Mikelly Posted February 25, 2002 Share Posted February 25, 2002 I have a brain teaser for you guys... 1989 240SX has a nocking in it at idle... I put it in gear (Automatic) and drive down my brother inlaws driveway (1/3rd of a mile long) and at certain RPMs the knocking goes away all together. Any idea what this could be??? We are going to pull the motor and trans over the next few weeks just to take measurements, as I'm gonna stuff a 5.0 mustang motor in it, but I'm curious as hell why it isn't knocking consistantly through the rev range... Mike Kelly Quote Link to comment Share on other sites More sharing options...
Tim240z Posted February 25, 2002 Share Posted February 25, 2002 Mike, AFAIK, it could be one of three things: Piston slap bad engine mount cracked flywheel (or flexplate in this case). My neighbour's 199x Maxima had what sounded to be a bearing knock....turns out the cracking of the flywheel is fairly common for the Maximas, so maybe SX's too? Tim Quote Link to comment Share on other sites More sharing options...
Scottie-GNZ Posted February 25, 2002 Share Posted February 25, 2002 Is it actually sound like a knock? Is it always there at idle? My Miata does the same thing but it is a known problem with the hydraulic lifters. Does not sound like a knock typical of a say a rod, but it is not the light ticking typical of a hydraulic lifter either. Difference with mine is that it is not there all the time and when it is, it goes away as soon as the RPMs come up. Hope it is something that "simple". Quote Link to comment Share on other sites More sharing options...
Mikelly Posted February 25, 2002 Author Share Posted February 25, 2002 This thing is a dead on KNock and I put it on a lift with it running to try and figure if it was coming from the top or bottom of the motor and it sounded like it was from all over... Which may be the reason if the flex plate is cracked... I'll check and see if the flex plate is cracked... If that is the case, I'll be replacing the flex plate and driving the thing daily until we get all the Ford Swap parts together... I HOPE it is the flex plate... $200 for the car, that would be TO FUNNY! Mike Quote Link to comment Share on other sites More sharing options...
John Scott Posted February 25, 2002 Share Posted February 25, 2002 Along the flexplate lines, loose converter bolts can mimick a deep engine knock, hope its somethin simple. JS Quote Link to comment Share on other sites More sharing options...
Guest Anonymous Posted March 7, 2002 Share Posted March 7, 2002 get a valve job Quote Link to comment Share on other sites More sharing options...
Tim240z Posted March 7, 2002 Share Posted March 7, 2002 Mike, Any updates. Did you find the problem? Just curious. Tim Quote Link to comment Share on other sites More sharing options...
pparaska Posted March 7, 2002 Share Posted March 7, 2002 Like John said, check the converter bolts while you're looking for cracks in the flexplate. I've seen where converter bolts that were loose sound alot like a rod pin or bearing knock. Quote Link to comment Share on other sites More sharing options...
Guest Anonymous Posted March 7, 2002 Share Posted March 7, 2002 Flex plate is a good possibility. Picked up on a 520 pickup 10 years ago for A $100.00 that had garage reciepts for over a $1000.00 for a recent motor rebuild that was thrashed (?) on the way home from the repair shop. The father of the owner lost interest in replacing all the rod bolts which he felt was the problem. He managed to get the oil pan off and lose about half the bolts. I towed it in and finished the job, cranked it over and about lost a few fillings in my teeth from all the shaking and loud knocking.A few days later I backed it out of the garage and all problems ceased to exist by just pushing in the clutch. Apparently Junior was doing some speed shifting on the return from the engine rebuild and chipped a major portion of a gear tooth in the transmission. That motor ran like the thousand dollars was well spent.Sold the pickup for a grand within a week Quote Link to comment Share on other sites More sharing options...
Guest Anonymous Posted March 7, 2002 Share Posted March 7, 2002 you know i have the same problem (loose converter bolts i think) on my GF's 77 firebird. it drive fine but if you hit the 2-3 shift in the auto while being on the throttle man does it make a unholy racket the first time i heard it i thought i had fragged the cam and the pieces were flyin all around in their Quote Link to comment Share on other sites More sharing options...
