Volvo B21-B230 Clutch & Flywheel

Part 1 - Volvo 9 1/2" CLUTCH Upgrade

Part 2 - Volvo FLYWHEEL / sensor Information

Part 3 - Volvo CLUTCH DISC Comparison

by Anthony Hyde, Australia. © September 2002. Updated 6/2008

This technical article demonstrates that a larger 9 1/2" clutch and pressure plate can be fitted onto a Volvo FLAT flywheel giving B230 turbo owners with 9" clutch + 'stepped' flywheel, or earlier B21/23 with 8.5" clutch + flat flywheel, an upgrade *possibility.

Volvo 4 cylinder turbo engines produce maximum torque at 3,450 rpm. If you've modified your engine for higher output / fitted wider tyres/tires with stickier compound / increased boost above 12-14 psi / race takeoffs - then with rapid acceleration sooner or later standard parts will wear down or glaze and slippage will occur. The 740/760 turbo engines use a stepped flywheel and this is a bit of a curse. The clutch disc sits on the inner step and the pressure plate mounts on the outer step.
As the clutch disc and flywheel surface wears down, the pressure plate exerts less clamping pressure on the disc, and hence slipping occurs at maximum torque, the beginning of the end. Come replacement time, the big question is does one refit standard turbo clutch components and hope once more it doesn't slip, or perhaps adapt a CentreForce, or consider a new alternative like a 9 1/2" system?
- With the flat flywheel, (All early model 240's with M45 / M46) used a flat flywheel) all the original tapped holes for the 8 1/2" pressure plate, dowels and balancing holes are located outside of the 9 1/2" clutch disc working area. No problem there.
- Thorough testing has been performed with general road use, and under racetrack club competition conditions. No slip and lower lap times.
This project is possible if the engine is controlled by an aftermarket computer, with timing information picked via a trigger wheel on crankshaft or ignition distributor. Also suitable without change is models with Bosch Ignition system EZ-117K with fuel LH 2.2 (1985-88) and early Motronic versions that use a Hall sensor in the distributor and NO flywheel speed sensor.

Before getting too excited, 'projects like this are not off the shelf items' but require parts research, machining, modification, trial fitment, a few dollars etc.

BACKGROUND: After a trusted friend Gerry had success with a prototype, I was convinced enough to carefully check through the fitment dimensions myself, coming to the conclusion that a 9.5" custom clutch system would indeed fit well onto the lighter Volvo B21/23 flat flywheel. My 240T'R' was fitted with the upgrade and outlined below are a number of details :

FLYWHEEL MACHINING STEPS: To match the pressure plate, the flat flywheel is drilled & tapped for 6 off M8 screws, with another 3 holes drilled for pressure plate alignment dowels. The flywheel is surface ground - Locating dowels pressed in - Flywheel and pressure plate are located together and sent off for a dynamic balance by professionals.

Carrier & Release bearing Modification : Function - The clutch fork slides the carrier (with attached release bearing) back and forth on a fixed tube around the gearbox input driveshaft. As the new clutch assembly is 13 mm (0.51") less in thickness (than stepped flywheel assembly), this requires a longer (steel) carrier to be made. (Perhaps not req'd if you have a B21ET/FT with flat flywheel to start with). The release bearing Dellow sells is KOYO (Japan) #RCT4064S and this is pressed onto the steel carrier. By comparison, the Volvo combined 'carrier & release bearing' is mainly plastic with an attached release bearing with questionable rigidty and long term durability issues in my experience.

- Lighter (flat) flywheel reduced overall weight by
2.5 kg OR 5.5 lbs and therefore less inertia.
- Less mass on outer perimeter of new assembly.
(compared to the turbo stepped flywheel that has a huge ring of steel around the outer edge to increase inertia)
- Overall thickness of the fly/clutch assembly is less by 13 mm or 0.51 inch - rotating mass sits closer to the crank/flywheel mount face
- Pressure plate designed to handle high torque 6 cylinder loadings
- Light clutch pedal action (increased if using HD pressure plate) with easy-feel organic clutch engagement or (grabier with button type)

- Increased frictional surface area by 17 cm2 - although not a huge difference in swept surface area between 9 and 9 1/2 inch clutch discs, the Dellow manufactured pressure plate clamped down further (preload) against the clutch disc compared to the Volvo OEM 9".
Click for 9 1/2" Clutch Pics
Side Assembly (1)
Flywheel mount holes (2)
Top Assembly (3)
9.5" Pressure plate (4)

PART 2 * * Volvo FLYWHEEL Infomation* * by Anthony Hyde

58T stepped fly with Sensor at top
(Pic: FSL Sweden)

INTRO - All early model 240's (1977-85) with mechanical K-Jet fuel injection used a flat flywheel with a clutch disc diameter of 8.5". No sensing of flywheel position is used when engine is starting or running. A breakerless magnetic coil system is located in the ignition distributor. Dealers use a stand-alone separate diagnostic port to determine TDC etc. - via 2 protruding pins mounted on the flywheel front face)

All EFI versions used a stepped flywheel with a 9" clutch from about 1985-86 in the 240s and 1983-84 in the 740.

