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'66 Sprint GT, '67 Duetto, '70 BMW 2800CS
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I have been told that the top chain is possible to replace without taking off the cylinder head however the bottom one does require the head being removed.
You have been told the truth!

As alfar7 says, you can install a new upper chain without removing the head. I use a length of coat hanger wire, with a hook formed at one end, to fish the chain around the intermediate sprocket.

However, to replace the lower chain you'll need to remove more than the head. The front cover needs to come off, and to do that, both the head and oil pan need to come off. A lot of work if the engine is still installed in the car.

Why do you feel the chains need to be replaced? Usually this gets done as part of an engine rebuild.
 

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'66 Sprint GT, '67 Duetto, '70 BMW 2800CS
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Also the engine seems to shake on idle. Both carbs and ignition timing have been checked and it was suggested buy mechanic to replace the chain and he believes that might be the cause
I haven't seen/heard/felt your engine shake on idle, but I'm skeptical that a loose chain would produce that symptom.

Agree with the above posts recommending that you tighten the upper chain before replacing it. Also second Gubi's advice to not do it with the engine running.
 

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'66 Sprint GT, '67 Duetto, '70 BMW 2800CS
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13,203 Posts
I have never heard of all these new procedures. Ya learn something new every day. I was just going by the Haynes Alfetta manual of yesteryear.
Not sure it's old versus new. More risky versus safe. Loosening the nut, running the engine, tightening the nut would probably work 49 times out of 50. But if the engine backfired during starting, you might get the cam timing far enough off to result in valve-piston contact.

The lower speeds & forces involved in Gubi's procedure just make it a lot safer. Sure, it will take another 10 minutes to remove & replace the cam cover, but while you're in there you can assess the condition of the chain, and use a screwdriver to add some force to the spring behind the tensioner.

My own procedure: with the cam cover off, use a cam turning tool to turn the exhaust cam fully CW (as viewed from the rear) taking up any slack on the exhaust side. Then use the tool to turn the intake cam CW, taking up any slack between the cams. Then loosen that nut, pry out the tensioner, retighten the nut. Replace the cam cover.
 
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