Catastrophic engine failure... MG ZT (BMW 2.0 diesel)
Discussion
My MG ZT CDTi broke down on the motorway the other day... the engine just died. No warning lights came on, just suddenly a lack of power. Managed to cruise onto the hard shoulder. AA turned up and immediately diagnosed a major engine problem of some sort. Was towed to Apple MG in Kent (nearest MG specialist).
The engine is the M47R, a 1951cc BMW diesel as used in the 3 and 5 series BMW around 2000-2003 or so (I think), although it has a different injection system and ECU, and of course it's rotated in the engine bay to run FWD. It has a timing chain, so no cambelt.
Initial tests showed no compression on 3 out of 4 cylinders. With the head off, there's no apparent damage to the head/valves etc, no apparent piston damage, but fluid poured into the cylinders disappears in about a minute. From this, I guess the suspected cause would be bore wash from overfuelling? The timing also seems to be slightly out, which shouldn't happen with a chain. They set the engine to TDC before they took the head off, but the pistons were slightly off the TDC position - almost like when a cambelt has jumped a tooth or two. So it's all still a bit of a mystery.
Any ideas?
I've sourced a replacement engine, and it's going to be fitted this week. Seems to be pretty rare for these engines to fail by themselves... the only real problem I've read about is on those in BMWs where the inlet swirl flaps detach themselves and go into the cylinders... but the Rover 75/MG ZTs don't have those.
The engine is the M47R, a 1951cc BMW diesel as used in the 3 and 5 series BMW around 2000-2003 or so (I think), although it has a different injection system and ECU, and of course it's rotated in the engine bay to run FWD. It has a timing chain, so no cambelt.
Initial tests showed no compression on 3 out of 4 cylinders. With the head off, there's no apparent damage to the head/valves etc, no apparent piston damage, but fluid poured into the cylinders disappears in about a minute. From this, I guess the suspected cause would be bore wash from overfuelling? The timing also seems to be slightly out, which shouldn't happen with a chain. They set the engine to TDC before they took the head off, but the pistons were slightly off the TDC position - almost like when a cambelt has jumped a tooth or two. So it's all still a bit of a mystery.
Any ideas?
I've sourced a replacement engine, and it's going to be fitted this week. Seems to be pretty rare for these engines to fail by themselves... the only real problem I've read about is on those in BMWs where the inlet swirl flaps detach themselves and go into the cylinders... but the Rover 75/MG ZTs don't have those.
You can't bore wash a diesel as it is basically running on oil. Fluild in the bores will run out as there are gaps in all the rings, so it will go through the gap in the first ring, fill the gap inbetween the two rings, down through the gap, etc.
You say intital test showed no compression? I'm guessing this was a proper compression test with a warm engine and wide open throttle?
The chances of the piston rings failing at the same time on three cylinders is so remote it can be discounted. The cam timing is very interesting, cam timing out, I'm going to guess it has very slightly bent valves on three cylinders, probably not enough to notice without looking *very* carefully.
I'd suggest if the head is off, then the head needs to be stripped and the valves checked. The good news is, if the valves have only slightly bent such that you can't really tell, then some news valves, cam chain and tensionsers should see it right
You say intital test showed no compression? I'm guessing this was a proper compression test with a warm engine and wide open throttle?
The chances of the piston rings failing at the same time on three cylinders is so remote it can be discounted. The cam timing is very interesting, cam timing out, I'm going to guess it has very slightly bent valves on three cylinders, probably not enough to notice without looking *very* carefully.
I'd suggest if the head is off, then the head needs to be stripped and the valves checked. The good news is, if the valves have only slightly bent such that you can't really tell, then some news valves, cam chain and tensionsers should see it right
calibrax said:
My MG ZT CDTi broke down on the motorway the other day... the engine just died. No warning lights came on, just suddenly a lack of power. Managed to cruise onto the hard shoulder. AA turned up and immediately diagnosed a major engine problem of some sort. Was towed to Apple MG in Kent (nearest MG specialist).
The engine is the M47R, a 1951cc BMW diesel as used in the 3 and 5 series BMW around 2000-2003 or so (I think), although it has a different injection system and ECU, and of course it's rotated in the engine bay to run FWD. It has a timing chain, so no cambelt.
