Hmm - I wonder if Dave Burns has returned to the fold - he could probably solve this one for me directly.
After discovering that the timing belt on my XM hadn't been replaced for 140 000 km (I havn't driven it that often for the past three years, since getting an A4 TDI as company car - but the wife has!), I decided to change the cam drive belt myself, something I accomplished with great satisfaction (smug type!).
HOWEVER after starting the car, it was very apparant that something wasn't as it was before the change. The combustion noise at tick over was very much louder and even att higher revs. Strangely, the performance also seems to have improved somewhat.
I was VERY particular to check the timing before starting and used the correct tools to lock the cam, crank, injection pump before removing the old belt (which has intact, but considerably thinner than the new one!). If this is what i imagine - too far advanced timing - then I can only guess that the pump timing was adjusted at some previous service when the old belt, which must have been rather slack -had retarded the injection timing - when I fitted the new belt, the timing got advanced since it wasn't slack at all.
Does this figure?
In which case, is there an easy way to retard the pump without going through all the bother of ripping the end off the engine AGAIN?
I don't dare to unclamp and rotate the pump without knowing in which direction - I don't want to knacker it for good!
//NiSk
XM diesel timing?
Moderator: RichardW
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Dave Burns
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I would discount the stretched belt theory Nigel, for starters if the belt had stretched to that degree it would no longer mesh with the teeth on the pulleys, secondly all though there will doubtless have been some relatively small elongation of the belt taken as a whole, the only bit of the belt that matters as far as advancing/retarding injection timing with regard to this particular scenario, is that between the crankshaft and fuel pump pulleys.
This section of the belt probably accounts for between 1/4 and 1/3 of its length, so you can see why a discrepancy large enough to cause a change in the timing and hence the diesel knock could not come from belt elongation, in my view at any rate.
If the pulleys are the same size (42 teeth) as the 1.9 diesel engines, then if you were to get the belt back on the pump sprocket one tooth out, this would cause a timing error of some 8.5 degrees "camshaft" and some 17 degrees "crankshaft", not small errors by any standard but ones likely to cause the symptoms you are experiencing.
I'm not farmiliar with the 2.1 but if the pulleys and crank are timed using the standard method for the XUD then a pulley one tooth out would prevent insertion of the timing peg, be it a dowel or a screw, unless of course any of the timing pegs were grossly undersized.
A 93 model is unlikely to have any ECU to interfere with the pump but there again I'm not farmiliar with it so have a look to see if there is any disturbed wiring going to it, on my 1.9 td Xantia (Bosch) there is a device to allow timing adjustment by the ECU, if I disconect it the diesel knock gets very pronounced indeed, to the extent that it sounds very sharp and metalic like.
The only other thing I can think of, but its a long shot and then only if a Bosch pump is fitted, is a trapped fuel return pipe.
I say this because this pump relies on increasing internal pressure due to engine speed to advance the injection timing, a restricted return would cause an increase in internal pressure and artificialy advance the timing, but as I say its a long shot since I would also expect any such restriction to cause a pipe to blow off as they are only pushed on normaly.
To retard the timing, turn the pump in the direction the pulley normaly runs (clockwise when viewed from the right wing) and against it to advance timing, I would make very sure that the timing of the shafts is true before altering the actual injection point.
Do not loosen the pump with the engine running.
Dave
This section of the belt probably accounts for between 1/4 and 1/3 of its length, so you can see why a discrepancy large enough to cause a change in the timing and hence the diesel knock could not come from belt elongation, in my view at any rate.
If the pulleys are the same size (42 teeth) as the 1.9 diesel engines, then if you were to get the belt back on the pump sprocket one tooth out, this would cause a timing error of some 8.5 degrees "camshaft" and some 17 degrees "crankshaft", not small errors by any standard but ones likely to cause the symptoms you are experiencing.
I'm not farmiliar with the 2.1 but if the pulleys and crank are timed using the standard method for the XUD then a pulley one tooth out would prevent insertion of the timing peg, be it a dowel or a screw, unless of course any of the timing pegs were grossly undersized.
A 93 model is unlikely to have any ECU to interfere with the pump but there again I'm not farmiliar with it so have a look to see if there is any disturbed wiring going to it, on my 1.9 td Xantia (Bosch) there is a device to allow timing adjustment by the ECU, if I disconect it the diesel knock gets very pronounced indeed, to the extent that it sounds very sharp and metalic like.
