Clutches in 1:8 scale off-road buggies are designed to let the vehicle stand still without stalling the engine. They also make it possible to speed up the car gradually from still stand to full speed.

Introduction

The Clutch of a Nitro-RC vehicle is the part responsible for transferring the engines power to the drive-chain of the vehicle. It is one of the most critical components. Unfortunately it is also one of the most underrated parts by many drivers. One can often see people vainly attempting to adjust their motors, not noticing that their clutch is the cause of their problem. Proper clutch tuning and maintenance is paramount to successful enjoyment of this hobby. In fact a well tuned clutch can often deliver more usable power then buying an expensive modified engine.

In this section of the TEAM TWF8 web site we will attempt to describe the basics of clutch operation and maintenance along with a description of some of the commonly used clutches. This is an ongoing project and we will attempt to keep it ‘up to date’ at regular intervals.  Feel free to contact us if you would like to contribute.

Basic Operation

All clutches we use for buggies use centrifugal force for engagement. A clutch consists of three basic parts.

	A flywheel attached to the crankshaft of the engine.
	Two or more clutch shoes/pads which are retained by one or more springs to the flywheel.
	A clutch bell that encases the the shoes pads and has the gearing to transfer the power to the drive train. This part is separated from the crankshaft/flywheel-shoes by one or more bearings.

Normally there is a small gap between the inner cylinder surface of the bell and the shoes. When the engine revs up the shoes will go outwards due to the centrifugal force of the rotating mass and will engage the crankshaft with the clutch bell transferring rotation and power to the bell and thus the drive train. As soon as the engine is below a certain number of rev's the clutch will dis-engage. The shoe returns to their rest position with the help of the return springs. The spring on each shoe also prevents  the car from crawling when the engine is idling. The lighter the weight of the shoes the later the clutch will engage. The heavier the shoes are the sooner the clutch will engage. Also the thickness of the return spring determines if the clutch shoe engages earlier or later.

Phases of clutch action

To be able to tune and maintain a clutch properly it is necessary to understand the different phases of operation that clutch goes through. Many think that clutches act like switches either engaged or disengaged. There is however a third phase; the transition between the two. This is the transition phase  (also called engagement characteristic) when the shoes are slipping and not transferring all of the engines power to the bell and drive train. Anybody who has driven a full sized car with manual transmission has to first learn to start moving the car while sliding the clutch to avoid stalling the engine. Additionally, adjusting or accounting for different engagement characteristics in RC buggy clutches can allow one to tune for ones driving style and the conditions of the track.

Types of Clutches

There are several different types of clutches used in buggies.
Click on the type below and see the basic construction of that type of clutch

Swinging

Sliding

Clutches Clutches Clutches

Here we have brief descriptions of clutches that Team-TWF8 members have experience with.

Note for Manufacturers and Importers. We are trying to describe as many clutches as possible. 
There are however many different clutches. If you would like us to publish a profile for one of your clutches please  contact the Webmaster.

RMV Standard Clutch 'Mielke'

RMV Speed I Clutch

RMV Speed II Adjustable Clutch

Fioroni Sliding Clutch

Fioroni Turbo Sliding Clutch

BBF Sliding Clutch

WERKS RACING POWERCLUTCH

Tuning Tips

The clutch is responsible for transferring power from the engine to the drive train. For optimum performance one should tune the clutch to match the characteristics of the engine, track and ones driving style

Click here for Tuning Tips

Installing a clutch

Here we show how to install a common 3 shoe swinging clutch with scissor springs.