All 4 cyl 240 to 940 flywheels have the same bolt up pattern (8 bolts), and all these will physically bolt up to any B21 through to B230 crankshaft.

The flywheel material is high quality cast iron. Flywheel bolts M10x25, 10.9 grade (Volvo #946379)

Misc - Flywheel pilot shaft bearing - If your a fanatic, a higher temperature rated bearing over standard types is made by NTN #6202LLHC3/L412

Misc - Flat flywheel - Pitch circle diameter (PCD) of 8.5" pressure plate mount holes is 250.6 mm as best as I can measure.

Misc - Newer style clutch fork VO-1220763 plus you will also need the fork Lock Spring VO-1377132

EFI versions Click pics

58 hole stepped manual flywheel

58 slot auto driveplate

20 holes, 2 missing, 20 holes, 2 missing = 44 pattern
NOT the one your after for a 240

Custom pattern on flat flywheel

EARLY type - NO pattern holes on outside -The Bosch Ignition system EZ-117K with Bosch fuel LH 2.2 (1985-88) and Bosch Motronic (1984-85 combined ign & fuel) uses a Hall sensor inside the front mounted ignition distributor. Therefore, on the early type there is NO crank position sensor, and the stepped flywheel has NO pattern holes drilled around the perimeter (other than for balancing purposes).
Extra info: The Hall sensor is a Siemens HKZ101 & the distributor wheel has 4 chopper vanes. The distributor mounted HZK101 switches to 0V in air (as it responds to a magnet field on the other side) and back to 5V when the rotating metal vane blocks the magnetic field. Therefore a rising edge from air to vane OR falling edge from vane to air.

TYPICAL - 60 Pattern with 58 holes - Bosch Ignition EZ-116K with Bosch fuel LH 2.4 (1988.5 on) uses a Stepped flywheel with 60 pattern = 58 holes plus 2 holes missing. Volvo term it 'one long tooth twice the length of a short tooth' - Imagine explaining this Double-Dutch to the bloke at the wrecking yard !
A crank position sensor is positioned over the flywheel to sense engine rpm. Bellhousings from (1988.5 on) have a notch machined out at the top to accomodate the sensor.
Strictly speaking the pattern is 58 hole, with an extra double space - the space being a crank position sensor reference point that the computer recognises. Pitch between holes is 6 degrees, and TDC is 90 deg after a long space. Correct flywheel orientation is critical.
Extra info: Fuel Injector timing from flywheel sensor - (as far as I'm aware) the fuel computer Bosch LH 2.2 uses batch firing of injectors - (two injectors spray together, engine rotates x degrees then 2nd pair spray) not the more advanced sequential injection. Bosch LH 2.4 spray all at once. To have true sequential you need two sensors - one to tell which cylinder number is coming up to fire and other where TDC is. Not just one on the flywheel as in EZ-116K. An aftermarket computer is required if you want the benefit of sequential injection.

Be Aware of incorrect 44 pattern if seeking 60 pattern - when buying a used flywheel count all the holes. I know its hard when the greasy engine is on the floor and you can't easily rotate the crank. But really check as a Volvo 360 2 litre B200 engine and flywheel look the same on first impression but has a different 44 pattern count on the perimeter.
Extra info: Cracks - very light surface cracks are normally machined out when resurfacing. Deeper cracks mean the flywheel is unserviceable. Glazing - surface becomes smooth and glossy -> remove by machining. Heat spots - localised deep blue spots indicate significant heat was the result of friction via a slipping clutch / abuse, and as a result these localised hard spots are in the cast iron forever - read clutch slip points.

OTHER Volvo EFI Flywheels:
44 Pattern with 40 holes - Renix Ignition eg Volvo 360 with B200E, 2L engine uses a Stepped flywheel with 44 pattern = 20 holes / 2 missing / 20 holes / 2 missing.
60/3 Pattern - Bosch Ignition EZ-115K on Volvo B280 V6 (PRV 1987-1990) uses 60/3 pattern with 60 holes and 3 hole(s) missing each 120 deg apart.

Bottom photo shows custom machining of tooth pattern on a flat flywheel (source: forgotton)
The owner went to a lot of trouble and expense, but got the best result to modernise his engine.

