Simon's new Xantia V6 and Leaf blog

[Stickyfinger]

Quick question, if the h-tappet has collapsed, why would you think it improve sometimes, would it not just be constantly restricting the engine ?

[Mandrake]

Quick question, if the h-tappet has collapsed, why would you think it improve sometimes, would it not just be constantly restricting the engine ?

Well I don't think there are any permanently collapsed tappets on this car, but there may have been one on my old V6. A completely collapsed tappet that won't pump up at all is usually due to either the feed channel being completely blocked, the non return ball valve on the input leaking (held open by a speck of muck) or bad wear causing the piston to be leaky. The first two causes can potentially be fixed by flushing and oil changes but bad wear would require replacement, although I've read that thicker oil can help if the wear is marginal.

However hydraulic tappets can also be "cranky" and intermittent... when the engine is stopped they will slowly drain and take a few seconds to re-pressurise again when the engine is started many hours later, and that's if they're working properly.

If the feed channel to the tappet is partially blocked (and they are very tiny channels so block easily) it may take some time to re-pressurise at idle, or it may not pressurise properly at all until the engine is revved - which both increases oil pressure and movement of the tappet. So I'm theorising that one or more tappets is not always pressurising quickly and reliably after a cold start and is requiring a bit of revving to give it a kick in the pants.

Most people will have noticed that hydraulic tappets can get a lot noisier by the time an oil change is due - the noise is an indication that they're not fully taking up the valve lash. Sometimes they will get quieter after a longer period of time when the oil is old, or they might not go quiet at all.

Sometimes if the problem is wear in the tappet piston they can actually start off quiet but then get noisy when the engine is hot due to the oil thinning with heat. (My old V6 had this problem on two tappets)

Another theory I've proposed before (in my other really long blog thread) is the idea of "false knock". Some engines are apparently prone to this problem - basically the knock sensor is a bit too sensitive and picks up mechanical noise from the engine (including valve train noise) and interprets it as knocking/pinging, thus retarding the timing.

On a nice new engine with quiet valve gear there is no problem, but when the engine gets old and worn and the hydraulic tappets get noisy possibly due to varnish build up and dirty oil the mechanical tapping can be enough to cause the cylinders to ring as if the engine was pinking.

Normally the ECU will retard the timing a small amount (like 0.5 degrees) per revolution until the knocking noise stops then hold steady there. However if the knocking is not real combustion related knocking but just mechanical noise, retarding the timing won't eliminate the noise, so it will keep retarding the timing further and further every revolution until it very quickly reaches the maximum allowed amount. (12 degrees of advance removed)

So over the engine RPM range where the engine is mechanically noisy you lose a lot of ignition timing and a lot of power. At 3500-4000 rpm and above on this engine the knock sensor sensitivity (in the ECU) is dramatically reduced, to allow for the fact that there is a lot more mechanical noise at higher RPM, so it is no longer falsely triggered.

So you end up with a situation where the timing advance is massively suppressed below 3500-4000 rpm but is normal above 4000 rpm, so as you accelerate you get sluggishness at first and then a massive power spike when you hit about 3500-4000 rpm right out to the red line.

When the timing gets retarded like this it takes quite a long time for it to be advanced again as the timing gets retarded very very quickly but advanced very very slowly, even after the source of noise has gone. (Tappets have started behaving and quietened down)

The knock retard table in the ECU is a number of cells in a grid with RPM along the X axis and engine load (from MAP / TPS signals) on the Y axis - in each cell there is a knock retard in degrees that applies when the engine is in that RPM/load combination. The value in a cell can only be changed if the engine runs at that load at that RPM for a period of time.

So if you drive the car at a higher load (throttle) through the low rpm range where its picking up noise from the tappets the cells in the table can quickly get filled with high negative values... However if you reach a higher RPM with a very light throttle and keep it there until the tappets have filled and gone quiet then these higher load cells won't be updated with bogus timing values.

Thus when you run the engine at higher throttle / low rpm later it will be fine.

Just a theory of course but that's a second possible mechanism by which noisy tappets from cold could hurt performance, but be somewhat avoided by a short period of high rpm low throttle running to get the tappets pumped up.

If this is what is happening then I really need to use some tappet additive to help flush out their small oilways then do an oil change. And I think I will use 10w-40 this time.

BTW what oil do you use in yours ?

[Stickyfinger]

Cheers for that, informative thinking

I use 10/40 Total Semi Synth.

I used Wynns 76864 Hydraulic Valve Lifter Treatment Oil after the the first oil change with a 10/40 desiel oil and kept that in for 1k before the change to Total 10/40 which I have change recently (@4k). I will put in a cheap oil (5/40 Semi) for the winter layup (weekly starts) then change to Total again come summer.

