When To Replace Timing Chain
 

Hello Everyone, Recently got a 1981 240d with an unknown service hx of the last 100k miles. Since I'm going to adjust the valves, while I'm in there is there any way to visually inspect the timing chain for condition and possible need for replacement? I'm not ready to do that job yet! Thanks, JEFF

Welcome to the forum Jeff,
If you use the search button you will find lots of good info there including how to set your valves and measure chain stretch.

I actually meant I was not ready for the timing chain job yet. Not too worried about the valve adjustment. Knock on wood.:):) When timing chains fail, do they actually just break or do they stretch first and then break? Thanks

In most cases they stretch, I have not heard of one breaking.
You can get by for quite a while with offset keys before
actually change the chain.

There is no specific miles to replace it at. You must measure the chain elongation to determine if it needs replacement.
http://www.peachparts.com/Wikka/OM617TimingChainStretch

Replacing the chain is pointless if you do not replace the guide rails at the same time.

the tensioners are just as importnat as the chain, but never let anyone ever tell you the chains never breaks. The chain on my uncles snapped

Jack;

Where do you place the woodruff keys on the timing chain/assembly?

John :confused:

come on people... the search button up top works great. type in offset key
or timing chain it's all there over and over.
http://www.peachparts.com/shopforum/showpost.php?p=1402601&postcount=5

Between the camshaft and camshaft sprocket.

Thanks. Are there pics posted anywhere?

John

It's basically impossible for a chain to "snap" of it's own accord. There must be a prior event.........such as the loss of a guide or the tensioning rail.........that precipitates the chain failure.

Not always. Metal does fatigue over time and everything man-made will have production flaws.

You know the old saying, a chain is only as strong as it's weakest link. All it takes is one bad link for the chain to break. Remember the member (Craig?) that happened to find his chain was missing a link bar?

Just to be clear, that was my original oil pump chain at about 300K miles that had worn to the point the one side link had basically just fallen off. Personally, I like to replace the timing chain/guide/etc. at about 200K miles and avoid playing around with offset keys.

can you see if you have a key installed, or must you remove the cam sprocket?

OK, I'll agree that 300K will cause sufficient wear on the pins to create the possibility of a failure and that it should be replaced at that mileage on principle, due to the potential for catstrophe if it fails.