Questions and Answers
Chevy Cavalier Heavy Engine Work
Q. I have been having motor problems. I had a motor replaced due to bearing damage. I got another motor put in my car and it ran great for the first few days the developed a loud knock. so my question is about the bearings, rod, and crank. I don't think I will need to replace the motor this time if I can help it. I need to know what to look for.
I have done only one job replacing bearings on a 350 many years ago and it was successful. My car is a 1986 Chevy Cavalier and has a 2.0 liter, 4 cylinder, throttle body, OHV motor, automatic transmission, power steering, regular brakes, and the exact milage is unknown but the mechanic said about 100,000 miles on the motor. It has a distributor and not the coil packs, oil pump in the oil pan and not by the timing chain. It is the motor with the taller valve cover pan that has the oil cap on it. I was told that my style motor was used in the later of 1985 and the earlier of 1986.
I am looking to replace the bearings and understand that there is not much you can do without seeing the problem, but can you give me a good "what may be" and possible fix? My diagnoses is the knock, which is not as loud now since the car has been sitting, but a definite knock. It started knocking loudly on the way home one day. The amount of driving time from the time it started knocking to the time I got home was 10 to 15 minutes. I drove at an average of 30 mph and some times slower ( 20 to 25 mph). I did drive 45 mph at one point down hill for about a minute.
I have not moved the car since, but I have started the motor to diagnose the noise. My motor never overheated during this ordeal. The oil pressure light never came on. I know that I will need to use a micrometer most likely on the bad rod journal of the crank, but do you think the rod will need to be replaced? Do you think that there is a good chance that the crank journal will need to be ground down?
Someone told me that if the bearing has spun, that the rod will get stretched out, is this true? What is a spun bearing exactly? What will a spun bearing do to the crank? Do you think that my situation is not severe and that I may get away with an oversized bearing? Should I replace the other bearings at the same time, I believed it was a good procedure to do so?
If the transmission goes bad and your motor races to keep up a certain speed, will this cause a knock in the motor and if so is it because the bearings were most likely ready to go bad anyway? Can a bad transmission or bad/cracked flywheel be causing this noise?
The reason I asked this is because the transmission seemed to be slipping or hesitating after I noticed the noise. It seemed like it was having a hard time going into and out of second gear. The motor did race a little before going into second or third gear.
As I said, the noise is still there when in park, but not as loud as when I was driving it home. As I said, not only do I need these answers, I need you to tell me what to look for in my situation and the best suggestions. I do not know the severities of this type of problem so I do not know how bad of a situation I should expect to fall in.
Thank you,
EdA. You need to isolate the noise to a particular cylinder first. Try to get it knocking in gear with the brake on and under a load of say 1,000 rpm's. Then pull plug wires one at a time to see if the noise goes away on any cylinder If it's a rod bearing, the noise should go away or diminish on one cylinder. Then you know which bearing to look at more than the others.
If it's spun, it will have turned inside the rod end and this will wear out the rod with little hope of re-use. There are little tangs on each bearing half that secure the halves in each side of the rod. You will know if it spun when you pull the cap off and see the parting line of the two halves of the bearing and it will stick to the crank journal.
Depending on the wear on the crankshaft, you may need to have it cut and fitted with bearings. Otherwise use "plastic-gauge" to measure the clearances of all the bearings.
