Topic: heavy duty drag racing clutch systems

[gschuld]

I'd like to get opinions regarding clutch options.  The challenge is for somethihg that can stand up to a full slick, ladder bar, big bore powered dragster, launching at high rpm off a two step.  Basically a rough environment for a cb750 clutch.

There have been a few revisions/redesigns of the clutch system from the factory over the years, some details below(more in the next posting).  If a full lock up clutch can be avoided, that would be great.

George

[gschuld]

The heavy duty clutch hub was offered in the 1978 RC catalog.

George

[POPS 911]

Who made a FULL LOCK UP CLUTCH system for the SOHC750 ??   I Talked to Tony and he said he never made one back in the day. KZ and Suzuki there must be more than a few and also the HARLEY SYSTEMS on drag bikes - 1 gear. That 750 Turbo V-Twin Ducati at Valdosta had a hand built system that team made up for that drag bike = real wrench spinners.

[gschuld]

Cycle X makes and sells a lock up clutch for the cb750.  I know back when these big bore cb750 engines were being heavily raced in the 70s, they all, or nearly all, ran without lockup clutches.

The biggest twin and triple engine monsters ran separate auto based clutches and Leno 2 speed auto transmissions, but that is a whole different subject.

Stroker, big bore, high compression, ported head, 327 cammed N/A 1162cc drag motors were still using factory cb750 based clutch systems.  RC offered a heavy duty clutch hub by 1978 or slightly earlier (the 1976 RC catalog had no mention of a new clutch hub)  RC, Action Fours, and MTC, Barnett (among others) offered aftermarket clutch discs and springs.

I'd like to know, for example, what the "hot setup" was back then for a high powered big bore N/A single engine dragster.  And what the "hot setup" is today.  And perhaps a comparison between them to understand why the modern thinking, gained from an extra 30 years of experience, is better.

George

[bear]

George,

I can't offer an opinion from a drag racing perspective but I can tell you that the cush drive or clutch hub as you call it over there is without doubt the key component if you want any sort of drive line reliability out of a 100+hp SOHC motor.
Many drive line failures ie; damaged gear sets, damaged shift forks,  broken chain tensioners, broken primary chains and a lot of clutch problems often come back to a failed clutch hub that's not up to the task.

As for clutches,  l reckon I could write a book on the many and veried attempted solutions we've tried to sort that one out.

Cheers,
Brian

[gschuld]

As for clutches,  l reckon I could write a book on the many and veried attempted solutions we've tried to sort that one out.

Cheers,
Brian

Please, feel free.  I'd read that book.....

George

[Big Jay]

Our extra plate clutch shown abobe ran 10:30s all tday long without a lockup.

[gschuld]

Jay,

Thanks for jumping in...

I have heard and read lots of good things about your extra plate clutch kit.  For curiosity, are you aware of anyone using your extra plate kit in a full slick tire, ladder bar, big bore cb750?  I ask since the strain on a clutch hub/basket/clutch plates would be measurably greater under a full throttle two step launch with a 5.5" full slick and ladder bars compared to a no bar street legal tire.

In your experience, which generation clutch hub would you consider ideal for the job and would you recommend any modifications like Hondaman's extra hole mods in the clutch basket for extra oil flow to the plates?

Thanks in advance.

George

[bear]

We have used a six bolt GL1000 clutch in the past to good affect.
There is a fair bit of enginering required though.

As for the hubs, it's the rubbers that are the limiting factor.
Honda rubbers are rated at around 70 duro and all the after market rubbers available  aren't much stronger.
All rubbers have a limited life in a comp motor no matter what you use.
We expect to get 100 hrs out of the current settup.

Cheers,
Brian

[754]

I think the hardest thing you can do to it is dumping it in first.. I think slipping it is far easier on components...everything is tightened up and under torque when the full hit comes on..
 Bill picked up an NOS RC extra plate from just up the lake here  with copper coated steels.. We will see how it works.
 Any thoughts on the copper plating ?

[NitroHunter]

Who made a FULL LOCK UP CLUTCH system for the SOHC750 ??

I know MRE made at least ONE.   

[gschuld]

We have used a six bolt GL1000 clutch in the past to good affect.
There is a fair bit of enginering required though.

As for the hubs, it's the rubbers that are the limiting factor.
Honda rubbers are rated at around 70 duro and all the after market rubbers available  aren't much stronger.
All rubbers have a limited life in a comp motor no matter what you use.
We expect to get 100 hrs out of the current settup.

