SL/R230: Balance Shaft Question
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Joined: Mar 2010
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2007 E350; 2018 GLE350
Balance Shaft Question
My R230 and I are in one of those slack-water periods in which everything in/on the car works perfectly, or reasonably so. This gives me an opportunity to invent things to worry about. Which brings me to this: My car's engine falls in the tail-end manufacture-date range when the anemic balance shafts were being installed. I've had no balance shaft-related problems or issues, and certainly don't want any. But I'm mildly curious: how does a balance shaft fail?--all at once, catastrophically, or gradually over time and use? If I were to open the viewing holes on the engine so I could view the timing marks, would visual observation disclose that the marks were gradually falling out of nick, or do they just look normal right up until the moment they are not?
As I've suggested before: owning an R230 is like being married to the twenty-something Ingrid Bergman.
As I've suggested before: owning an R230 is like being married to the twenty-something Ingrid Bergman.
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The issue is that the timing chain idler sprocket was improperly forged so that it is too soft and wears away. Ont he V6, this sprocket is on the end of and drive the balance shaft. On the V8, it's just an idler bolted to the block. It fails very gradually bey wearing away. The sprocket diameter shrinks, introducing slack in the timing chain. The only symptoms you will get are DTCs 120 and 1208 (OBDII codes P0017 and P0016 respectively). At first, the codes will illuminate the MIL intermittently After a while, the MIL will remain illuminated and even after cleaning the errors, it will register again on startup. The variable valve timing system can compensate for this, so other than the DTCs, there will be no other symptoms. Some people claim they could hear some noises due to the extra slack in the timing chain after time. In reality, you could probably drive 20K miles or more after the MIL illuminates and never have an issue. The failure will not cause the timing chain to jump teeth on the camshaft or crankshaft sprockets. Eventually, it could cause the timing chain to fail, but I suspect that would require a significant wear over a long time.
Thread Starter
Senior Member
Joined: Mar 2010
Posts: 451
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2007 E350; 2018 GLE350
Rodney: Many many thanks for your discussion of balance sprocket failures. I have seen You Tube vids of balance sprockets and shafts being replaced on V6 engines ... I just assumed there was a similar shaft on the V8. Anyhow ... I sure would like to avoid replacing the sprocket.
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The V6 balance shaft requires that the engine be removed for replacement. On the V8, the idler sprocket can be replaced with the engine in place. However, the engine still has to be lifted to remove the oil pan so that the timing chain cover can then be removed. That job is about 85% of the work of pulling the engine. And that extra 15% of work is probably equal to the frustration of working in the tight space between the radiator and the engine. Most dealers that do the job will also pull the engine on the V8's.