Initial tests showed no compression on 3 out of 4 cylinders. With the head off, there's no apparent damage to the head/valves etc,
Hmmmmmmm. Maybe if someone who knew what they were doing had actually looked properly?The engine is the M47R, a 1951cc BMW diesel as used in the 3 and 5 series BMW around 2000-2003 or so (I think), although it has a different injection system and ECU, and of course it's rotated in the engine bay to run FWD. It has a timing chain, so no cambelt.
Initial tests showed no compression on 3 out of 4 cylinders. With the head off, there's no apparent damage to the head/valves etc,
calibrax said:
no apparent piston damage, but fluid poured into the cylinders disappears in about a minute.
So?calibrax said:
From this, I guess the suspected cause would be bore wash from overfuelling?
Don't be daft. It's a diesel not a petrol. Anyway do you seriously think bore wash manifests instantaneously as a catastrophic failure with no prior warning?calibrax said:
The timing also seems to be slightly out, which shouldn't happen with a chain. They set the engine to TDC before they took the head off, but the pistons were slightly off the TDC position - almost like when a cambelt has jumped a tooth or two. So it's all still a bit of a mystery.
What has the piston position as determined only by a MkI eyeball got to do with cam timing? If the pistons were at TDC then they really were at TDC - end of. Doesn't mean they had to be exactly flush with the top of the block and in fact rarely would be. Where the cam was is a whole nuther story though!calibrax said:
Any ideas?
Yes lots. You've just been stitched up by a completely incompetent garage which is par for the course as the average garage mechanic knows three fifths of sod all about how engines actually work.Either the head gasket failed or the valves did kiss the pistons for some reason. Or they screwed up the compression test which was a red herring and it was a fuel pump failure or indeed something else altogether. Clearly any mechanic who pours fluid down bores and then thinks it ought to stay there forever when piston rings have gaps can't be trusted to do a compression test. Nothing whatsoever to do with the bottom end anyway.
Reminds me of my favourite anecdote about just how much garage mechanics actually know about engines. So many many years ago, probably nigh on 20, a guy I knew somewhat from work I'd done on the Crossflow cylinder head in his kit car also apparently had a Renault 25 with a 2.8 V6 engine. This started losing water and he had the engine removed and stripped as a homer job by a mechanic at his local garage. Turned out the seals under the cylinder liners were leaking and water was getting into the sump.
Anyway he got cold feet about the guy putting it back together again and asked if I'd do it. Now I hate working on engines someone else has stripped down and especially if it's a type of engine I haven't worked on before but he said he had a Haynes manual and anyway an engine's just a bloody engine to me so foolishly I said yes.
What I didn't know, having never seen the car, was the bloody Haynes manual he had was the wrong one! It was a later model year car than the manual and the 2.9 engine or summat like that. No great differences other than the bore and some detail stuff but ain't the devil always in the details?
So he turns up with this huge collection of random bits, I measure up and order the right thickness liner seals and other bits and eventually start to reassemble it all a week or so later. Everything goes swimmingly until it's time to set the cam timing. Two chain drives, one on each bank with one behind the other. Trouble was the timing marks on the sprockets and chains looked nothing like the photos in the manual. There were certainly dots on the sprockets and white paint on the chains but nothing to actually indicate when each bank was on a firing stroke. I puzzled over it for most of the afternoon until he turns up after work to collect it. I said I was still not at all happy and needed to go right back to basics with a dial gauge and degree wheel and make sure the inlet valves on each bank were reaching full lift at appropriate times. Then came the fatal words.
"It'll be ok Dave, I trust you."
I should have made him sign something that it was down to him if the cam timing was wrong.
I tried to explain it was sod all to do with trusting me, there was clearly some problem with the Haynes manual but he wasn't prepared to wait another day, hoiked it into the back of his van and away. Some time later after the mechanic had fitted it back into the car I get a frantic phone call to say he'd started it up, left it ticking over on the drive and come back to find the catalytic convertor on fire and only just managed to get a hosepipe on it before the whole car went up. Eeek. Clearly one bank was just pumping raw petrol into its exhaust manifold and not firing at all. 360 degrees out on that bank methinks. The inlet valves were opening on a power stroke.
Anyway it's apparently up to me to fix it all FOC so I load up the car with tools and make my way to the this local garage of his it had been towed back to. The chief mechanic has this smirk on his face like "here's the monkey who can't put an engine back together properly" not knowing of course what the actual story had been.
