engine has been doing this for a while but am not sure if its as serious as i think it is. it has this knock for a very short time after it starts up. can even be heard inside the car. i usualy wont hear it in the morning when it's been sitting all night. only after i leave it about 15 or 20 minutes after driving it. also what makes me believe it's somethin internal is that at startup after an oil change, the sound is louder and lasts longer. i was just under the car and started it up and sounds like it's coming from the rear, where the pump would be. like i said it's been doing this since shortly after i bought it which was about 2 years ago. but once running, the car runs fine. have made 4 dyno runs now without any problems. i also have a slight vibration even with the car not moving,,,around 1200-2000 RPMs and my oil pressure gauge has always been on the low side (when warm reads about 15 at idle). not sure if they have anything to do with the noise. so what can i do here?? i have no idea what my next step should be. dont have the money to overhaul it. all i've been thinking about is selling it, getting decent money for it and getting another thirdgen but this time with lower miles and an original engine.

any input appreciated!! from reading different posts sounds like the start of a rod knock.

 

i'd stick a mechanical gauge in the block and see what i really have plus do a compression test. that ought to tell you a little bit more about the engine. i'd also make sure the tune up is good, i'll bet your vibration is related to a miss.

 

what about the knock? this is what i'm more concerned with. does it sound typical of something major? tune up stuff is good and before i put in the L98 heads the car had even compression. and even if my oil PSI is normal and it's the gauge's fault for readng low, that knock is not going away.

 

sounds major, your oil is thick in the morning but after warming up gets thin)as i'm sure u already know) but a lifter/valve knock can be heard most of the time..

maybe a bearing is spun, was/is there any metal flakes in the oil? only way to know for sure is to have a look at the bearing n rods.

a compression test will help you too

 

First, are you ABSOLUTELY sure the 'knock' isnt something like an exhaust leak or something in the valvetrain like a misadjusted or failing lifter? What does your oil pressure gauge read at high-RPMs? As hydric asked, does your oil feel gritty or does it seem black and tary faster than you'd normally expect?

 

Any history on the engine? Modifications, mileage, what pump, does the used oil come out clean or dirty, etc?

I'd suggest verifying the oil pressure to be sure you have at least 10 PSIG per 1,000 RPM at fulle engine temperature. If that's correct, try a flush with ATF and a clean filter.

What oil and filter are you using?

 

You might want to look at the trans. If you have a 5-spd,
occasionally in the morning when it's cold, the head gear
bearing has been known to make noise. I know of 4 or 5
people who panicked and thought it was the motor. The
combination of a sloppy head gear and worn pilot bushing/
bearing, can sound just like a rod knock in the rear of the
motor.

My L-69 5-spd ( in the cold ) will knock like hell until I drive
for about 10 minutes. I have checked my trans, and the
condition I have mentioned exists on my car. I will be needing
a 5-spd very soon. Check it out, it may be your problem.

Of course this is assuming that you do not have a motor
with a bearing problem.


John B.

More cars than I know what to do with !

 

i'm afraid it sounds a lot like it's internal. definitely not exhaust. also the noise was there long before i put in the new heads. it's louder at startup right after an oil change. my gauge doesn't really go higher than 30 PSI, only in the mornings it will read slightly higher. on the highway it's about 30 and at idle about 15 warm. but my gauge has gone down to almost the red mark with no signs of trouble. likely a bad sender although i did replace it. whenever i change the oil at about 2500 miles, its already dark. but it doesnt feel gritty. i can only hear it for a very short time after the starter has finished cranking and the engine starts to run.

i have no history on the engine unfortunately. all i know is that there is a "remanufactured" tag with a number on the block. odometer reads 150k right now. bought it with about 112k. i've always used Valvoline 10w30 with AC delco filter. first the PF25 now the 454.

the car is automatic

i've never checked the oil pressure so i'm gonna try and do that. the car has always had a lil bit of a rough idle. but the inside is clean, pistons were clean, no sludge noticeable when i had the intake and heads out.

and all mods are in my sig.

thanks

 

Find somebody with a leakdown gauge and test the engine, If all is well, Pull the oil pan off the car. check for anything obvious. then get a torque wrench and 1 by 1 remove, check , replace and re-torque your main and rod bearings. make sure that all caps are reinstalled the same way as they came off. You may have to rotatee the crank by hand to get to all the rod nuts and caps.
If bearings look good, that's a major relief because then you really know the condition off the bottom end. Also while your down there pull the oil pump and have the pick tube welded on if
it isn't already.
Alot of work, but it can save you alot of money by diagnosing and fixing the problem before the engine gets trashed.