LOCK UP CLUTCH CONVERSIONS

Words & pics: UK_Lee

As with most of my previous tech contributions this article is based on the GSXR / Bandit oil cooled family of engines, But the principles and usage of this lock up clutch will apply to most of today’s motorcycle engines.
In the distant past I explained how to convert your weak ass ’89-‘91 GSXR diaphragm clutch and the woefully feeble Bandit 1200 clutch to the much more beefy Coil spring unit that could be found in the early ’86-’88 Slabside GSXR’s. This unit should be able to put up with around 160 bhp & even the most ham-fisted abuse from your typical streetfighter rider. But what happens when you’ve just bolted on the big shiny turbo kit you found in the smalls section or that 100bhp nitrous oxide kit you’ve blagged of ebay? , Well after upping the NOS jets on my own bike I’ve just found out – Clutch slip! Arrgghhh!! . Previously, my 1216cc B12 engined GSXR750 was kicking around 160bhp at the rear hoop and the coil spring converted clutch coped admirably, even with the occasional 40hp shot of N20 . I’ve recently upped the ante with the jetting and it’s now shooting an extra 80 snorting horses through the clutch and despite it’s best efforts, I’m getting major clutch slip, especially in the higher gears. So what’s the answer? – A ‘Lock – up’ unit.

WHAT IS A ‘LOCK UP CLUTCH’ & HOW DOES IT WORK?

Well, it’s pretty simple really, a flat plate with four (or in some cases six) pivoted arms (or ‘stations’) bolts on top of your existing pressure plate, using longer versions of your existing bolts. As engine speed increases the arms ‘swing out’ under centrifugal force and push against the pressure plate – gripping the clutch pack (the fibre & steel plates) tighter & tighter as rpm increases, preventing slip – simple!

DOES A LOCK UP AFFECT NORMAL ROAD USE / ABUSE?

No, it doesn’t affect the normal action of the clutch at all, and it hardly influences the force needed at the lever .You can still hold the clutch in with the transmission in gear when your sitting at the lights / junction etc. You are still able to ‘slip’ the clutch (when crawling in traffic etc) .You can still pull the clutch completely in, even at the red line - to save your underwear in the unfortunate event of your chain coming off or the motor seizing. And yes, you can still ‘clutch it up’ in 2nd (as you do) for those ‘through the box’ mingers that you like to do for those schoolgirls hanging out at the local chippie.