So I rip out the rad and all the other stuff you need to remove to get at the timing covers on this bloody thing, get the covers off and start investigating as I actually had the right Haynes manual by then. The chief mechanic saunters over. "That's a bugger" he says grinning, "it's the front bank it was actually firing properly on so you'll have to get all the front timing gear off just to reset the rear one 360 degrees."
"No worries" I say, "I'll just move the front bank 360 degrees instead."
He looks at me with horror on his face and comes out with this little gem. "Then both banks will be 360 degrees out and it won't run at all!"
Priceless.
So I whipped the front chain off, turned the crank 360 degrees, popped the chain back on and Bob's your aunty's husband.
I doubt if he ever managed to work out how an hour or two later it purred back into life and ticked over as sweet as a nut without me touching the rear bank that was originally the wrongly set one.
Anyway he got cold feet about the guy putting it back together again and asked if I'd do it. Now I hate working on engines someone else has stripped down and especially if it's a type of engine I haven't worked on before but he said he had a Haynes manual and anyway an engine's just a bloody engine to me so foolishly I said yes.
What I didn't know, having never seen the car, was the bloody Haynes manual he had was the wrong one! It was a later model year car than the manual and the 2.9 engine or summat like that. No great differences other than the bore and some detail stuff but ain't the devil always in the details?
So he turns up with this huge collection of random bits, I measure up and order the right thickness liner seals and other bits and eventually start to reassemble it all a week or so later. Everything goes swimmingly until it's time to set the cam timing. Two chain drives, one on each bank with one behind the other. Trouble was the timing marks on the sprockets and chains looked nothing like the photos in the manual. There were certainly dots on the sprockets and white paint on the chains but nothing to actually indicate when each bank was on a firing stroke. I puzzled over it for most of the afternoon until he turns up after work to collect it. I said I was still not at all happy and needed to go right back to basics with a dial gauge and degree wheel and make sure the inlet valves on each bank were reaching full lift at appropriate times. Then came the fatal words.
"It'll be ok Dave, I trust you."
I should have made him sign something that it was down to him if the cam timing was wrong.
I tried to explain it was sod all to do with trusting me, there was clearly some problem with the Haynes manual but he wasn't prepared to wait another day, hoiked it into the back of his van and away. Some time later after the mechanic had fitted it back into the car I get a frantic phone call to say he'd started it up, left it ticking over on the drive and come back to find the catalytic convertor on fire and only just managed to get a hosepipe on it before the whole car went up. Eeek. Clearly one bank was just pumping raw petrol into its exhaust manifold and not firing at all. 360 degrees out on that bank methinks. The inlet valves were opening on a power stroke.
Anyway it's apparently up to me to fix it all FOC so I load up the car with tools and make my way to the this local garage of his it had been towed back to. The chief mechanic has this smirk on his face like "here's the monkey who can't put an engine back together properly" not knowing of course what the actual story had been.
So I rip out the rad and all the other stuff you need to remove to get at the timing covers on this bloody thing, get the covers off and start investigating as I actually had the right Haynes manual by then. The chief mechanic saunters over. "That's a bugger" he says grinning, "it's the front bank it was actually firing properly on so you'll have to get all the front timing gear off just to reset the rear one 360 degrees."
"No worries" I say, "I'll just move the front bank 360 degrees instead."
He looks at me with horror on his face and comes out with this little gem. "Then both banks will be 360 degrees out and it won't run at all!"
Priceless.
So I whipped the front chain off, turned the crank 360 degrees, popped the chain back on and Bob's your aunty's husband.
I doubt if he ever managed to work out how an hour or two later it purred back into life and ticked over as sweet as a nut without me touching the rear bank that was originally the wrongly set one.
Edited by Pumaracing on Thursday 20th January 12:12
Pumaracing said:
Yes lots. You've just been stitched up by a completely incompetent garage which is par for the course as the average garage mechanic knows three fifths of sod all about how engines actually work.
Either the head gasket failed or the valves did kiss the pistons for some reason. Or they screwed up the compression test which was a red herring and it was a fuel pump failure or indeed something else altogether. Clearly any mechanic who pours fluid down bores and then thinks it ought to stay there forever when piston rings have gaps can't be trusted to do a compression test. Nothing whatsoever to do with the bottom end anyway.
