S2 with PRV & Diravi

[citroenxm]

Very good but Germany isn't the UK

I've not seen a UK s2 prv 24v model either..

[russ92xmsed]

Exactly. I had no idea as I don't really look at German cars for sale. But it is interesting. Learn something everyday with these cars!

[xmexclusive]

Hi Russ & Paul

Have a look in version XM-GB-5005 pages 72, 73 & 123.
That is the 95 model year owners handbook the start of the Mk2's.
The only owners handbook with the Mk2 xm symbol.
Your will see the PRV V6-24V diagram and spec.
I cannot get to my copies for 96 and 97 model year but think they are the same.
The Citroen workshop manual model year statements also mention the V6-24v.

1994 model year was the change of PRV engine capacity from 2975cc to 2963cc.
The piston travel was reduced by 0.7mm, piston shape modified and diameter of combustion chamber increased by 1mm.
The camshaft settings were changed, injection ECU, injectors and engine harness changed.

1995 model year saw the gear box changed to MG5TB(2KM01) with hydraulic clutch for V6 and V6-24v.
Front struts and rear hydraulic cylinders were beefed up.

1996 model year saw the V6-24v retain Bendix ABS when all other models changed to Teves ABS.

The 1997 model year UK workshop booklet (pub Oct 1996) still lists the V6-24v as available with the ZPJ4 engine.

The 1998 model year booklet Lists the V6-24v with the new ES9J4 (XFZ) engine.
It has a section on the V6 changes and this gives details of the end of the ZPJ4 engine.
It also seems to provide answers to some of the engine gearbox options etc.
The ZPJ engine was fitted to V6's right up until the end of the 1997 model year.
Production of the ZPJ4 engine ceased from 01/1997.
For the ES9J4 engine (manual version) the MG5TB gearbox is replaced by the ML5T.
All V6's and 2.5's got uprated (Bendix 5Z0) 288mm disc front brakes.

John

[russ92xmsed]

So they still continued to develop and and tweak things with that engine and spec. Well this is totally the opposite to how I thought the PRV 24V was dropped due to poor sales or reputation. Clearly not. Kind of nice to know they kept the faith, even if it was more for the continental markets.

[citroenxm]

I think the valve train issue was only a problem for early examples H J and possibly K where citroen then fitted new cars with the modified setup already installed in the engine so the problem is not there on later engines.

[marc61]

Thanks for explaining that John. Would be interested to know why PRV engine was modified with those changes? Changing the internals of a long established engine must have been a lot of hassle for them at the time.

Marc

[citroenxm]

The 12 v engine wasn't a problem but when they filled the remaining spaces up for the extra 12 valves to makes 24v i believe the oil pump was not strong enough to provide enough oil pressure and supply to the heads so rather drill out bigger oil ways in the block cast it was easier to install ceramic followers which then solved the problem.

This is only what I've heard. I would love to really know why it happened. But I assume that if two working metal parts in an engine have lack of oil then wear away will occur which is what happend in the early 24v heads.

Anyone elaborate more?

The 605 and XM was the first time the PRV got 24v heads in a production version in the prv history. Though I think venturi the french sports car maker also did a 24v head too but not sure what else they modified. I think also think venturi had turbos aswell as 24v .. but then they are small production not mass produce for profit.

I can elaborate a bit more. The issue was apparently the fact that the exhaust valves used the same cam lobe to operate both valves where was the 12 inlets valves all had a cam lobe of their own. I guess then the extra valve spring pressure from the combined exhaust valves is What caused the wear away of the valve lifter. I'm not sure yet if the 24v was hydraulic lifters like the later psa 16v engines or still manual adjusters. From what i recall from the opend prv 24v in my shed they are hydraulic lifters like the later psa 16v engines in which theres a tappet bucket with hydraulic lifter under it and its the top of the bucket that wore away along with the exhaust lobe

must have a go at dismantling one of the heads on the buggered engine. Prehaps remove the head complete and bring it to cxm to dismantle or x rally... hmmmm there's a thought..

[russ92xmsed]

Good idea Paul. I would be very interested to see that.

[citroenxm]

So will I ...

[White Exec]

"...and its the top of the bucket that wore away along with the exhaust lobe."

Interesting. The Rover (ex-Buick) V8 3.5 petrol engine suffered a similar wear problem, this time with alloy rockers running on an internally-oil-fed hollow steel rocker shaft. Despite the presence of hydraulic tappets, with age the valve lift decreased, and power dropped off. Amazingly, the alloy rockers wore right through the lower portion of the steel shaft (around 20mm dia and 5mm thick wall, IIRC) ! You would expect the other way round, with the alloy parts getting the wear.

The cause was abrasive microparticles, which built up in the engine oil, embedding themselves in the alloy rockers, which eventually destroyed the shaft they ran on.

At the bottom end of the Vee, the single camshaft lobes would also lose profile, gradually turning circular.

To minimise this, oil and filter changes were recommended at 3000 mi, but this only put off the evil day. The two shafts could be expected to last around 150,000 mi, before needing a "top end rebuild".

I wonder whether other dissimilar metal pairings could suffer a similar problem, particularly if lubrication were marginal? And can hydraulic tappets accelerate wear, by keeping all the surfaces in constant contact, again more so where lubrication is sparse?

Aren't higher output (but standard pressure) oil pumps often used for competition purposes too?