Hey guys.. appreciate any thoughts... I have a 1950 Chevy truck with a small block 350... driving to work today the engine detonated a few times when excellerating.. Engine seems to run fine at idle and at cruising speeds.. however, got to work.. popped the hood to hear some lovely engine knock from the driver side.. Is it time to replace this engine? thoughts?
First post should have been an intro. Anyway, make sure the timing isnt advanced to far but if its knocking at idle there could be a terminal problem.
Yeah, first thing you need to do is check the timing...I've seen the distributor hold down bolts loosen up (or those crappy wire hold down clamps lose their tension) and the distributor rotates a little, throwing off your timing. Check timing, check hold down clamp and bolt. Could also be cheap gas. Did you recently fill up the tank? -Brad
Engines detonate all the time. It's how they make the vroom vroom noises. What you're talking about is PRE-detonation. As mentioned, check the advance on the timing and check the vacuum advance to be sure it moves and isn't stuck in the advanced position. You say you hear a "knock" at idle? Assuming by knock you mean it's louder than a "ping". You could be in trouble. Any idea if it was coming from upper or lower?
If it's knocking at idle.....you may have more problems than detonation....like a rod knocking at the big end......
How can you tell the difference? I don't know what pre-detonation sounds like. does it sound like "dieseling" where it's kinda making noises like it's stalling? I had an old straight six in a ford van that sounded like that when I stepped on it on the highway. It didn't do much faster, but sounded like it was going to stall out.
Ping is a light noise, kind of a metalic fluttering sound. It's caused when the valves are not fully in position when the fire hits, making the rockers and lifters bounce. Probably an over-simple explanation but the only one that ever made sense to me. When it's knocking, it's usually a "bigger" sound and has a beat to it. Dieseling is usually cause by having the idle to high or some other defect that causes the vacuum to stay high enough that it continues to pull fuel into the hot cylinders where it ignites from the heat, causing it to keep running. Your straight six problem sounds like something else entirely. It actually sounds like what my 41 is doing right now. I think it's spark related but have grown so disgusted with it that I parked it, stacked shit around it and took a break. It basically sounds like the firing is "overlapping" I don't know how else to describe it. It runs fine until I stick my foot in it and then it's like someone has swapped wires as I run down the road.
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