Cheers,
Brian

Bear,

I have been reading about stronger clutch hub (cush drive) rubbers for high output engines.  M3 sells them, below.

I'd be interested to hear about the modifications required to adapt a gl1000 clutch system to a cb750.  If for no other reason but curiosity.  It's good to keep up with possible options.  For me it's about chasing the weakest link in the system.  The sudden jolt from a big bore engine, full throttle, full slick, ladder bar launch has got to be pretty severe on a factory clutch.

George

[NitroHunter]

The early Goldwing 6 spring hubs have a different drive spline. I've seen one bored out and re-sleeved with the 750 style.

[Bill/BentON Racing]

I'll call Jay Regan on that!  , Bill

[POPS 911]

Since CYCLE-X makes one ? why not buy a new CYCLE-X LOCK UP and run in your motor, then do a write up on the improvement [ Before and After the install ] Valdosta track with that smooth all concrete , low DA would be a excellent place for this ET trial. .  Bill MWS should be running one of those in his COBRA powered ST/ET bike maybe 9.90s ??

[gschuld]

Yes, it is an option.  I have several purely logistical reasons to prefer not to go with a lock up clutch set up. 

-This dragster will likely be raced for only a few events. Harder to justify(if it isn't necessary, don't know yet).
-I am trying to keep it as period correct as feasible, billet parts are working against that.
-The Cycle X lock up clutch system is advertised as "brand new", presumably designed for the monster Cycle X dragbike project, which I'm guessing hasn't run in anger yet.  So I have no idea if the new lock up clutch system has been tested or how much(or on what driveline wise) it has been tested.  Reliability is important to me, field testing critical new driveline parts doesn't interest me if that is what is required.  I am not in it for the "long haul".

Of course I could check with Cycle X to see about the lock up status. 
And I will.  But I'd like to know how it was handled back then, when hundreds of these cb750 big bore dragbikes were successfully running slicks and no lock up.

I assume there is a tipping point somewhere.  Say, overall power level and slick size, X 60ft times, weight of overall bike and rider, rider technique. All would impact the strain on the clutch at launch I would think.

Frankie has been running consistent mid 10s on his fairly heavy stretched F bike for years using all standard factory hub/basket/ hub cush rubbers, even clutch plates/cork, with only stiffer springs if I remember correctly.  And he has run a 5.5" slick with the same motor/chassis with success previously with the same clutch.  1.4 60ft times offers a pretty decent test with a reasonably heavy stretched f chassis.

I'm thinking the dragster would not offer TOO much more strain on a clutch compared to Frankie's bike on the 5.5 slick.  The dragster is 75lbs lighter and should have a similar power output, running the very same 5.5x18 ET Drag slick as Frankie has in the past.

The extra bite(perhaps 1.3 60ft vs Frankie's 1.4) offered by the two step launch and ladder bars may well be partially offset by the lower overall weight of thr dragster chssis being propelled.

I don't have a problem getting what is necessary, I'd just like to get a feel for what is really necessary...

George

[Bill/BentON Racing]

CycleX lockup does work, is not new,  I have one, Bear has or does use them!, Bill

[NalleyRacing]

Larry Hayes also runs one in his Hilborn injected turbo funny bike..2step, long bars, big slick...

[gschuld]

Helpful news, that's great.

Any ideas what Larry Hayes funnibike has produced in the 60ft times?

I'm trying to get an idea about run time, power levels, etc.  Does Larry Hayes run much?  That is certainly far more strain than I could conceivably expect.

I'd be interested in knowing who has run in the 8s or 9s with a cb750 based engine and what clutch they were running.

How about the old high 8s, low 9s N/A big bore "Ancient Warrier" Billy?  Did you end up with that bike?  What clutch was he running?

George

[kmb69]

.....
I have been reading about stronger clutch hub (cush drive) rubbers for high output engines.  M3 sells them, below.
.....

The kit from France is of better quality and cheaper than Mr. Magoo's (M3) IMO. Bought one of Magoo's, got the shirt! I have used the French kit to rebuild several primaries and they work GOOD.

http://honda60-70s.net/Pieces/23110-300-030_GB/23110-300-030_gb.html

[MRieck]

I have one of the French kits in my current engine.

[gschuld]

Good to know, thanks.

George

[Bill/BentON Racing]

Hehe!!!  Took this po boy 2 years to save up enough for it,  thank you  Gary Pena. ..and Byron Hines! K, Bill

[dragracer]

What type clutch did Gary run in that motor Bill?? Modified basket/welded?

[Bill/BentON Racing]

 I'll call him and ask tomorrow, Bill