Author: raymondw
Date Written: 27 July 2004
Document changes: None
Applicable models:
Primarily intended for the E34S ///M5 3.6 and the E34S ///M5 3.8.
Also applicable to the E28S ///M5, E24 ///M635CSI and E24 ///M6.
Total Amount of time: Approx. 2hr30min
Required parts: Price information is based on European price information system and are ex VAT and without discount.
Amount: Description: BMW P/N Price:
1 (pc) Gasket ring A26x31-AL 07 11 9 963 418 ~0.10 Euro
1 (pc) Timing Chain Tensioner 11 31 1 405 081 ~59.00 Euro
Warning: This article is intended as a guide only and all usual precautions should be heeded when attempting work on a motor vehicle. Neither the author nor the webmaster accepts any responsibility for damage sustained as a result of using the information in this document.
Foreword: During my vacation in Switzerland in the summer of 2003, I noticed that the timing chain of my E34 ///M5 rattled for a few seconds after I cold started the engine. I never heard the engine of my E34 ///M5 doing this before, but the altitude was 1600mtr above sea level which is high enough to make a difference when trapped air escapes through the grooves in the chain tensioner-plug. Another reason to replace the tensioner was the small oil-leak that I pin pointed to the 'chain tensioner' some time ago. In both E30 ///M3 and E34 ///M5 communities, many people rave about the S50B32 chain tensioner. This engine is used in the later E36 ///M3 with the 3.2 engine. On the various user groups, people keep telling that this is a simple upgrade, but is it really? And is it applicable for the S38 engine as well.
![Image]()
S50B32 chain tensioner (without O-ring)
Background: The S14 and M88 engine families share the same simplex timing chain, but for the S38 engine, BMW used a duplex timing chain. This increased the overall reliability of the engine and reduced the risk of a broken timing chain to almost zero. However, a duplex timing chain also stresses the entire distribution more then the simplex chain.
With the S38 being an evolution of the earlier S14 and M88 engine families, the S50 engine family also relates to the S38 family for some of it's parts. Therefore, one can assume that it is not a coincidence that the S14, M88, S38 and S50 engine families share the same 32mm threaded socket to fit the 'chain-tensioner'. However, its design has changed over the years and according to BMW is engine specific. An interesting question is why BMW has changed the tensioner design so rigorously with the introduction of the S50B32 engine for the second model version of the E36 ///M3? If the S50B32 chain tensioner is an improvement, why didn't BMW release it for the older engines that share the same 32mm socket? Even though that from a technical perspective, the S50B32 may be an improvement, from a testing perspective, it is not. When the S50B32 engine was introduced in 1996, the S50B30, the S38, S14 and M88 engine families where already out of production. Releasing the new tensioner design for the older engines also would have lead to a more extensive test program. Since the previous ///M-engines where purportedly running without problems and the new tensioner design was intended for the S50B32 engine only, testing the new part for the older engines would not have made any sense.
However, compared to the S14 and M88 engines, the S38B36 has a diaphragm added to the tensioner socket. The diaphragm functions as a small oil reservoir to boost the oil pressure locally when the oil pressure in the engine hasn't reached operating level yet. The weakness of this design is its complexity. The entire S38B36 tensioner assembly builds tall and requires three seals to prevent oil leasking out. During the years, it is not uncommon for the Diaphragm to locker from the tensioner socket and thus causing a tiny oil spill. The tiny oil spill is one thing, second and more worse is the impact this has on the hydraulic function of the tensioner. A leakage spot to the environment results in a lower oil pressure in the tensioner. At lower engine speed, the spring is still able to compensate for the loss in hydraulic pressure, but as the engine speed increases, the spring is just to stiff for that. At this point, the tensioner can't provide for a constant tension on the tensioner rails with far going consequences. Eventually, you even risk the camshaft timing to retard.
