MK4 ASTRA TURBO FLYWHEEL UPGRADE
A stronger clutch and a lighter flywheel are better for coping with extra torque and better acceleration from power upgrades.
Lighter flywheels are guaranteed to put some extra zing into any engine by reducing its rotating mass. The easiest way to imagine the role of this component is to think for a moment about the opposite effect. What would happen if an Astra flywheel was doubled from its standard 9.6kg to nearly 20 kg? The result would be a sluggish engine response as it drags the flywheel up to speed. Inertia on the overrun would also take all the snap out of the downshifts.
Courtenay Sport have come up with a popular flywheel upgrade for the Zafira GSi Turbo, Astra Mk4 GSi Turbo, SRi Turbo, and Coupe Turbo models (the Astra here is a Stage 4 Triple 8). The replacement flywheel is around 5 kgs lighter at 4.25kg and is machined from billet steel and plated for extra durability. It costs £255 and with more power to tame, goes together well with
PERFORMANCE VAUXHALL a Courtenay fast road clutch assembly (cover and plate) at £199.95. This is good for outputs up to 300 bhp, but beyond that, an uprated competition type clutch is best at £432. Clutch life under normal use tends to be good, so it’s worth making sure that other components will perform reliably over the same period of time by splashing out on a new hydraulic slave cylinder. This is £119.95 from Courtenay with the clutch.
Removing the gearbox and fitting a new flywheel and clutch is an advanced DIY task but it’s mainly a nut-and-bolt job that includes disconnecting cabling, gear linkages and the driveshafts. The two important tasks are supporting the engine and dropping the engine bed. Most critical is making sure that this subframe – which has about 10 mm of movement in the captive nuts – is properly aligned when it goes back.
Aligning the frame without using a jig needs careful preparation before removal. It will need some reference points marked between the body and frame, ideally with a metal scribe and steel ruler for maximum accuracy. If there are any doubts about how accurately it’s been screwed back, it’s always possible to have it checked with a jig later. This is worth doing anyway, because there is no way of telling if the bed was previously misaligned. Keeping the engine in a raised position while the frame is dropped is done professionally using a supporting beam that locates in the wing channels. A DIY solution is to use an engine crane. Alternatively, it’s not rocket science to cobble up a homemade steel beam assembly using a bolt with chain attached to the engine to keep it in position. If this all sounds like a lot of work, it’s worth knowing that Courtenay normally charge about £324 for fitting a supplied flywheel and clutch providing no other Universal centering tool Angle gauge Trolley jack Engine crane problems crop up along the way.
Reassembly of the flywheel and clutch includes centring the friction plate with the cover to allow the gearbox splined input shaft to glide into place as it’s replaced. One way to be sure of an accurate result is to use a universal centring tool. A basic tool can be bought for as little as £15. Cheaper alternatives include an old gearbox first motion shaft, or a piece of pipe or even an old jack handle that is the right size to fit perfectly into the friction plate. Then while the cover is only just nipped up – allowing for the friction plate to be moved – the plate can hopefully be centred by eye, but this can be a bit hit and miss. Once everything is back in its place, one of the final jobs will be filling the gearbox with oil. It’s not advisable to re-use the original oil even if the gearbox has only done low mileage because it is probably not synthetic.