Guest 4.3L 280z Posted January 4, 2005 Share Posted January 4, 2005 I've been noticing a sound coming from my motor at part throttle. It's sort of a rattling knocking sound but I don't notice it at idle or full throttle(might just not here it) whenever its at about 2000rpm its worse and it slowly increases with rpm. I can't tell were it is really the rockers are tight, could it be the hydraulic lifters? And if so do I have to replace them or do you think they could be clogged? Quote Link to comment Share on other sites More sharing options...
Guest 4.3L 280z Posted January 4, 2005 Share Posted January 4, 2005 Something I think I should add is it seems to increase slightly when I advance to timing(its only eight with the vaccum advance plugged up) and an increase to 10 makes it slightly louder. I'm really not sure what pinging sounds like, I guess my distributor could be advancing way to much. I'm going to get one of my friends to increase the throttle while I listen under the car. My luck it would be a rod bearing(the part of the motor I was going to keep stock) Quote Link to comment Share on other sites More sharing options...
Pop N Wood Posted January 4, 2005 Share Posted January 4, 2005 Try a tank of premium gas and see if that makes a difference. Quote Link to comment Share on other sites More sharing options...
Guest 4.3L 280z Posted January 4, 2005 Share Posted January 4, 2005 its got 93 octane right now Quote Link to comment Share on other sites More sharing options...
Guest Magnum Rockwilder Posted January 4, 2005 Share Posted January 4, 2005 That's knock. It means the engine is lean at part throttle. You need to set the carb up better and maybe get a distributor with a different curve. Quote Link to comment Share on other sites More sharing options...
Guest 4.3L 280z Posted January 4, 2005 Share Posted January 4, 2005 I can't make it go away by retarding the timing and it doesn't get much better. I stuck my head next to the oil pan and its very loud! I'm thinking rebuilding a 350 a friend has and dropping it in. Then that will solve the power problem. I hope its nothing major. Quote Link to comment Share on other sites More sharing options...
datsunlover Posted January 5, 2005 Share Posted January 5, 2005 What you are describing sounds like a frined of mines old s10.. well, his fathers truck.. Started making that noise, and all they could come up with (after going through simmilar troubleshooting stuff) was the motor was 'tired' and possibly a main bearing was starting to let go. The thing was burning oil as well, so they got rid of it.. got $500 or something as a trade in on a 99 cavileir. IIRC, it blew up shortly after.. wow was that used car dealer pissed off.. Quote Link to comment Share on other sites More sharing options...
Guest Magnum Rockwilder Posted January 5, 2005 Share Posted January 5, 2005 If you're hearing it in the oil pan it's probably a rod bearing. It could also be a wrist pin. Quote Link to comment Share on other sites More sharing options...
Guest 4.3L 280z Posted January 5, 2005 Share Posted January 5, 2005 Well I haven't had much time to mess with it but I did get it jacked up and listened underneath again. It's definately coming from the bottom but it seems like its coming from the back of the motor around the flywheel. I don't see any wear and the starters not part way engaged I haven't checked the other two torque converter bolts yet because I've got to get cleaned up and go to work. Is it possibly the torque converter internals? It wouldn't be the torque converter itself would it? I pulled all the spark plug wires and didn't seem to notice the noise changing on a certain one but it seemed to quiet a tiny bit if I pulled any of them. Its real hard to tell were its coming from it might still be from the motor I just wish I could no for sure what it was, if it is a rod bearing does that mean the cranks junk now or could I replace the bearing. I think I'm still taking it to the drag strip this weekend, if it goes completely I'll at least no what it was. I only live a halfmile away. Quote Link to comment Share on other sites More sharing options...
Guest 4.3L 280z Posted January 5, 2005 Share Posted January 5, 2005 I guess I'll also add that the motor was "supposedly" rebuilt with 1000 miles when I got it. He said the truck it was in was tore up and he had to get rid of it cause it couldn't set were it was but kept the motor. He seemed honest and trustworthy and the motor had new freeze plugs, good compression, and the topend at lease from what I've seen looks good. Quote Link to comment Share on other sites More sharing options...
jbk240z Posted January 5, 2005 Share Posted January 5, 2005 Yo, I had this same problem once, it turned out to be a cracked flywheel. Start the engine, let it idle, put the car in gear with your foot on the brake, if the noise gets softer, it's most likley the flywheel. I hope this helps. Quote Link to comment Share on other sites More sharing options...
80LS1T Posted January 6, 2005 Share Posted January 6, 2005 Yeah a cracked pressure plate could cause a that kind of noise. Or a collapse lifter could cause a knocking noise. Can you run it with the valve covers off? Make sure all the rockers are moving about the same amount. I heard from a guy at a Chevy dealership that they are having problems with the 4.3L lifters. Just a heads up. You could call a local dealership and ask them what to look to see if your lifters are junk? Guy Quote Link to comment Share on other sites More sharing options...
