The 79 20R engine I just put in my 80 pickup runs fine, but the timing reading doesn't make sense. It should show 8 BTDC. Instead it shows something more like 10 ATDC. But if you try to advance it to the correct setting, the engine is up to 2000 rpm before you're even close to TDC. I've never had the crankshaft pulley off the crankshaft on one of these engines, but from pictures it looks as if the two are keyed together with a removable key. If so, somebody may have installed it without the key and allowed it to slip out of position. Is the key removable?

 

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