Nissan Rebuild Problems...

[Ollie300z]

1990 blown head gasket.

Highlights
- Hydro-locked Engine
- Tore the engine down to short block
- Had the heads done at a machine shop. Ended up replacing all intake valves.
- Torqued cam brackets/mounts per manual before installation
- Used engine lube on cam surfaces
- Had problem with block bolt holes. Ended up using Heli-coil on two.
- Not my first reassemble of engine
- Project has taken more then 5 year due to moving and changes in personal life.


Problem: After assembly, engine turns over and starts, but there is a loud, deep knocking noise on the right head. The first time I ran the motor I thought it was lifters pumping up or heads taking time to get oil to the top of the engine. I am very familiar with chevy engines as I dirt track race so if pushed, it sounded louder than a stuck lifter , but not deep like a main. I let it run as I saw oil being pumped when I looked into the oil fill hole. The sound goes away if revved up to like 2k rpm or higher. Eventually the sound started to go intermittent and then went away all together. Thought I was all clear. However, the next day I went to start it, it was back. I did not want to cause additional damage by running it like I did previous day without some more feedback on possible causes. Oh and the responsiveness of the throttle is sluggish. If goosed will bog first before a slow climb to higher rpm.

I have checked the timing and the cogs are all correct to the timing marks on the cam and crank gears.

Looking for possibilities from the easiest to the hardest.

Thx!

Kansas 300z

[NolimitZ32]

Post a video of the noise and general area where its coming from.

[Ollie300z]

Sure thing. Will be later tonight or tomorrow before I can.

[budget300zx]

check and see if its in your cam gear. about 2k is when the vtc kicks in that spring is pretty common for a noise source.

[Ollie300z]

Posted on youtube...

[itsa300zx]

Sounds like the VTC to me. They are active at low rpm for increased torque and are deactivated at about 3k rpm.
The springs in the intake cam gears may be weak due to age.

[Ollie300z]

Thank you. What are the symptoms of a bad VTC? Would it account for poor response or is that a different issue? I do have another set. Are the VTC inchangeable or are they left/right specific?

The heads and cams, were dry, except for engine lube, when they were installed. It is possible I should have primed something and it isn't in the book?

[budget300zx]

id try changing out the spring in the gear. theres 4 bolts on the cam that allow you to remove the vtc spring cover. then just swap another spring into place the vtc is surposed to be active from 2000rpm up 6000rpm. on my car it was actually more around 2300-2700rpm to 5800-6000rpm. it varies slightly.

if that doesnt work id swap cam gears and pull and soak the lifters in an oil bath while its apart just to be on the safe side.

[Ollie300z]

Thank you. I will do that. Not looking forward to pulling that damn plenum, but what'cha gonna do? lol

[budget300zx]

no problem! if you deleted the coolant lines and egr setup the plenum is a fairly easy. took me literally 15mins to have it off on my NA. i also removed the the damper and have an aftermarket regulator too though.

[Ollie300z]

I am just getting into the 300z setup. I can remove the egr and coolant lines under the plenum? What should I keep if anything? Also, Are the VTC specific to either side or are they swappable?

Thanks again,

Steve

[DCaff300ZX]

I think that the plenum deletes may be detailed in the stickies at the top of the page, or for sure at the tt.net site.
Not sure on the VTC's but for safety I think I'd keep them where they were, labeling them for original position for future re-assembly if removed.

[Ollie300z]

I think that the plenum deletes may be detailed in the stickies at the top of the page, or for sure at the tt.net site.
Not sure on the VTC's but for safety I think I'd keep them where they were, labeling them for original position for future re-assembly if removed.

Thank you for the reply. I am going off a previous reply thinking that the vtc is bad. If so, I have a couple off another engine, but don't know if they are l/r specific. I will compare numbers and see or I have a contact at the Nissan dealership that can help. The contact can help with parts, but their mechanics have not broken into 300z engines before.

BTW nice looking Z.