Clutch releasing

RCJ

Member
2 disk Noram,425 clone. Right at the apex of the corner I am completly off the throttle. While watching my mychron playback ,I noticed that the rpm falls back to around 2500.It is like the clutch is releasing. Is this normal?
 
If your completely off the throttle rpm's will drop but not 4000 + rpm, So no not normal. You are turning it 6500 + for max rpm ?
 
The clutch engages/disengages only when the engine RPM reaches the the point where it can. If you, it's my understanding, the clutch does not disengage. I have to wonder, now that I think about it, how are you getting, and from where, the readings that the clutch is disengaged? In my experience, if I fully let off the throttle, the clutch does not disengage. You can feel it, and you can hear the engine quickly losing RPM as a kart slows down. Just my thoughts.
 
Al if it helps you out to help him figure this out, I don't think he's saying he's seeing any readings that makes him think it's releasing, he's just asking because of such drastic rpm drops on his tach, could it be releasing without slowing down drastically ? You should be the go to guy on this to help him figure out what's up.
 
It's a matter of personal preference. My driver preferred the clutch to grab, coast, grab, coast, on parade laps. The cheetah was best at this.
Adjust the air gap to get rid of this.
Less air gap is what you'll want.
 
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2 disk Noram,425 clone. Right at the apex of the corner I am completly off the throttle. While watching my mychron playback ,I noticed that the rpm falls back to around 2500.It is like the clutch is releasing. Is this normal?

RCJ,

Depending on many factors, yes: it's possible the clutch is releasing.

There are many variables which could be effecting that "point of release" in the clutch (which your driver may feel and your gauge is picking up). As you can imagine, when the throttle is closed, the kart is "driving" the engine (in other words: the centrifugal force is still enough to keep the clutch engaged). How much this happens and for how long this happens (as the kart is slowing) can depend on static vs. dynamic friction in the clutch material, how the clutch is configured internally (lots of spring and lots of weight versus lighter spring and lighter weight), and of course lever shape and air gap can enter into it as well. In a shoe clutch with pivots, this can also be effected by the "energizing" effect as the shoes will attempt to "cam" outward into the drum as the kart is "driving" the engine, keeping the clutch engaged to a lower rpm as the kart is slowing.

Very generally speaking, having more spring and more weight in the clutch (still set up to slip at the same RPM), will cause the clutch to disengage quicker as you are slowing.

PM
 
Unlike the clutch drum, I'm going to guess, the chain doesn't drive the clutch drum wedging the shoes up against the drum, making it harder for the clutch to release. When a disk clutch gets below the preset stall RPM, it releases, letting the engine free to drop down in RPM.
What is the stall RPM on your clutch? Do you think the engine is getting below that RPM in the turn? Could be I don't understand the problem.
There's a hill at Laguna Seca that you go up just before the corkscrew. The last time I raced there, with a Horstman disk clutch, I noticed the clutch was releasing going up the hill. The engine was at the stall RPM, 10,300, but apparently the clutch was releasing.
 
I don't think it's that simple Al.

The point at which the clutch releases "off the throttle" (what I believe RCJ is talking about) is not only a function of a number of variables inside the clutch, but also how much resistance (braking) the engine is providing when off the throttle.

The shoes are in contact with the drum (or the disc stack is all "in contact") before the stall rpm of an engine/clutch package as revs pick up. (if the spring-force and weight combo is high, then the contact point gets closer to engagement speed, however the opposite is also true) The clutch does not freewheel and then magically load the engine precisely at the point the discs go in contact.

Just like during acceleration, the clutch probably "slips" for a bit as the speed of the kart falls below the normal clutch engagement speed. At what speed the engine becomes completely disconnected from the clutch drum speed varies due to a number of items. My guess is that even if the idle speed was slightly increased, the speed of the "disconnect" would change simple due to a difference in engine braking.

If RCJ wants to "delay" the disconnect, then using lighter springs and lighter weights (still setting the clutch to the same stall rpm) would probably cause that disconnect of the engine from the clutch to happen later into the corner. Or bump the idle speed up a touch. Or both. :unsure:

PM
 
I'll add another note on this -- and explain why 95shaw says to reduce the air gap:

Since the formula for centrifugal force is a function of weight of the "shoe" (or lever in the case of a disc clutch), AND the radius of the center of mass of the shoe (or lever), and square of the rpm....

When the air gap is tightened up, the levers (or wedges, or whatever they are) that move outward from centrifugal force to squeeze the disc stack will no longer fling outward as far to close the disc stack (less air gap, less movement is required). Since the center of mass of the lever no longer goes as far "outward", it's like making the lever lighter (or removing weight from the shoe of a straight centrifugal shoe clutch).

Close the air gap, and now the clutch will typically over-slip a bit, which means that typically the spring force needs to be reduced a touch to get the stall rpm back to the desired revs. End result: less "weight" (force on the stack, in this case), and less spring... makes the clutch a bit "drag-ier" below the stall rpm, which will cause it to NOT disengage quite so quickly as the revs are coming down.

Very generally speaking, clutches with a lot of spring and weight tend to act like 95shaw's driver likes it... almost feels like the engine is freewheeling until the revs get close to stall speed, and the the clutch grabs very quickly. Clutches that are light on spring and weight tend to feel a bit "lazy", as they make contact and drag earlier, yet if adjusted correctly will stall at the same rpm.

In Al's scenario of going up a hill at Laguna Seca where the revs are dropping and may go just under clutch stall rpm, it can sometimes be beneficial to *keep* the clutch engaged, depending on the track layout. In that case, removing some spring and weight, (or tightening up the air gap and reducing spring preload on a Horstman clutch), may be a fine tuning option that is beneficial.

One of the great things about disc clutches is that there are generally more "tuning" options: springs, air gap, lever size/shape/weight can all be tweaked to subtly change how the clutch functions. On top of that, experimenting with different lining (and sometimes even the exact same lining that came out of a different batch!) can be really interesting.

PM
 
Got the clutch off,did have .056 air gap. There were no shims in clutch to close air gap,ordered new disc. I put a 3 disc bully on that was set maybe a little looser. The track is rough and at least .75 slower ,I have been off on gear. The bully clutch had red springs that were not screwed down tight, I am going to add some weight to the levers.
 
New disc's aren't much thicker then .125 .
I do not know if the bully floater will interchange with noram .
In that case yes noram a .110 or .105 depending on avalibility .
Cutting the pedestal down is an option , need an expert for that .
 
Off subject what size washer is used on a bully two disc for a thrust washer or is a speciality. Item
 
Inside between drum and clutch .
Is a thrust bearing and one or two thin hard washers . Seems like stainless .
So yes a special item .
 
Off subject what size washer is used on a bully two disc for a thrust washer or is a speciality. Item
They have a thick and a thin in that thrust setup. Stock it takes one of each. I was told I could use whatever I need to make end play correct but never had any luck with the clutch I was trying it on
 
They are .015" & .030" thick.
They come in either stainless or hardened steel with a black oxide finish.
You can use a combination of thicknesses if you choose, or use a different thickness spacer washer on the outside of the driver to achieve the proper endplay.


-----
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Brian Carlson
Carlson Racing Engines
Vector Cutz
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Linden, IN
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To give an update. It turned out to be my mychron not reading correctly . The clutch did need some tuning. After working on both ,my rpm range is 4800 to 6500 with my clutch set to 3900
 
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