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Old 11-30-2002, 05:19 PM
Regular User
Join Date: Nov 2002
Location: Flyover State
Posts: 1,364
Question Cam Timing

I recently had the timing chain replaced in my '76 300D. The engine has 280,000 miles on it. First of all, was it worn? When my mechanic pushed back on the tensioner, there was enough slack in the chain to skip a tooth. My other mechanic was not very concerned by that fact. So whatever, the new chain is in it now and I guess that's not a bad thing. However here is the problem. Since then, the car has run differently. It doesn't sound the same at 65-75 mph and doesn't run as smoothly. It used to find it's groove there. There was a tapping noise which turned out to be a tight valve. But the valves were adjusted 1,000 miles ago. The mechanic said the cam was worn and the valves would get tight. Also, the cam timing was 2 degrees advanced. I had my other mechanic adjust the pump timing which was at 22 degrees BTDC and now is at 24. He said the Cam timing should be right on the mark or a little bit retarded.
So, could the cam timing cause it to run just a little bit off? I'm sure it would, I don't know why my other mechanic doesn't seem too concerned about it.
Also, he recommends replacing the cam and rockers. I don't know why that valve got tight so quickly but should I pull the heads and have a valve job done or will the new cam be enough? If the bearing edges are worn, he said the valves will get tight very quickly that way as well.
What are your thoughts.
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Old 11-30-2002, 05:45 PM
Registered User
Join Date: Jan 2001
Location: Los Angeles CA
Posts: 140
"He said the Cam timing should be right on the mark or a little bit retarded. "

Right on the mark, yes. A little bit retarded, NO. Where did this fellow learn auto machanics? This may well be the reason the car is exhbiting a performance loss, i.e. the cam timing is off. Also, valves getting tight with a worn cam does not sound entirely correct either. If anything the valves would be likely get looser.

I would make that the last visit to that mechanic.
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Old 11-30-2002, 06:47 PM
Regular User
Join Date: Nov 2002
Location: Flyover State
Posts: 1,364
Harry, I agree it sounds counterintuitive. Indeed, why should the clearance of the valves change at all?
These mechanics seem to know these cars like the back of their hands. One of them was working on these 115's back when they came rolling off the assembly line.
So I think I'll start at least with an offset keyway on a new cam sprocket.
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