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Paco 08-17-2002 03:39 PM

Engine Knock at low RPM
 
just purchased a '69 Riviera with 32K original miles, has a 430 V8, everything about the car looks almost brand new. Drove it about 150 miles back home and noticed at idle,low rpm, the oil light comes on and the engine has a "knock" like a main bearing knocking. It goes away with the slightest of rpm increase and the oil light also goes off. The previous owner, an extremely meticulous person, rebuilt the oil pump(but put it back to factory specs) and runs 50wt oil in the engine. The car runs and drives as good as the day it was brand new. Is it possible that the oil pump could be upgraded to a high volume version to increase the oil pressure at low rpm and maybe make this knock disappear as well as the oil light problem??? It's hard for me to believe that it has main bearing problems when the engine is in as good shape other wise as it appears to be. I followed my dad for the entire 150 mile trip while he drove the car, not a sign of tale-tell smoke other than a little black carbon when he would stand on it to pass someone. No oil smoke...period. Anyone with any experience with one of these early 430-4V Buicks please respond..give me hint what I need to do to cure the problem...PACO

4 Jaw Chuck 08-17-2002 04:57 PM

Could be worn rod bearings, the presentation is typical.

HotRodMan 08-17-2002 05:40 PM

I had this exact same problem with a 1973 Javalin. I changed the oil and filter. I used 4 quarts of 10w-40 regular motor oil, and two containers of STP (total 5 quarts) and the problem cleared right up. I drove the car for years like this and everything worked fine. I finally tore the motor down for a rebuild and found the main and rod bearings were worn. I'll bet you have the same problem.

KULTULZ 08-17-2002 11:17 PM

[*] First, you want to put a reliable mechanical oil pressure on the engine and check the pressure cold and hot.

If the owner rebuilt the pump (kinda hard to figure out with the cheap replacement cost) and still had to use 50W motor oil, it tells you something.

I would drop the pan and remove a few crank/rod inserts and check the condition (plasti-gauge if possible). Inserts can be installed in-frame.

A high volume pump may mask the symptoms for awhile.

Harlequin 08-18-2002 09:30 AM

Could it be somthing as simple as when the car drops off to idle to oil pump cant pump that 50w oil up into the heads and the lifters could be tapping?.....Just a thought

SJFast 08-18-2002 11:59 AM

Don't look for a high-volume pump to increase your oil pressure....only the volume passing through the bearings. Put some main bearings in it.

Paco 08-18-2002 06:27 PM

thanks for all of the ideas, although deep down I kinda figured it needs mains in it....figure on putting rods, mains, cam bearings, freeze plugs, at least in it while I have it out, may even do a complete ring job and valve job while it's this far down. Should be able to do it all for less than a grand, and I'll know what I got for sure then. Hard to believe it needs those bearings as clean and low milage as it is...and runs like a brand new engine.

MHenricks 08-19-2002 06:42 AM

I'd be concerned with the oil pump rebuild and why is it using 50wt oil. I'd check with a mechanical gauge before doing anything. Is the mileage 32K or 132K with good care, than I'd suspect bearings.

78 monte 08-19-2002 06:12 PM

I dought it but I had the pick up fall out of the pump on a 350 once brand new motor w/ 20psi and a clanking sound.
Did the car sit a while befor you bought it????I had a friend who bought a caddy w/ a brand new 425 car sat,carb leaked into the oil.He bought it fired it reved it like a prostock and drove it home w/ gas in the oil. That car died within weeks.
Your best bet would be to pull the pan.A pickup prob would be there.If that ain't it plastigauge the bearings.More than likely the 50wt oil and pump rebuild tell me he pawned it off.
Good Luck


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