mxwrench

iTrader: (1)

I agree, but unfortunately, this is a must in utilizing this engine to it's potential!

Also to rich LSN can kill the bottom performance even more, and it is easy to mistake too early of clutch setting as LSN adj. problem! This makes problems even worse for tuning!!

Just be right with the clutch and gearing and everything becomes so much easier to adjust properly.

BK

M7H

I just have a general question/remark about clutch settings for this engine, but this also goes for other engines of which the clutch is set "late".

Lets assume the following:
Engine has a max rpm of 40K
Clutch engagement @ 25K

This leaves a rpm range of 15K left to "push" the clutch to maximum "grip"

If you set the engagement @20K, you will have 20K rpm left for maximum "grip", and this in my opinion will result in a clutch with less "slip".

So if your clutch gap is set to big, and you also use a strong spring, to ensure late engagement, it will result in a clutch with to much slip, and therefore one which will wear fast.

AMGRacer

And you tested this theory when?

M7H

well not really tested it, but it's my conclusion after several clutch set-up tests, in which a lot of things went wrong (including losing the flyweights), but that is what testing is for..

Also lightening your flyweights will give you earlier clutch engagemant, but with less "push"......

Don't forget I drive .21 Engines, not this .12 WASP. but the theory is the same......

I now have the newest Serpent flyweights, who are made to be installed "leading" instead of "trailing" but also with them I had to much "slip", after putting in a grubscrew in each weight, this should be fixed, but I haven't tested that yet.......

But still, it's a theory, which in my opinion makes sense, or not?

mxwrench

iTrader: (1)

M7H,
You are correct, if you have an engine with a peak rpm of 40,000 and engage the clutch at 25,000 rpm then you only have 15,000 rpm to obtain maximum grip.

However, with this engine you have maximum rpm of 48,000 , so if you engage the clutch late at 28,000 then you still have 20,000 rpm for maximum grip.

But still the one with the lower rpm will achieve more wear (due to the engagement process happening at a lower rpm with less inertia to the clutch weights) But I will say, that this is just my thoery.

BK

afm

Lets review some of theory behind Centax clutches, and from there a practical example, which i hope helps....


Clutch gap is the amount that the clutch shoe moves before it contacts the clutch housing; this affects the WAY that the clutch engages more so than WHEN it engages.

1.- Larger clutch gap: Causes a harder, more sudden engagement. Better on a wider track or a track with high traction. A larger clutch gap puts excess stress on the clutch components, especially the thrust bearing.

2.- Smaller clutch gap: Gives a softer engagement, and smoother acceleration. Better on a tighter track or a track with low traction. A smaller clutch gap may result in engine bogging and premature clutch shoe wear.
If you change the clutch gap to a larger or smaller value (by adjusting the shimming), you must compensate by adjusting the tension on the main clutch tension spring.

End Play Clutch housing end play is the amount that the clutch housing moves along the crankshaft.

1.-Too much end play: Causes more wear on the thrust bearing. When the clutch is not engaged, the plates of the thrust bearing are further apart. When the clutch engages, the thrust bearing plates travel further before they are 'sandwiched' together... by traveling further more force is built up so when the clutch engages, the thrust bearing has more force applied to it. This causes premature thrust bearing wear and leads to failure.

2.-Too little end play (or none at all): means that the thrust bearing spends most of its time sandwiched together, which may lead to overheating and premature wear.

It is always better to have a small amount of end play rather than a larger amount of end play. Do not set up the clutch to have no end play at all.

Since our Centax clutches transform Centrifugal force into Axial force (thus it’s name), if you use lighter flyweights which operate under the centrifugal force, you will need more rpm’s to have them expand, so actually you are getting a later engament, and if you use a harder tension spring, even more later engament and slippage (also depending on how much tension adjustment you placed on the spring). The opposite is true for heavier flyweights and softer spring.

