68 Firebird - Has Rattle in Engine when Rev'd - Also oil pressure Drops when...

[justin d]

...warm - Thoughts? I have a 68 Firebird with a 400 in it, and when the car is running idle, the oil pressue sits at a reasonable level somewhere around 50lbs.. But after its ran for about 30 minutes it will drop to around 28lbs or a little less. - It constantly has a little ticking in the engine, but when you rev it up and let go of the throttle it has this smacking noise for a few seconds then goes back to the light ticking. - Any Thoughts of the problem? - I'm guessin a Spun Bearing? - but I wasn't for sure. - Engine is still in the car and hasn't been disassembled.

 

[knowitall]

Sounds to me like a sticking valve. Without hearing it it is hard to say. I would pull the lifters and replace the cam to get some extra miles out of it before a rebuild is required.

Your oil pressure is off the charts considering normal is 20lbs and it is common for them to drop when warn and older. My 80 vett drops to about 7lbs at idle when warn but that is normal.

 

[Crevace s]

oil pump could be going out, not enough oil pumping through causing ticking, lifters could be noisey, theres always going to be a drop in pressure when vehicle warms up but not that much dont think.

 

[robert r]

one of the lifters isnt getting enough oil when it should and is sticking in the thrroat of its bearing in the cyl head, the ticking is the sticking lifter letting go to finish the cycle, get a mechanics long stethoscope to determine which one, you may only have to pull off a valve cover and adjust the lash and clean out the gunk in the cylinder head the oil pressure is normal, in that it takes a few seconds for the liquid to drain from the top thru the various berings and back to the sump, as long as it stays constant, you should be ok. if you need to clean the entire motor of gunk build up, in the next oil change, put k-1 kerosene in there instead of motor oil and flush out the entire system,(only run the k-1 for 30 minutes total) then follow up with fresh oil of the proper strenght, in a separate fluid change there should be a noticeable difference in performance good luck

______________________________

 

[Goatman]

First off the oil pressure is in the OK range for that engine so I would suspect a sticking lifter (which is common in the 60s Pontiac engines).. you may want to consider changing out the cam and lifters and checking for build up and wear in the engine ...
Knowitall ... oil pressure on any smallblock chevy should be above 20 Psi to be considered normal GMs recomendation of 10 Psi for every 1000 RPM only applies above that point ..
at 7 PSI your engine is in SERIOUS need of bearings ... but I would have a mechanical guage installed to check as factory ones are notoriously inaccurate..

Also robert r, NEVER and I mean NEVER run an engine with Kerosene in place of oil it has NO lubricating qualitys and will Wipe out the bearings in seconds
the clean it out with kerosene is a Wives tale that has killed many an engine...