1972GS

Fan clutch is also new.

Block's cylinder head planes are not machined.

Frequency has no relation to engine speed.

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.

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.

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

I wanted to post this follow-up since I started the whole thread. Finally I had my 72 GS seats with custom covers replaced by standard covers. Because there isn't company who makes them (as custom covers), a very skilled upholster made the new seats just by looking the reference pictures (the same at the beginning of this thread). I'm very happy. Below are pictures before and after. Cheers, Markku

Hi, Is there any vendor that sells so called standard seat covers for 1971...73 Riv? I know OPGI sells custom seat covers but the do not have standard. Below are two reference pics of standard seats. BR, Markku