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BEC Clutch & Pulling Away
Jeano - 2/12/21 at 11:36 AM

Morning All,

I sold my ZX12R Dax Rush a few years ago and i want to fulfill my itch once more. The one thing i didnt like about my BEC was the clutch when pulling away. Im unsure if it was just my car.

Im aware the BEC engine cars are difficult to pull away but i couldn't launch my car off the line ever, because it would just stall. I had to move away very slowly. Are all BEC cars like this?

russbost - 2/12/21 at 11:50 AM

quote:
Originally posted by Jeano
Morning All,

I sold my ZX12R Dax Rush a few years ago and i want to fulfill my itch once more. The one thing i didnt like about my BEC was the clutch when pulling away. Im unsure if it was just my car.

Im aware the BEC engine cars are difficult to pull away but i couldn't launch my car off the line ever, because it would just stall. I had to move away very slowly. Are all BEC cars like this?


Absolutely not, the only BEC I've known that was like this was an old Fireblade engined car & the early Fireblade may have been a great engine in a bike, but it was far from ideal in a car, a distinct lack of torque, which is where the whole, "bike engines have no torque" (absolute rubbish!) came from

I have the ZZR1400 engine & can easily pull away slowly on tickover should I choose to.a lightweight Rush with the ZX12 should have been similar. I think the ZX12 has a hydraulic clutch same as ZX10 & ZZR1400 do? In which case my guess is that it had a car master cylinder & the ratio of cylinder sizes was "over geared" such that a tiny pedal movement resulted in a large slave cylinder movement, if cable operated then similar "over gearing" can occur if pivot point ratio is too coarse

Simplest answer is use a bike master cylinder if you have a bike slave cyl. If you have a cable operated system adjust the pedal pivot ratio by moving the location point of the cable, more pedal movement for less cable movement is what you want, that way you can use a large portion of the pedal movement to control the clutch engagement in a gentle, slipping manner rather than an on/off switch

Sanzomat - 2/12/21 at 12:53 PM

As above. My R1 engined Locost does need a bit of care on the clutch (cable operated) but just needed a bit of getting used to. One thing to add is that I found the feather lightness of the pedal to be part of the problem. I had to double up the diaphragm springs to cure clutch slip and this had the unintended but very welcome side effect of making the pedal heavier and I find it so much easier to control the taking up of drive now.

Jeano - 2/12/21 at 01:30 PM

Cheers Guys. opens up my world again

smart51 - 2/12/21 at 05:52 PM

When I first built my BEC it was a nightmare. Until I worked out what was wrong. Leverage. I had too much leverage from pedal to clutch cable. The biting point range was a nanometre long. I moved the connection point of the cable until it was touching the boss on the clutch pedal. Much better. Smooth pulling away in traffic with just one foot if you were careful. I guess you could move the other end towards the pivot point as well if you wanted to.

motorcycle_mayhem - 2/12/21 at 07:42 PM

quote:
Originally posted by Jeano
Morning All,

I
Im aware the BEC engine cars are difficult to pull away but i couldn't launch my car off the line ever, because it would just stall. I had to move away very slowly. Are all BEC cars like this?


No, if a GSXR750 can repeatedly launch a 418Kg Westfield, it may be a technique issue.

https://www.youtube.com/watch?v=hUjR3JWL0WY

ReMan - 2/12/21 at 10:44 PM

Agreed, heavy duty springs and the right pedal pivot points make for a perfectly OK experience.
Also gearing too, with my baby fire blade the difference getting moving between a 3.62 and 3.38 axel is significant

number-1 - 3/12/21 at 04:42 PM

Ive had a couple of BEC.

The first was a GSXR 1100 WP engine track car. The clutch on that was either......at a stand still.......or warp speed 9. No in between.

The other was a road legal single seater Road Runner Racing SR1. Once you figure out the pressures needed etc it wasn't too bad. As someone has already said, pulling away on tickover is the easiest way

TimC - 4/12/21 at 12:27 AM

More here:
http://www.locostbuilders.co.uk/viewthread.php?tid=211450

sonic - 4/12/21 at 08:15 PM

I think it must have been a setup issue, i have a Rush with a 919 Blade engine and never had a problem. uprated clutch spring and it will pull away on tickover, all my other cars are Auto's and this is the only one i have with a clutch and in 2 years of owning it i think i have only stalled it twice