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Got a mystery sputtering/knocking sound from the Thunderbird, specifically that exhaust leak like tappy sound. It happens once a cycle so it's gotta be one cylinder. I thought it was an exhaust leak, wasn't. I thought it was valve lash. Wasn't. All rockers were tighter than reccomended spec.
Doesn't sound like rod knock to me. It does scale with RPM though, but it's clearly one cylinder and too consistent for piston slap. Does anyone have any ideas what this is? My only remaining guess is a failed exhaust valve seat but I'm just out of ideas.
Steve, the 302 in my '79 truck had the same sound. I ruled out everything obvious and simple. It came down to carefully listening to the dual exhaust and pinpointing it to one side of the block. I pulled the head and found that the head gasket had a break between two cylinders. The two cylinders were fighting each other during their strokes and the noise was the result.
I still haven't fully re-assembled the engine. As long as I had it apart I did the rings, bearings, new Lunati camshaft, etc.
I should have just turned the radio up and drove a six-cylinder 302.
Tom
Steve, the 302 in my '79 truck had the same sound. I ruled out everything obvious and simple. It came down to carefully listening to the dual exhaust and pinpointing it to one side of the block. I pulled the head and found that the head gasket had a break between two cylinders. The two cylinders were fighting each other during their strokes and the noise was the result.
I still haven't fully re-assembled the engine. As long as I had it apart I did the rings, bearings, new Lunati camshaft, etc.
I should have just turned the radio up and drove a six-cylinder 302.
Tom
<edit - a picture is worth 82 words>
Yeah i'm afraid it's something like that. Hopefully it's just a gasket and the head doesnt need a machine shop trip.
I suppose a compression check would illustrate something like that, surely.
Yes, I forgot to mention that. My 302's compression was 65 and 85 on those offending cylinders. I was surprised it was that high to be honest since there was a Suez canal sized path between the two.
Compression test was about 80psi on 2 and 4, head's gotta come off for sure.
Can't be a valve guide because it's two cylinders, head gasket seems the most likely culprit. If it's rings i'll be livid, i've got enough motors to tear apart already.
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