All above being said, the clutch adjustment depends on where the power band and torque of your engine is.
For example: my OS TZ .12 has it’s max torque at around 20,000rpm and it’s max hp at 33, 400rpm
So I need to set my clutch at around the engine’s max torque. If I set the clutch above the 20K mark, engines revs up and makes clutch to slip and heat up because I’m not using the max force of engine to make clutch engage, if I set it up at a lower rpm (below 20K), engine bogs and heats up….

Resuming: one has to set up the clutch to wherever the engines max torque is to use its usable power and make the clutch engage solidly without to much slippage and / or bog.

AFM

mxwrench

iTrader: (1)

Very nicely written AFM,

But I would like to add that the lighter the fly weights the less inertial holding force is exerted against the spring and shoe. This can lead to constant slippage if too light of flyweights are used.

On the other hand, if heavier flyweights are used against a stronger clutch spring the inertial force of the flyweights can overcome the spring and still have force left to drive the shoe into the clutch bell causing good engagement.

But this is always a balancing act between the flyweights and spring tension.

BK

Data

i thought it was the otherway around.

M7H

I agree on your theory......

Well, what about this theory I've read somewhere (3hobby.net?)

Remind that the clutch flyweights are "trailing" the pin the are attached to.

Take a piece of rope, attached to a tennisball, now sping the rope around, the ball will start lifting at a certain rpm.
Now attach a bowlingball to the rope, you can imaging you need more rpm to lift the heavier bowlingball or not.
This is the same for our clutch, but I also do see that because the flyweights are lighter, more rpm is needed to overcome the springtension.......

AMGRacer

Agree which is why I doubt M7Hs theory. At lower RPM you may have more RPM to "clamp" but also you will have more drag on the clutch shoe since it is engaging too low. Engaging low with a grippy clutch shoe on a high grip track can also cause the clutch shoe to bounce off the face of the clutchbell a few times before it finally grips which adds heat and wear. With the correct flyweights and spring tension any RPM band should be achieveable with sufficiently good clamping force.

M7H

Hmmm...

I think the clutch shoe doesn't move fast enough to the bell, to start bouncing......

But I do like this "brainstorming" session...

And we are going WAY off topic.......
But saying that, this might help for all the WASP people out there, to set there clutch correct......

mxwrench

iTrader: (1)

M7H, I think that only serpent OEM flyweights still are attached to the pin, everyone else uses floating flyweights. Just FYI.

In fact the Team Orion clutch system for the serpent, (that I tested last week and let me tell you it works wonderfully!) uses the floating flyweight system as well.

BK

afm

Centax flyweights are not attached to pins, they are guided by the pins during their expansion travel caused by centrifugal force.....

A better test than the rope example is done by placing two different weights over a disc...now start spinning the disc incrementing the speed...at a certain speed the heavier load will be ejected earlier by the centrifugal force, and then if you keep up incrementing the speed the lighter load will be ejected
later.....

But let's make it simpler..............remember the standard clutches (purely centrifugal) before the Centax that are still used on 1/8 Off Road??......well the shoes are attached at one end by pins, so in order to tune engament you either change the springs for larger diameter, thus incrementing the tension, or you cut the flyweights to make them lighter (or both) in order to get a later engament at certain rpm's...opposite holds true for early engament....

AFM

Slo-MTX4

iTrader: (1)

Just going back a bit to afm's post. My understanding was end play and clutch gap are both adjusted by the shims under the thrust bearing?

Cheers
Daniel

afm

Clutch Gap:

Clutch gap is the FIRST thing you should adjust on the Centax clutch, and is done with the bearings NOT installed.

When building the Centax clutch, you must first place a large diameter shim (typically 0.5mm thick) behind the flywheel cone.

You adjust clutch gap by placing shims (medium size) on the thrust bearing holder, in front of the thrust bearing assembly. When properly shimmed, there should be approximately 0.7mm of clutch gap.

End Play:

End play is the LAST thing you should adjust on the Centax clutch, and this is done with the clutch fully assembled with all bearings.

When properly shimmed, there should be approximately 0.2~0.3mm of end play (axial play).

You adjust end play by placing shims (small size) in front of the clutch nut that holds the flywheel to the crankshaft.

AFM