Re-torquing 1.6 Hdi injector bolts

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Bob L'eponge
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Re-torquing 1.6 Hdi injector bolts

Post by Bob L'eponge »

Hi all,

First post from a long-time reader of this forum!

As you are aware, a pretty common problem on many diesel engines is the bolts that hold the injectors in place losing their torque values, perhaps due to heat cycling, vibration and so forth. This can then lead to the seals leaking and the dreaded 'coal' building up around the injector, perhaps causing it to seize solid.

In this thread below it was suggested that the tightness of the bolts holding the injectors in place on the 1.6 Hdi unit be checked at each service, as they will almost certainly be found to be loose. This certainly accords with my experience.

http://www.frenchcarforum.co.uk/forum/v ... =3&t=42948" onclick="window.open(this.href);return false;

Anyhow, for what it is worth, here are some of my thoughts on this problem.

The bolts (well, studs and nuts) that hold the injectors in place on this unit are tightened by the angular torque method, being pre-tightened to 4 Nm, and then finally tightened by 65 degrees. This suggests that they are 'torque to yield' bolts, something that would make good engineering sense as this means they should hold their torque more reliably. I would also suspect that this is pretty standard practice for such bolts on many engines. As such, re-tightening them to the specified value each time they are found to be loose is, strictly speaking, not good practice as with repeated re-torquing it is likely that they will stretch excessively and / or eventually fail. The official Citroen service documentation does have a 'Caution' on this point and states that these studs, and the associated nuts, must always be changed each time the injector is refitted.

The first time I checked the studs on my car, a number were loose, although not yet leaking. Because they seem to be torque to yield bolts I was loath to slacken them all off and re-torque them from scratch, so I tried to work out what sort of torque reading would indicate they were still 'tight'. By comparing the readings across a couple of the loose studs when retightening, it seemed that the final angular tightening takes them up to somewhere close to 15 N/m, or about 11 ft/lb. Of course, if this is anywhere near accurate, if they were slack even just 'tweaking' a loose nut with a torque wrench up to 15 N/m would still be re-tightening them past their yield point. On the other hand, if they were 'tweaked' to say 10 N/m or 7 ft/lb so as to not stretch them excessively, they would not be as tight as the specifications demand and so might start leaking.

Unfortunately, the studs are fitted with a shoulder that tightens against the cylinder head, so it is not possible to replace them whilst leaving the injector in place. This means that replacing the studs means removing the injector, replacing the seals and all that entails!

Bottom line is that there seems to be no 'ideal solution' here. Options seem to be

1) Re-torque the studs to the specified value, until they finally fail that is…

2) Just 'tweak' the studs to a lower value and hope they don't leak, which has to be better than simply doing nothing.

3) Do the job 'properly' by removing the injectors and replacing all the studs and seals whenever they are found to be loose.

Does anyone else have any thoughts on this issue or has experienced this problem? Are my assumptions sound? What option would you follow? If 2), what sort of torque value would you use in the hope that they probably won't leak, whilst at the same time are not being re-tightened so much that they are being repeatedly stretched past their yield point and so will eventually fail?

Cheers!
Last edited by Bob L'eponge on 19 Dec 2013, 18:22, edited 1 time in total.

Bob L'eponge
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Re: Re-torquing 1.6 Hdi injector bolts

Post by Bob L'eponge »

Just a quick follow up to the above. Take a look at this picture of one of the studs that hold the injector in place:

Image


As you can see, the longer part which screws into the head uses an M6 thread. However, the bit that takes the nut which secures the injector has an M7 thread. It may well be that the lower part has to be M6 due to the thickness of the castings and space available, but if this is a torque to yield bolt, as the tightening procedure suggests, then it seems that the two half of the bolts must be differentially heat treated or some other trickery used, otherwise the bolt would probably fail just below the shoulder under the load needed to stretch the larger diameter upper section by the required amount. In fact on some forums such failures have been reported by those who think that the best thing to do is to keep on tightening these bolts up to 4 Nm, plus another 65 degree turn, every time they are found to be loose.

I don't think that the design can intend the injector securing plate to be simply tightened up against the shoulder as tightening the nut can only exert pressure on the sealing washer if this load is countered by that holding the stud into the head.

Personally, I would much prefer to see the larger diameter thread mounted into the head, and the small diameter thread used might go some way to explaining why these bolts seem prone to slackening / stretching. It certainly explains why they are prone to sheering off flush with the head if they are over tightened!