FLYWHEEL WEIGHT COMPARISON (commercial scales used)

Volvo 9" Stepped flywheel (B230 era) 12.8 kg + Clutch disc 1.33 kg + Pressure plate 5.46 kg. Total = 19.5 kg OR 43 lbs
Exedy make a clutch for this Volvo version.

Flat flywheel (B21-23 era) weight range - 9.2 to 9.4 kg depending on times refaced, and scales used
This example: Modified Flat flywheel
(for 9-1/2" clutch) 9.2 kg + Clutch disc 1.26 kg + Pressure plate 6.6 kg. Total = 17 kg OR 37.1 lbs
Comparing the new flat flywheel conversion against the Volvo OEM stepped flywheel, the Overall Weight Saving is a significant 2.5 kg OR 5.5 lbs.

Lightened Volvo Flat flywheel - precision CNC cutouts saved another 1 kg. So 9.4 - 1 = 8.4 kg. Approx 10% lighter, but importantly weight was removed from the outer perimeter.
Click Pic to enlarge (authors flywheel). After machining, precision balancing of flywheel and pressure plate is required.

Extra info: On a stepped flywheel the distance from the flywheel crank mounting face to the (clamped down) pressure plate fingers is 71 mm. On the flat flywheel to the (clamped down) pressure plate fingers is 61 mm -> So a flat flywheel hangs out from crankshaft 10 mm less (less wear and tear on the crankshaft rear main bearing).


Brunton Engineering located at Hornsby, Sydney, Australia, has developed a unique alloy stepped flywheel system for performance applications.For the Volvo 740 application, the Brunton Engineering alloy flywheel plus steel ring-gear weighs only 4.8kg, compared to near 13kg for the standard steel flywheel. The standard steel flywheel is duplicated in high strength aluminium, reducing mass by 60%. The clutch plate contact surface is then hot-metal sprayed with a specially developed formulation of alloys to provide a high friction, durable wearing surface direct on the alloy flywheel (see flywheel surface on pic). This eliminates the traditional steel plate wearing surface previously required on alloy flywheel applications.

The hot-metal sprayed surface has been race-proven in the Rev Doctor's Championship-winning RX-7 over two racing seasons, with negligible wear of the contact surface against a ceramic button clutch plate.

PART 3 * * Volvo CLUTCH DISC Infomation* * by Anthony Hyde

Click Pic to enlarge Exedy 'cushioned button clutch' disc

For my second conversion, I used Exedy brand components. Exedy TYD011CB cushioned button clutch disc features a sprung centre with wave cushion disc between disc faces, and 8 sintered pads are attached either side. Clutch action has high feel and easy to use. My wife could hardly tell the difference between an organic clutch and this button unit. Outside dia 234.4 mm, inside dia 160 mm

Disc in picture has a 22 spline centre that suits a Supra W55-58 gearbox used in Volvo gearbox conversions. Link to Volvo - Supra conversion article.

Click Pic to enlarge Exedy pressure plate

Exedy FMC9153 HD (HD heavy duty version) cover assembly (pressure plate) from an Australian 6cyl Ford Falcon engine, 1978-1988 models XC,XD,XE,XF (huge number of common generation models in Australia) being a proven component used in many conversions. Weight Exedy 6.28 kg. This cover comes standard with only a three bolt attachment, so extra mount and alignment dowel holes need to be drilled, making it a rigid 6 bolt attachment.

DIMENSIONS OF CLUTCH DISCS (as measured by author)


Trick - 9 1/2" organic vs Exedy button
9" Volvo OEM
8 1/2" Volvo OEM

Disc Swept Area

246 cm2. vs Exedy uses 8 pads
229 cm2
212 cm2

Outside diameter

240 mm. vs Exedy 234.4 mm
226 mm
216 mm

Inside diameter

162 mm. vs Exedy 160 mm
148 mm
140 mm

Disc face width

39 mm. vs Exedy 37.2 mm
39 mm
38 mm
Volvo Clutch kit - 8.5" (to end 85)
flat flywheel # VO - 271266
Volvo Clutch kit - 8.5" (1986->)
stepped flywheel # VO - 271267

Examples of Clutch Disc available from:

Another site: Clutch Masters

This detailed web article is completely original *, and so is subject to copyright ©. *(Flywheel hole pattern information interpreted from Volvo reference book)
Anthony Hyde, Australia, September 2002

PLEASE NOTE any information offered on this web page is free and without guarantee. Should you choose to perform any of the procedures listed on this page, you will be doing so of your own free will, and I will not be held responsible or liable for any damages that might occur from using information obtained here. The information stated here, is to the best of my knowledge, accurate. However, in order to safeguard myself legally, I make no claims that it is in fact accurate in every, or any detail.
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