Gawain

Greetings Everyone, So this mystery needs a bit of context so that someone of the many clever and knowledgeable individuals who read this can deduce the correct answer....as I cannot. So, the 324 engine was completely rebuilt by last owner, including new pistons, cam, cam bearings, timing chain/gears, oil pump, just everything. I buy the car online. I drive it home, 1500 miles, from point of delivery. Car now has 7,000 miles on rebuilt engine, including drive home. Once home, engine has developed a bad miss ( two cylinders are not firing..deduced by pulling plug wires while engine running, lots of jumping spark). And, on the way home, engine spark knocked a lot....I did not realize this at first ( hearing less the best), but my wife told me.....after about 800 miles....then began putting premium in tank...spark knock goes away, but engine miss persists, gets worse. And, now ( but not when I picked car up; oh yes ,and car did not miss when picked up) a "knock" can be heard when engine idles and is hot..... no knock when cold.... And no knock when engine rev'd a bit. So, as it sounded like it might be coming from the fuel pump and as previous owner had put on electric fuel pump ( which I do not want, noisy and not needed) , I replaced the fuel pump, but sitll noise. So despair sets in... I feel confidant it is not in the bearings ( 60 lbs of oil pressure is constant on road, even after 11 hours of driving, 20 lbs at hot idle) and it just does not sound like a crank related noise...

So, I put yet another new fuel pump....just in case, got the vacuum line correct on this one ( was not on first go) and engine runs a bit better but still knock when hot, but not quite as bad....and then, I thought "I will just remove this oil filler cap to see if I can hear something down that oil filler tube.... and when I take the cap off, the noise diminishes dramatically...but is still there... voila, the filler tube is acting like a mega phone, amplifying and making the noise sound "worse" that it is.... because, I just put the palm of my hand over the filler tube, pressed down to seal, and....can you believe it, no noise, as is none, as in the engine sounds like a sewing machine..... So there is the mystery....anyone have a Shylockian moment?

Thanks , Gawain

DFitz

Crank Case breather blocked? Either at the top or at the bottom vent?


I'm presuming you've checked the timing and all the valves are working? You can pull the valve covers and coil lead. Crank the engine and verify all the valves are moving. Also, presume you've checked the condenser and points?


A long shot, but make sure the distributor is not loose and turning.


What have you done for a fuel filter? The stock fuel pumps have a paper filter in the glass bowl that you can't get anymore. Has the tank been cleaned or drained to check for rust/dirt?


Need more info. Tough to diagnose. How experienced are you working on this vintage cars?

oldcutlass

I would first figure out the engine miss issue and make sure all the cylinders are firing. Check dwell/timing and do an oil/filter change.

Tedd Thompson

Hard to tell without hearing the sound and not knowing what all was done on the rebuild.... But was it broken in with a zinc rich oil? There is a chance the cam is flat on a couple cylinders. If mine I would do a compression check or as mentioned above pull the valve covers off and see if a couple of valves aren't moving as high as the rest If original pistons were used ( I know you said complete rebuild) there is a chance you are hearing wrist pin knock. Sometimes wrist pins will knock at idle and go away at higher RPM's above that.

I can't see how covering up the oil filler tube would mechanically change anything other than just hiding some of the noise. The system is vented at the other end at the down draft tube so no pressure has been changed or anything like that. Did you cut open up the oil filter and see if there was any metal flakes in the filter material? That would tell you if the cam material left anything harmful for the bearings to be concerned about. Other than that I'm at a loss... Let us know if you find the answer.... Tedd

Ozzie

I agree with a lot that's already been said; correct the misfire(s); do a proper compression check; try using a mechanic's stethoscope; and if possible, post an audio of the sound.

Travlr

[QUOTE=Gawain; I just put the palm of my hand over the filler tube, pressed down to seal, and....can you believe it, no noise, as is none, as in the engine sounds like a sewing machine.....

So you are saying that both the noise... and the miss... disappeared?