M52 chain tensioner mechanical or hydraulic?

**importbanana** · 01-08-2022, 08:48 AM

Was looking for M52 lower chain tensioner torque spec, and keep reading about upgrading it to the hydraulic tensioner design from the S52. The M52 is said to have a mechanical tensioner.

Is this true?

The M52 block would need to supply oil pressure to the tensioner in order for the S52 tensioner to work in an M52, which means if the M52 tensioner is only mechanical BMW designed this oil path for nothing on the M52. The M52 tensioner also has an oil inlet. I think it's hydraulic. The spring is probably what makes people think it's mechanical. The spring is only there to supply tension when no oil pressure is present (startup), after that oil pressure takes over.

1) Does someone know the correct torque spec for M52 lower chain tensioner? I read 50Nm and 70Nm. If there's no definiteve spec I guess hand tightening will do.

2) M52 tensioner, is it really hydraulic or mechanical?

**bluptgm3** · 01-08-2022, 01:23 PM

That can be verified by observing part numbers for each in www.realoem.com

I am fairly certain ALL M/S52s got the same updated primary chain tensioner.

edit
Both tensioners are hydraulic in addition to containing a spring. The S52 version is a single assembly and must hold pressure better. The M52s (and ALL M50s and S50s) tensioner are all the multi-component assemble-on-installation tensioner.

The components of the M/S50 and M52 primary chain tensioner

The OE S52 primary chain tensioner

This Hydraulic Tensioner is made by INA, an OE supplier, the INA OEM part is available for 1/4 the cost.

**Eric93se** · 01-08-2022, 02:33 PM

My m52 1997 came with a mechanical tensioner, recently upgraded to the hydraulic version (weighs 3x original). Original uses the oil feed just as a lube.

Torquing, because its aluminum and there's no way to use a tq wrench I simply get it tight without much torque then I go a bit more compressing the crush washer (which should be brand new).

- - - Updated - - -

Be careful when starting the aluminum threads, a guy on here used a wrench to start the threads and stripped them.

**importbanana** · 01-08-2022, 06:57 PM

How do you know the M52 tensioner is mechanical and the S52 tensioner is hydraulic? Doesn't the S52 one use a spring as well? If yes then both use a spring and an oil inlet. I don't see how the M52 tensioner isn't hydraulic as well.

**bluptgm3** · 01-08-2022, 07:14 PM

Originally Posted by Eric93se

Be careful when starting the aluminum threads, a guy on here used a wrench to start the threads and stripped them.

LOL!! Fasteners should always be started by hand. Additionally, several threads further by hand as well. If resistance is encountered investigate prior to applying force…..

Sent from my iPhone using Tapatalk

**Eric93se** · 01-08-2022, 09:53 PM

I suggest you posses one of each then you can study the different designs.

Originally Posted by importbanana

How do you know the M52 tensioner is mechanical and the S52 tensioner is hydraulic? Doesn't the S52 one use a spring as well? If yes then both use a spring and an oil inlet. I don't see how the M52 tensioner isn't hydraulic as well.

**spyderg0d** · 01-10-2022, 11:32 AM

Be careful with info guys. This is a big thing that screws ppl up. Il break it down for you.

The first was the mechanical tensioner,. This has a large flat end, and a heavy rate spring inside. BUT, this ALSO came paired with its specific timing chain rail that has a large flat meeting place to the tensioner tip. If you have this Chai guide, you WILL NOT be able to use the hydraulic timing tensioner.

The second, hydraulic chain tensioner has a slotted tip that slides over the updated timing chain guide. This updated timing chain guide will fit EITHER tensioner as it's fitted to do so.

Both the tensioner are hydraulic in a sense, the terminology is only to determine the difference as the "hydraulic" style tensioner relies completely on oil pressure with better design to hold pressure, while the mechanical relies "mostly" on the springs mechanical pressure.

**Eric93se** · 01-10-2022, 02:48 PM

So spyder that's not entirely true. For the m52 it came with a flat end spring loaded tensioner, the upgrade is the s52 version which is also flat ended but uses hydraulic pressure for tensioning. Both have a spring, which is needed because pressure is not held after engine shutdown. The designs are very different, the s52 hydraulic weighs almost 3x the regular spring loaded version. I'd like to think my engine is a bit quieter after the upgrade.

FCP has an article on the upgrade but its not very indepth.