Guest Pegasus76 Posted November 14, 2004 Share Posted November 14, 2004 I have an 86 300ZX stock, and there is this knocking sound from the engine compartment. I thought they were the lifters but was explained otherwise by someone else. I was simply told to pour in some Marvels Mystery Oil and the problem should go away. I did that and the problem did go away but it returns after a few days. So what is the problem? and how do I remedy it? Thanks for your time guys, look forward to hearing your replies. Quote Link to comment Share on other sites More sharing options...
datsunlover Posted November 14, 2004 Share Posted November 14, 2004 Kind of hard to diagnose your particular "knock" but I'd guess maybe a main bearing/rod is going.. Does the knock get louder/change pitch with RPM change? Does the motor shake and vibrate a bit? Does it seam to be on one side or just from 'somewhere' inside the engine block? Quote Link to comment Share on other sites More sharing options...
Guest Magnum Rockwilder Posted November 14, 2004 Share Posted November 14, 2004 Describe what it sounds like. Does it sound like someone hitting the bottom of the engine with a block of wood, or does it sound like marbles clacking together under the hood? Give a good verbal description of the sound. Quote Link to comment Share on other sites More sharing options...
Guest Pegasus76 Posted November 14, 2004 Share Posted November 14, 2004 It sounds like a clacking whenever idle...Then as the engine begins to rev the sound gets faster till it is muffled from the sound of the engine or just stops clacking. The engine doesn't vibrate erradically or anything and the sound seems to come from the driver's side I believe. Quote Link to comment Share on other sites More sharing options...
SHO-Z Posted November 14, 2004 Share Posted November 14, 2004 This is the shade tree mechanic way. At idle pull one of the plug wires at a time. If the knock goes away when you pull one of the plug wires that cylinder has the bad rod. Quote Link to comment Share on other sites More sharing options...
datsunlover Posted November 14, 2004 Share Posted November 14, 2004 Um.. could it be coming from the rockers? This is another shade tree check; Use a long screwdriver like a stethescope. Put the tip on the rocker (roughly over each cylinder, one at a time) and hole your ear on the handle. You may hear the noise louder in one area.. (possibly on the drivers side in your case) maybe one of the rockers is bad.. And seeing as its more on one side.. are you sure it's not a manifold leaking? Sometimes it can sound like a knock.. (my 93 king cab has esentialy the same 3.0 V6 and has a bad maifold leak on the drivers side.. they arepron to this problem.) Quote Link to comment Share on other sites More sharing options...
Guest Magnum Rockwilder Posted November 14, 2004 Share Posted November 14, 2004 It sounds like a clacking whenever idle...Then as the engine begins to rev the sound gets faster till it is muffled from the sound of the engine or just stops clacking. That's the lifters (lash adjusters). They are little hollow doo-dads that are supposed to cushion the rocker arms' movement. They have tiny holes that keep them pumped up with oil, and when the holes get clogged and they can't pump up, they don't fill the gap and it makes a ticking noise. Your oil pressure goes up when your rpm's go up, so the noise goes away. You can try running a cleaner in the oil to clean out the holes, but it can sometimes take a long time to take effect. Try this: Get a can of Seafoam from Napa or Carquest and pour the whole quart into your engine. Run the engine at idle for about 10 minutes, occasionally bringing the revs gently up to around 2k rpm. Drain the oil while it's still hot and refill with a thin (5w-20 or 5w-30) conventional oil, and replace 1 quart of oil with a quart of Dexron tranny fluid. The tranny fluid has a high detergent content and will help clean the gunk out, but it isn't as slick as oil so don't use more than 25% of your crankcase capacity. Change your oil once a month, or more often if you can stand it... but only change the filter every OTHER time. It may take a week, or it may take 3 months, but this might make the noise stop. Once the nose stops, go back to using regular weight oil for the weather, and only add 1/2 qt of Dexron at each oil change. If it doesn't, your only other option is to disassemble the heads and replace the lifters (lash adjusters). l Quote Link to comment Share on other sites More sharing options...
Guest Pegasus76 Posted November 15, 2004 Share Posted November 15, 2004 Thanks a lot for your help...I will try as you suggested and hopefully everything works out Quote Link to comment Share on other sites More sharing options...
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