WWW.TWF8.WS

Test and reviews RMV Speed III

Click on the pictures to enlarge them

One of the components of 1:8 scale buggies that have evolved the last few years is the clutch.

The previous designs of clutches by Renato Vita from Vita Tuning are the speed 1, 2, 2.5 and now the SPEED 3 is there.
According to Renato Vita competition drivers liked the adjustable speed II design but favored more for the standard 3 scissor spring speed 2.5 design that came after the SPEED II.
Renato went further in his clutch innovation and added something new to the scissor spring design.
In cooperation with former world and European champion Daniel Reckward, Renato designed and introduced a new 2 stage lock up feature.
RMV is the worldwide distributor of all Vita tuning designed clutches and parts.
It incorporates the normal 3 scissor style shoes and springs for engaging the first stage.
The carbon composite shoes will contact the inner side of the clutch bell.
Then when this stage is established due to the torque of the engine an bronze colored inner part of the clutch that holds the clutch pins will rotate clock-wise.
This causing the shoes to be pushed and lock even more then by the weight of the carbon clutch shoes itself as with a standard design.
So almost no slip is the end result.

The clutch kit comes as one complete package containing:
* A flywheel (35 or 38 mm diameter)
* Three black colored shoes with 1.0 mm springs scissor.
* Grooved clutch nut
* One 5 x 10 coned shim washer.

We received a TU9630 package for review and testing from RMV.
Thanks Daniel!

The package!

	The TU9630 (35 mm) black shoe (75% Teflon / 25% carbon) package with it contents
	The things found in the package. Complete assembled clutch, coned 5x10 mm shim washer, sticker and an user manual in German and English language.
	The complete clutch comes with the clutch nut readily installed.
	All the mechanical parts separated.
	The three carbon composite clutch shoes operate standard with 1.0 mm scissor springs. 1.1 mm springs can be used.
	The rear side of the flywheel is designed to cover up the front bearing.
	The grooved 8 mm clutch nut.

Building the Speed III

	You have to mount a cone that normally comes with the engine This cone is not provided with this clutch kit!
	Place the complete clutch and tighten the clutch nut with 8 mm tube tool holding the flywheel with a large plyer.
	Place first the coned 5 x 10 mm shim washer. Make sure the high side tip of the coned shim washer touches the inner race of the next to be placed ball bearing.
	From here on all parts are not supplied with the clutch. Slide the 5 x 10 x 4 mm ball bearing on the crank shaft.
	Slide the clutch bell on the crank shaft and place the second 5 x 10 x 4 mm ball bearing. This clutch is designed to work as standard with 26.3 mm inner diameter clutch bells. Other inner diameter clutch bells can change the characteristic of the clutch.
	Secure the end of the crank shaft with a 3 x 8 x 1 mm washer and a 3 mm hexagon screw. Use 5 x 10 mm shim washers if needed to reduce the play. Make sure now you used the supplied coned 5 x 10 shim washer there is less then 0.1 mm axial play of the clutch bell.

How it works?

	This is the position where the clutch shoes are in neutral position and will be kept inwards as long as the centrifugal forces are lower as the mass of the shoes and the force of the return scissor springs. This is how all standard scissor spring clutches work.
	Due to the centrifugal force at a certain point the clutch shoes will be forced to rotate outwards on the flywheel pins. This picture shows the motion of the shoes when the flywheel turns anti clock-wise. This is how all standard scissor spring clutches work.
	The green marked parts are fixed together. The bronze colored part can rotate clockwise in the flywheel part. Large coil return springs provide a counter pressure for the bronze inner part when it start to lock up and when force is lower can return the bronze part to its original position.
	A model care engines crank shaft rotates anti clock-wise. When the clutch shoes hit the inner side of the clutch bell engagement will be forced and the connection between both parts is made. This is how all standard scissor spring clutches work. As soon as the torque provided by the engine passes the friction of the clutch shoes the bronze inner body will rotate against the rotation of the flywheel. The tip of the clutch shoes already in locked position, will now be forced/wedged even more against the green marked spots and force more locking and so will reduce available slippage. This is how the extra part of this clutch works.

Maintenance, set up and tips

Although the clutch has a trouble free design some point have to take care of for proper use and maintenance
TIP	Allow the clutch 1 to 2 tanks of fuel to get broken in.
TIP	Never lube or oil the ball bearings as this can cause extra slippage that can blow your bearings premature Check here for more info
TIP	Regularly clean the inside of the clutch bell with a dry cloth. Do not sand it!
TIP	Always change all the 3 scissor springs at one time when one is broken or replaced for maintenance
TIP	If the part of the shoe that contact the inside of the clutch bell is glazed use fine sanding paper to get the glaze off
TIP	Do never use a clutch bell that has been used with aluminum shoes as this will cause extra slippage on the clutch

Verdict

Only at first glance, this masterpiece of engineering looks like a standard clutch.
It is very easy to handle for maintenance and the torque sensing system with mechanical lock up works really well.
Due to reduced slippage, the engine's revs are used for acceleration instead of generating heat and the shoes wear very slowly.
On the other hand, more moving parts result in more wear that affects the clutch in a negative way. I hope that these problems will be solved with an updated design.

Comment by
RMV Products

Performance

31-07-2005
Performance test will be done by Thomas Weber one of TEAM TWF8 members.

Report of second half of 2005 season:

Hello,

I am very happy that I have had the opportunity to test this clutch. Since August, I have used the Speed 3 for more than 15 liters of fuel while it had to prove itself in four races and many practise sessions. For the most time, I used it on an LRP Z.21R in a Thunder Tiger S3. I was using Mugen and Thunder Tiger clutch bells, which are a bit smaller in inside diameter than the RMV clutch bells (go here for additional information). This makes the clutch engage a bit earlier, which I prefer.

