300ZX NA Knocking. How Bad is it? [VIDEO]

[Matt616]

Just got this car about a month ago (1990 NA auto). Was looking for a decent car for my DD and I found this car for sale for $1800. Well I kinda jumped on it because Ive always liked these cars and I thought it was a good deal. The car is in pretty good condition, but a couple days after I bought it I noticed the engine had a knocking sound.

The knocking usually starts ~1min after you start it and gradually gets worse to the point seen in the video below. I can only really hear the knocking during idle, it might be there while driving but I cant hear it. When I first noticed it, I took it on the freeway for about 5 mins and then went back home and the sound was gone. However, if Im just driving short distances around town, the sound will become a bit less audible but will remain. The only thing I have done to the car is changed some squeaking belts and changed fluids.

Here is the video (sorry about the moving, was trying to get the mic close to the engine):

http://www.youtube.com/watch?v=zhH6vNbrY2g

What could this be? Is it worth fixing or will I need a new engine? Any help would be appreciated

[chaosdrifter06]

First of all, what kind of gas are you using? These things have to run on 93.

[Matt616]

First of all, what kind of gas are you using? These things have to run on 93.

The guy who sold it to me said he ran 91 octane only (highest octane in cali) and recommended that I do the same, so Ive only used 91 octane shell gas since I bought it..
Modified by Matt616 at 12:22 AM 10/14/2008

[Z-owned]

i would try running some seafoam through it. Thats known to help with lifter tick. Otherwise you gotta tear down to the heads. I am in riverside as well.
Modified by Z-owned at 2:45 AM 10/14/2008

[pintovit]

I also have the same problem with lifters ticking mostly when cold... I hate that noise... It doesn't sound healthy at all.

But before disassembling the engine head I would like to try a simpler approach (like the one just presented).

What you guys make of those seamfoam types of engine cleaners? Are they thrustworthy?

I'm a little reluctant about them... There are some articles saying those are mostly frauds and that they can react with the detergents present in your engine oil or with the gasoline adictives and create even worst problems!

Thanks for sharing your thoughts.

Regards,Vítor

[mkhoid]

previous owner probably abused it.

[evildky]

hard to tell form video, but I don't think you have a rod knocking, sounds more like a bent valve ro colapsed lifter to me, but again hard to tell over the intraweb

neither problem is caused by cheap gas, and no seafoam nor any other chemical is going to fix it, at the very least, the heads need to come off

[SpeedFreak_Josh]

My PC is crap so I can't view the vid but I'd guess it'd be hard to tell anyway.You say it's quiet at 1st start-up or after a good run?When sitting at idle, rev the enine. Hold it around 4k or so for a few seconds and see if the noise diminishes. This will show oil pressure easily.I've ran into this issue with noisy lifters before and often it can mislead to a condemned motor/head.

BTW, skip seafoam. Try Rislone to clean up that varnish. Add this to a couple of oil changes.

First of all, what kind of gas are you using? These things have to run on 93.

Stock models only require 91 octane.

[Geronimo77]

yeah, if you run seafoam throught it and give it a good oil change and it still does it, check your vtc gears..this happened to mine less than a month ago. i thought it was lifter tick but it turned out to be my intake cam gears.

[Sgt]

I know that exhaust leaks can sometimes sound like a ticking that is coming from the engine. Get it on a hoist and take a close look and make sure it isn't just an exhaust leak.

[Matt616]

I am in riverside as well.

Modified by Z-owned at 2:45 AM 10/14/2008

Nice to know there are knowledgeable people in my area if I ever have questions.

I know that exhaust leaks can sometimes sound like a ticking that is coming from the engine. Get it on a hoist and take a close look and make sure it isn't just an exhaust leak.

I dont think its a leak because I can physically feel the engine vibrating pretty bad in sync with the ticking (mostly in the upper leftt area).

hard to tell form video, but I don't think you have a rod knocking, sounds more like a bent valve ro colapsed lifter to me, but again hard to tell over the intraweb

neither problem is caused by cheap gas, and no seafoam nor any other chemical is going to fix it, at the very least, the heads need to come off

Well I dont really have the knowledge to do this myself. How much do you think it would cost to have someone look at it?

[Matt616]

BUMP

[SpeedFreak_Josh]

You say it's quiet at 1st start-up or after a good run?When sitting at idle, rev the enine. Hold it around 4k or so for a few seconds and see if the noise diminishes. This will show oil pressure easily.I've ran into this issue with noisy lifters before and often it can mislead to a condemned motor/head.

Try Rislone to clean up that varnish. Add this to a couple of oil changes.

Does it sound like only 1 or all of the lifters? ie, does the whole engine "clatter"

[Ksizz13]

I took my car to the dealer today to get diagnosed, call around, make sure there is a set fee, mine wass 90 bucks and make sure you tell them not to do things where you would owe more money , until they talk to you about that.

[gnr_70]

I have the same issue with my 1993 Z n/a...what was the fix?

Just got this car about a month ago (1990 NA auto). Was looking for a decent car for my DD and I found this car for sale for $1800. Well I kinda jumped on it because Ive always liked these cars and I thought it was a good deal. The car is in pretty good condition, but a couple days after I bought it I noticed the engine had a knocking sound.

The knocking usually starts ~1min after you start it and gradually gets worse to the point seen in the video below. I can only really hear the knocking during idle, it might be there while driving but I cant hear it. When I first noticed it, I took it on the freeway for about 5 mins and then went back home and the sound was gone. However, if Im just driving short distances around town, the sound will become a bit less audible but will remain. The only thing I have done to the car is changed some squeaking belts and changed fluids.

Here is the video (sorry about the moving, was trying to get the mic close to the engine):

http://www.youtube.com/watch?v=zhH6vNbrY2g

What could this be? Is it worth fixing or will I need a new engine? Any help would be appreciated

[Z32 TwinZ]

ive used seafome and it hasnt harmed the car.

I use it every other fill up in the gas tank. Also run it through the vacuum hose (it looks like an "S". go watch it on youtube. Alot of cars have alot of build up in it. When i did mine, there was like nothing that came out.

I run 93 octane and mobile one synthetic oil, so when i seafoam it is clean

[carmo]

You can use a long screw driver as a stethoscope. Place the screw driver on the valve cover and put your ear on the end of the handle. Check several different points and try to isolate the noise. I just had a customers sentra with a knock that turned out to be the alternator. If the belts are on too tight, you can wear idler bearings and alternator/compressor bearings. Try taking the belts off and then run the vehicle to see if the noise is different or gone all together. The noise in the video sounds like valvetrain to me. The old school guys in my shop say you can isolate a rod knock by disabling one cylinder at a time (unplug the coil pack) and see if the noise goes away or changes. I have never had any luck with this test however. Good luck