With the introduction of the S38B38 engine, the diaphragm disappeared from the chain tensioner, which BMW claimed to have improved again2. It is unclear to me what else they have changed, but I assume they have added a stiffer spring and reduced the time that is needed for the tensioner to operate on oil-pressure. The S50B30 chain tensioner almost looks the same and will fit your M88/S14/S38 engine, but it is the S50B32 tensioner that you want. I won't go into detail about the differences between the S50B32 tensioner from its predecessors, since Gustave already wrote an excellent article about that on his E30 ///M3 dedicated website1. The main difference is that the spring is compressed between to halve open cylinders that slide into each other and are secured with a circular-clip. This spring also has a higher spring constant then the older tensioners. This helps to improve tensioner effectiveness. Another advantage of the S50B32 tensioner is the simplification of its installation. First of all, one doesn't have to screw in the socket whilst at the same time keeping the plug alligned to the tensioner rail against the force of the compressed spring!! Second, the S50B32 tensioner doesn't have to be 'unlocked' by rotating the crankshaft. This is required to slacken the chain a bit to compensate for the reaction forces applied by the starter engine during start-up of the engine.
![Image]()
Socket (left) and plug (right) of the chain tensioner
Above picture show the socket and the plug of the S50B32 chain tensioner. Please note the opening in the upper cylinder of the plug. Through this hole, trapped air in the two cylinders can escape. Also the engine oil finds it's way through this oval shaped hole.
![Image]()
Original S38B36 vs. the S50B32 chain tensioner.
To understand why the S50B32 chain tensioner may replace the old tensioner in your S14/M88/S38 engine, you have to get a better understanding of the timing chain and the forces that apply on it. The timing chain drives the two camshafts in the cylinder head and is driven by the crankshaft. The energy that is needed to drive the timing chain, sprockets and camshafts depends on the mass and the rotating speed. The force is a product of mass and velocity (F = m * v) and the required energy is the integrated function of it (W = 0.5*m*v2). Normalized to the maximum engine speed of the S38 engine (7250RPM), the Energy that is required to drive the S50B32 distribution at its max engine speed (7600RPM) is roughly 10% more. This means that a safe application of the S50B32 chain tensioner in your S38 engine depends on it's rotating masses. Compared to the S38B36 and S38B38, there is a margin of 10% that the rotating masses may be higher to stay within the operating area of the S50B32. This margin is even higher for the M88 and the S38B35 engines (up to ~18%) as these have a lower rev limit. The S14 with two less pistons definitely has less rotating masses, thus the S50B32 chain tensioner may be safely applied here.
Since I don't have reliable data about the rotating masses of these engines at hand, It is impossible to provide hard evidence whether or not the S38B36 and S38B38 may use the S50B32 chain tensioner. However, based on the crank and camshaft length, I am pretty sure that the rotating masses on the S38 engine exceed those of the S50B32 engine with more then 10%. End of the story? Not quite! Even though it is illegal to justify the use of the S50B32 chain tensioner on the results of the E30 ///M3 community, fact is that the spring of the S50B32 tensioner is stiffer1, thus having a higher spring constant. This results in a lowered resonance frequency of the chain, chain-guide, tensioner-plug & tensioner spring. This extends the operating area more then sufficient to allow the use in the larger S38 engine, hence the positive results of a large part of the E34 ///M5 owners that carried out this 'unofficial' upgrade.
Important Notes:
#1: During removal and installation of the chain-tensioner, the car must stay in a fixed position. Therefore, fix the cars position by engaging first car and the car's handbrake.
#2: Although this upgrade is highly recommended by enthusiast owners, nobody is willing to give a warranty. I am not going to give you one either as otherwise, you can either continue to use your current chain tensioner until it breaks down or go to your local dealer and have them carry out the work. They will be happy to install the original tensioner for you, but not the S50B32 tensioner as BMW did not release it for us in the M88, S14, S38 and S50B30 engines, possibly because of above mentioned reasons. So it is your own decision whether or not you will install of the S50B32 chain tensioner on your M88, S14 or S38 engine.
Preliminary Checks: With the application of the S50B32 chain tensioner, there is no need to place the engine in TDC. However in Europe, some people have experienced that the camshafts have retarded by one tooth. This is caused by a lengthened timing chain. I have never experienced problems with my timing chain, hence the reason I didn't check its length by removing the cam cover and placing both camshafts at TDC.
Removing auxiliary parts: The chain tensioner is screwed in the engine block directly near the exhaust manifold of #1 cylinder. Unlike the S14 engines of the E30 ///M3's and the E30 320iS, there isn't that much room to replace it without removing some parts. From underneath, the A/C compressor and the O2 air pump prevent an easy access to the chain tensioner. From above, it is the windscreen-fluid reservoir that sits in the way. Especially if you like me have the large capacity reservoir, you need to remove this part first.
