Ben Womersley Posted August 3, 2011 Share Posted August 3, 2011 I noticed lots of smoke and a loss of power while on the motorway followed closely by high coolant temperature and low oil pressure (1.6 bar rather than its usual 3.2 bar). I limped the car home and had a play the next morning. Long story short, I cracked the injectors and found injector 3 wasnt doing anything. Swapped 2 injectors round and found cylinder 3 still wasnt doing anything. I have taken off the head expecting a head gasket failure and found the piston in cylinder 3 is bug**red . Would this explain all of these symptoms? The other pistons look fine, the head looks fine (slightly more carbon build up around valves on cylinder 3) The liner in this cylinder has slight damage so this would also need replacing. Would I be advised to replace all of the pistons or would i get away with this one? Also I have no idea what causes piston damage like this... If anybody could shed any light for me that would be great! The engine has about 100k miles on it and has always been well serviced and totally reliable up to now so im reluctant to fit a different 300Tdi. Thanks, Ben Quote Link to comment Share on other sites More sharing options...
disco_al Posted August 3, 2011 Share Posted August 3, 2011 looking at it, i would say you could get away with just replacing that one piston assy, just give the bore a slight hone to get rid of the glaze Quote Link to comment Share on other sites More sharing options...
Les Henson Posted August 3, 2011 Share Posted August 3, 2011 Is there a step at the top of the bore (disregarding the carbon deposit)? Looks to me like the piston edge is breaking up in small bits, so perhaps the top ring groove badly worn/ ring broken. Wipe the bore and see if it's scored - if it is, then rebore time probably. If you have a large step at the top of the bore, then perhaps piston slap has caused it as well. I would take the piston out and have a look before deciding on what to do. At least you can do this with the engine still in the vehicle. Les. Quote Link to comment Share on other sites More sharing options...
CwazyWabbit Posted August 3, 2011 Share Posted August 3, 2011 Erm, is the marking to the head just where the bits of piston have hit it or is it what caused the piston to break... is there a chance that one of the bearings is buggered and allowing the piston to slap the head? Just a thought and probably wildly off the mark..... Quote Link to comment Share on other sites More sharing options...
Disco-Ron Posted August 3, 2011 Share Posted August 3, 2011 Looks to me like either the big end or little end, or both on number three have gone, hence low oil pressure.... that then lead to the piston boucing off the head... causing the damage to the piston..... which may have then pushed the head slightly off the gasket which caused coolant loss and high engione temps........... but, as above, i could be totally wrong! Quote Link to comment Share on other sites More sharing options...
Ben Womersley Posted August 3, 2011 Author Share Posted August 3, 2011 looking at it, i would say you could get away with just replacing that one piston assy, just give the bore a slight hone to get rid of the glaze Thats what I was hoping... I was thinking it could be something to do with the timing on the fuel pump providing fuel at the wrong point causing the damage to the piston, but again could be totally wrong. Il take the pistons out in the morning and see if there is any damage to the rings on the others, if not then it looks likely that the bearings on 3 are buggered. Thats the only thing I can think of which could cause the oil pressure drop (assuming pump and reg valve are working correctly!). Just taken a better look at the pictures, the silver inprint on the piston looks very much like a reverse image of the inprint on the head so yes the piston has hit the head. What is involved in changing the big / little end bearings / bushes? Can it be done with the engine in? I will check the oil jets while I am in there, something has to have caused the damage... This is really not my area of expertise! Thanks guys, Ben Quote Link to comment Share on other sites More sharing options...
Ben Womersley Posted August 3, 2011 Author Share Posted August 3, 2011 Is there a step at the top of the bore (disregarding the carbon deposit)? Looks to me like the piston edge is breaking up in small bits, so perhaps the top ring groove badly worn/ ring broken. Wipe the bore and see if it's scored - if it is, then rebore time probably. If you have a large step at the top of the bore, then perhaps piston slap has caused it as well. I would take the piston out and have a look before deciding on what to do. At least you can do this with the engine still in the vehicle. Les. I will have a look for a 'step' in the morning Quote Link to comment Share on other sites More sharing options...
Somethingwitty Posted August 3, 2011 Share Posted August 3, 2011 Concur with Disco Ron - big or little end on #3 has failed and allowed the piston to contact the head - the proof from the phot is the silver 'wiggley worm' mark on the piston crown opposite the camshaft is nigh on identical to that on the head in the same location. There is no way the piston could hit the head without either of those bearings failing (or crankshaft failure... I know of one two cylinder 2.5D - the other 2 were driving the water pump!). I would guess the head is also scrap or at least needs some careful blending of the damage? I'd be surprised if a re-bore was not required given the damage as shown. Engine mechanics aren't my forte but the above seems logical... Good luck Jim Quote Link to comment Share on other sites More sharing options...
Les Henson Posted August 4, 2011 Share Posted August 4, 2011 If the big or small end had gone, then I would have expected you to hear it. Low oil pressure indicates the big end (small end is splash lubed by the oil jet). To remove the piston/conrod assembly - head off, sump off, undo big end cap, and then push the assembly up through the bore. If the big end is badly worn, then crank regrind/ rebuild/ replace. Small end would be better as then it's just conrod and piston. If the bore is badly scored as well, then it's possibly going to get expensive to repair. Les. Quote Link to comment Share on other sites More sharing options...
Ben Womersley Posted August 4, 2011 Author Share Posted August 4, 2011 If the big or small end had gone, then I would have expected you to hear it.... It was making a lot more noise than usual but Im fairly sure it was top end, it sounded like like it was 'chuffing' (probably as it fired on the buggered cylinder) I will drop the sump (again... last time I changed the oil a few thou ago the drain plug sheared!) pull out the pistons and crank. If it needs a rebore I might be looking at a new engine, anybody have one for sale?!. Dont think the head is damaged somehow, I will put it on a steel table and make sure there is no distortion. Ben Quote Link to comment Share on other sites More sharing options...
CwazyWabbit Posted August 4, 2011 Share Posted August 4, 2011 It was making a lot more noise than usual but Im fairly sure it was top end, it sounded like like it was 'chuffing' (probably as it fired on the buggered cylinder) I will drop the sump (again... last time I changed the oil a few thou ago the drain plug sheared!) pull out the pistons and crank. If it needs a rebore I might be looking at a new engine, anybody have one for sale?!. Dont think the head is damaged somehow, I will put it on a steel table and make sure there is no distortion. Ben You won't get the crank out without removing the engine, but you should be able to check it in situ and the piston can obviously be pushed out the top of the block. Quote Link to comment Share on other sites More sharing options...
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