Timing chain for a '80 300TD

After 280K it's on borrowed time. But after 280K the engine may soon be due for and overhaul anyway so add a chain to the list.

You can check the chain's wear and stretch - or more pragmatically its odds of breaking, for that's what really matters.

Remove the valve cover. Turn the engine crankshaft, not the cam, in its normal rotation, not backward, until the notch in the thrust collar immediately behind the chain sprocket is aligned with a mark cut into the left (driver's) side of the front most cam support. Read the crankshaft angle on the crankshaft's harmonic damper. Replace the chain if the angle exceeds 5 degrees.

Thanks for the info. What's the easiest way to read the angle on the crankshaft's harmonic damper (i.e. where the heck can I find it)? AJ

Open the hood. Stand next to the left front wheel. Look at the drive belts, follow their path to their lowest point - that's the crankshaft. The harmonic balancer is immediately to the rear of the belts' pulleys. Near the top of the balancer you'll see - under the dirt and grease - a metal pointer protruding from the front of the engine it has a tip like the point of a nail. Under that tip - under the dirt - is a scale stamped onto the balancer.

00 is zero degrees - top dead center of cylinder #1.

Done, and done. I'm showing 00 (...and certain that I pulled it through the right way via the power steering pulley nut...) Checked it twice. Is that possible after close to 300k miles? AJ

Maybe it has been changed before...

I think you're right. Was at the MB dealer this am, happened to talk to a mech. about it. HE SAYS the same thing. Showing |0|, then don't mess with it. Also, if it ain't makin' noise, sprocket teeth are symetrical (i.e. no wear) then leave it. Thanks all. AJ

I'd say having 0 degrees difference between the cam and the crank shafts after 300K miles is indeed a miraculous timing chain!

I recently checked my 380SE with Snap-On timing light that you can manually check the timing. With 201,000 miles on clock, when the timing mark hit 180 degree visually, the Snap-On timing light said 179 degree.

So, it means my timing chain is stretched to only 1 degree... dang! Now I got a new chain for nothing. I will change the tensioner however... I think it is good insurance.

How does your snap-on timing light allow you to check valve timing without looking at a camshaft timing sprocket? Are you measuring crank position via ignition timing? If that's what you're doing, it's not an accurate way to measure chain wear because distributor position can and will be adjusted even if you have chain wear. If you're using another method, please enlighten me.

The way the Snap-On timing work is that it has a variable timing capability. Regular timing light simply shine when spark plug is ignited... stating the timing at that point.

With Snap-On, you can manually set it to any degree you want regardless of the engine's ignition. So, the light pulses is not in sync with the engine's ignition... That way, you can check, if you set timing light to 10 degree BTDC, the engine should also read the same... if you set it 180 degree, it should read 180 degree.

You mentioned that the distributor position can be adjusted to chain wear... Thank you for bringing it up... I am thinking... you are right when you set it at idle or whichever MB specified...

However, with timing chain stretch, what you set at idle isn't the same at

180 degree, so that's where this adjustable timing light gun comes into play... it can verify how far off you are.

Please correct me if I am wrong, but it sounds like your Snap-On timing light is still an inductive timing light. By that I mean that it uses an inductive pickup clamped around a high voltage ignition wire going to a spark plug.

While you can dial in 180 degrees on the Snap-On timing light control, you are still only measuring a 180 degree offset from the timing of the ignition spark. I assume you have your ignition timing set to factory specs which would compensate for chain wear. So you are not really measuring crank position in relation to camshaft sprocket position using an inductive timing light. You still need to observe both crank and camshaft position to check for chain wear.

Remember, ignition timing is adjusted by moving distributor position while pointing the timing light at the timing marks on the crankshaft pulley. Once ignition timing is set, dialing your Snap-On timing light control to 180 degrees will show 180 degrees on the crankshaft pulley (assuming your initial ignition timing was 0 degrees BTDC). But this tells you little about valve timing because valve timing is fixed by timing chain wear (unless you install an offset wood drift keys on the camshaft sprockets). Pull a valve cover and check your valve timing.

Right! This was T.G.'s point is I believe. There is no magic light that will show you the actual physical valve opening... Only the spark in relation to the mark...

Marty

I see what you are saying... I'll check it if I get a chance.