I just traded a laptop for a 95 Cutlass Supreme SL w/ a 3.1 engine 163K miles. Owner noticed knocking so parked it since Dec of 07.

At idle, knock is faint, anything over 1000K-1500K the knock becomes very audible at any temp, louder and louder thru the RPM range. I have NOT had the car over 3kRPM in fear of severely damaging the engine. Org owner tried adding oil + STP with no luck before parking (duh).

Here is my WIP on the repair on the issue. Please comment or add suggestions.

There can be numerous issues such as rod bearings, crankshaft degradation, bent pushrods, broken valve spring(s), piston slap, oil starvation (oil pump or clogged journals), and/or just simply a worn engine with multiple damages.



Testing methods:
Remove one spark plug at a time and see if the noise changes per cylinder, if it does, then it is rod/piston slap from lack of force on the piston crown
Check for noise under and top of car to see if top or bottom end

Remove oil pan and check rod bearings (50ft l/b + 1/4 turn) for reassembly
Remove valve cover and move rockers to see if loose, visually inspect
Check pushrods by rolling on table to check straightness also length NOTE which is EXHAUST and INTAKE as these rods are different sizes, do NOT drop down into engine.
Compression test cylinders for valve bypass


Order of testing:
Find source of noise (top or bottom) removal of oil cap MAY help in diagnosis
Remove valve cover and inspect valves for free play
Drain oil and drop oil pan, check rod bearings (furthest from front worn, bad oil pump/low pres. Nearest or random, gunk plugging oil journals)
Remove lifters, bag & tag, remove pushrods and check for deformations
Oil pan back on + new gasket or RTV DO NOT SNAP BOLTS!
Fill with oil + 1 qt lucas + filter
If no fault found, do a compression test to check for stuck/burnt valves or piston blowby


Order of solution:
Bad pushrods = new pushrods
Broken spring(s) = new spring(s)
Bad rod bearing = replace engine
Fail compression test = replace engine


Website says that the engine is prone to stretch rods and spin bearings, fun.


Parts to fix engine: +/-$200 + tools that I do not have ($200-$400) IF repair even solves problem

Cost of used engine : $200 (+/-$200 labor)
Used engine: most are over 100K, fear same issue later


:EDIT:
Noise is the same as posted video just NOT as bad at idle
http://www.youtube.com/watch?v=KfhbtQQ_LRI
Just like this Dodge..
http://www.youtube.com/watch?v=q6VMHqbHmcs

 

I think I would move compression test up to second in the order of testing list. Pulling the plugs may help your diagnosis also.
My opinion has always been to do the easiest tests first, to help rule out some problems. The more you can narrow it down, the cheaper it becomes.

My '95 Cutlass was still running great when I traded it in at 188K. The 3.1 is a good engine overall. I hope it's a simple fix for you. Keep us informed.

 

I have traced the knocking down to metal specs in the oil and a rod or rod bearing going. The previous owners put 4 new tires on and when I got the car, the front 2 are almost bald and the rear looks new. The brake line was also ruptured so I can only imagine that someone was hard on it. I talked to numerous mechanics and motor operation near the rev limiter easily stretches OEM rods. One dealer mechanic had a kid go through 3 sets before they threatened to invalidate his warranty.

I'm starting to think forged rods and lighter pistons to combat this and it doesn't make much sense that GM opted for pure aluminum rod and main bearings as new technology has been out for some time on imports. Bi metal with silicone or other coating makes more sense to me as I have not had issues on any of my 200K+ import motors (that were never rebuilt).

I am only speaking of such blasphemy as my first car was a oldsmobile cutlass 1991 with wicked body lean and handling (Gm 3200) AND the rear brake line ruptured in the SAME spot as this Olds. Mother's GMC Jimmy threw a rod out the engine and had 2 transmissions put in by 200K along with horrible steering issues such as needing to replace ends every 50-60K. I also had a Jeep Cherokee w/ a inline 6, 160K miles. Motor ran great but shortly after buying a solenoid in the transmission went so it ran for 300 miles with no OD THEN the wiring harness went bad or ECU and the jeep backfired and cut out badly. I also had a Ford Taurus, trans slipped, motor had to be replaced at 100K, and the rear calipers locked up.

I have had a 90 Toyota Corolla that I got for $500. The strut was so worn the wheel slapped around, fixed for $100. The car had so much rust that the trunk and rear bumper was trashed. 230K miles and the previous owner didnt change the oil. The car ran until 250K miles then I put in a faulty rebuilt CV axle which separated and stripped teeth in the trans, the car ran great. Had a 1986 Honda Civic 4 sp. This car had 280K on stock motor, ran great in exception to worn motor mounts. 1986 Subaru XT 1.8 turbo. The car sat for 3 years and ran great after flushing the fuel system.

I just seem not to have luck with american cars. Everyone talks of this or that faulty part but I believe it is planned obsolescence. It is only too perfect that Gm's 3100 just happened to have a inferior intake gasket that makes most motors fail at around 100k, which if I can remember, a interview I read an american engineer said that any car going over 100K is just plain nuts.


Back on topic. A used motor is going in along with a brake line. I'll keep this car for a year or so until I can buy a low mileage Jetta TDI. 50+ MPG and they go for $5k even at 300k miles. Peak oil? If SHTF, I'll brew up bio diesel.

 

Just in case some one looks at this thread, always start with the easiest. One thing nobody ever mentions is a cracked flex plate. This also gives you a noise that sounds like a knock, Is not so loud at idle and gets louder with increased RPM.