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Building the Perfect Centax-3 Clutch (04/05/2004)

By:: Glenn M. Cauley
Linked to:: Centax 3 clutch-set (excl. Flywheel), Serpent 720 1/10th scale 200mm, Serpent 720 07 1/10th scale 200mm

This article describes how to build and maintain the new Centax-3 clutch included with the new Serpent 710. I have borrowed from the advice of many knowledgeable sources in the RC world to write this article.

Using the building methods and parts described here should result in a Centax-3 clutch that engages much better and is more responsive on adjustment.

There are many factors that come into play in engine and clutch building/tuning, and any one of them may cause your car not to run properly or best. Please note that the ideas presented here may or may not work for you… they are only offered as one possible group ideas to get a better-performing Centax-3 clutch.

Check out my other article at http://www.mytsn.com/publ/publ.asp?pid=9829
which discusses the in’s and out’s of Centax clutches.

Hot Topic: Centax-3 Clutch

In many RC forums across the world, there are many people discussing the pro’s and con’s about the Centax-3 clutch. And unfortunately there are some people who are having problems with this great new clutch. There are issues about excessive slip, too early or too late engagement, engine bogging, and premature thrustbearing failure.

It is important to note that there are many factors that may affect engine and clutch performance. Things like proper engine tuning, clutch gap, clutch endplay, and improper assembly can all have an impact on your clutch performance.

Summary of Good Centax-3 Combinations

Here is a summary of a few good combinations of parts and settings when building your Centax-3 clutch.

Note that these combinations are not the ONLY combinations that may work, but they are a good starting place. As time goes on, different people will find different combinations that work for them. But as mentioned before, bear in mind that there are many factors that may influence clutch performance.

Centax-3 assembly combination 1
* Flyweights: modified
* spring: hard
* clutch shoe: original black clutch shoe (802508)
* clutch gap: 0.5mm
* end play: minimal

Centax-3 assembly combination 2
* flyweights: original, unmodified
* spring: hard
* clutch shoe: new yellow clutch shoe (802509)
* clutch gap: 0.6mm
* end play: minimal

Centax-3 assembly combination 3
* flyweights: original, unmodified
* spring: original
* clutch shoe: new yellow clutch shoe (802509)
* clutch gap: 0.5mm
* end play: minimal
(not as much 'kick' as other combinations)

Flywheel Installation

When installing the flywheel on the engine crankshaft, take note of the following:

* Do not forget to install the 0.5mm shim on the crankshaft, behind the brass cone and flywheel

* Install ONLY the brass cone included with the Centax-3 clutch. DO NOT install the cone that came with the engine.

Flyweights

There is a clutch flyweight modification that has gained popularity recently. It involves cutting a 1-piece clutch shoe into 3 pieces, and installing these pieces upside down between the pins of the flywheel. This gives better acceleration since the flyweights have nothing holding them in. However, this method also has its own problems: the weights may move and bind in strange ways, which may result in uneven engagement and an inconsistent clutch.

The standard three flyweights that come with the Centax-3 clutch will work better with a bit of modification. Use the modified flyweights in combination with the recommended parts and settings mentioned in “Summary of Good Centax-3 Combinations” earlier in this article.

On one end of each flyweight there is a hole where it fits over the flywheel pin. Drill a small hole on the other side of the weight, and install a small setscrew (M3x4mm). Make sure the setscrew does not protrude on the top or the bottom. Also, make sure that after installing the setscrew that the flyweight is not deformed in any way. If there are any ‘bulges’ in the flyweight, lightly sand them away until all surfaces are smooth and uniform.

This results in a heavier flyweight, which generates more pressure on the clutch shoe.

Be sure to modify all three flyweights exactly the same way, otherwise your clutch may suffer improper engagement and wobbling of the clutch shoe, and eventually bearing failure.

Clutch Shoe

You can use the new 802509 Centax-3 Clutch Shoe (Yellow) instead of the black clutch shoe included in the kit. The yellow clutch shoe is slightly grippier with less pressure, and the original black XP clutch shoe will bite more if the clutch pressure (from modified flyweights) is increased.

Use the new clutch shoe in combination with the recommended parts and settings mentioned in “Summary of Good Centax-3 Combinations” earlier in this article.

The 802509 yellow clutch shoe has more grip with less pressure, which should reduce clutch slippage. This is both good and bad. Good because the entire torque of the engine goes to the wheels; bad because without any slip the engine must work harder and may become more hot. This new yellow clutch shoe would not work best in very warm conditions; the original black clutch shoe (802508) would be better in that case.

IMPORTANT!
You cannot use a Centax or Centax-2 clutch shoe in the Centax-3 clutch.

Centax & Centax-2 clutch shoes:
6587, 6587N (brown), 6587XP (black)

Centax-3 clutch shoes:
802508 (black), 802509 (yellow)

Clutch Spring

You can use the harder 909518 Centax Coilspring 1.8 in combination with the recommended parts and settings mentioned in “Summary of Good Centax-3 Combinations” earlier in this article.

When adjusting the preload on the clutch spring, start with a preload setting of 0.5~1.0mm between the end of the flywheel nut and the top of the tension collar. I recommend using the 1462 Centax Nut Tool to adjust the spring tension.

You will have to play with the spring tension at the track to get the best engagement point. Adjust the clutch until it begins to slip heavily, then loosen the spring a little and that's it.

It takes time and experience to get the feeling of a properly adjusted clutch, but that is the best way to get a really good clutch.

Thrustbearing Installation & Maintenance

The thrustbearing has two rings… one with a large inner diameter, and one with a small inner diameter. The ring with large inner diameter MUST go towards the flywheel.

Use a thick, sticky grease on the thrustbearing, such as 87022 Tamiya Molybdenum Grease or B0308 Mugen Super Grease. Re-grease the thrustbearing every 30 minutes at least or more often if you run on dirty tracks or your car sees grass often.

Clutch Gap

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 than WHEN it engages.

Set the clutch gap in combination with the recommended parts and settings mentioned in “Summary of Good Centax-3 Combinations” earlier in this article.

Clutch gap is the FIRST thing you should adjust on the Centax clutch, and is done with the bearings NOT installed. For more information, refer to your Serpent car or clutch manual or the appropriate i-manual at www.myTSN.com.

In the images shown here, clutch gap is the difference between values A and B. You adjust clutch gap by placing shims (medium size) on the thrustbearing holder, in front of the thrustbearing assembly.

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 thrustbearing.

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.

Adjust the Centax-3 so there is minimal end play (0.05~0.15mm). There should be only a slight amount of movement detectable. The clutch housing should rotate freely.

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. For more information, refer to your Serpent car manual or the appropriate i-manual at www.myTSN.com.

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

Too much endplay will cause more wear on the thrustbearing. When the clutch is not engaged, the plates of the thrustbearing are further apart. When the clutch engages, the thrustbearing plates travel further before they are 'sandwiched' together... by traveling further more force is built up so when the clutch engages, the thrustbearing has more force applied to it. This causes premature thrustbearing wear and leads to failure.

Conclusion

I hope that this collection of ideas for building the Centax-3 clutch will help you get the most of your car, and give you great racing experiences.

Note that these combinations are not the ONLY combinations that may work, but they are a good starting place. As time goes on, different people will find different combinations that work for them. But as mentioned before, bear in mind that there are many factors that may influence clutch performance.

As always, take great care when working with hand or power tools, soldering equipment or heat sources. ALWAYS use proper eye and hand protection, and take all necessary precautions to avoid injury or damage.