The only other thing I can think of, but its a long shot and then only if a Bosch pump is fitted, is a trapped fuel return pipe.
I say this because this pump relies on increasing internal pressure due to engine speed to advance the injection timing, a restricted return would cause an increase in internal pressure and artificialy advance the timing, but as I say its a long shot since I would also expect any such restriction to cause a pipe to blow off as they are only pushed on normaly.
To retard the timing, turn the pump in the direction the pulley normaly runs (clockwise when viewed from the right wing) and against it to advance timing, I would make very sure that the timing of the shafts is true before altering the actual injection point.
Do not loosen the pump with the engine running.
Dave
The engine is the XUD11 PA8 i.e. mechanical injection with Bosch VE 532 pump. Their are 42 teeth on the cam drive (I'm reluctant to tear down the entire side of the engine just to count the teeth on the injection pump drive).
Roughly how much retardation do you think rotating the pump would give? Not a whole tooth I guess? The fuel lines havn't been moved at all. Looks like i cocked it up in any case! //NiSk
Roughly how much retardation do you think rotating the pump would give? Not a whole tooth I guess? The fuel lines havn't been moved at all. Looks like i cocked it up in any case! //NiSk
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Dave Burns
- Posts: 1915
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- x 2
You are probably right in thinking that there wont be enough range on the mounting slots to go one full tooth, but then it may not need to.
You have gained a performance increase by advancing the timing this way (if thats whats happened) and I would be inclined to retain some of that increase, so retard the timing to where the knock is acceptable if thats possible on the slots and leave it at that, so long as its not very much louder than before.
The position it was in prior to this work would have been slightly retarded as a result of normal internal wear of the pump at this mileage anyway.
Both the camshaft and the injection pump rotate at half engine speed so their pulleys both have the same number of teeth at 42, the crankshaft as stated travels at twice camshaft speed so it has a pulley with 21 teeth.
Dave
You have gained a performance increase by advancing the timing this way (if thats whats happened) and I would be inclined to retain some of that increase, so retard the timing to where the knock is acceptable if thats possible on the slots and leave it at that, so long as its not very much louder than before.
The position it was in prior to this work would have been slightly retarded as a result of normal internal wear of the pump at this mileage anyway.
Both the camshaft and the injection pump rotate at half engine speed so their pulleys both have the same number of teeth at 42, the crankshaft as stated travels at twice camshaft speed so it has a pulley with 21 teeth.
Dave
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Pardon me for butting in - I had this very same result when I did my BX TD the first time. A much more clattery tickover. Having stripped the end down once again to re-check the timing holes, I found some of the positions to be one tooth out. Don't know about the 2.1 in the XM, but on mine in the Xantia, it's impossible to reach the flywheel hole with the starter in place.
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Dave Burns
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Not sure, maybe overheating and damage to the glow plugs and injectors, then again maybe none especialy in the short term.
The increased noise comes about as more of the fuel detonates at the same time since injection will be finished well before TDC, so you are getting a more agressive explosion of the fuel and probably sustained higher pressure.
Have you run it up to operating temperature and if so was that temperature reached noticably sooner than before.
Does the pump have a solenoid on the side with a small metal pipe going up to the front of the pump, if so this device retards injection timing under certain conditions by releasing some of the internal pressure on the timing advance piston, you could try disconecting it from its wiring and permenantly energise it from the fuel cut of solenoids wiring, it may aleviate the problem by a small degree.
Dave
The increased noise comes about as more of the fuel detonates at the same time since injection will be finished well before TDC, so you are getting a more agressive explosion of the fuel and probably sustained higher pressure.
Have you run it up to operating temperature and if so was that temperature reached noticably sooner than before.
Does the pump have a solenoid on the side with a small metal pipe going up to the front of the pump, if so this device retards injection timing under certain conditions by releasing some of the internal pressure on the timing advance piston, you could try disconecting it from its wiring and permenantly energise it from the fuel cut of solenoids wiring, it may aleviate the problem by a small degree.
Dave
Right,
Been adjusting the timing! The pump is held in place by three nuts at the front - two relativly easy to undo (well, you can see them in any case) and one invisible ba*s*d under the pump - which requires that you have an obstruction spanner and disconnect the main LHM feed pipe, the fuel feed pipe, the HP line from the LHM pump, etc. etc. There is also another invisible (almost) nut on the rear of the pump, clamping against the timing housing plate. This last nut can be turned 1/3 of a turn with a long open-ended spanner through the connectors to the injectors (just).