Ron240zxt Posted March 7, 2002 Share Posted March 7, 2002 By any chance is there damage to the oil pan, Possible crank slap against the pan if dented bad enough..Seen this if someone desides to go over parking blocks... Quote Link to comment Share on other sites More sharing options...
Mikelly Posted March 7, 2002 Author Share Posted March 7, 2002 ....I haven't had the time to work that issue. I'm ognna pull it into the garage over the weekend and get it on the lift and drop the starter to see if I can find anything amiss. Hopefully there will be an inspection panel on the trans for me to remove and have a look. Mike Quote Link to comment Share on other sites More sharing options...
Danno74Z Posted March 7, 2002 Share Posted March 7, 2002 Mike, I maybe way off but to me that sounds like low oil pressure with worn bearings. At idle or low speeds you hear the noise more readily but as speed/engine RPM goes up the pressure builds and the noise (knock) decreases. How many miles on the engine? MTC Danno74Z Quote Link to comment Share on other sites More sharing options...
Mikelly Posted March 7, 2002 Author Share Posted March 7, 2002 Motor has 92,000 on it and the knocking isn't there only in a very narrow power range (Somewhere between 2-2500RPMS it goes away)... But knocks ALL THE TIME at adle... Strange, but I'll find out this weekend! Mike Quote Link to comment Share on other sites More sharing options...
Modern Motorsports Ltd Posted March 8, 2002 Share Posted March 8, 2002 Have you run any engine cleaner with the oil thru it? Scotties 'lifter' comment might be spot on....it's happend on VG30's as well. Going down to Shasta the 'knock' hit my freinds VG30. Screwdriver/ear seemed to pinpoint it to the intake but it was quite prominent all over and not crystal clear by any means. Good luck. Quote Link to comment Share on other sites More sharing options...
Mikelly Posted March 8, 2002 Author Share Posted March 8, 2002 Guys, Here is the extent that I have worked on the 240SX...Pulled it home from Connecticut... Unloaded it at my brother inlaws house. Threw a battery in it and was shocked when it actually ran. Put it on a lift and did the screw driver test with the car running on the lift in the raised and lowered position and quite frankly that has been it. Oh, and I put a set of 16 inch 5 stars my buddy gave me on it. My brother inlaw took a trip in it down the driveway and found that it actually quit knocking in a specific RPM range driving downt he driveway. I'm gonna make time for it, just trying to do about a 100 different things right now! Reason for this thread is that I need to be armed with as many clues from you guys as possible so I can just start trying stuff until I find it... I'm hoping the motor won't have to be torn down! Mike Quote Link to comment Share on other sites More sharing options...
clint78z Posted March 8, 2002 Share Posted March 8, 2002 I had a weird experience with a motor I was sure it was a rod knock. It banged so damned hard I was sure it spun a bearing. It turned out to be the valve train needed shims in a ford festiva. I was completely shocked Quote Link to comment Share on other sites More sharing options...
Scottie-GNZ Posted March 9, 2002 Share Posted March 9, 2002 Knock going away as RPMs go up sounds awfully familiar. Rod knock would not go away. I like Ross' idea of the engine cleaner, then starting over with fresh oil, especially if the engine sat for awhile. Quote Link to comment Share on other sites More sharing options...
blueovalz Posted March 9, 2002 Share Posted March 9, 2002 Here are my thoughts or rather experience. Back in '76 when I bought my first car ('71 Pinto-yeah, I hear all you guys out there laughing, but it really was a good car), I dogged it (headers, 390 holley, etc) until it started knocking. It was a periodic knock, just as you describe, and if I kept the rpms just right, it would go away. It did get progressively worse, and toward the end, the "quiet" rpm range had deminished to a very narrow band, but by then I had set up an A-frame and swapped to a new motor late Saturday night at the apt complex I lived at, and finished up Sunday morning just in time for the owners of the complex to drive by and see the carnage on the way to church. Lessons learned: 1) After tearing down the motor, I found the a rod bearing that was nearly gone, and that was where the noise came from. 2) Found out how expensive it was to have to move to another apt complex after the owner kicked me out of my current apt. Quote Link to comment Share on other sites More sharing options...
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