FJ Dragbike Project

[andyb]

Wait a minute, I thought you were running that as a slider clutch?

[fj1289]

Yes, it was set up as a slider initially. For the last outing (Albuquerque last Oct) I converted to a multistage setup. Still has the base tune since I don't have the rear suspension well enough to even take that yet.

For those that don't keep up with the drag race scene - a little lesson in alternative clutches (starting with stock of course!).   The stock FJ clutch operates like most motorcycle clutches - with the exception of using a single diagram spring vice multiple coil springs.   The clutch friction plates are keyed to and turn with the clutch basket.  The clutch basket is geared to the crankshaft - so the speed of the clutch basket varies directly with engine RPM.  The steels are keyed to the inner clutch hub that is splined to the end of the input shaft of the transmission.

In normal use, the clutch spring pushes on the pressure plate and forces the friction plates and steel pates together, effectively connecting the crankshaft to the transmission (and the rear wheel).
When you pull the clutch lever, the clutch slave (working through the clutch rod - aka "kitty killer", the easily lost ball bearing, and the "top hat" clutch pusher) overcomes spring pressure to move the pressure plate away from the clutch pack and allows the frictional and steels to rotate independently - and engine power to be disconnected from the transmission (and rear wheel).  Most clutches handle both these duties very well. The difficulty occurs when you WANT to slip the clutch - like getting moving from a standing start. The vast majority of motorcyclists have few demands if their clutch - release completely so it doesn't "creep", hold full power so it doesn't slip, and engage smoothly when starting off -- oh, and not build excessive muscles in their left forearm.

As you start demanding more from the clutch, it gets more difficult to meet all the demands. Really up the power of the engine and you have to use a lot more force to keep the clutch pack clamped together. Making all this force with just clutch springs gets to a point where it is difficult to smoothly control the clutch engagement.
Take this to the extreme - lots of power, lots of traction (or maybe not!), and a need to smoothly and quickly engage the clutch (and the need to do it all consistently!) - is where a lot of the art of drag racing lies.

An alternative way to provide a lot of clamping force at high power (high speeds generally and the associated higher RPMs) but still maintain a lighter and more controllable spring pressure is to use centrifugal force to lever more clamping force on the pressure plate. The first common means of accomplishing was the "single stage" lockup. This is a modified pressure plate that incorporates L shaped levers to add increasing force to the pressure plate as the pressure plate spins faster.  Add more weight to the arms to get more clamping pressure to hold more power.  Here's the picture of the last one available from Orient Express...


As you add more weight to hold more power, the added force on the pressure plate comes in sooner and increases more rapidly. As you are trying to apply ever increasing amounts of power on the launch, control becomes more critical. Somewhere along the way, someone thought to use springs to "hold back" the centrifugal arms to delay when they begin to apply added force to the pressure plate.   Depending on how the idea is implemented, it may be possible delay some arms, but allow others to add force sooner. This is known as a "multistage" clutch.

Up to this point, the discussion has been about "wheel driven" lock ups.  The "wheel driven" label comes from the fact the pressure plate spins with the clutch hub that is splined to the trans shaft that is ultimately connected to the rear wheel.  This works well until the rear wheel begins to spin....then, just when you need the clutch to slip a little more, you're getting more pressure added to the pressure plate locking the clutch up more and increasing wheel spin.

Another alternative clutch is the "slipper" clutch. The function is easiest described as a go kart or minibike clutch - twist the throttle and go!  There are a set of springs that push the pressure plate AWAY from the clutch pack. The pressure plate and centrifugal lock up is attached to a "hat" that goes on top of or across the clutch basket. Now, the centrifugal force depends on engine RPM vice rear wheel speed. The result is more controllable application of added clutch force and more consistent launches.  New problem now - clutch won't engage below the set launch RPM - so you really can't ride it back to the pits after a pass, so you need a tow vehicle and a crew, and racing just got a LOT more complicated and difficult as a result.

Yet another alternative is a hybrid of those two designs - the "engine driven" lockup. Using the same idea of the "hat" from the slider clutch, but with a "normal" pressure plate function (springs applying force to the clutch pack) you get a lockup that increases clutch force in relation to engine speed vice rear wheel speed - benefitting from increased controllability and consistency of the slider clutch, but with the ability to ride back "normally" to the pits after a pass. Now we can have the best of both worlds!  Except...who makes something like that for an FJ?!!!