I decided to access the chain tensioner from above by removing the windscreen fluid reservoirs. First, disconnect the connectors from the electrical pumps in the fluid reservoirs. Then pull them out of the reservoir. All the cleaning fluid will escape from the containers so place a bucket underneath containers on the floor. When the cleaning fluid has drain from the reservoir(s), unscrew the two plastic screws from the large reservoir. Now, the reservoir can be pulled out carefully. Unfortunately I didn't make any pictures from this procedure, but it is rather straightforward and shouldn't cause any trouble at all.
Removing the old chain tensioner: To remove the chain tensioner, the diaphragm has to be dismounted first. Use a small wrench and a 17mm nut to remove the bolt at the diaphragm's end while at the same time holding the diaphragm in place with for instance a water-pump plier. After the 17mm bolt has been loosened and removed, you can removed the diaphragm by pulling it of the tensioner socket. Place a small reservoir to drain the oil-seepage from the diaphragm. If you are lucky, you can remove the cover-nut on top of the chain-tensioner socket by hand, else use an appropriate socket to release it first and then remove it by hand. This decompresses the spring and allows its removal. Now, use a ½" 32mm socket and an appropriate extension tool and wrench to release the chain-tensioner socket after which it can be removed by hand. The only thing that needs to be removed is the chain-tensioner plug that will slide out of the threaded hole in the engine block, if it hasn't done that already.
![Image]()
Threaded chain-tensioner socket in the engine block
If necessary, clean the parts around the chain tensioner from dirt (if present). Be careful not to contaminate the threaded 32mm hole in the engine block.
Installing the new chain tensioner: In principle, the installation of the new tensioner is straightforward. First, align the plug with the tensioner rail with the plug's groove positioned vertical. With the other hand, the socket can be screwed into the threaded hole (Don't forget to install the seal). But here starts the tricky part. The plug must stay aligned with the tensioner rail, but at one point, you have to withdraw your hand from the plug. However, there still is a cm clearance left in the socket and you will hear a small 'doing', prove that the plug did slide back in the tensioner socket. If this happens (and it does a few times before you see the light), you have the remove the socket to align the plug again.
Without the tensioner-rail locked into fixed position, it is impossible to screw the socket in the threaded hole. The point is that the air trapped in the socket has the same pressure as in the atmosphere, so I opted for a large viscosity fluid to damp the plug and preventing it from sliding back. Engine oil does the trick, and thus I filled the socket with Castrol TWS 10W60 motor oil before screwing it in. This was the trick that helped me installing the tensioner. The oil trapped in the socket is pressurized with every turn that the socket is screwed into the threaded hole. This pressure is enough to push the tensioner plug towards the tensioner rail so keeping a firm alignment. This is the tricky part with installing the S50B32 tensioner and I didn't read a word about this in the TIS instructions for installing the chain-tensioner on a S50B32 engine. It requires a sense of touch and patience as it takes a few attempts to do this right. If you didn't hear a 'doing', you may continue to screw in the tensioner socket by hand. Finally, torque the 32mm socket with 70Nm as specified by the TIS for installing the S50B32 tensioner. Note that the original S38B38 tensioner requires 55Nm.
![Image]()
S50B32 chain tensioner installed
This is all what is needed. Reinstall the removed parts and don't forget to fill the reservoirs.
Results after 2 months: Since installing the new chain-tensioner, roughly 2300km has been added, mostly speed unrestricted autobahns in Germany. I also have completed 5 laps on the (in) famous North-loop of the Nürburgring, a 20,8km long track in the German Eifl region. During this endurance's, the car showed no fault. The engine now runs much smoother directly after start up. With the new chain-tensioner, the timing chain sings and for the first time, I can hear the pumping noises generated by the air pump for reducing the carbon monoxide emissions. All in all, I am very happy with the results.
The small oil-leaks didn't disappear though. After removing the oil contamination in front of the engine, a small oil leak was discovered. This turned out to be a second leak, this time caused by the front crankshaft seal. This part will be replaced on short notice also.