Bob L'eponge
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Re: Re-torquing 1.6 Hdi injector bolts

Post by Bob L'eponge »

P.s. I reply to the question I asked in my first post:
what sort of torque value would you use in the hope that they probably won't leak, whilst at the same time are not being re-tightened so much that they are being repeatedly stretched past their yield point and so will eventually fail?
10 N/m seems to be about the maximum amount of torque that can be repeatedly used to 'tweak' these bolts without this leading them to fail. In fact 9 N/m will usually cause the wrench to 'click' before the nut turns at all, whilst using 10 N/m can result in the nut turning a rather worrying amount!

citroenxm
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Re: Re-torquing 1.6 Hdi injector bolts

Post by citroenxm »

Hmmm i was not useing a torque wrench but just my experiance when i did my sisters injectors.. and tightening down no.4 i snapped that bolt above.. and it bloody broke at the bottom end inside the bolt hole casting...

Snookered... so in the end i got some quick steel and tried to quick steal the stud into the head and then bolt the injector down after.

Not sure how sucessfull it was. I saw my sisters car today.. there was more of an oil weep and leak then coal but i think i could also hear ever so slight compression leak. So there may be trouble ahead.

Incidentally.. the 2.0 8v hdi first gen engines dont seem to suffer loosening. They use a single 13mm nut and clamp to hold the injectors. Ive never had an issue with that design..

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Lighty
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Re: Re-torquing 1.6 Hdi injector bolts

Post by Lighty »

Interesting thread, pardon the pun. I feel that by advising people to tighten these bolts, you may cause a lot of issues, as they do break VERY easily. I managed to snap at least 2 new ones when rebuilding the head on an 807 recently. They are a total pig to get out once snapped, I used a scroll tool on the half way "boss" but this meant cutting off the excess stud first in order for the shallow scroll tool to get onto said boss.
Quite a relief to get them out,and a bit beyond your average Sunday afternoon mechanic.

Bob L'eponge
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Re: Re-torquing 1.6 Hdi injector bolts

Post by Bob L'eponge »

Lighty wrote:Interesting thread, pardon the pun. I feel that by advising people to tighten these bolts, you may cause a lot of issues, as they do break VERY easily.
Thing is, if they have loosened the injector seal will probably end up leaking, with all that entails. Also, if they are loose due to heat cycling or whatever, the stud won't be holding much torque so it should be possible to re-tighten it without it failing. The big question is by how much! I feel it is certainly a big mistake to torque these up to the original specified load of 4 N/m plus 65 degrees. This suggests that they are torque to yield bolts and so should really be replaced each time that are tightened. Obviously this is a big pain as it involves removing the injector and the things will probably be loose again after a while.

I think that the best thing to do is to consider these to be effectively M6 bolts and treat them with care, making a compromise between sealing the injector to the head and avoiding over-loading the studs. We don't know what the toughness of these studs is, but looking at a table of standard torque values 9 - 10 N/m should be safe for even an 8.8 class M6 bolt.

I did say that, if we follow best practice, (i.e. 'do the job properly') these bolts should really be replaced if they are found to be loose as they were initially tightened to their yield point on fitting!

Bob L'eponge
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Re: Re-torquing 1.6 Hdi injector bolts

Post by Bob L'eponge »

Lighty wrote:I managed to snap at least 2 new ones when rebuilding the head on an 807 recently. They are a total pig to get out once snapped, I used a scroll tool on the half way "boss" but this meant cutting off the excess stud first in order for the shallow scroll tool to get onto said boss.
I am surprised that new bolts failed. Did you follow the specified tightening sequence and were the bolts and threads clean? (As I am sure you know excess oil or any grease on threads can make it impossible to tighten a fastening to a specified load.)

From what you say it sounds as though yours failed across the fatter M7 section, which from what I have read is also quite unusual!

Bob L'eponge
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Re: Re-torquing 1.6 Hdi injector bolts

Post by Bob L'eponge »

citroenxm wrote:Hmmm i was not useing a torque wrench but just my experiance when i did my sisters injectors.. and tightening down no.4 i snapped that bolt above.. and it bloody broke at the bottom end inside the bolt hole casting...
To clarify, are you saying that yours failed some way along the long M6 section, with the top section presumably stripping the threads in the head as it pulled out? Did you also have to drill out the remaining part of the stud from the bottom of its mounting hole? If so that really is the worst possible scenario! They usually seem to go just below the shoulder leaving the M6 section more or less flush with the head where, with care, it can be removed without damaging the thread.