[Mandrake]

I think I will use 10w-40 next time. Not entirely sure why I chose 5W-40 previously, and maybe on an old engine with worn hydraulic tappets a thinner oil will just make noisy tappets worse.

Before you did all that, how were the tappets - were they noisy after starting ? After a minute or two ? When the engine was fully warmed up ? How are they now, cold and hot ?

On my old V6 I did try the same Wynns Hydraulic Valve lifter treatment and found that it did work for cold tappet noise - they went from very noisy indeed, cold or hot to almost silent within about 10 seconds from a cold start, however after treatment although most remained quiet when hot, about two of them (a guess based on the noise) would get noisy again - which I believe means wear in the tappet pistons causing excessive bleed down as the oil thins with heat.

I have not tried the Wynns treatment in this V6 but I am planning to put it in for about a month before the next oil change to see if it has a similar effect on cold tappet noise, and whether there are any that get noisy again when hot.

[Stickyfinger]

When I got back from France they were a little, I had noticed it when there inspecting the car. I checked the oil which was on the low side of middle in France and added some 10/40 at a garage about 20 miles out.

When I got back I changed to the diesel 10/40 oil and added the conditioner, after about a couple of days use there was no noise on cold start up other than normal.

About 20 odd miles before the change (1k ish) I added an engine cleaner then drained it hot, new filter and the 10/40 Total.
I did not notice any difference/improvement after that change.
I have not used it since

[Mandrake]

Well, it's MOT time, I've booked it in at 10:30 on Friday at a local Garage I have not tried before - so far I've been unhappy with the places I've had my MOT's over the last few years - Citroen did a good enough job but are far too expensive and a fair trek to get to, another one I went to last year was half the price and a lot closer but failed it on two bogus complaints the first time, so I'm trying yet another garage to see if I can finally find a half decent local garage.

I have four new Michelins on the car at last to replace the two second hand ones on the front that got me through the last MOT, and the two rear Klebbers which were on the car when I bought it 2 years ago, and were already about 6 years old and cracked at the time! Those Klebberes would never balance 100% because the tyres were actually slightly distorted due to age and the car having sat basically unused for a couple of years before I bought it, so it's nice to finally get some brand new tyres on it. The difference in the ride, grip, steering etc is amazing.

They are not correctly balanced yet though as thus far I have been unable to find anywhere to balance the centreless rims that can get it right, as evidenced in my frustrated rant here:

http://www.frenchcarforum.co.uk/forum/v ... =3&t=55530

A 75mph imbalance will not fail or even be detected on an MOT of course and since money is extremely tight at the moment I have no choice but to postpone further balancing attempts until at least next month. Fortunately I rarely travel at motorway speeds for any length of time.

The only thing I'm aware of that they might grumble about in the MOT is the exhaust - as luck would have it the infamous joint between the cat and the middle silencer has started blowing slightly and has a nice black sooty mark around where it is leaking for evidence. It's not a loud noise - I only noticed it when I was looking under the car while doing wheel swaps...

It should only be an advisory, and I don't want to touch it or mess around with it until after the MOT in case I run into any difficulties. They will also no doubt notice the hole in the exhaust down pipe on the front engine bank, but as it's a dual skin pipe and the inner skin is fine and not leaking at all it should only be an advisory.

The rattle/clonk near the front right suspension is still there - its unlikely to be found on the MOT due to the way the suspension keeps tension on the joints. I still have no idea what it is after multiple attempts to find it - could be the lower swivel balljoint, an inner trackrod end, the front bush on the lower arm, play in the rack and pinion mesh, or a loose bolt on the power steering ram - take your pick!!

[CitroJim]

All the best with the MOT Simon....

[RichardW]

Simon

Someone else mentioned in another thread that a mystery clonk on the front was solved by tightening up the strut top nut. Worth a check?

Good luck with the MOT.....!!!

[Mandrake]

That's an odd one Richard - not sure how that nut could be loose enough to cause a clonk without massive fluid leakage!

The top of the shaft has a taper on it that rests in a tapered seat, and the oil flow goes through a side port in the shaft, which has an o-ring on either side of the port area. I would have thought there would be no way it could seal if the shaft had dropped down in the taper far enough to clonk.

Can't try torquing it at the moment though as the nut is supposed to have its face that goes against the strut top coated with locktite and I don't think I have any on hand...

(I found out the hard way years ago that if you don't use locktite on the nut face as Citroen specifies you get a bit of weepage past the nut - its there for both locking and sealing residual leakage!)

When I get a chance to grab some locktite I'll re-torque both strut top nuts with my torque wrench - it's feeling unloved at the moment as I've only used it a couple of times in the few years I've owned it.

[Mandrake]

Well she passed, without so much as an advisory.

I took it to a small local Indy that I haven't tried before and I must say that I think I've found myself a keeper.

