My 450SL engine has 100K since i rebuilt it (car is over 200k miles). I had replaced the chain, sprockets, rails and tensioner.

Recently I started hearing a slight timing chain slap only on hot startup. took the valve covers off to check chain and rails. i rotated the engine 4 times in clockwise direction only (didn't bother removing the spark plugs) and each time I measured 12 degrees ATDC on the crank damper when the right cam marks lined up. The weird thing is that the left cam lined up almost perfectly with the crank damper at TDC (actually looks like 2 degrees BTDC which kind of baffles me). The car runs well but need your advise.


Why is one cam timed OK and the other off by so much (not by a whole tooth though)? Does the evidence suggest stretched chain or bad tensioner? Why would a stretched chain only effect one cam's timing and not the other?

The rails look fine, no cracks etc but they are 18 years old with 100K on them. I'd hate to change everything (chain, 3 side tensioners and tensioner) only to find out that something else is wrong.

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1972 450SL
1982 300D Turbo

If you prefer to set your cam timing to a specific crank angle MB does offer offset woodruff keys too reposition the camshafts. When you use these keys you need keep in mind that the alignment mark(s) on the cam thrust washer may not line up with the mark on the cam bearing. The offset keys will advance or retard the camshaft without effecting the position of the alignment marks. To set the camshafts to an exact crank angle requires the use of a dial indicator and the appropriate vices with the base to support it. Should you choose to set your camshaft timing in this manner be prepared to spend a little time getting it exactly it where you want it. This can be a rather involved process for something you may not even recognize when completed.

When it is all said and done you may notice an improvement with your idle quality but personally, you may want to reconsider how close your alignment marks really need to be.

The greatest offset woodruff key can correct up to 10 degrees at the crank maximum. I am already at 12 degrees. Something in the timing is beyond allowable I believe. My question though remains, why is the right cam so far off and the left one so good? Does chain stretch only affect the right cam or is it the tensioner located on the right side that is the culprit. Does anyone else suggest offset keys or should I just bellyup and buy chain, tensioner and 3 side rails (forget the tensioner rail?). I would like to order all the parts at one time since it is my daily driver.

I did try using a dial indicator and magnetic base but just about everything is aluminum. i finally rigged it up and after getting my readings i realised I did not adjust the valves for 0 cleareance so my measures are probably off. I measured 17 degrees when #1 intake opened 2mm and 10 degrees on the crank when #6 opened 2mm. in reading some other posts the convention is not to bother with the dial indicator, just line up the cam marks and read the crank.

In the photo you can see the pulling side of the gear teeth on the cam sprocket. They appear gray in the photo. They are slightly rough, not polished smooth so I think i need to change the cam sprocket(s) as well. You can also see the 18 year old rails with 100k on them. i guess the color would indicate that they may still be OK but I should probably change them anyway for peace of mind.

Attached Thumbnails

 

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1972 450SL
1982 300D Turbo

Chain stretch and lower gears worn will contribute to the overall length of the chain. When the gears are worn the chain will sit lower in the groove, a .5mm here .5mm there will add up. Since the R/S cam is the last gear it only stands to reason that timing mark would be the most effected. As well if the chain sets deeper in a rail in the lower end of the engine, the semi curved one, it too can add to the length of the chain. If your engine has 250k or > on the original lower gears and rails it may be a good time to consider going in! New chain, all gears, all rails in the chain drive assembly could reduce the majority of the offset, may not get all of it, but the offset keyways will assist you with getting the timing on the money.

Is it possible the sprocket is off a tooth?

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Regards

Warren

Currently 1965 220Sb, 2002 FORD Crown Vic Police Interceptor

Had 1965 220SEb, 1967 230S, 280SE 4.5, 300SE (W126), 420SEL

ENTER > = (HP RPN)

Not part of the in-crowd since 1952.

You may find that the alignemnt mark will be slightly advanced or slightly retarded either way you set it. You may want to advance the mark then retard the mark, afterward drive the vehicle in both positions and determine the performance you are most comfortable with.

I have been more comfortable leaving them set slightly retarded, never had a complaint during my 15 years of service. Now it is more part ime, or when I am in the mood.

Thank you all for your help with this. It's the only mercedes V8 I've ever worked on so without you I'm alone with my factory manual.

i put in new cam sprockets, 3 upper side rails, tensioner, tensioner rail and timing chain. I also rotated the right sprocket one tooth which helped things quite a bit (each tooth represents 10° as there are 36 teeth in the sprocket). I can't believe the right cam shaft was off by one tooth all these years!

Now the left cam is 5° BTDC and the right cam is 5° ATDC. Isn't that strange or it lower gear wear or uneven thickness cylinder heads causing this? Will there be no obvious performance difference if i just leave it alone? Woulkd you put in two offset keys, one to retard the left cam and another to advance the right cam. If so i guess i should rig up the dial indicator, set the valve to 0 free play and determine the crank angle at 2mm of valve lift.

I rebuilt the engine 100k miles ago and I replaced all the lower rails at that time but not the gears. I really don't want to take the timing cover off.

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1972 450SL
1982 300D Turbo

I decided to measure the cam timing the shop manual way. I set the #1 and #6 valve to zero cleareance and set up my dial indicator. When the #1 intake began compressing and moved 2mm vertically the crankshaft recorded 2° ATDC. For the same procedure on the #6 intake valve I read 3° ATDC. These seem like very reasonable numbers. I wonder if this prooves that timing the camshaft by ligning up the markings on the cam can not be trusted for evaluating the cam timing and chain stretch. I believe Stevebfl wrote that the cam marks are there only to make sure you didn't skip a tooth, not for timing the camshaft. If I hadn't done the dial indicator thing I may have bought offset keys and made a correction based on incorrect findings.

Could someone tell me what degree it should be for 52/53 cams in a 117.982 engine and if my latest measurements are good enough? Oddlty enough my factory manual does not give this info for the stock engine in my 1972 450SL (I have 52/53 cams in a 117.982 engine).

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1972 450SL
1982 300D Turbo

Hi

Per factory: A 1972, 117.98(1,2,4) using cams 52/53 measured on cylinders 1 & 6.

With a new chain

Left Cam
Intake valve opens@ 4 degrees TDC then closes @ 14 degrees BDC
Exhaust valve opens@ 30 degrees BDC then closes@ 16 degrees TDC

Right Cam
Intake valve opens@ 2 degrees TDC then closes@ 12 degrees BDC
Exhaust valve opens@32 degrees BDC then closes@ 18 degrees TDC

I believe it is Before TDC & Before BDC

If anybody has more to offer feel free to chime in!

MrCjames,

Well then my set up is just about perfect.Thank you so much for looking it up and letting me know!

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1972 450SL
1982 300D Turbo