1985 chevy blazer 2.8 automatic carb.

Since I got this car it's had a constant knocking sound from the front of the engine. I put 20/50 oil in the engine at the last oil change and now the knocking is randomly intermittent. Doesn't matter if it's cold/hot; sometimes it knocks and sometimes it doesn't. Occasionally I can hear it get louder the higher the RPMs go. I just want to know exactly what is wrong or making that knock so I can fix it.

 

Im having a similar issue with my Blazer but the knocking only happens when the engine has warmed up. I hear it at Idle and just before the engine shifts but only between the 1st 2 gears. Someone told me to add 20/50 motor oil in due to it being a higher mileage engine. Prior to changing the oil, was your Blazer ticking all the time? was it Rhythmic? Possibly louder just before shifting? Any idea which part of the engine your knock sounds like its coming from?

 

sometimes a cracked flexplate can sound like a engine knock. had a few vehicles do that.

 

Before I added 20/50 oil, the noise was always there. It was and still is louder before shifting. The noise is coming from the front of the engine by the timing chain cover.