Well, having loosen the pump, I retarded it as far as it would go (the attachment studs where quite close to the most advanced end of the adjustment slot). All the bits I had removed then had to be replaced before I could tell if the adjustment had had any effect.
The result was that the engine was now far too retaded - It would hardly start, hunted like crazy and gave out lots of blue smoke.
Same procedure again, unscrew all those bl***y screws and remove all the junk in the way of the spanner. This time I moved the pump to exactly midway in the adjustment slot. This resulted in a far more harmonious tick over, still somewhat louder that before the belt replacement, but not at all as frightning as directly after.
Since its a real knuckle busting job, I think I will try running it at this setting a few days and see what happens (and let my knuckles heal). By the way - anyone who says silly dope should wear gloves, is welcome to try! I assure you it ain't possible!
Apart from the bloodied knuckles, my back is now killing me!
By the way if any other XM 2,1 Bosch-injected enthusiasts are thinking of playing with their injection pump, you will need:
1 x 13mm (or 1/2") swivel-socket headed spanner (upper attachment nuts)
1 x 13mm " looong open ended spanner (rear clampp nut)
1 x 13mm " curved obstruction spanner with ring end at 90 degrees to shaft (bottom attachment nut)
And as meantioned above, you need to remove quite a lot of stuff to get at the attachment nuts and bend some water pipes to get a purchase on the rear nut.
AH! coffee is served! (good old wifey!)
//NiSk
Been adjusting the timing! The pump is held in place by three nuts at the front - two relativly easy to undo (well, you can see them in any case) and one invisible ba*s*d under the pump - which requires that you have an obstruction spanner and disconnect the main LHM feed pipe, the fuel feed pipe, the HP line from the LHM pump, etc. etc. There is also another invisible (almost) nut on the rear of the pump, clamping against the timing housing plate. This last nut can be turned 1/3 of a turn with a long open-ended spanner through the connectors to the injectors (just).
Well, having loosen the pump, I retarded it as far as it would go (the attachment studs where quite close to the most advanced end of the adjustment slot). All the bits I had removed then had to be replaced before I could tell if the adjustment had had any effect.
The result was that the engine was now far too retaded - It would hardly start, hunted like crazy and gave out lots of blue smoke.
Same procedure again, unscrew all those bl***y screws and remove all the junk in the way of the spanner. This time I moved the pump to exactly midway in the adjustment slot. This resulted in a far more harmonious tick over, still somewhat louder that before the belt replacement, but not at all as frightning as directly after.
Since its a real knuckle busting job, I think I will try running it at this setting a few days and see what happens (and let my knuckles heal). By the way - anyone who says silly dope should wear gloves, is welcome to try! I assure you it ain't possible!
Apart from the bloodied knuckles, my back is now killing me!
By the way if any other XM 2,1 Bosch-injected enthusiasts are thinking of playing with their injection pump, you will need:
1 x 13mm (or 1/2") swivel-socket headed spanner (upper attachment nuts)
1 x 13mm " looong open ended spanner (rear clampp nut)
1 x 13mm " curved obstruction spanner with ring end at 90 degrees to shaft (bottom attachment nut)
And as meantioned above, you need to remove quite a lot of stuff to get at the attachment nuts and bend some water pipes to get a purchase on the rear nut.
AH! coffee is served! (good old wifey!)
//NiSk
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Dave Burns
- Posts: 1915
- Joined: 14 May 2001, 05:30
- Location: United Kingdom
- My Cars:
- x 2
Well done, you will of course be much more carefull about changeing belts in the future from this experience.
I'm just in the process of tweaking a ZX td, intercooler off to get the oil filler tube out, so I can get the dial indicator in, what a ball ache.
I went and set it a the Haynes figure of 0.66mm when I had the lump out a bit back and could get to all bits and pieces easily, but the car dont want to know at that setting so going up 0.2mm to 0.86 that should perk it up a bit.
Dave
I'm just in the process of tweaking a ZX td, intercooler off to get the oil filler tube out, so I can get the dial indicator in, what a ball ache.
I went and set it a the Haynes figure of 0.66mm when I had the lump out a bit back and could get to all bits and pieces easily, but the car dont want to know at that setting so going up 0.2mm to 0.86 that should perk it up a bit.
Dave