Ok, take the stick out of your arse and lighten up, there's simply no need to be so rude in your reply.Either the head gasket failed or the valves did kiss the pistons for some reason. Or they screwed up the compression test which was a red herring and it was a fuel pump failure or indeed something else altogether. Clearly any mechanic who pours fluid down bores and then thinks it ought to stay there forever when piston rings have gaps can't be trusted to do a compression test. Nothing whatsoever to do with the bottom end anyway.
As it turns out, it WAS the bottom end, the head was completely undamaged, and the valves were all seating correctly. The head gasket had no sign of failure. It was piston ring damage on three cylinders.
Car is now back up and running perfectly with a replacement engine, and the garage bill came in well under the estimate. My total bill (including a second-hand engine) was £1,750 and the first £475 of that is covered by my AA Breakdown Repair cover. Not bad considering.
calibrax said:
As it turns out, it WAS the bottom end, the head was completely undamaged, and the valves were all seating correctly. The head gasket had no sign of failure. It was piston ring damage on three cylinders.
What exactly was the cause of three sets of piston rings spontaneously being damaged? Sounds like you've been fed another load of BS to me, unless you'd maybe driven through a very deep puddle and hydrolocked the engine. But I'm sure you'd have mentioned that in your opening post.Edited by Mr2Mike on Friday 4th February 14:03
There's no conceiveable mechanism I can envisage that would cause three out of four sets of piston rings to just fail, apparently instantaneously, apparently without any obvious cause and leaving the fourth set and the rest of the engine ok. An oil pump failure would cause piston seizure but probably not before the crank bearings and the top end had gone too.
Severe overheating from a cooling system failure could also cause piston seizure but again not without creating other obvious damage such as a warped head.
In the absence of a second opinion by a properly qualified engineer I don't believe a word of what you've been told or at the very least it's an incomplete and logically inconsistent story that doesn't establish the real cause of whatever happened.
Severe overheating from a cooling system failure could also cause piston seizure but again not without creating other obvious damage such as a warped head.
In the absence of a second opinion by a properly qualified engineer I don't believe a word of what you've been told or at the very least it's an incomplete and logically inconsistent story that doesn't establish the real cause of whatever happened.
The only times i have ever seen multiple piston ring failures have been because:
1) we were doing ring profile development, which is still (even now) a bit of a black art, and when you get it wrong, you tend to get the rings wearing excessively, or worse, picking up
OR:
2) someone has built the engine with the piston rings on upside down (don't laugh, it's been done more times than you might think :-)
1) we were doing ring profile development, which is still (even now) a bit of a black art, and when you get it wrong, you tend to get the rings wearing excessively, or worse, picking up
OR:
2) someone has built the engine with the piston rings on upside down (don't laugh, it's been done more times than you might think :-)
stevieturbo said:
Dodgy remap somewhere along the way ?
Someone put petrol in instead of diesel ?
No to either I think. This was apparently a sudden failure not preceded by any symptoms, or at least not as far as we've been told. That means a breakage rather than a gradually manifesting failure with some prior poor running.Someone put petrol in instead of diesel ?
Unfortunately all the information given is untrustworthy. The TDC stuff is a red herring because if the engine had indeed been set at TDC from a crank pulley notch then the pistons were indeed at TDC and someone has confused them being a bit down from the top of the block with them not being at TDC.
The compression test ought to be foolproof on a diesel with no throttle to remember to open but the piston rings can't just fail without other signs. I would like to see someone check the head for warping with a straight edge but I suspect that this is now a "cold case". I hate not getting to the bottom of something but the OP will probably not be motivated to find out that what he had been told was wrong and a whole new engine wasn't needed or it would mean admitting he's spent money he didn't need to.
Would be nice to get the old engine back though.
Pumaracing said:
stevieturbo said:
Dodgy remap somewhere along the way ?
Someone put petrol in instead of diesel ?
No to either I think. This was apparently a sudden failure not preceded by any symptoms, or at least not as far as we've been told. That means a breakage rather than a gradually manifesting failure with some prior poor running.Someone put petrol in instead of diesel ?
Unfortunately all the information given is untrustworthy. The TDC stuff is a red herring because if the engine had indeed been set at TDC from a crank pulley notch then the pistons were indeed at TDC and someone has confused them being a bit down from the top of the block with them not being at TDC.
