1972GS Posted December 28, 2023 Share Posted December 28, 2023 (edited) Hi thrusted community, Case: Buick Riviera GS 1972 ie. 455 stage 1 I need your expertise What might be the cause of the knocking sound that you can hear on the video? Symptoms: - comes only when engine is really hot and running idle. Never even during during highway driving - but appears when slowed down and stopped to traffic lights. - Same time upper radiator hose occasionally sucks flat but after few seconds expands to normal - might or might not be related: When engine is warm (never when cold) reading on vacuum gauge unevenly jumps a little bit down. Like it is missing spark some times. I have replace thermostat two times and checked it in a pot on a stove. Opens at right temp. Water pump is new. All valve rockers are in tact. I'm suspecting sticking valve guides and planning to do head job. Any ideas? Thanks in advance! - Markku PS. below only pic, video link embedded to text above Edited December 29, 2023 by 1972GS Added WORKING video link into text (see edit history) Link to comment Share on other sites More sharing options...
60FlatTop Posted December 28, 2023 Share Posted December 28, 2023 Something looks fishy about that vacuum advance hose and the fitting near the temperature sensor. Got a closer shot? Most of my experience is with Nailheads, but looking at the window in the distributor cap makes me have all kinds of bad thought about adjusting the points while it is running. I would double check the advance hoses and watch the timing from cold to hot. Link to comment Share on other sites More sharing options...
1972GS Posted December 29, 2023 Author Share Posted December 29, 2023 16 hours ago, 60FlatTop said: Something looks fishy about that vacuum advance hose and the fitting near the temperature sensor. Got a closer shot? Most of my experience is with Nailheads, but looking at the window in the distributor cap makes me have all kinds of bad thought about adjusting the points while it is running. I would double check the advance hoses and watch the timing from cold to hot. Thanks for your thoughts! On the video & pic the vacuum hose fitting has one open nipple, which is normally connected to air cleaner snorkel valve sensor. Since air cleaner is removed nipple is open but it makes no difference to knocking sound if it is plugged or not. Distributor has been converted to Pertronix ignition. Timing has been checked. I corrected the video link. In video you hear irregular sound that i call "knocking". It is mechanical sound. In the video it might sound like some wire is loose and hits somewhere but that is not the case. To me it sounds like thermostat spring bangs but I have changed thermostat twice. Link to comment Share on other sites More sharing options...
EmTee Posted December 29, 2023 Share Posted December 29, 2023 Step 1 would be to buy a mechanical oil pressure gauge and attach it temporarily in place of the electrical oil pressure switch (near the oil filter). You need to see what the actual hot oil pressure is at idle. I'm going to guess it's very low (~5 psi?). If so, it may indicate a worn oil pump or worn main and/or rod bearings. How many miles on the engine? Are there any bad oil leaks (i.e. under pressure) in the vicinity of the oil filter or oil pump? Best case scenario would be a bad or leaky oil filter, next would be a worn oil pump. The pump is mounted externally, so that would not be a difficult fix. My guess is the pump is bad and combined with worn bearings pressure is low at idle when hot. One last thing to check is make sure the fuel pump is not leaking gasoline into the crankcase. Sometimes a failed diaphragm can allow gasoline to enter the crankcase. Pull the dipstick and check the oil level. If the level is over full and the oil smells like gasoline, replace the fuel pump and change the engine oil & filter before running the engine any more. Link to comment Share on other sites More sharing options...
George Buick Riviera Posted December 29, 2023 Share Posted December 29, 2023 (edited) On 12/28/2023 at 4:11 PM, 1972GS said: - Same time upper radiator hose occasionally sucks flat but after few seconds expands to normal My friend had such situation in the upper radiator hose in his car: And the problem was in the radiator cap ..... Your engine bay looks very clean, so I don't think your radiator cap will be in that bad condition, but maybe try to replace it with the other cap, just for a test ? Edited December 29, 2023 by George Buick Riviera typo (see edit history) Link to comment Share on other sites More sharing options...
1972GS Posted December 31, 2023 Author Share Posted December 31, 2023 Thank you for your great tips, I have not yet connected extrrnal oil gauge but I do not think the sound is caused by low oil pressure, since the sound is so irregular. But you never know... No oil leaks anywhere. Oli level is fine as the oil. The radiator is new 4 row model and cooling system flushed. Radiator cap is new and works, since expansion tank fills after drive and and declines after cooling down. Link to comment Share on other sites More sharing options...
NTX5467 Posted December 31, 2023 Share Posted December 31, 2023 ( "Mechanical" sound is "irregular"? Variable happening frequency at same engine speed? ) Heat riser valve, if equipped? Link to comment Share on other sites More sharing options...
arnulfo de l.a. Posted January 1 Share Posted January 1 If the block was machined to address poor quench ( poor quench causes detonation issues) which 430 and 455 engines are known for and too much was taken off the deck, then when it warms up and everything expands the piston kisses the head. If thats the case its a relatively easy fix. A thicker head gasket. Good luck. Link to comment Share on other sites More sharing options...
edinmass Posted January 1 Share Posted January 1 Strange noise. Possible timing chain slap on the cover? I think I would pull all the belts off, run a large fan in front of the radiator and see if there is any change to the noise. At least that will give a definitive answer to internal or external. 1 Link to comment Share on other sites More sharing options...
1972GS Posted January 1 Author Share Posted January 1 Just now, NTX5467 said: ( "Mechanical" sound is "irregular"? Variable happening frequency at same engine speed? ) Heat riser valve, if equipped? Frequency has no relation to engine speed. 1 Link to comment Share on other sites More sharing options...
1972GS Posted January 1 Author Share Posted January 1 Just now, arnulfo de l.a. said: If the block was machined to address poor quench ( poor quench causes detonation issues) which 430 and 455 engines are known for and too much was taken off the deck, then when it warms up and everything expands the piston kisses the head. If thats the case its a relatively easy fix. A thicker head gasket. Good luck. Block's cylinder head planes are not machined. Link to comment Share on other sites More sharing options...
NTX5467 Posted January 1 Share Posted January 1 How new is the fan clutch? Link to comment Share on other sites More sharing options...
1972GS Posted January 1 Author Share Posted January 1 Just now, NTX5467 said: How new is the fan clutch? Fan clutch is also new. 1 Link to comment Share on other sites More sharing options...
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