBay add says "May not ship to United States" - "Contact Seller". 

Our own Budman on this forum has a similar solution: http://forums.sohc4.net/index.php/topic,174117.msg2026017.html#msg2026017

[PeWe]

Yes, same about Sweden. I contacted the seller that could fix it or if I ordered via their web page where I wrote my interest after. He sent a PayPal invoice.
I'll update here when I'll install it.

[MRieck]

I have one of Kenny's 4 plate clutch systems and will try it in the spring. Going to the dyno this Wednesday (as long as the weather is OK). Going down 2 main jet sizes (will be running a 127.5)

[PeWe]

Mike, lets see how much better result you will get with better A/F mixture. >100whp is a good test for a clutch!
I hope to get a dyno time before winter. I can't change cam until I have the data of current one, RC295 profile.

[PeWe]

Finally got my thumbs out and installed the billet pressure plate before the stock one fails.
The 4 stock towers for the 4 M6 bolts holding this plate must be next weak area.

[MCRider]

attending

[PeWe]

First impression after a short ride...
Clutch does not change as before when play at handlebar changed when warm compared with cold. Slip could happen if play was perfectly adjusted when warm, no play next ride when cold.

I need to verify this more.

I was extra careful when adjusting the play with stop screw on clutch cover this time. Better with a little bit extra. I adjusted 1/2 turn out from the first soft stop when tighten it (possible to tighten harder, almost 1/4 turn.
I have got slip before when open just a little as 1/4 turn out.

[PeWe]

Update:
I changed the clutch this winter.
F2 clutch with deeper outer steel basket and the matching deeper alu hub and double steel disc in the middle of the pack.

 Friction discs are my old EBC not much used and harder Barnett springs.
The alu pressure plate with the 4 spring towers still the same as earlier clutches.

This means that the spring pretension increase with the depth change/clutch package + 2mm compared to K6 and earlier.

The washers I used under the springs before not needed then.

Result:
Clutch felt good at the first ride today. Less rattle and maybe harder for my left office fingers to shift gear than before

I'll follow Sam's recommendation to not use the clutch when gearing up to save my fingers

The later clutch must be the must for bigger bore CB750.

My other engine build will get a later clutch too.