References:
1: http://www.e30m3performance.com/installs/installs-3/tensioner/index.htm
2: M5 / M5 Touring Seminar-Arbeits-Material, BMW AG Service training (German language)
Date Written: 27 July 2004
Document changes: None
Applicable models:
Primarily intended for the E34S ///M5 3.6 and the E34S ///M5 3.8.
Also applicable to the E28S ///M5, E24 ///M635CSI and E24 ///M6.
Total Amount of time: Approx. 2hr30min
Required parts: Price information is based on European price information system and are ex VAT and without discount.
Amount: Description: BMW P/N Price:
1 (pc) Gasket ring A26x31-AL 07 11 9 963 418 ~0.10 Euro
1 (pc) Timing Chain Tensioner 11 31 1 405 081 ~59.00 Euro
Warning: This article is intended as a guide only and all usual precautions should be heeded when attempting work on a motor vehicle. Neither the author nor the webmaster accepts any responsibility for damage sustained as a result of using the information in this document.
Foreword: During my vacation in Switzerland in the summer of 2003, I noticed that the timing chain of my E34 ///M5 rattled for a few seconds after I cold started the engine. I never heard the engine of my E34 ///M5 doing this before, but the altitude was 1600mtr above sea level which is high enough to make a difference when trapped air escapes through the grooves in the chain tensioner-plug. Another reason to replace the tensioner was the small oil-leak that I pin pointed to the 'chain tensioner' some time ago. In both E30 ///M3 and E34 ///M5 communities, many people rave about the S50B32 chain tensioner. This engine is used in the later E36 ///M3 with the 3.2 engine. On the various user groups, people keep telling that this is a simple upgrade, but is it really? And is it applicable for the S38 engine as well.
S50B32 chain tensioner (without O-ring)
Background: The S14 and M88 engine families share the same simplex timing chain, but for the S38 engine, BMW used a duplex timing chain. This increased the overall reliability of the engine and reduced the risk of a broken timing chain to almost zero. However, a duplex timing chain also stresses the entire distribution more then the simplex chain.
With the S38 being an evolution of the earlier S14 and M88 engine families, the S50 engine family also relates to the S38 family for some of it's parts. Therefore, one can assume that it is not a coincidence that the S14, M88, S38 and S50 engine families share the same 32mm threaded socket to fit the 'chain-tensioner'. However, its design has changed over the years and according to BMW is engine specific. An interesting question is why BMW has changed the tensioner design so rigorously with the introduction of the S50B32 engine for the second model version of the E36 ///M3? If the S50B32 chain tensioner is an improvement, why didn't BMW release it for the older engines that share the same 32mm socket? Even though that from a technical perspective, the S50B32 may be an improvement, from a testing perspective, it is not. When the S50B32 engine was introduced in 1996, the S50B30, the S38, S14 and M88 engine families where already out of production. Releasing the new tensioner design for the older engines also would have lead to a more extensive test program. Since the previous ///M-engines where purportedly running without problems and the new tensioner design was intended for the S50B32 engine only, testing the new part for the older engines would not have made any sense.
However, compared to the S14 and M88 engines, the S38B36 has a diaphragm added to the tensioner socket. The diaphragm functions as a small oil reservoir to boost the oil pressure locally when the oil pressure in the engine hasn't reached operating level yet. The weakness of this design is its complexity. The entire S38B36 tensioner assembly builds tall and requires three seals to prevent oil leasking out. During the years, it is not uncommon for the Diaphragm to locker from the tensioner socket and thus causing a tiny oil spill. The tiny oil spill is one thing, second and more worse is the impact this has on the hydraulic function of the tensioner. A leakage spot to the environment results in a lower oil pressure in the tensioner. At lower engine speed, the spring is still able to compensate for the loss in hydraulic pressure, but as the engine speed increases, the spring is just to stiff for that. At this point, the tensioner can't provide for a constant tension on the tensioner rails with far going consequences. Eventually, you even risk the camshaft timing to retard.