I installed the clutch like described by Paco. From the first lap on, I liked the feel of it. The engine doesn't rev up high, but the car accelerates quickly. This is because of the torque sensing clutch action that presses the shoes against the bell when torque from the engine is applied, which results in less slippage. One part of our practise track leads a bit uphill. In that section, I had the feeling that I had better throttle control than with my old-style composite clutch.

At the third day of use, I noticed a lack of acceleration, like caused by excessive slippage. When taking the clutch off, I noticed that it was loose on the cone and there was a lot of dust and some metal splinters.

After an interesting conversation with Renato Vita, I knew that there needs to be some space between the flywheel and the front engine bearing. The dirt shield on the flywheel prevents debris from damaging the front engine bearing, but only if the fine dust can pass freely. I installed a washer between the engine bearing and the metal cone and never had the problem of a loose clutch again. This was after 3 liters of fuel and the clutch shoes looked like new.

On the subject of clutch bearings, I'm using those with metal shields and blow out most of the grease before mounting them. I once put in greased bearings and after driving, there was some grease on the clutch shoes (but I didn't notice additional slippage). After about two litres, I replace the bearings for new ones. Not because they are broken, but old bearings tend to wear the crankshaft.
In my EB4 S3, the Speed 3's flywheel was about level with the chassis plate. I didn't want to take the chance that a rock might stall my engine, so I turned down the flywheel to 32 mm (from 35 mm standard). My Thunder Tiger Pro Starter Box can still reach it well to start the engine. This modifaction is just a personal preference, not required. The Speed 3 will work very well as it comes.

After 7.5 liters, the clutch shoes still look like new:

The second weekend in September, we had a race on a grass circuit. The permanent resistance puts a lot more stress on the drivetrain than running on dirt. My engine seemed to have less revs, but I believe this is because the clutch has almost no slippage. With a conventional clutch, the shoes slip a bit even at full throttle. With aluminium shoes, it is better, but these wear pretty fast. So, does the Speed 3 combine the bite of aluminium shoes with the longevity of composite shoes? To be honest, I have never used aluminium shoes, but I think the answer is yes. After around 10 liters of fuel (1.5 of them on grass), the shoes showed very little wear. Judging by this, they should easily last 30 liters.

But on the 1st of October, a real challenge was awaiting the Speed 3. Robin Frischkopf and me were participating in the 4 hour endurance race of Gland. Because of heavy rain, the race was ended after 90 minutes, but the stress on the drivetrain was greater than 360 minutes of running in the dry. My S3 weighed an estimated 8 kg during the race! I believe that more than one team has ruined their clutch during this race, but the Speed 3 was working just fine. The revs were constantly low because the engine couldn't accelerate the car enough, so any other clutch would have slipped a lot. But the torque sensing clutch action of the Speed 3 pressed the shoes onto the clutch bell and allowed only little slippage.

After this torture, the shoes did show some wear, but I believe regular clutch shoes would have had to be replaced. By the way, we took third place by driving consistently without any defects.

The last race was on a dirt track with some pretty impressive jumps, in Chiasso. I took the Speed 3 apart completely on Saturday night. The rotational movement felt a bit gritty, so I cleaned everything. I noticed that the scissor springs were worn where they touch the nut. This must have happened when the clutch became loose. I replaced them with 1.0 mm Mugen springs. The clutch shoes had a small dimple at the end where they're pressed out by the aluminium piece (I'll call it "star"). After putting everything back together, it moved freely again. The clutch was working well on Sunday and I became 6th in the final.

Now, after 15 liters of fuel and some serious abuse, the shoes still have life in them and don't need to be replaced yet. I like this clutch a lot. Renato Vita has created a masterpiece. The Speed 3 does not only work better than other clutches, but it is much easier to handle. Similar to the Speed 2.5, everything is in one piece. No need to take off a nut or springs to remove the clutch from the engine.
I will do more testing during winter and happily use this clutch next season. Big thanks go to Paco Raap, Daniel Reckward (RMV Distribution) and Renato Vita.

Greetings, Thomas

Contact: H-Trainer'at'gmx.ch (replace the 'at' with @)
Visit my website

May 2006:

Hello,

after two more liters of using the Speed 3 and taking it apart completely for close inspection several times, my conclusion has changed quite a bit. First, I recognized that the shoes rotated very easily. I later found out that two of the three compression springs were broken. Further, the scissor springs were worn where they touch the nut and the "pins" that hold the compression springs had deep grooves. The rest of the clutch is still in good condition.
By the way, I turned down the flywheel to 32 mm diameter (as explained at the beginning of the test report), it's not worn down. I am now using Mugen clutch bells that I grinded to 26.3 mm inside diameter to have the correct point of engagement.

Here's a picture after 17 liters:

A close-up of the pins in the flywheel that hold the compression springs:

After assembling the clutch with new springs, I recognized that these deep grooves affect the "torsen function" of the clutch in such a way that the shoes get pushed outwards more easily and don't disengage properly. There's just not enough tension because of the grooves. This forced me to put the Speed 3 away and use a Speed 2.5 instead.
I have sent these results to RMV and Vita (May 15th) but have not got a reply yet. I will probably return the parts with excessive wear and hope to get new ones, as I haven't finished all the testing that I wanted to do (try different springs and shoes to alter the characteristics).

Addition to the verdict: Because there are more moving parts, there is more wear as well, which affects the clutch in a negative way. These problems could be faced with a modified design, e.g. steel pins to hold the compression springs.

Greetings, Thomas