I have just obtained a 1991 Toyota Corolla with a loud engine knock. I was told that his daughter possibly ran the engine without oil. Don’t know. I suspect that it is a rod. More so possibly a spun bearing or something. Is it possible that one of the bolts that bolt the rod to the crank has possibly broke or stretched? What is the most likely cause of ANY engine knock? Be specific. I will be doing the repairs myself du to no money for repair.
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Most likely is the rod bearings have failed due to lack of lubrication, just as you stated. A stretched rod cap bolt could theoretically cause it, but it would be under a high RPM situation I think. When replacing the rod bearings, obviously check the crank for damage, the rods themselves could be damaged as well. While you have the engine apart go ahead and replace the main bearings and oil pump.
If I had to hazard a guess without knowing if it was run low or out of oil or operating conditions, depending on how loud it is, it could be the wrist pin in the piston has cracked or the connecting rod has completely broken, in which case the engine is shot. It is possible if its still low on oil it could be a bearing making the noise, but if its loud, I doubt it. Any way you cut it, you need to remove the oil pan and look…if its a real loud noise, the problem will probably be pretty apparent. Best of luck!
Josh
i hope u didnt pay much for the corolla and if u plan to fix the block then whatever you do turn that engine off and KEEP IT OFF!!! the more you run it the more likely you are to scar and ruin the block. it is probally a rod but it could be a number of other things. your best bet is to rip apart the block before you buy any parts for the engine because you may find that the block is no good once you rip it open. if you dont know much about engine internals (and from the question im guessing this is your first time) then your definaltly going to want to find someone with some experience because there are alot of things you could mess up trying to do it your self. dont get me wrong, dont drop it off at a shop, you’d spend less money just buying a newer car lol. but yeah, unless someone has supernatural powers on here, your guess is as good as ours, good luck!
Once you remove the pan and find what is actually causing the problem you will end up replacing so many components that the cost of parts and tools is going to exceed the price of a running pull out engine. That’s most likely your cheapest bet. With the engine being that old its getting way up there in miles for sure. You can get some great deals on the jap engines from Engine world as well and they are low mileage engines with good warranty’s.
I agree with most of the previous answers, that it sounds like a main or rod bearing, but it’s impossible to tell until you get into the engine itself. Doing a compression test will help to determine which cylinder is at fault.
As for the knock, it is impossible to tell with out actually hearing it. I have known several small block chevys that were diagnosed with an internal engine knock, but it was a broken flywheel or a blade broke on the coolant fan. Noise travels like crazy inside an engine and it is difficult to find by just listening. After market tool companies make an inexpensive stethiscope which can help in pin-pointing the problem. I have also used a wooden dowel. place one end against your ear and the other end on different spots on the engine, the closer the problem, the louder the noise. Be careful when searching around the fan and pulleys. If the sound gets louder the lower down the engine you check, will indicate a bottom end problem. Them listen along the oil pan, if it gets louder toward the rear of the engine, it is possible that the flywheel is broke or the starter may be stuck engaged.
There are so many diffirent noises that an engine can make, that trying to explain all of them would take alot of time. The most common are a knock, which usually indicates an internal problem, a ticking sound usually indicates a valve adjustment problem, and a squealing sound indicates a worn or loose belt. There are many minor differences in the intensity of the sound that can also help diagnose the possible problem.
I hope this helps in locating the problem and good luck. Christopher