Hey everyone,
Tell me what you think. The car is a 91 RS with a 305TBI & 156,XXX miles. I usually drive the car pretty hard. However, this morning I was just crusing around. I was running really low on gas, looking for a gas station. While stopped at a red light, the car died on me. I had a really hard time starting it up again. Once I got it started back up the engine was making a loud metal to metal knocking sound. A couple blocks later I found a gas station and filled her up. However the sound hasnt gone away. At idle, you can hear the sound but its not very loud. As RPM's increase, the sound gets faster & louder. The car has no ***** at all. What did I break? Time for a new motor?

 

Test the compression on each cylinder. Pull all of the spark plugs first. Crank each one over for five or six seconds. They should measure about 160 psi.

 

Pull the valve covers, see if a rocker came off.

 

i wouldnt expect to see 160psi out of a worn L03 i am betting low 100s 110-120 psi

 

valve train problem is your best case. take them valve covers off and see.

 

Probly valvetrain related, but dont push it. If it is a rod you can throw it quick. Have seen some throw them in a matter of seconds at 2k, on the other hand i got pissed when mine started knocking and just stomped it. It got to 6800 when i shifted and stayed togeather. Also survived the 30 min ride home.

 

Does it sound kind of like a dull bell going off in your engine as it runs? Not the little ones mind you, like a big church bell but muffled?

My 350 did that in my Camaro....I spun a bearing...two of them actually. If you can get it home, take the valve covers off and see if you tossed a rocker. If that's good, then you'll have to dig down and probably take the heads off and see if you have any other damage. If you don't see any, put it together and start it up. If it still does it, it's probably in the bottom end which is going to have to come apart...which means you'll probably need to rebuild it.

 

have you checked your oil lately?

 

Oil level is good. I replaced it about 2k miles ago. I will be taking the valve covers off tonight to see what I can see. Will keep you posted. Now heres the real question... What do I replace it with?

I can get another used L03 for about $400 at a local salvage yard.
-or-
I can get a TPI motor for a little more
-or-
I can get an LT1 motor for a little more than that.

 

The LT1 is going to need more than just to be dropped in. But...with the right effort, it would be a great motor for you. It depends on how much time/money you have or are willing to put into it. And what you want.

 

A cracked flexplate will knock to beat the band at crankshaft speed and have your timing so retarded it will hardly run. <$60 to fix.

Can you determine if it is coming from under the car or on top?

Does it appear to be crankshaft speed or 1/2 crankshaft speed? The valve train runs at 50% of crankshaft speed so that should help you decide if it's valve train or crankshaft related.

Does it appear to have a misfire or weak cylinder?

 

You can determin if it is in the botom end by pulling one sparkplug wire at a time. Dont do it wile it is running kill it then pull the wire then crank. If it is in one of the rods the pitch of the knock will change. If you do all 8 and the sound dosent change then it is not your botom end.

Dont buy another motor till you find out what is wrong with the one you have.

 

Knew a guy that replaced a motor and had the new one knock just like the old. D'oh! Knock was not in the motor...

 

I agree, wait until you find out what's wrong unless you have a hankering for a different engine.

 

Now the engine seems frozen. I had it idling yesterday while trying to find out where the knock was coming from. And the engine died again. This time though I cant get it started. The starter sounds likes its got the power, but the engine wont turn. Heres the new plan...

-Remove starter & inspect flywheel
-Remove valve covers to see if any of the rockers are screwed up
-Remove all spark plugs.

I will try to turn the engine over by hand after each step. If the engine still wont turn over after removing the items below, what should my next course of action be? Is it possible the clutch/trans is causing my problems? Any way to check without removing the gear box?

 

IF the motor tied up it's probably in the bottom end. You can check the clutch and Gearbox by having someone push it while you hold the clutch in and have it in gear. IF you have the clutch depressed and still in gear and you can't move it then it's the clutch or gearbox. Did it make a funny noise when it died last. Sound kind of like a klunk. Or shutter. Check the oil and look on the dipstick for metal shavings in the oil or pull the oil filter and cut it up and look for shavings there too. If you see a lot of shavings it's probably the bottom end.
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How much oil pressure did you have before and after it started making noise? After it started making noise did the oil pressure jump around a lot?