HOW TO INSTALL THE LOCK UP UNIT Installation really is a piece of piss, On GSXR / B12 motors you would have probably converted to the coil spring type clutch already mentioned, so when you remove the nine M6 bolts on the clutch cover, you’ll be faced with this...
Remove the four bolts on the pressure plate, and remove the springs & spacers. Check the length of the spacers before reinstalling (they need to be their stock size of 0.550” / 13.97mm) as they are made from alloy and often get crushed with use. Although not required, it would be a good idea to remove the entire clutch and inspect it for wear and damage, check your steel pates for glazing and warpage and replace any worn fibre plates. Gasket surfaces on both clutch cover and engine cases should be inspected for potential leak paths and cleaned thoroughly in preparation for final assembly. If you’re using heavy duty springs, then put the stock ones back in – you wont need them at first, and if you can get away without them permanently – your left hand will be glad of the break! Providing everything is hunkey dorey and the clutch assembly is re-installed and ready (less the stock spring bolts), place the lock up unit into position and secure it using the four longer fixings provided in the kit .A rotational bolt tightening sequence (similar to a car tyre change) works best.
Once the lockup plate assy is installed, you need to fit & tighten the ‘weights’ supplied (nuts & bolts!) on the arms .The instructions in the kits usually specify the use of threadlocker, personally I prefer to use locking nuts (the deformed head type NOT nyloc) but it’s your choice. Even if the desired weight hasn’t yet been selected, thread locker (or locking nuts) must be used to keep the weights from working loose during initial assembly. Assemble the weights in such a way that the unit will be balanced – see pic
Once you’ve got to this stage you need to check the clearance gap between the pressure plate and the lock up arms. There needs to be a gap for the clutch to work properly. With the arm weights pivoted toward the centre-most position, measure the ‘air gap’ between the outside of the stock pressure plate and the inside (closest point) of the lockup plate assy. The spec for this measurement will come in the kits instructions, on this particular M.R.E. unit the gap needs to be 0.125” +/- 0.025” (3.175mm +/- 0.635mm). If you are out of range you’ll need to modify it accordingly by removing material from the spring spacers or adding washers / making new longer spring spacers)
You’re now ready to refit your clutch cover, but as it won’t fit over then new lockup unit you’ll need to use one of two options. Option one is the spacer plate; fitted in between the stock cover and the engine casings it’s a neat and simple solution to the problem. The only downside is the need for two gaskets - hence doubling the chance of a leak from the joints.
The other option is a modified cover, Basically a copy of the stock cover but with an extended ‘bowl’ to give clearance for the lockup unit. Some kits will come with this special cover, some will come with the spacer, and some will give you an option of either. The advantage is that you keep the stock length bolts and only one gasket – but the covers that usually come with these types of kits are sometimes of very poor quality (certainly not good enough for polishing!) and more importantly the oil sight glass is often missing or blanked off completely! , Which is a right pain in the arse. However for the more flush amongst you there is a very good looking & practical variation on the theme. You know these ‘windowed’ clutch covers that are all the rage at the moment? , Well ,by design they need to have a machined ‘ring’ welded to the case to accept the window. Just ask the engineering firm that supplies the windowed cover to make yours with a thicker (about 1 ½” / 40mm) machined ring. It shouldn’t add much to the cost of the cover, you still only need one gasket, you get to keep the all important oil level sight, and of course you can now see your trick lockup unit through the window!
Once you’ve decided on which method your going to use, you can refit you clutch cover, secure all the fixings and check / top up the oil level as necessary.
POST ASSEMBLY Pull the clutch lever in slowly; turn the motor over by hand to ensure you have no binding or clearance problems. If all is OK, your installation should be complete and you can fire up the bike to further check and set any remaining clutch adjustments. “TUNING” THE LOCKUP CLUTCH One of the best features of the lockup is its adjustability – especially on the drag strip. As there are so many variables to a good launch -this can only ever be a ‘rough guide’ to tuning your newly fitted lockup. Things like wheelbase, power, weight, and personal technique all have an effect on how your clutch is expected to perform. Tuning your clutch involves two basic areas; SPRING and WEIGHT. SPRING The combined amount of spring pressure you have determines how “hard” your initial move is. Too much spring pressure causes excessive wheel spin, too little results in clutch slippage. Generally, you want to use as heavy a spring as you can without spinning the wheel of the line, but you should still begin with stock springs regardless. Use your 60’ time as a tuning reference. If the bike is “lazy” off the line, step up to heavier springs until your 60’ time slows due to wheel spin. Likewise, if you are spinning the wheel, step-down or “soften” the springs until you get a spin free launch, or your 60’ time slows due to clutch slippage. The secret is to find a happy medium and stick with it. WEIGHT For drag racing, as far as weight is concerned you want to lock-up the clutch as early into the run as possible. With most kits available, the amount of weight supplied ( basically a bag of matched washers !) should be sufficient to lock-up anything short of a 7 second funny bike. Although you may want to experiment with different weight values, critical weight selection really depends on information supplied by a computerised data recorder, and as most folks haven’t got access to this kind of equipment (I know I certainly haven’t!) we’ll have to rely on the ‘seat of the pants’ data logger commonly known as trial & error. Some general weight tuning tips are; 1) stay away from the pies (oops, sorry!) 1) Reducing weight may provoke some slippage in higher gears, but will also delay the lock-up effect on the clutch pack; possibly helping to reduce wheel spin at the top of 1st and beyond. 2) Adding weight will help to correct clutch slippage in higher gears. Particularly if your turbo starts boosting in earnest or you hit the button for the laughing gas Begin by adding a pair of M6x 0.5mm washers to each arm or ‘station’, gradually adding a washer to each station until slippage stops. NOTE most kits advise that 6 washers per station should be considered the maximum. “STAGING” THE WEIGHT, AND / OR SPRINGS For an example “Staging” can be especially helpful to adjust a bike that leaves the line perfectly, but starts spinning the wheel as it gets towards the top of first / second gear. If necessary most lockup kits available can be set up as 2 or even 3 stage systems of both spring & weight. The only requirements are; 1) the lock up plate must have either 4 ( like the unit in the pics ) or 6 stations, and , 2) you must have the knowledge to set it up. The standard ( single stage ) set up requires all arm stations have the same weight, and the springs the same pressures each. A two-stage set up is defined by every other arm / spring station having one weight / spring value , and the remaining stations a different ( lighter or heavier ) value. A three-stage set-up (6 station only) is defined by each pair of opposing arm / spring stations having the same value, but every pair having different (lighter and heavier) values from each other. Thus the plate assembly may be staged, whilst still remaining balanced , Critical weight / spring selection really requires a spring tester and a gram scale .. A point should be made that weight staging is not dependent upon spring staging and vice-versa .The most important point is to keep the whole assembly balanced . And that’s about it really , realistically the possibilities are endless .It’s just a case of experimenting with the weights and noting what differences you can feel on the bike . There’s nothing ‘magical’ about they way a lockup works ,You don’t need any special tools or equipment, and there’s no real reason why you shouldn’t have one on your road bike if you really need / want one. Hopefully I’ve explained some of the commonly asked questions about lock up clutches and If you need to refresh your memory on the GSXR or B12 coil spring conversions look for them here.
Here are some details on how a T.E.S. Performance windowed clutch cover could be modified to make room for a lock-up clutch, as well as some critical dimensions...