While I was building the dragbike I had a LOT of valuable or difficult to find parts stolen that were in a utility trailer. Included were two billet clutch baskets, two single stage lock ups, and two different coil spring conversions to go along with the lock ups.  I started sourcing replacement parts - and I couldn't find a lock up anymore!  -- seems there's some nutter in the UK that bought the last one to use in some derelict project -- something about an FJ engine, a Katana frame, turbo, EFI !!  Very fucking cool project by the way!  I looked at trying to adapt a Hayabusa multistage lockup to the FJ clutch hub and pressure plate.  Looked into having a single stage lock up machined locally. Looked into adapting an entire Busa clutch assembly. I talked to Tim Hays about the feasibility of making a hybrid clutch using a Busa basket and frictions with an FJ hub and steels. All said and done it wasn't cheap, but it wasn't too expensive considering I'd have to buy everything new anyway - billet basket, coil spring conversion, and source a custom lock up from somewhere.

Here's what something like this looks like (WARNING!  Metal porn follows!)





NOTE - as pictured, you may be able to see how the springs are setup to hold the pressure plate away from the clutch pack. This was a picture of the initial install - as a slider clutch as Andy originally asked about!

[racerrad8]

Chris,

I have to inquire...

How does the oil escape the center section of the clutch. I see the small holes around the ring of the pressure plate cover, but those seem kind of small to get all of the oil out.

Or dose this convert the clutch to a dry disc?

Randy - RPM

[andyb]

Can answer part of that.  It's still a wet clutch, though I don't know what the oil path is on that one.

I can say that when the clutch is set in slider mode, it's usually pushed back after a run by a pit bike (harder than it looks to do, too!), and when you take things apart to adjust/inspect immediately after a run, the fibers come out shockingly dry.  Not that it matters after the first few feet, as the clutch should remain fully locked, but it does take you aback when you first see it happen.

[fj1289]

Chris,

I have to inquire...

How does the oil escape the center section of the clutch. I see the small holes around the ring of the pressure plate cover, but those seem kind of small to get all of the oil out.

Or dose this convert the clutch to a dry disc?

Randy - RPM

Randy,

As Andy replied, it is still a wet clutch. After the first outing, I found we needed to increase oiling to the clutch plates. I did two things.  First added more oiling holes to the clutch hub 180 degrees out from where the stock ones were.  Second, after talking through different options with Tim Hays, removed the o-ring from the clutch pusher.

In multistage mode,the pressure plate doesn't rest against the hat like it does in the picture (where it is in slider mode) which allows for more oil drainage. Also, around the perimeter of the pressure plate there are a series of scallops that allow for oil drainage (I never really thought before of why those scallops were cut in the pressure plate!)

When you get the clutch set up right, you can get an entire season out of a set of clutch plates.  Right now I'm still using the base tune that was recommended for my setup while I concentrate on the suspension setup and, more importantly, rider skills!

[Pat Conlon]

Thank you Chris! What a bitchen write up...ok if I copy and paste it over to our clutch files?

Single vs multi stage vs lockup....good stuff.

Yea, that's some metal porn right there...

[fintip]

My understanding of clutches was expanded today.

However, I still didn't catch a lot of that. Deep. Someone obviously knows their shit.

When are you going to hit a nine already?!

[fj1289]

When are you going to hit a nine already?!

No doubt! That's my question! 
Really expected to last time out -- but I didn't do my part. I've got to be better prepped when I go and be more focused while there.  I will be really bummed if I go out next time, get in four passes or so, and don't make it.

No worries Pat, but it is probably more just a curiosity than useful for most on here. If you go to psychobike.com or dragbike.com, this is just an overview of Clutch 101! 

As you get away from the stock clutches with heavy springs, you start moving away from the "rider" side of the game and start getting into the "tuner" side of it. The extreme is probably ProStreet these days. Although it takes a hell of a rider to take a production based bike on DOT tires and no wheely bars into the low 7s or high 6s at 190 - 200+ mph in the quarter mile!  - it takes a hell of a tuner to make that much horsepower, make it controllable, and set up the clutch and suspension to deliver it all.  I really like both parts of the game - which is a good thing since I'm not a good enough rider to have my own tuner, and not a good enough tuner to have my own rider - and I wouldn't want one either!

