If a PD TDi engined car is parked in gear and it rolls then the engine is turned. Is it detrimental to the engine if this causes the engine to turn backwards?

My previous experience includes V6 Alfa engines and for some of them it's a big risk of expensive damage.

So, if there is a risk of the car rolling backwards and I want to park it in gear, should I always use reverse?

Edited 11 February, 201016 yr by AnotherGareth

I can't see why it would be?

For some Alfa V6 engines it can result in the cambelt jumping a few teeth - for that series of engines I think the main factor is what sort of belt detensioner is used.

Edited 11 February, 201016 yr by AnotherGareth

How? I just can't understand how that can happen?

I think the issue with some Alfa's was the cambelt was only under correct tension when the engine was rotating in its normal direction. When turned backwards the belt could slacken and jump a few teeth. PD should be ok, I turned mine backwards when changing the belt and waterpump and it didnt seem to affect the tension at all.

Ah right, fair enough I geddit now!

The Alfa problem I came across was mainly when the engine was longitudinally mounted. These engines originally had a hydraulic cambelt detensioner fitted which, by many expert accounts, worked exceedingly well. However the design was prone to oil leaks if the car wasn't well looked after or if the detensioner wasn't rebuilt carefully, so many owners changed to using a mechanical detensioner fitted to later transverse mounted engines, a relatively simple 'upgrade'. One of the problems then was that the belt could jump a few teeth when the engine was moved backwards, but there were sporadic reports of the same problem happening on older engines without the upgrade and, indeed, on newer engines that came with the 'upgrade' as a standard factory fit.

Because of my experience of expensive engine repair bills I've always been extremely wary of allowing engines to be rotated backwards, and so I wondered if there are or were any similar issues with PD engines.