	Make sure the engine mounts are flat.
	In some cases depending on the crankcase size you might first need to add one or more 7 x 14 x 0.5 mm shim washers. In the case of the CMB EVO 3 RALLY engine we do not need to add on of these.
	Slide the black cone up to the crank shaft until it touches the front bearing.
	Slide the flywheel on the crank shaft.
	Place the flywheel nut on the crank shaft as the picture shows.
	Secure the flywheel nut with the use of 10 mm tool and a large pliers.
	A clutch kit can come with aluminum or nylon composite clutch shoes. Also the scissor spring thickness can vary from 0.9 to 1.1 mm
	In case you use aluminum clutch shoes you need to place the small 2.6 x 6 x 0.5 mm washer on the flywheel pins. If you use nylon shoes this is not needed.
	Place the clutch shoe return spring in the clutch shoe and place it on a flywheel pin. The end of the clutch shoe return spring needs to be placed on top of the flywheel nut.
	Now with a small screwdriver tip press the end of the clutch shoe return spring in the groove of the flywheel nut.
	Do the same for the second clutch shoe. As the second clutch shoe is placed open it by putting a 3 mm hexagon tool in between so it stays open.
	Now you can easily place the third clutch shoe. When finished remove the 3 mm hexagon tool.
	The three clutch shoes ready.
	Slide a 5 x 10 x 1.0 mm steel shim washer on the crank shaft.
	Press a 5 x 10 x 4 mm ball bearing in the inside of the clutch bell.
	Press a 5 x 10 x 4 mm ball bearing in the outside of the clutch bell.
	Slide the clutch bell on the crank shaft.
	We advise you to use a regular 3 x 8 mm flat head hexagon screw using a 2.5 mm hexagon tool. Screws with a 2 mm hexagon are damaged to quick!
	Slide a 5 x 10 x 1.0 steel shim washer on the crank shaft. Slide a 3 x 8 x 0.5 washer on the 3 x 8 screw and secure it firmly with a 2.5 mm hexagon tool. Never use thread lock on this screw!
	Make sure there is 0.5 mm play in the direction of the red arrow. If there is no play replace the shim washer for thinner ones. If there is to much play add a shim washer.

FLYWHEEL SIZE

There are different sizes of flywheels.
This has mainly to do with the height of the engine compared to the chassis regardless the flywheel system itself.
So if you use a swing or a sliding clutch has nothing to say about the diameter of the flywheel.
The flywheel must be inside the starting slot of the chassis 2 to 3 mm higher as the lowest point of the chassis.
A flywheel may never be level or below (coming through) the chassis itself!
Flywheels are generally not interchangeable so don't try to install a Hobao Hyper-7 clutch on a Kyosho MP-7.5 and vice versa.

Brand/Type	diameter in mm	Part number
Crono RS01 (2 Pin)	38	S2311
Fioroni MP-7.5 / MBX-5 / Storm PRO (3 Pin)	34	OT-FR39 FR41 FR46 FR50 FR51
Fioroni Universal (3 Pin)	36	OT-FR01 FR21 FR31 FR38
Fioroni MP-5/6 (3 Pin)	39	OT-FR06 FR26 FR30 FR37
GS-Racing Storm PRO (3 Pin)	36	?
GS-Racing Storm RTR/Sports (3 Pin)	38	?
Hobao Hyper 7 PRO (3 Pin)	37.7	18057
Hong Nor Speed 9.5 PRO (3 pin)	?	#174A
Kyosho MP-5/6 Standard (2 Pin)	39	IFW054
Kyosho MP-7.5  Kanai versions (3 Pin)	34	IFW110
Kyosho MP-7.5  Standard versions (2 Pin)	34	IFW109
Kyosho MP-7.5 Sports (2 pin)	?	IF109
Mugen MBX-5 (3 Pin)	34	E0702
Mugen MBX-4/RR/XR (3 Pin)	36	C0706
Protech Enigma (3 Pin)	34	T56.060
RMV Speed II (2 Pin)	35	TU9530
RMV Speed II (2 Pin)	38	TU9531
Thunder Tiger (3 pin)	38	BD2447
Tunder Tiger S3 (3 pin)	35	PD1870
Xray XB8 (3 pin)	34	35-8531

FLYWHEEL PINS

The distance of the pins for a swinging clutch compared to the centerline can vary from brand to brand which can change the clutch characteristics!
Kyosho uses as only manufacturer 2.6 mm swinging pins on their flywheels.
Other brands known so far are using 2.5 mm swinging pins.
If you fit shoes in combination with scissor springs from any other brand then Kyosho to a Kyosho flywheel the springs are prone to break.
Due to the smaller inner diameter of the non Kyosho springs these scissor springs made for 2.5 mm pins will strangle themselves around the pins and can break pre mature.