[andyb]

After the first outing, I found we needed to increase oiling to the clutch plates. I did two things.  First added more oiling holes to the clutch hub 180 degrees out from where the stock ones were.  Second, after talking through different options with Tim Hays, removed the o-ring from the clutch pusher.

Chris, because oil is fed through the middle along the pushrod, you can also put a bevel along the length of the pushrod (obviously not so far to where you'll ruin the seal on the other side) by taking about .040" off, and that'll further increase the oil heading into the clutch assembly.

When you get the clutch set up right, you can get an entire season out of a set of clutch plates.  Right now I'm still using the base tune that was recommended for my setup while I concentrate on the suspension setup and, more importantly, rider skills!

You can also burn up a new pack in a few runs if it's wrong 

I'll skip the obvious poke at rider skills when you're using a throw and go setup.      I'll bet you could get deep into the 9's if you went with heavy static and rode it like a handclutch, but that's not going to be anything like as consistent as getting the lockup working right.  Are you using a 2-step and a clutch switch?

[fj1289]

Andy - we discussed machining a flat on the pushrod. Also, if that didn't allow enough oil flow, then EDM a hole through the center of the pusher along with an intersecting one to route oil through it. Then I looked again at the parts on the table and realized the easiest thing to do would be to remove the o-ring from the pusher. I need to get into the clutch before I go back again and make sure the mod is doing its job!

No, no 2-step. Had one in the pile of parts stolen in the trailer and have never replaced it. I have thought about getting one - but would put me into the electronics class at the tracks I've run. Also thought if I went that far I'd use a mico-lock to hold the clutch and launch off a button.

First time out in multistage mode I did a good job getting to WOT and snapping out the clutch by hand. But this last time I was way off my game - slow on both the throttle and clutch! I'll do a lot more "chair flying" of the launch before next time out!

[JMR]

I work with a fella in Finland on a small 1327 GS...no bars...foot shift etc etc...lock up...9.4... and it beats some turbo busa's just because turbo's suck off the line. I have an 1150 head here almost done to go into a 1500cc engine....mucho time and money in that. That kind of racing..IMO...is real.

[fj1289]

Are you using a 2-step and a clutch switch?

Dam you Andy!  I looked at the rules here at Bandimere - 2-steps are allowed in the street bike class...now I've got a used DRL-300 that should be sitting in the mailbox waiting for me to get back from Toronto. Picking up this plane in Toronto has probably cost me 3 trips to the dragstrip now!   This plane has been delayed so many times for so many things it is ridiculous - mods behind schedule, routine maintenance taking much longer than planned, hidden airframe damage (and all the paperwork it takes to fly with that to a suitable repair facility!).  And more paperwork fouled up today - may delay us until Wednesday (which of course is test and tune day...)

So I'm here typing here instead of running some new wires on the dragbike in my free time.

So, what's a 2-step?  Basically a second rev limiter used to hold the engine at your chosen launch RPM while you hold the throttle WFO (hope everyone knows that acronym!). A few different ways to setup and use a 2-step. I am going to go with the clutch switch AndyB mentioned a few posts back.

Among the boxes of parts I had stolen were a couple Dyna 4000 ignition boxes and a two magnet trigger wheel and special coil pack to go with.  The Dyna 4000 is a drag race specific ignition that includes a few good features including a "low limiter" (aka 2-step) as well as the usual "high limiter" for redline.  The high limiter is always "active",   but the low limiter is only active when the clutch switch is activated (clutch lever pulled in). The bad feature is it runs at a fixed ignition timing only -- no advance curve, no ignition retard for start. This is fine for a "classic" car tire, wheelie bar dragbike that uses an off board starter and start cart. We are talking 1 or 2 car batteries connected to a car starter with a frame or handlebars built onto it.  It generally has an impact socket welded to the end to engage a nut welded to the end of the crankshaft of the dragbike.  It'll spin the hell out of it and doesn't give a shit (like the honey badger) about the ignition timing being fixed at 35,40, or even 45 degrees.  But once again, this is making racing a bit difficult without a dedicated crew to take to the track.

