Lockup clutch question

[mike J]

I just about have my lock up clutch finished and hope to get to run this weekend. I was wondering what some of you guys have run as far as springs and weights? I also had another question that maybe you guys can answer. Is it possible to slow down how the bike reacts by altering the spring pressure? Thanks Mike J

[RacingJake]

Start with 200 pounds static spring pressure and just three bolts/nuts on the arm's.

I'm using Schnitz springs rated at 41 pounds at 1 inch, but my MRE lockup only compresses them to 1 1/4 of an inch so I'm around 190 pounds static. I use 6 bolts/nuts on the arms. I can run 1.38 60 footer's all day and no slippage on the topend.

[mike J]

Jake, how are you measuring your static pressure? Mike J

[lecroy]

I wrote a little program that you may want to play with to help you calculate the force on the pack.

http://www.dragbike.com/forum/forum_posts.asp?TID=344&PN=1

Once you know the how far the springs are compressed, it is simple enough to measure their force with a force guage.

I am not even going to toss out numbers for you. There are so many things to consider. Track conditions, power of the engine, gearing, pack thickness, gap, bike and rider weight, tire size .... and on and on. I end up just chasing my tail a lot.

Why do you want to run a lockup anyway?













[/url]

[rosco15]

I'm running 209 static. I have all the arms on with bolts and nuts on four of them. My bike probably makes almost 140 HP. I would start on the light side or you will kill the motor if your dumping the clutch out.

[mike J]

Lecroy, my reason for wanting to run the lock up are this, I installed new clutch plates (Suzuki) a few months ago and I can feel the clutch slipping again in 4th gear. I also have the stock rear wheel with a hard street tire. I want be able to slow down the shock of the clutch release to keep the tire from spinning, I'm thinking that softer springs would help this. My last reason is this, my bike doesn't react very quickly (heavy bike, 200 lb rider, stock tire, weak motor) If I leave when the last yellow light comes on I'm late on my reaction times , usually .07 to .150. If I can slow down or soften up the clutch maybe I can leave on the next to last yellow. Right now I have to try and time it to leave between the last and next to last yellow light if that makes sense and that's a very hard thing to do.

[rosco15]

When you stage just shove the bike in further. It will come out of the beams faster and make your reaction times quicker. Also try letting the clutch out till the bike just begins to move then pull it back in a hair. That way when you let go you will move instantly.

[lecroy]

I would start on the light side or you will kill the motor if your dumping the clutch out.

And there goes the new plates.

"I installed new clutch plates (Suzuki) a few months ago and I can feel the clutch slipping again in 4th gear."

Ah, the feel.

"(heavy bike, 200 lb rider, stock tire, weak motor) "

This seems to conflict with the first comment. Weak motors don't blow a new pack away in 4th unless there is something wrong.

It could be that the "feel" is not correct, or the springs / gap are not set right.

Why the hard rubber street tire?

[mike J]

Well what I may be feeling is tire slip. I don't know what my local track uses for traction compund but I do know that if you get out of the groove it's slicker than dry pavement, go figure. The hard street tire is just because I want to keep it 100% streetable and not have to replace tires every 1000 miles. I'm more interested in the lockup because it should let me leave softer (weaker springs) and not spin the tire. I agree that the new clutch shouldn't be slipping with a weak motor but it's either that or wheel spin. I'm assuming that if my clutch is slipping I should see more mph with the lockup. Mike J

[RacingJake]

Jake, how are you measuring your static pressure? Mike J

It's not the best but I use a digital bathroom scale, a ruler and push the spring down to 1 1/4 and get a ball park reading :?

[mike J]

OK, ran my lockup this weekend. Bike didn't gain anything anywhere so I guess my clutch hasn't been slipping. I'm still fighting tire spin problems. I may be trying to run too low air pressure in the tire. Anyone played with how soft you can run the spring pressure? What will happen if it's too soft, burn the clutch plates? Mike J

[rosco15]

If I go too soft it will turn the shift light on when I pop the clutch out. Right near the tree my arms come in and start to lock it up.

[lecroy]

Not a simple problem in a lot of cases. Glad to hear that your diving in feet first.

Spring pressure is again, not a one size fits all. I played around with numbers below 100 pounds. Too low (0) and the clutch will never enguage. At this extrem, no your not going to damage the pack. As you start to add weight, the clutch will start to enguage, and now you will slip. The more you slip, the more clutch dust in your oil and the more often you need to change the pack the hotter things get. Even with very low spring numbers, you may still come out too hard because once things start moving that arm weight is going to start kicking in.

I think you have you work cut out for you. That hard rubber and wanting to keep it a street bike is just not a good combination for a drag strip.

[lecroy]

If I go too soft it will turn the shift light on when I pop the clutch out. Right near the tree my arms come in and start to lock it up.

My auto has a programmable dead time for this. So, if the wheel spins, or you launch higher than the shift point it will not shift until the timeout. I normally set this to about a half second.

[nastyjones]

Mike,

If your tire is still spinning on launch with the lock-up then it is not set correctly. We settled on well used soft gs750 springs on our low 9 second gs1000. The clutch pull was so soft I couldn't believe it. We then concentrated on weights. We had the bike running a best of 1.25-60 foots.
I tried lots of weight combos on the arms til we found one that started to "come in" just at the 60 ft mark.
On launch the bike would spin the tire maybe 1/2 a revolution then bite & be gone.

Paul