With the introduction of the S38B38 engine, the diaphragm disappeared from the chain tensioner, which BMW claimed to have improved again2. It is unclear to me what else they have changed, but I assume they have added a stiffer spring and reduced the time that is needed for the tensioner to operate on oil-pressure. The S50B30 chain tensioner almost looks the same and will fit your M88/S14/S38 engine, but it is the S50B32 tensioner that you want. I won't go into detail about the differences between the S50B32 tensioner from its predecessors, since Gustave already wrote an excellent article about that on his E30 ///M3 dedicated website1. The main difference is that the spring is compressed between to halve open cylinders that slide into each other and are secured with a circular-clip. This spring also has a higher spring constant then the older tensioners. This helps to improve tensioner effectiveness. Another advantage of the S50B32 tensioner is the simplification of its installation. First of all, one doesn't have to screw in the socket whilst at the same time keeping the plug alligned to the tensioner rail against the force of the compressed spring!! Second, the S50B32 tensioner doesn't have to be 'unlocked' by rotating the crankshaft. This is required to slacken the chain a bit to compensate for the reaction forces applied by the starter engine during start-up of the engine.
Socket (left) and plug (right) of the chain tensioner
Above picture show the socket and the plug of the S50B32 chain tensioner. Please note the opening in the upper cylinder of the plug. Through this hole, trapped air in the two cylinders can escape. Also the engine oil finds it's way through this oval shaped hole.
Original S38B36 vs. the S50B32 chain tensioner.
To understand why the S50B32 chain tensioner may replace the old tensioner in your S14/M88/S38 engine, you have to get a better understanding of the timing chain and the forces that apply on it. The timing chain drives the two camshafts in the cylinder head and is driven by the crankshaft. The energy that is needed to drive the timing chain, sprockets and camshafts depends on the mass and the rotating speed. The force is a product of mass and velocity (F = m * v) and the required energy is the integrated function of it (W = 0.5*m*v2). Normalized to the maximum engine speed of the S38 engine (7250RPM), the Energy that is required to drive the S50B32 distribution at its max engine speed (7600RPM) is roughly 10% more. This means that a safe application of the S50B32 chain tensioner in your S38 engine depends on it's rotating masses. Compared to the S38B36 and S38B38, there is a margin of 10% that the rotating masses may be higher to stay within the operating area of the S50B32. This margin is even higher for the M88 and the S38B35 engines (up to ~18%) as these have a lower rev limit. The S14 with two less pistons definitely has less rotating masses, thus the S50B32 chain tensioner may be safely applied here.
Since I don't have reliable data about the rotating masses of these engines at hand, It is impossible to provide hard evidence whether or not the S38B36 and S38B38 may use the S50B32 chain tensioner. However, based on the crank and camshaft length, I am pretty sure that the rotating masses on the S38 engine exceed those of the S50B32 engine with more then 10%. End of the story? Not quite! Even though it is illegal to justify the use of the S50B32 chain tensioner on the results of the E30 ///M3 community, fact is that the spring of the S50B32 tensioner is stiffer1, thus having a higher spring constant. This results in a lowered resonance frequency of the chain, chain-guide, tensioner-plug & tensioner spring. This extends the operating area more then sufficient to allow the use in the larger S38 engine, hence the positive results of a large part of the E34 ///M5 owners that carried out this 'unofficial' upgrade.
Important Notes:
#1: During removal and installation of the chain-tensioner, the car must stay in a fixed position. Therefore, fix the cars position by engaging first car and the car's handbrake.
#2: Although this upgrade is highly recommended by enthusiast owners, nobody is willing to give a warranty. I am not going to give you one either as otherwise, you can either continue to use your current chain tensioner until it breaks down or go to your local dealer and have them carry out the work. They will be happy to install the original tensioner for you, but not the S50B32 tensioner as BMW did not release it for us in the M88, S14, S38 and S50B30 engines, possibly because of above mentioned reasons. So it is your own decision whether or not you will install of the S50B32 chain tensioner on your M88, S14 or S38 engine.
Preliminary Checks: With the application of the S50B32 chain tensioner, there is no need to place the engine in TDC. However in Europe, some people have experienced that the camshafts have retarded by one tooth. This is caused by a lengthened timing chain. I have never experienced problems with my timing chain, hence the reason I didn't check its length by removing the cam cover and placing both camshafts at TDC.
Removing auxiliary parts: The chain tensioner is screwed in the engine block directly near the exhaust manifold of #1 cylinder. Unlike the S14 engines of the E30 ///M3's and the E30 320iS, there isn't that much room to replace it without removing some parts. From underneath, the A/C compressor and the O2 air pump prevent an easy access to the chain tensioner. From above, it is the windscreen-fluid reservoir that sits in the way. Especially if you like me have the large capacity reservoir, you need to remove this part first.
