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'80 450SLC Afro RHD Ikonengold
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Discussion Starter #1 (Edited)
Hello all,

been in the garage today, to finally begin the timing chain job and I must admit I prepared for much worse. Fairly Straight forward job. Tedious in some instances.
Replaced only the chain so far in few hours I had available and dodged a bullet when the head end of the new chain fell down towards the tensioner bottomless well (rare earth magnet will pull it no questions asked).

It started with about +8° advance at the RHS (as seen seating in the driver's seat) and after chain is fitted it came to about +15° advance. No interference of valves and pistons.
Effectively new chain (no sprockets replaced yet) advanced the timing by 7° which is in line with the common experience. Master link has signs of wear.
I was baffled by the advance and then I remember that approx 13yrs ago when I was replacing the chewed up cams,in order to have it go my mate (a proper mechanic) jumped unknown qty of teeth at the sprocket to cancel excessive delay. His logic was that it is a better trade off to be as close to 0° from either side of advance or retard than other options. This was because I did not have the service manual and no time to get the parts. Engine ran quite well ever since. Made only about 20000km since.

Fonzi mentioned in this response that crank sprocket is 18 teeth and cam sprocket is 36 teeth therefore each tooth on sprocket is about 10° crank advance or retard.
Now if I retard the cam sprocket by 1 tooth when I return to replace it, this will make the timing from +15° (advance) to +5° (advance) which is within woodruff key adjustment. New sprocket may change a few ° and then I can fine tune it with woodruff.

Another thing crossed my mind. If a life span of a chain is about 6°, isn't it better to set the timing about at +3° (advanced) so that durning most of its lifespan it will be within +/- 3° rather than 0° to -6° as per factory?

Seeking opinions and sanity check of my thoughts

Edit 1:

Images of initial state

See sprocket wear (edges) due to chain elongation so rollers do not sit in the valley any more

2613320


Original cam position and timing
2613321
2613322


and after chain (only) replacement
2613323
2613324
2613325

2613326
 

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1986 560SL with M120 V12 Engine, 1988 560SL Stock
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9,836 Posts
One of the thinks I'm not quite sure of is if you use a 2° offset key way, is it 2° at the crank or 2° at the cam??.

" crank sprocket is 18 teeth and cam sprocket is 36 teeth therefore each tooth on sprocket is about 10° crank advance or retard." Not exactly, each tooth on the cam sprocket = 10° on the cam and 20° on the crank.
 

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Registered
'80 450SLC Afro RHD Ikonengold
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2,861 Posts
Discussion Starter #3
One of the thinks I'm not quite sure of is if you use a 2° offset key way, is it 2° at the crank or 2° at the cam??.

" crank sprocket is 18 teeth and cam sprocket is 36 teeth therefore each tooth on sprocket is about 10° crank advance or retard." Not exactly, each tooth on the cam sprocket = 10° on the cam and 20° on the crank.
I understand now... 1 tooth skip at cam will effectively require 1 tooth movement on the crank to "catch up" which is 20° crank movement (and 10° cam movement).
So skipping the cam tooth back will make my 15° advanced cam to 5° delayed cam and then I check my options with woodruff key.
Different way round from my mistaken assessment but solution about the same. Tnx for clarifying this mistake.
Did not come yet to see the offset woorduff key setup as it is. Cannot find my wheel puller :-(
Not sure about which 2°'s your talking about though

Ignition is now in line with RHS cam at 0 mark but I guess ignition can be meshed to whatever the cam position.

Any thoughts on adjusting the cam to 3° advance with a new chain and sprockets so as it stretches over time it goes towards 0° and as it stretches to 3° delayed it would be total 6° of stretch (lifetime in my arbitrary assessment) dwelling closer to 0° over lifetime rather than seting it ideal 0° and as it stretches it travels further away from ideal?
 
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