The compression test ought to be foolproof on a diesel with no throttle to remember to open but the piston rings can't just fail without other signs. I would like to see someone check the head for warping with a straight edge but I suspect that this is now a "cold case". I hate not getting to the bottom of something but the OP will probably not be motivated to find out that what he had been told was wrong and a whole new engine wasn't needed or it would mean admitting he's spent money he didn't need to.
Would be nice to get the old engine back though.
On the compression test, some modern diesel do now use throttles to control the re-gen stratergy of the aftertreatment. That said, I can't imagine the diesel in the ZT is that modern.
The actual cause is still unknown. I hadn't filled the tank recently, so that rules out the petrol theory. The car did have a diesel tuning box fitted, but that had been in place for nearly 2 years, so it's unlikely that could have been the cause. The only thing I could count as prior symptoms would be a slight hesitancy which happened just twice in the months preceding the failure, and both times before the car had got up to temperature. Only momentary, kinda like a misfire, but the car was fine after that. We're talking about two misfires, in maybe 4,000 miles of driving. I put it down to the cold (as it happened during the two cold snaps we had).
In any case... the fact is, I need a car for my job, as my commute is a 90 mile round trip and public transport just isn't an option. So I basically had to make a decision. Sure, I could have got a second opinion on the diagnosis, which would have cost me more time and money. Or I could have paid for them to fully strip down the engine to determine the exact cause. But bearing in mind it's a 6 year old ZT worth maybe £3,000 - £3,500 then the cost wouldn't need to go up very much to make it uneconomical to fix.
I trust this garage - they are specialists with MG and Rover cars, and have a good reputation with the owners club. So I took their advice (and what was IMO the cheapest option)... to replace the engine. As a new engine from BMW was £7,500 and a reconditioned one was around £3,000, I sourced an engine from an accident damaged Rover 75 for much less, which had around 10,000 miles less than my existing engine. All the other options would have led to my car being effectively worthless, and me having to buy a new car to replace it.
The engine I supplied was meant to come as a bare engine, but it actually turned up at the garage with a lot of ancillaries attached, so the MG specialist took these off and put them in a box for me to save money on spares in future - full set of injectors, cam/crank sensors, fuel rail, etc etc. (the four injectors alone would cost about £800 new). The service from the garage was impeccable.
And let's face it, most garages these days wouldn't even have known it was a BMW engine. When I originally bought the car and took it for a routine oil change at a local garage, the mechanic there actually said they were very prone to HGF, when that's simply not the case on the diesels. He just assumed "it's an MG Rover = HGF". Obviously not realising it's not a K series, despite the fact he'd just changed the oil and filter on it.
So I really have no regrets... my car is back on the road and running well, and the total cost to me was under £1,300 which is a very good result in my eyes, given the alternatives.
In any case... the fact is, I need a car for my job, as my commute is a 90 mile round trip and public transport just isn't an option. So I basically had to make a decision. Sure, I could have got a second opinion on the diagnosis, which would have cost me more time and money. Or I could have paid for them to fully strip down the engine to determine the exact cause. But bearing in mind it's a 6 year old ZT worth maybe £3,000 - £3,500 then the cost wouldn't need to go up very much to make it uneconomical to fix.
I trust this garage - they are specialists with MG and Rover cars, and have a good reputation with the owners club. So I took their advice (and what was IMO the cheapest option)... to replace the engine. As a new engine from BMW was £7,500 and a reconditioned one was around £3,000, I sourced an engine from an accident damaged Rover 75 for much less, which had around 10,000 miles less than my existing engine. All the other options would have led to my car being effectively worthless, and me having to buy a new car to replace it.
The engine I supplied was meant to come as a bare engine, but it actually turned up at the garage with a lot of ancillaries attached, so the MG specialist took these off and put them in a box for me to save money on spares in future - full set of injectors, cam/crank sensors, fuel rail, etc etc. (the four injectors alone would cost about £800 new). The service from the garage was impeccable.
And let's face it, most garages these days wouldn't even have known it was a BMW engine. When I originally bought the car and took it for a routine oil change at a local garage, the mechanic there actually said they were very prone to HGF, when that's simply not the case on the diesels. He just assumed "it's an MG Rover = HGF". Obviously not realising it's not a K series, despite the fact he'd just changed the oil and filter on it.
So I really have no regrets... my car is back on the road and running well, and the total cost to me was under £1,300 which is a very good result in my eyes, given the alternatives.
Edited by calibrax on Monday 7th February 01:33
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