Hi all, first post, but I'm not new to BMW at all. Over the years and many cars, I've had many different E39s (528i touring, 540, etc.), so I'm not new to the vehicle at all. Back in november 2021 though, one of my friends decided to sell his M5 as he had found a tiny piece of brown/red plastic in the oil filter. This immediately made him think timing chain guides. As he was moving to NC, he wanted to slim down his fleet. I was happy to pick the car up from him, as I've done countless timing jobs on M62s, N62/3s, S63, S62s, etc. This was my chance to own a beautiful carbon black/black, well maintained, and low-ish mileage M5 for a great price.
The teardown was straightforward, and reassembly easy as well. I have access to the AIR tool, which provides me with all of the aftersales instructions, so each step could be printed, crossed off, and tracked. Being that I travel often for work, I ended up not making it to the car until February 2022 even though this was taking up my personal garage. After a couple weeks of off/on work, I had the car reassembled with all new seals, timing chain guides/parts, and much more preventative work (CPSs, TPSs, VANOS cleaning/filter removal, evap vent, vacuum hoses, water pump, thermostat, etc.). The center guide was definitely past its prime, and the plastic pieces in the oil pickup/filter had definitely come from this.
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The time came to start the car, and I expected a bit of rattling on first startup. What I received though was a horrible racket. I had confirmed timing over and over, and had even used the starter over and over to build oil pressure without issue. Looking back... I should have turned the car off right away, but after 3 seconds the noise greatly reduced. Some errors appeared, and the engine certainly wasn't happy. I started digging in with INPA to find any faults, and spent some time trying to diagnose VANOS solenoids, sensors, connections, and more.
youtube.com
Frustrated, I let the car wait for another month as more trips took me away. Coming back, I had decided to do a leakdown test to confirm things from the basic mechanical first. I checked on my 528i touring as a sanity check, and its bulletproof 200k mile M52TU had only 2-3% leakage when cold. Measuring the M5 though, gave me some horrible results. 80-90% leakage, nearly all through the exhaust. I couldn't believe this at first. I tried multiple times, checking over and over that the engine was at TDC for the right cylinder, checking air hoses, etc. I finally caved into believing that the valves had lost in a fight with the pistons, and used my borescope to confirm.
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The decision I needed to make was: replace the head or pull the engine for a full rebuild. I need to investigate more, so the disassembly began again. With the bank 1 valve cover off, I noticed that the chain still had tension, but after removing the VANOS and the VANOS valve, I realized the problem. To my surprise, the tensioning guide was sitting loose at the bottom of the timing cover! More disassembly revealed that the bolt for the tensioning guide had snapped! The threads appeared to have been flattened (normally they look like this due to cross-threading), but the other half of the bolt was easily spun out of the engine block by hand. The tensioner had fully extended and was still keeping medium tension on the chain. The timing parts had some damage, so I reordered most of the them.
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Next began removal of the bank 1 head. Bank 2 was completely OK when it came to the leakdown test, so I assumed the damage was localized to only the exhaust valves of bank 1. The removal was again straightforward with out many hiccups. The carnage was apparent with the head off. Every one of the bank 1 exhaust valves were bent. Intake was all OK, so it was time for the head to visit a shop. The shop unfortunately was very slow in diagnosis and requesting parts (months...) which wasn't a huge problem as again, I was travelling for work. In the end @mishkinm5 came in with a used bank 1 head. He was able to get it off of a good engine, ship (very well packaged by the way), and deliver it to my door within a week. Without him, the project would have dragged on for more months.
The pistons were not exactly happy either, but my experiece from VERY boosted engines in the past has been that as long as I sanded down the rolled-over sharp edges, that I wouldn't have any issues with pre-detonation. A couple of pistons looked to have damage on the edges as well, most likely from pieces of something bouncing around. At this point, if the engine was trashed, I would find out when I reassembled... The piston walls were all inspected and great other than one mark, which looks to have been much older. This might not be everyone's decision, but for my situation, it worked out well. If the engine had to come out, I would have trailered it down to my shop and rebuilt it from the block up.
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With our plant's summer shutdown, I had a week to get the M5 done. In reality, with sporadic work over the break, it took only 6 or so hours to get the head installed, retime the engine, and diagnose any other small problems like damage thermostat o-rings, a missed throttle position sensor connection, etc. Finally, 8 months after buying the car, it's running as it should! Quiet, strong, and without error. In the engine, I'm still not certain of my mistake, but I believe it may have come down to mis-timing the exhaust cam on bank 1. I didn't touch the chain between the CAMS, but my setting of the VANOS must have been wrong. I'm still not certain how this could have broken the tensioning rail bolt, but I'm open to feedback!
youtube.com
Looking forward to being more involved on the forum, as I'm normally a lurker, but I think my experience and network could help many people. As an added bonus, here's my other cars!