CLUTCH BELL SIZE

A clutch bell inner diameter varies from brand to brand.
Below a table with the different known sizes.
A smaller inner size diameter can cause earlier engagement.
A larger inner size diameter can cause later engagement.

Brand	Diameter in mm
Bergonzoni
Crono
Fioroni	26.3
GS-Racing	26.0
Hobao	26.8
Hong Nor
Kyosho	26.3
K-Factory / RMV	26.3
Mugen	26.0
Nuova Faor	26.0
Protech (YUSA MODEL)	26.3
Thunder Tiger EB4 S1/S2	25.8
Thunder Tiger EB4 S3	26.0
Xray	26.3

 

Maintenance

Clutches are one of the most stressed parts of an Off-road-Buggy and need regular maintenance to ensure reliability

A properly installed and tuned clutch will normally last 2-8 liters of running time before failure. To avoid it failing at an unhappy moment we should  subject it to regular maintenance. This allows us keep it working in a consistent manner. We recommend a minimum maintenance cycle of 1 liter, and additional maintenance before every race.

1. Remove the engine from the buggy.
2. Clean the engine with a brush removing loose dirt and dust we don't want in the clutch.
3. Check the radial play of the bell and bearings by wiggling the bell in a tipping motion.
4. Remove the bell and check the teeth for excessive wear.
5. If point 3 showed too much play (more than 1/10th mm) put the bearings on the shaft to test if the play is from the bearings or the bell.
   
6. If the bell is still OK, clean the inside surface with some steel wool and denatured alcohol (I use brake cleaner) to remove dust and grime from the wear of the shoes..
7. Check the shoes for excessive wear. If more than 1 mm of shoe depth has been used you might consider using a new set of shoes.
8. If you are using the old shoes, check and remove any burs that might have built up on the edges with a sharp knife.
9. Clean the contact surface of the shoes with some steel wool and denatured alcohol.
10. Reassemble.

Tips and tricks

 

click here for clutch bearing trouble shooting

If you have used aluminum shoes remember that the clutch-bell(s) you used with them should NEVER be used with a different material. Aluminum shoes leave a residue in the bell which will cause other materials to slip and overheat the clutch and cause premature bearing failure.

When installing a new clutch-bell, take some emery cloth or steel wool to clean up the clutch bell inner surface. Then clean it with denatured alcohol or a spray bottle BRAKE CLEAN. This is done to remove in an easy way as much as possible any manufacturing residues that can cause extra slippage. Other option that requires more work and a special tool engraver is: To get the composite shoes to engage quicker requires lines or "grooves" in the bell that you can actually feel with your finger. The Dremel Engraver tool is not a rotary tool or a bit for a rotary tool. It is a separate tool that looks like a rotary tool but works via vibration. It has several settings, I crank it up to high, pin the inside of clutch bell to a flat workbench with it and then run the engraver tip slowly in and out of the bell ten times or so to make each line or "groove". Then rotate the bell a little and do the next groove. There really isn't much "careful" about it. You have to push down HARD to make any sort of groove with the engraver. If you can't feel the lines with your finger they won't do much. When you can feel them even shoes with heavy springs reach out and grab the bell really well and show very little wear.

Springs wear out with usage and get softer, especially if they have gotten hot. Some top drivers use new springs for every other race-weekend. If your clutch seems to be engaging earlier then it used to, it might be time to change the springs.