Citroen XM Forum

MTXM wrote:in this case do we mean the eight bolts connecting between the crankshaft and the flex plate and starter ring, which is not strictly a flywheel on the auto is it?

It is still part of the flywheel, which in this case is made up of the thin flywheel plate, the starter ring, the flexplate and the torque converter. That thin plate is transmitting the roational mass of all those components back to the cankshaft to keep the engine spinning smoothly.

As you say, the torque convertor provides the additional mass required in the case of an auto box Will and all three (or four) components together constitute the 'flywheel' With regards, Matthew T.

I know it's a bit semantic, but Matthew is right - a torque converter set-up really doesn't feature a flywheel. The torque converter, being big and heavy, functions as a flywheel, but isn't one. Flywheels are what you see on manuals, either SMF or DMF. I know. I have seen quite enough of these, I really have. Don't get me started on DMFs - the work of the devil.

Trouble is, the poor t/c-carrying flexplate has to transmit god-knows-what in the way of shocks and snatches: starting (if only one plate), drive engagement, unsympathetic driving, occasional engine stalling, engine being switched off while still in Drive (by unhelpful drivers). I know the t/c has a slipping/cushioning action, but it still transmits shocks. It is also very heavy, and has an inertia all of its own, and will (for example) slow more slowly than the engine if the power if suddenly lifted off.

It is no wonder that vehicle manufacturers have been slow to offer automatics on their diesel vehicles. At one point, the only diesel auto offered by Citroen was the non-turbo ZX, iirc. I think that was as much to do with preventing damage to the autobox and its bits, as it was to any "mismatch" between the torque-rev characteristics of engine and box. A harsh, high-compression and torquey diesel gives a flexplate an even harder life. It would never have survived the 2.5, I guess.

Citroen offered the Bx first chris as early as H 1990 in auto with ZFs 4hp13 box..

Yes, they did. I had forgotten that. Would have been NA though, and a modest 71bhp 1905 ?

White Exec wrote:A harsh, high-compression and torquey diesel gives a flexplate an even harder life. It would never have survived the 2.5, I guess.

Nearly all larger diesel engined cars are automatic, but I don't think the HP18/20 gearboxes can take the torque.

Noting that Matthews grey car has both fractured flex-plate and drive plate does make me remember that car suffered with locking of the TC causing stalling and snatchy starts, at one time. I suspect that could have contributed to the fracturing.

Hp20s are fitted to the c5 2.2 hdi 136bhp engines and also in peugeots 406 derv autos too..

Hp18 only ever mated to petrol engines and 2.1 td xud psa engines.. but saab fitted it to their 9000 2.3 turbos with 240bhp

So did Alfa on the 164. They definitely seem to suffer from a more powerful engine.

that car suffered with locking of the TC causing stalling and snatchy starts

As earlier mentioned, the problem to which you refer was failing governor seals Will, which was fairly soon afterwards addressed. I think the main contributing factors to fracture of the flex plate and starter ring were age and hard useage by previous owners, if the condition of the car generally and engine and gearbox in particular were any guide! Regards, Matthew T.

I fitted the solid flywheel today and am pleased to report there is pleanty of clearence between it and the block and i tried to lever the flywheel and crank pully and there is zero side to side movement from what i can see.. so im rather pleased to say the engine is fine and must be a shoddy install on the autobox somewhere..