![Image]()
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The teardown was straightforward, and reassembly easy as well. I have access to the AIR tool, which provides me with all of the aftersales instructions, so each step could be printed, crossed off, and tracked. Being that I travel often for work, I ended up not making it to the car until February 2022 even though this was taking up my personal garage. After a couple weeks of off/on work, I had the car reassembled with all new seals, timing chain guides/parts, and much more preventative work (CPSs, TPSs, VANOS cleaning/filter removal, evap vent, vacuum hoses, water pump, thermostat, etc.). The center guide was definitely past its prime, and the plastic pieces in the oil pickup/filter had definitely come from this.
The time came to start the car, and I expected a bit of rattling on first startup. What I received though was a horrible racket. I had confirmed timing over and over, and had even used the starter over and over to build oil pressure without issue. Looking back... I should have turned the car off right away, but after 3 seconds the noise greatly reduced. Some errors appeared, and the engine certainly wasn't happy. I started digging in with INPA to find any faults, and spent some time trying to diagnose VANOS solenoids, sensors, connections, and more.
- YouTube
Enjoy the videos and music you love, upload original content, and share it all with friends, family, and the world on YouTube.
youtube.com
Frustrated, I let the car wait for another month as more trips took me away. Coming back, I had decided to do a leakdown test to confirm things from the basic mechanical first. I checked on my 528i touring as a sanity check, and its bulletproof 200k mile M52TU had only 2-3% leakage when cold. Measuring the M5 though, gave me some horrible results. 80-90% leakage, nearly all through the exhaust. I couldn't believe this at first. I tried multiple times, checking over and over that the engine was at TDC for the right cylinder, checking air hoses, etc. I finally caved into believing that the valves had lost in a fight with the pistons, and used my borescope to confirm.
The decision I needed to make was: replace the head or pull the engine for a full rebuild. I need to investigate more, so the disassembly began again. With the bank 1 valve cover off, I noticed that the chain still had tension, but after removing the VANOS and the VANOS valve, I realized the problem. To my surprise, the tensioning guide was sitting loose at the bottom of the timing cover! More disassembly revealed that the bolt for the tensioning guide had snapped! The threads appeared to have been flattened (normally they look like this due to cross-threading), but the other half of the bolt was easily spun out of the engine block by hand. The tensioner had fully extended and was still keeping medium tension on the chain. The timing parts had some damage, so I reordered most of the them.
Next began removal of the bank 1 head. Bank 2 was completely OK when it came to the leakdown test, so I assumed the damage was localized to only the exhaust valves of bank 1. The removal was again straightforward with out many hiccups. The carnage was apparent with the head off. Every one of the bank 1 exhaust valves were bent. Intake was all OK, so it was time for the head to visit a shop. The shop unfortunately was very slow in diagnosis and requesting parts (months...) which wasn't a huge problem as again, I was travelling for work. In the end @mishkinm5 came in with a used bank 1 head. He was able to get it off of a good engine, ship (very well packaged by the way), and deliver it to my door within a week. Without him, the project would have dragged on for more months.
The pistons were not exactly happy either, but my experiece from VERY boosted engines in the past has been that as long as I sanded down the rolled-over sharp edges, that I wouldn't have any issues with pre-detonation. A couple of pistons looked to have damage on the edges as well, most likely from pieces of something bouncing around. At this point, if the engine was trashed, I would find out when I reassembled... The piston walls were all inspected and great other than one mark, which looks to have been much older. This might not be everyone's decision, but for my situation, it worked out well. If the engine had to come out, I would have trailered it down to my shop and rebuilt it from the block up.
With our plant's summer shutdown, I had a week to get the M5 done. In reality, with sporadic work over the break, it took only 6 or so hours to get the head installed, retime the engine, and diagnose any other small problems like damage thermostat o-rings, a missed throttle position sensor connection, etc. Finally, 8 months after buying the car, it's running as it should! Quiet, strong, and without error. In the engine, I'm still not certain of my mistake, but I believe it may have come down to mis-timing the exhaust cam on bank 1. I didn't touch the chain between the CAMS, but my setting of the VANOS must have been wrong. I'm still not certain how this could have broken the tensioning rail bolt, but I'm open to feedback!
- YouTube
Enjoy the videos and music you love, upload original content, and share it all with friends, family, and the world on YouTube.
youtube.com
Looking forward to being more involved on the forum, as I'm normally a lurker, but I think my experience and network could help many people. As an added bonus, here's my other cars!