I decided to access the chain tensioner from above by removing the windscreen fluid reservoirs. First, disconnect the connectors from the electrical pumps in the fluid reservoirs. Then pull them out of the reservoir. All the cleaning fluid will escape from the containers so place a bucket underneath containers on the floor. When the cleaning fluid has drain from the reservoir(s), unscrew the two plastic screws from the large reservoir. Now, the reservoir can be pulled out carefully. Unfortunately I didn't make any pictures from this procedure, but it is rather straightforward and shouldn't cause any trouble at all.
Removing the old chain tensioner: To remove the chain tensioner, the diaphragm has to be dismounted first. Use a small wrench and a 17mm nut to remove the bolt at the diaphragm's end while at the same time holding the diaphragm in place with for instance a water-pump plier. After the 17mm bolt has been loosened and removed, you can removed the diaphragm by pulling it of the tensioner socket. Place a small reservoir to drain the oil-seepage from the diaphragm. If you are lucky, you can remove the cover-nut on top of the chain-tensioner socket by hand, else use an appropriate socket to release it first and then remove it by hand. This decompresses the spring and allows its removal. Now, use a ½" 32mm socket and an appropriate extension tool and wrench to release the chain-tensioner socket after which it can be removed by hand. The only thing that needs to be removed is the chain-tensioner plug that will slide out of the threaded hole in the engine block, if it hasn't done that already.
Threaded chain-tensioner socket in the engine block
If necessary, clean the parts around the chain tensioner from dirt (if present). Be careful not to contaminate the threaded 32mm hole in the engine block.
Installing the new chain tensioner: In principle, the installation of the new tensioner is straightforward. First, align the plug with the tensioner rail with the plug's groove positioned vertical. With the other hand, the socket can be screwed into the threaded hole (Don't forget to install the seal). But here starts the tricky part. The plug must stay aligned with the tensioner rail, but at one point, you have to withdraw your hand from the plug. However, there still is a cm clearance left in the socket and you will hear a small 'doing', prove that the plug did slide back in the tensioner socket. If this happens (and it does a few times before you see the light), you have the remove the socket to align the plug again.
Without the tensioner-rail locked into fixed position, it is impossible to screw the socket in the threaded hole. The point is that the air trapped in the socket has the same pressure as in the atmosphere, so I opted for a large viscosity fluid to damp the plug and preventing it from sliding back. Engine oil does the trick, and thus I filled the socket with Castrol TWS 10W60 motor oil before screwing it in. This was the trick that helped me installing the tensioner. The oil trapped in the socket is pressurized with every turn that the socket is screwed into the threaded hole. This pressure is enough to push the tensioner plug towards the tensioner rail so keeping a firm alignment. This is the tricky part with installing the S50B32 tensioner and I didn't read a word about this in the TIS instructions for installing the chain-tensioner on a S50B32 engine. It requires a sense of touch and patience as it takes a few attempts to do this right. If you didn't hear a 'doing', you may continue to screw in the tensioner socket by hand. Finally, torque the 32mm socket with 70Nm as specified by the TIS for installing the S50B32 tensioner. Note that the original S38B38 tensioner requires 55Nm.
S50B32 chain tensioner installed
This is all what is needed. Reinstall the removed parts and don't forget to fill the reservoirs.
Results after 2 months: Since installing the new chain-tensioner, roughly 2300km has been added, mostly speed unrestricted autobahns in Germany. I also have completed 5 laps on the (in) famous North-loop of the Nürburgring, a 20,8km long track in the German Eifl region. During this endurance's, the car showed no fault. The engine now runs much smoother directly after start up. With the new chain-tensioner, the timing chain sings and for the first time, I can hear the pumping noises generated by the air pump for reducing the carbon monoxide emissions. All in all, I am very happy with the results.
The small oil-leaks didn't disappear though. After removing the oil contamination in front of the engine, a small oil leak was discovered. This turned out to be a second leak, this time caused by the front crankshaft seal. This part will be replaced on short notice also.
References:
1: http://www.e30m3performance.com/installs/installs-3/tensioner/index.htm
2: M5 / M5 Touring Seminar-Arbeits-Material, BMW AG Service training (German language)
