Michael Posted September 15, 2000 Share Posted September 15, 2000 Yesterday I drove my '78 280z for the first time. It has a near-stock 454 big block engine and Doug Nash 5-speed transmission. With the stock tires, wheel spin is unavoidable in any gear. In traffic, the car is best driven by starting in 5th gear and never shifting. Maneuvering around the parking lot is possible in 1st gear, provided that the gas pedal is never touched and the clutch is feathered while the engine just idles. Quote Link to comment Share on other sites More sharing options...
Michael Posted September 15, 2000 Author Share Posted September 15, 2000 whoops - the previous post got cut off. Anyway, after a few laps around the block, I noticed a loud and annoying knocking sound coming from the engine. It is proportionate to the rpm, but it is not constant. Rather, when the sound is loudest (at any given rpm), oil pressure appears to drop. Then the sound intensity ebbs, and oil pressure returns. While I have no tachometer (yet), I doubt that the engine ever saw above 3000 rpm. Trivial errors such as crossed plug wires and vibration of under-hood components were elliminated. Is this the tell-tale sound of a spun rod bearing? I'd hate to have to rebuild the engine before the car even makes its first pass down the drag strip. Quote Link to comment Share on other sites More sharing options...
Andrew Bayley Posted September 15, 2000 Share Posted September 15, 2000 Hmmm... The one time I spun a rod bearing, it too got louder when oil pressure dropped. However, the frequency of the noise (knock) was consistent. It would get loudest whenever I would lift off the gas at +3000 rpm. I was really young when I did this (eighteen), so I foolishly thought a simple new set of rod bearings would fix the problem. No one ever told me new rod bearings wouldn't fix an oblonged rod. Looking back, I probably did actually know this but was too far into denial to admit it (my very first V8). Another knocking problem I've had was loose transmission components. I know a 700R4 has nothing in common with a Nash 5-speed, but any transmission is capable of creating noises that sound A LOT like banging engine components. It never hurts to check the tranny out before the entire engine is ripped apart. Good luck anyway. Keep us informed, it sounds like one hell of a ride! -Andy Quote Link to comment Share on other sites More sharing options...
pparaska Posted September 15, 2000 Share Posted September 15, 2000 My first engine rebuild, when I was 17, was a Chevy 327. I put a Holley chrome mechanical fuel pump on it. Shortly after driving it the first several hundred miles, it started to knock. I was young so I thought it was a lifter. I pulled the valve covers and started it to try to determine which lifter. It was hard to pin down, but I pulled the intake and put new lifters in a few suspect positions. No difference. I took it to a local machine/hot rod shop, and they thought it was a lifter or rocker arm, but said it did sound like it was a deeper noise than these make. I just kept driving it since most people that listened to it thought it wasn't loud enough to be a rod bearing. Plus I didn't have the money to pull it apart just to look. Years later, the Holley pump failed. I put on a Carter mechanical unit (much nicer piece) and the sound STOPPED! Just a thought, but the fact that it's oil pressure dependent on your motor makes it sound unfortunately like a rod bearing or piston pin. Hard to tell over the Internet . Time for a 502/502 crate motor maybe? Quote Link to comment Share on other sites More sharing options...
jeromio Posted September 15, 2000 Share Posted September 15, 2000 Definately sucks that you're having problems, but I think it's cruel to post something about a BBC in a Z without including any pictures! Are you running a live axle, or an R200? Sounds like maybe you need a lower (numerically) ratio diff. Quote Link to comment Share on other sites More sharing options...
John Scott Posted September 15, 2000 Share Posted September 15, 2000 Michael, I had a roller rocker come loose and sound like a rod. When lifters are pumped up it will subside. I can't believe this (rod bearing) could happen on a fesh engine. Check with the rockers, and pushrods (bent) and work your way down. No one needs this kind of misery. Good luck and keep us posted on what you find. JS Quote Link to comment Share on other sites More sharing options...
Guest mattrp Posted September 15, 2000 Share Posted September 15, 2000 Well, since I just spun a rod bearing on my 305 4 months ago (Yes, my first v8 build, but i didnt do the bottom end, and the motor had 115,000 on it. And I did quite a few autocrosses with it before 15 minutes at 4-5,000 killed it) I know the sound. For mine, it was not there really at idle. I could rev it as high as 2000 in neutral without it really appearing. Anything above that and a knocking metal on metal deeper sounding than a lifter appeared. Anything above 3 and it hurt just to listen to it. Now if I loaded the engine the knock became more apparent more rapidly, around 2. This sound was completely consistent and reproducable. When I had my machine shop do the bottom end on the rebuild they said one bearing was so spun that they had to weld the crank and replace the rod because it was so ovalled out. I sure hope this isnt your problem. That wheel spin sure sounds nice though. I can only bust em loose in 1,2 when going in a straight line. I am only at like 300 hp and torque though, so its not bad for a road car. Enjoy! Matt 72 500Z Quote Link to comment Share on other sites More sharing options...
Guest Drewz Posted September 15, 2000 Share Posted September 15, 2000 Where to start? Rod bering is usually the first conclusion jumped to. Do not fall into this trap! Rocker arm loose, overtightened can cause a pushrod to jump. Too loose and you loose oil pressure, to some degree, as this interrupts oil flow through the passages. bent pushrod is also an item to address as is the possibility of a bad piston pin. I wish I was there so Iwish I was there to help you nip this in the bud, bud! Try to get some more symptoms so we can try to help a little more. Sorry to hear about your problems as I am sure everyone here can relate to the disappointment you must feel at this time. Keep your head up and your spirits as I am sure the end result will be worth it. LATER BUD ------------------ The only stupid question is one you wanted to ask but never did!!! Drewz Quote Link to comment Share on other sites More sharing options...
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