There is a procedure in the service manual for this. You put a dial indicator on one of the valves (#1 intake, I think) and at a certain valve lift (i.e., 3.42mm) the crank indicator should indicate a certain degree (i.e., 12 degrees ATDC). The number of degrees this is off indicates the amount of stretch. 3-4 degrees past spec is about the point where you want to replace the chain. If it gets more, like 5-10 degrees, the pistons will hit the valves and cause some SERIOUS damage. They generally go 200-300kmi though. On my 1987 it's at 4 degrees stretch at 230kmi, so I'll be replacing mine soon.<br>
You can also do this without the dial indicator by lining up the 'TDC' marks on the camshaft and #1 cam bearing cap. This is less accurate, but is usually within about a 1/2 degree, close enough to give you an idea. You just need to pull the valve cover and be able to turn the crank by hand s-l-o-w-l-y so you don't overshoot. Oh, it helps if your TDC indicator is set accurately, hopefully it hasn't been monkeyed with. (Mine was, and when I fixed it, it was off by 1 degree [max adjustment range was 3 degrees total]).<br>
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