Guest 4.3L 280z Posted January 6, 2005 Share Posted January 6, 2005 I'm going to pull the motor tomorrow and check the flywheel then I'll take the pan off and check the rod and main bearings. It could just be the flywheel because it does get way quieter even under a light load. I'll stop wining and just find out tomorrow. At least I got to drive it a bit this time, the first time I drove it with the straight six the gauge said the oil pressure was good but the motor just died and I couldn't start it. Pulled the valve cover and the cam was dry and the cam was snapped! I want to learn more anyways, I have a good understanding from reading books about how to do things and how everything works but have never really tore into a motor except for head work. Quote Link to comment Share on other sites More sharing options...
jbk240z Posted January 6, 2005 Share Posted January 6, 2005 Yo, I hope it's just the flywheel, good luck. It may be easier to just remove the trans instead of the engine, then if flywheel is cracked, just change it in the car. Do you have any pics of your swap by chance? Quote Link to comment Share on other sites More sharing options...
Guest 4.3L 280z Posted January 6, 2005 Share Posted January 6, 2005 I was going to take some pictures this week but my dad has the camera and hes a truck driver so it will be this weekend before he gets back. Quote Link to comment Share on other sites More sharing options...
Guest 4.3L 280z Posted January 7, 2005 Share Posted January 7, 2005 Well today first I started the car and pulled all the plugs again and when number 6 was pulled the knocking stopped. Pulled the motor and checked it out and it turns out that the number 6 rod bearing is completely gone for some reason but the rod looks in spec when compared to another rod with a bearing. Please tell me I can still replace the bearing alone. My parents don't want me to drive their truck for long. Also how would I tell what caused this, could it be the oil hole in the crank got clogged? It looks smooth and shiny. If it will last 6 months that will give me time to build another motor and switch them out. Quote Link to comment Share on other sites More sharing options...
waynekarnes Posted January 7, 2005 Share Posted January 7, 2005 had two rod bearings go bad on a 55 chevy, way back when ... rebuilder got finger acid on the bearing, bearing delaminated and spun. i used plastigauge, checked, clearance was still good. used some emory cloth, polished the crank, did what i could to get to the rod cap and the piston side of the rod. checked with the plastigauge again. took the plastigauge and original bearing with me to machine shop, they were hesitant to sell me just one bearing ... man went into the back and came back with one from a broken box. was the correct bearing, all was well, no more knocking. drove the car another 3 years. my friend did a chevy into his land cruiser ... rebuilt the 350, low oil pressure, but seemed to run fine ... developed a slight knock. my brother bought the engine for his camaro, my friend sold the cruiser as was ... turned out 4 of the bearing were under sized, spun, markings were on the bearings, all the rest were correct as marked correctly. things happen, mistakes are made ... one, two bearings can go bad, be mismarked, crank turned to wrong size, rod end and cap sized wrong. if you don't intend to pull the engine down, get some plastigauge, check all the bearings, see a reputable machine shop, see if they can help you with some new bearings, and advice on how to check for damage, and repairs, if needed. best of luck on this wayne Quote Link to comment Share on other sites More sharing options...
Guest 4.3L 280z Posted January 7, 2005 Share Posted January 7, 2005 Well I could see better today it was dark last night. The bearing was just on the crank, I picked it off today(its my first time doing this don't laugh) the bearings were worn to copper and the crank was a little rough I polished it the best I could, its still in the car so I didn't get it real good if it happens again I'll take more time on it. The rest of the bearings look great maybe he torqued it down to much. I did use the plastigue and it was within factory specs so I guess that means I have the right bearing size. Back to looking for a used nitrous kit for cheap so I can mess something else up and learn a little more.lol Quote Link to comment Share on other sites More sharing options...
jbk240z Posted January 7, 2005 Share Posted January 7, 2005 Unfortunately, breaing stuff is part of the learning process, I've been there a few times myself. The good thing about playing with the 4.3 is they are pretty common and cheap, check ebay for stuff, lots of people swap them for v8's too. My stepdad is putting one in a 72 240z, fits nicely, not sure what he is going to do for exhaust though. Anyway, good luck going back-together with it. Quote Link to comment Share on other sites More sharing options...
waynekarnes Posted January 8, 2005 Share Posted January 8, 2005 no such thing as a foolish question ... we don't ask, we don't learn ... are you planning on adding nitrous on this engine ??? with that weak link, i don't think you are gonna want to do that ... with even the slightest damage to the rod, cap, crank, you are going to have issues with that bearing. now under normal, and a little spirited driving, you may be just fine, polishing the affected areas and using a new bearing ... plastic guage the new bearing, when you install it ( standard practice when ever you install bearings ), put plastic, torque, remove ... check the chart ... if all is good, reinstall bearing, and torque to spec. if no good, find correct bearing or why it's not right. again, i think, i'd pass on running nitrous or most horse power adding devices , until you've put a few thousand on it ... make sure it's gonna be reliable .. not to be a pessimist...if i was gonna use nitrous, i'd yank the crank, take it to a machine shop, along with rod and cap, have em checked. of course there is that element of excitement when a crank lets loose LOL seriously, maybe speak with a local motor head in the business see what he says ... good luck with it, wayne Quote Link to comment Share on other sites More sharing options...
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