TIMING CHAINS and BALANCE SHAFT REPAIRS

The M112 and M113 engines built between 1999 and 2005 have been very reliable with respect to timing chains and in general. The M272 and M273 engine introduced in 2006 have had problems with the timing resulting from a worn balance shaft sprocket (M272) or timing chain idler gear on the M273. That gear may not have been hardened properly and is a subject of a class action lawsuit. The manufacturer will cover a decreasing percentage of the repair up to 125,000 miles. Check with the dealer of you have this issue with either or both codes 1200 and 1208 as they may cover part of the repair.

The repair involves removal of the engine, oil pans and front cover and all cam actuators, we replace the balance shaft or idler gear, the chain, any worn guides, the sheet metal pan if bent, the oil pump, the oil level sensor, and all parts supplied in the kit. This is a repair that we do regularly if you need it done please contact us. Due to the high cost this is sometimes put off, although it doesn’t lead to catastrophic failure it does shed a lot of metal bits into the engine and when the gear is worn to a nub we often find the guides are more worn. Some the guide require head removal to replace, so it may be beneficial to do the repair when the code is coming on/off rather than after it’s been on solid for awhile.

Modern timing chains can be expected to last the life of the engines if all the parts are manufactured correctly. We have seen some early M271 engines with broken chains, these are single row chains. If you have any abnormal engines noise on startup or chain noise you should have it checked. If your OBDII engine (built after 1997) has more than 150,000 miles on it and you have done all the scheduled maintenance chances are the timing chain is fine. If it isn't you might have code relative to the timing being off beyond a specified limit in the engine software. If it's an older engine from the 1970s or 1980s or has a single roller chain it may be needed. The only way to know for sure on an old engine or even a suspect newer engine is to check the base timing, if it’s off beyond the specification replace the chain and any worn guides. To check it, with the valve covers off rotate the engine at the crank bolt manually clockwise in the direction of engine rotation to TDC, either the cam timing marks line up or they will be off. If you are off 5 degrees of crank angle that’s 2.5 degrees of cam angle. It may require two revolutions of the crank to get the lines in a position where they can be checked. Don’t rotate counterclockwise if you overshoot TDC, you may brake a guide, over tighten the tensioner or jump timing. Regardless, you need to take up the chain slack to get a valid measurement so always only rotate in the direction of normal engine rotation.

Know the correct procedure as the M272 and M273 valve covers are bonded on and the timing is checked with the four cam sensor removed and the engine rotated until all 4 stamped circles on the pulse wheels are centered in the holes at a specific crank angle. On an installed engine this centering can be subjective with limited room using a mirror particular on a V8. The timing will be off on the right bank only, the off centering can be very slight in some cases. On a repaired or good motor it will be perfect. If the timing marks don’t line up you may have chain stretch or a worn sprocket. Installing an offset woodruff key in the crank sprocket is one solution for small corrections if you are building an vintage motor, but for anything more than a several degrees replace the chain. A chain may be up to $300 but consider the time involved to replace it later or if it fails. On an interference engine loss of the chain is loss of the engine in many cases, unless it occurs at low engine speeds. Even then valves will be bent on several cylinders, bent valves usually damage the guides on removal. If you replace the chain check the sprockets, and if blunted or rounded they should also be replaced. A worn sprocket will quickly wear out a new chain and it will cause the timing to be off. Consider chain and sprocket wear fitted parts, if either are worn replace them both. Realize that the labor to pull the front cover and replace all the sprockets is considerably more than feeding a new chain in, but it won’t last long if your sprockets are worn.

If you remove the timing chain then you removed the chain tensioner. If it’s the ratcheting hydraulic type or you may end up with a chain that's far too tight if you don’t reset it. You'll hear the chain noise if you missed this step and risk snapping a camshaft or braking the chain. To reset a ratcheting chain tensioner remove the Allen nut then the spring and spacer. Pull the pin out fully, it only goes one way. Then insert the pin in through the back make sure its not extended. Install the tensioner with the 27mm nut with the Allen nut not installed yet, torque in place. The chain should be properly installed and timed before installing the tensioner spring. Now insert the spring and spacer, compress the spring, with the Allen nut. Installing the Allen nut while compressing the spring is most easily done with an air ratchet, if you use air tools to start the job make sure to finish with a torque wrench. Some tensioners particularly on the newer engines after 2005 are disposable one use parts. They are released by turning the engine backwards at a specified torque while holding the right exhaust camshaft fixed. This presses the chain against the tensioner releasing it, as you rotate the engine clockwise from that point the tensioner will advance until the chain is properly tensioned. Know the type and design of the tensioner you are working with as this step is critical to having a successful repair.

To schedule an appointment to Service your Mercedes Benz with Foreign MotorWorks please contact us today