So, when I bought a new ignition for the dragbike, I was advised to go with a Dyna 2000 since I was building it to be self starting.  The 2000 has been good in this application - especially with the Cashio modified starter. I literally just thumb the button and it spins this 1447 cc high compression engine fast enough you can hear it slow slightly to idle (about 1700 RPMs or so)!   The 2000 was also very simple to wire to the Dyna Shift counter to provide adjustable ignition kill for the air shifter.   
What the 2000 doesn't have is a 2-step.  Dyna makes a rev limiter called the DRL-400 and includes both a low and high limiter.  A bit of overkill with the 2000 since it already includes the high limiter.  After doing a bit of research, found some people are using the DRL-300 as a 2-step.  The 300 is meant to be used as a high limiter and is always active when installed as directed.  One advantage it has is the limit is infinitely adjustable vice the 400 that has click style settings.  The trick is to wire power to it through the clutch switch - then it is only active with the clutch lever pulled in.  I'll add another toggle switch in line so I can turn off the 2-step for the burnout. 

Next issue is to ensure the 2-step "releases" at the right time with relation to the clutch. If the clutch "hits" before the 2-step releases you can bog the engine.  If the 2-step releases too much before the clutch "hits" you may drive they the clutch (a good way to burn up a clutch pack), spin, or stand it up. So you need to be able to fine tune where the clutch switch deactivates. After a good look at the lever and switch setup (I'm using a ZX-7R clutch master) I think I've found a straight forward way to make it adjustable. I've taken a fairly shallow button head screw ( like used for fairings) and have modified it a bit. Ground down the head a bit shallower and filled in the Phillips screw slots with JB Weld - this is what the plunger from the switch will ride against. Next I'll drill and tap the lever underneath for the modified button head screw. Turn it in to engage later, turn it out to engage sooner.

What are the advantages?  Mostly consistency - especially for bracket racing.  While its fun to build a bike to go fast at the strip, I also enjoy the challenge of competition.  This has driven many of the decisions made for this build. Right now I'm trying to stage at 4500 RPM. The Lectron carbs are VERY touchy around there and it is very difficult to hold the RPMs steady there. Which means too much attention spent on holding launch RPMs and not enough spent on cutting a good light and launching the bike off the line properly. 
Consistency should help both the bracket racing side of things as well as the tuning side. Much easier to isolate changes and make adjustments when the launches don't vary as much...

Pics to follow once I make it home and hopefully get a little free time finish setting up the dragbike.

[Pat Conlon]

Thanks Chris. Don't you guys just love this forum? Good stuff.

[The General]

Shit this place is an education. You blokes make Sidney Poitier look amateur. ...Sir, would`nt that mean you risk a blow up if you missed a gear or stayed too long in one while using the DLR 300 as a 2-step? (just curious) - or are you using it in addition to the Dyna 2000-(Way out of my comfort zone here but encouraged by someone saying there was no such thing as a stupid question)

[fj1289]

General - not a stupid question - if anything just means I didn't explain it fully!

The high limit on the Dyna 2000 stays fully functional.

For the DRL-300, it is wired up differently from the directions so it is only powered when the clutch lever is pulled in.  Run +12 volts to one side of the clutch switch. The other side if the clutch switch goes to the red wire (power) of the DRL-300.  The rest of the wiring is standard - black to ground, and a white and a blue wire go to the ( - ) terminal of each coil.  The DRL-300 senses the RPMs from the wires on the coil ( - ) terminals. Those same wires are used to ground out the coils to keep them from firing above the set RPM limit.  When you let go of the clutch lever, the clutch switch opens and kills power to DRL-300 and the engine is free to rev (up to the rev limit in the Dyna 2000!)

Little fly in the ointment though is the rev range of the DRL-300 -- it's listed as 6,000 - 12,000 RPM. A bit high for my needs!   Luckily there are dip switches to set the number of pulses for every 2 revs - 4 pulses for the wasted spark arrangement of our FJs (and still retained by the Dyna 2000 box).  By setting it for 2 pulses instead, the DRL will limit at half the normal range -- 3,000 - 6,000 RPM -- perfect!  Surprisingly, the Dyna instructions go into great detail about changing the rev range this way.

Just gotta get it wired in and give it a go on the track!