 

You can also kill an individual cylinder by putting a 1"-1.5" long piece of vacuum hose (1/4" should work well) between the plug wire and the terminal on the cap, they can easily be shorted with a test light to ground. That's the suggested way of testing a DIS ignition sys and it is easier than reaching around exhaust. After a cylinder is shorted give it a few seconds for the cylinder to clear for most accurate results.

FWIW make sure an accessory didn't sieze.

 

It sounds like he siezed up the motor finally. From his description I was betting on a spun bearing but...who knows until you take it apart to look.

 

Sounds like it, if spun then stacked it tends to put the brakes on pretty hard.

 

Off topic a little but my uncle got a 90 IROC 5.7 TPI for 1200 bucks in 95. Beautiful car inside and out, I think immacualte is the word. Owner thought it was knocking, which there was a loud erratic peck, but to a trained ear you could tell it wasn't a rod. Anyway the owner just had chip upgraded and a shift kit and stall converter add. Turned out the knock was a tourqe converter bolt that had backed off and was bouncing around inside the bellhousing. This thread just reminded me of that fact.

 

Well I kept trying to start it over & over and eventually, the engine turned over & started up. However, in addition to the knocking sound I had before, it sounds like there is something floping around inside the engine now. I drained the oil & didnt see any metal shavings. I took the valve covers off & had someone crank over the engine while I watched the rockers. The rockers seem to be moving correctly. I didnt remove the intake manifold. Any other checks I can do before spending alot of $$$ on a new engine?

Oh, I also was able to push the car while in gear with the clutch depressed, so that rules out trans problems.

 

Did you try to shake the rockers when you had the valve covers off. Just cause the move doesn't mean their not loose. What about the oil pressure? Last thing to try and help diagnose where the noise is coming from, take a really long screw driver or a whole bunch of extensions and with the motor running put one end on various parts of the engine and your ear on the other end. If the knock is bad enough you'll hear it pretty much every where but it'll get louder when you find the cylinder or whatever is the problem. I'm pretty sure the small block harmonic balancer is a better design than the 3.3l that gm used in the 90's but i have seen a few of them that the balancer started coming apart and it sounded like a severe knock until you would get on the gas. The easiest way to check that is to grab the pulley on the alternator and try to turn it if all the pulleys move a little but the center of the crank pulley doesn't then it could be that. I don't think that would cause the motor not to turn over though. Just a thought.

 

how was oil pressure?? it kinda sounds like a spun bearing.. its only a matter of time before you seize up the motor.. did the noise go away when you rev it??


EDIT: one more thing, my avatar pic is the result of the motor seizing at 6300rpm.. threw 2 rods, bent 4 valves, 4 pushrods, burned up all my bearings, pistons got seized to the rods, twisted the crank, you get the idea.. but i highly doubt your motor will be capable of that.. check all the rockers again, if that checks out, then i say time to rebuild.. or go bigger

 

I tried to move the rockers around with my hand last night. A couple of the were a LITTLE loose. Nowhere near where they would have to be cause all of my problems. As far as oil pressure. I didnt really notice where it was at before the problems started... But the guage looks good now. (Who knows how accurate it is)

Its sounding more & more like its time for a new engine. I have almost decided on a LT1. However, theres still a small chance that I will just drop in another L03. My biggest problem right now is having a place to do the work. I dont have a garage. I know if I borrow a friends garage, I can drop in another L03 in a weekend. A LT1 is a different story.

 

If your gonna drop another lo3 in it, i have an idea for you. If you havn't purchased it already find an lo5 350 tbi from a full size chevy or gmc truck or a caprice. and put that in there. you can steel the chip from said vehicle or the whole computer and you won't have a bit of a problem. The main thing to remember is to use your serpentine belt assembly.

 

The L03 harness will work with the L05? Will my stock fuel pump be able to handle the increased fuel demands?

 

The lo3 harness, computer, and fuel pump will meet the demands for the lo5. You can run the 350 on the 305 chip but for maximized performance run an lo5 chip or you can call someone like hypertech for a performance chip for the lo5. Good luck.

 

My firebird one night started making loud grinding noise. Sound like the engine would rip in half. Then locked up solid. The starter had gone. Be sure to check everything.

 

the day after i brought my car home with the new motor i had a bad knock and turned out to be the same thing as stated above. i also broke a few pushrods and rockers kept comming loose then found that there was a grove in that rockerstud and allowed the rocker move side to side i eventually pulled the heads and had screw in studs and guide plates installed. like everyone says check everything. look at the oil psi also try a mech oil psi gauge for a little more acurite reading