Out of interest, if the thread in the head was damaged, was there insufficient room to re-thread the hole to M7, or even a 'slightly bigger than M6' Imperial size, replacing the stud with a high-tensile bolt? (Unfortunately, a Time-Sert repair probably wouldn't work as the inserts are quite short and that long M6 shank is probably necessary, especially given that it screws directly into the soft aluminium alloy head.)
Last edited by Bob L'eponge on 20 Dec 2013, 09:44, edited 1 time in total.

Xantidote
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Re: Re-torquing 1.6 Hdi injector bolts

Post by Xantidote »

Well, with the problems with the 1.6 HDI injector bolts, and the turbo/oil issues as discussed in another thread, which are both issues I don't expect of a "properly" designed engine, I shall simply avoid any vehicle with the PSA/Ford engine

Bob L'eponge
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Re: Re-torquing 1.6 Hdi injector bolts

Post by Bob L'eponge »

Xantidote wrote:Well, with the problems with the 1.6 HDI injector bolts, and the turbo/oil issues as discussed in another thread, which are both issues I don't expect of a "properly" designed engine, I shall simply avoid any vehicle with the PSA/Ford engine
On the other hand, the application of a little knowledge seems to be enough to vastly reduce the possibility of these issues arising.

To avoid the 'turbo' issue just use the correct fully synthetic oil, changing it more frequently than specified. (This is probably 90% of the solution in itself). Also, keep the oil topped up the the maximum mark and drain it properly when doing a change, following the PSA guidance note, also ensuring that the small drain hole drilled though the threads in the drain plug mounting boss are not blocked. If you are keen, remove or replace the mesh in the banjo bolt that feeds oil to the turbo as well, as PSA recommend.

For the 'injector leak' issue, just periodically check the tightness of the securing bolts, ensuring they are holding 9 - 10 N/m with an accurate torque wrench. This is literally a five minute job!

Xantidote
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Re: Re-torquing 1.6 Hdi injector bolts

Post by Xantidote »

Bob,

I accept all you suggest as regards the PSA 1.6 engine, and I would follow everything as you outline, and there are probably issues with other manufacturers' engines/cars, but I what I'm really saying is that as the customer, we should not have to put up with what I consider to be rather basic issues. They are of the manufacturers' own making, yet we have to pick up the pieces.

addo
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Post by addo »

Agree wholeheartedly. Very poor corporate attitude.

Bob L'eponge
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Re: Re-torquing 1.6 Hdi injector bolts

Post by Bob L'eponge »

Xantidote wrote: what I'm really saying is that as the customer, we should not have to put up with what I consider to be rather basic issues. They are of the manufacturers' own making, yet we have to pick up the pieces.
I agree! It is also the case that few owners will do the sort of research that people who frequent this forum might do, so are likely to fall foul of issues that have serious and expensive consequences, even if the solutions are very simple.

Whilst errors in design often don't come to light until products are used by the consumer, manufacturers really should offer better technical support to address any issues, which is available to everyone and not just their main dealers. Also, in my view, cars really should be provided with full technical documentation, from wiring diagrams to service and repair information. Similarly, why not allow the on-board computers to reports directly to the dash display?

Amazingly, even products like Service Box provide incomplete technical information, as I found when looking to top up the additive on my 2009 'X7' C5 Tourer. I would guess the the real aim is to keep their dealers happy and supplied with punters looking for solutions to problems that not even professional but independent garages can sort out! At least, unlike some Audi's and so forth, Citroen still allow the user to open the bonnet without having to go to a main dealer!
Last edited by Bob L'eponge on 20 Dec 2013, 11:03, edited 1 time in total.

Bob L'eponge
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Re:

Post by Bob L'eponge »

addo wrote:Agree wholeheartedly. Very poor corporate attitude.
True, and yet PSA are far from the worst!

addo
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Post by addo »

The reason I feel so narked is other aspects of the PSA product have generally - since the early nineties - been among the world's best for production cars, mainly things like the quality of shells and fastener finishes. I see newer Japanese cars with more rust, things like Benzes with inferior fastener coatings, also for many years the French excelled at some of the widest opening rear doors on sedans. Then they wet their metaphorical nest with a silly design flaw and pretend it will go away if they ignore it.