I originally emailed them to ask about wheel balancing, and whilst they don't have an adaptor for the centerless wheels and thus can't balance my wheels the guy seemed very helpful so I thought I'd try them for an MOT.

I arrived to find that it was indeed a small indy, complete with a dog that seemed to have permanent residence on one of the waiting room sofa's. Everyone was very friendly and I got to chat directly to the manager who was also the one who did the test, although I saw two other mechanics about too.

After the test he had an enthusiastic chat with me and made an amusing comment - "Thanks for looking after that, there's not many of them left on the road!", he told me he could see the work I'd done to keep it in shape and that it was in excellent condition. That made me feel really good and was totally unexpected. He was then telling me about his Citroen/Peugeot mad friend in Ireland...

Although he didn't put it on the advisory he did let me know about a minor click in the front right suspension that they'd noticed and we got talking about it... He said that when it was up on the lift with the hand brake on that rocking the car back and forward was clicking slightly in the front right suspension but they couldn't find exactly what it was - he said it wasn't any of the lower joints or lower suspension arm as they had no movement, and that it seemed to be the "top mount" that was allowing some lateral movement of the strut at the top end when the car was rocked.

I immediately though of Richard's suggestion of checking the nut on the top of the strut top to make sure the shaft is seated correctly in the taper and the nut is correctly torqued - I was initially sceptical that this could be loose without causing an oil leak but on reflection if the hydraulic port and o-rings are in the parallel section of shaft not the taper the shaft could potentially move up and down a millimetre or so without actually causing a leak...

Does anyone have the torque figure for the top nut on the strut top that screws onto the strut ram handy ? If so I'll get the torque wrench onto it tomorrow to see if it could be loose.

We also talked about the possibility of a worn bush on the steering rack but I'm now leaning towards the strut top - whether its a loose nut or not I'm not sure...

[RichardW]

BOL says 65 NM / 48 lbft with thread lock. There is an O-ring under the nut, no idea how it could be loose without leaking, but stranger things have happened. I can't find it now...it was in a thread of work done on a car as a bit of a throwaway, but I did think of yours right away!

[CitroJim]

Simon, excellent news on the MoT Well done, shows the hard work you do to maintain it really pays off...

[Mandrake]

Well its not a loose nut on the strut top, I think.

I checked them with the torque wrench and they were already up to the correct torque. I gave them a bit of an extra turn (about 1/8th of a turn) and it didn't feel to me like there was any thread lock as it turned smoothly without any feeling of thread lock breaking free.

Either that or the thread lock was holding the nut to the shaft solidly and I was just turning the nut and the shaft together with the shaft turning on its taper seat - without being able to see the Allen hex on the top of the shaft turning (obscured by the socket) or holding onto the shaft below the strut top to feel if it's turning there's no easy way to know.

In any case, I don't think it is that. I'm leaning strongly back towards a steering rack problem - I've recently observed multiple instances of the left front wheel hitting potholes while steering causing the same rattle noise coming from the exact same location on the right hand side of the car, roughly in line with the driver - eg where the steering rack resides...

It doesn't do it as easily as hitting a pothole on the right hand side but the rattle is the same and it is felt on the steering wheel as well as heard.

So I figure it must be one of the following:

1) Excessive play in the pinion mesh - is there even an adjustment for this, or is it pre-set with a fixed bush ?

2) Excessive play in one or both of the internal (not external) rack end bushes ?

3) Badly worn inner track rod end ? (Both outer track rod ends have been replaced with no change) Would this allow both sides to trigger the rattle on the right hand side though ?

4) Loose mounting bolts between the rack and the hydraulic ram ? (Is this possible ?)

5) Loose mounting bolts between the rack and the chassis - this can probably be ruled out as I'm pretty sure Richard checked those when I was visiting.

While I'm familiar with the generalities of the power steering design used in the Xantia I don't have any specific experience of actually working on a Xantia steering rack and haven't even looked closely at one before so I'm looking for some advice on how I can check each one of these possibilities off, preferably from easiest to hardest.

There's not a lot of room to work on the steering rack on the V6 so knowing where things are and aren't and how to get to them would certainly be beneficial...

[RichardW]

Another suspect crossed off then...

Yes, rack mount bolts were tight. Can't be the inner track rods, these would have shown up on the MOT. I couldn't detect any differential play between the shaft and the rack, and it doesn't appear to have any slack at the wheel either, does it? There did seem to be a bit of a clonk in it somewhere when the steering was waggled, but I couldn't pin it down, or even know if it was normal or not, not having another to compare it against. Chris Morewood was complaining about a knock on his on the steering which is probably the ram bushes; but his has done 4x the mileage of yours!! Stumped I'm afraid.... There is that bit of radial play in the steering column, perhaps it's just that?

[lexi]

A good pass on the Mot and result on finding a fair and decent garage.