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1984 720, new head gasket and now noisy, valve lash??


Stewart

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Hi Friends!

My trusty 84 cab and chassis blew a head gasket a month ago.  Right before the gasket went I started to get a clicking noise that increased with rpm.  Head gasket was a bit beyond me so I had a local shop do it, didn't need resurfacing but they did have a machine shop rebore the cylinders.  I got it back and it runs just fine but has that annoying clicking noise still.  They said it was just lifters and that z24s just get noisy after a while (it's only got 75k on it).  They didn't seem inclined to help fix it, which sucks since i just paid them $2k.

 

Here is a video of the noise: https://www.youtube.com/watch?v=golIMaf3YP8   In the vid I'm revving the engine up and down.

 

Thoughts?  Do I just need to fiddle around with the valve lash to smooth it out or is there something else going on?  

 

Also when adjusting valve lash by myself can I just go with a visual of when the cam is pushing straight up on #1 lifter as TDC?  I can't crank the engine and cover the spark plug hole by myself.

 

Thanks!

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Check and adjust the valve lash to 0.014" for all. This is for the '84 per the FSM. Do this on a hot engine. You might try a thou tighter for more quietness.

 

The 720 does not have 'lifters'. The cam lobes bear directly on the rocker arms. No 'lifters' or push rods. A good mechanic would know this and suggest setting the valve lash.

 

 

I don't understand sending it in for a head gasket and it's costs you $2,000. Re-bore the cylinders? What for????... new over size pistons and rings???? If so the rods were removed. Did they replace the rod and main bearings?.. probably a good idea if it's apart. Look on your bill for what parts were replaced. Mechanics are crooks. SMH A good mechanic drives a piece of shit car and is broke.

 

 

If the bearings were replaced, likely we can rule out a rod going. On the other hand I would expect when the head is removed that the valve lash would be checked.

 

 In 6 months re-torque the head bolts (loosen only one at a time, any order, and torque to 60 ft lbs) with the engine cold. Do this once a year and the headgasket will last forever.

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Thanks Mike!   I'm clearly tired after a long day!  I meant valve lash!  My mechanic said they were all set to 0.012 which is what is says on the hood tag.  I'd like to check that but I wasn't sure how to get top dead center by myself and I'm not very experienced.  I run it till it warms up, pull off the valve cover, disconnect the distributor and use the key to turn the engine over till I get TDC.  I just want to make sure I have the right spot as I'm not sure the current lash settings are what they should be.  Can I tell it's TDC just by looking at the cams on the shaft when the cam next to the #1 valve is pointing straight up? 

 

I also tried pulling spark plug wires off while running to try and isolate the cylinder/valve causing noise and if I pull both wires off #4 it get's quieter until I rev it up.  Would that still possible be valve lash?  Does it sound like it in my clip?  

 

My $2k was $945 in labor, $400 in parts (mostly gaskets, plugs, head bolts, etc).  The machine shop was $400, not cylinder boring because they only heave the head off but I don't have it written down what they did.  

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You only need to be close to TDC. Turn the engine till the #1 cam lobes are pointing down at 8 and 4 o'clock as viewed from the front. Adjust both #1 valves, Intake on #2, Exhaust on #3 and none on #4.... turn engine ONE turn so that #1 valves are at 10 and 2 o'clock and adjust the following.... Exhaust on #2, Intake on #3 and both on #4. Done this way you aren't wasting time bumping the engine over and it's done so fast the engine doesn't cool down.

 

A bad rod will quiet if the cylinder is deactivated, but will NOT quiet a valve clearance noise. Before you run that long enough to damage the crank have it looked at. May be able to get away with new bearings.

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Thanks Mike, that makes sense to me for TDC and helped a lot!  I went in an adjusted the valve lash when hot a bit but nothing was too far out of the 0.012 spec.  Didn't make a difference to the noise.

 

Mechanic did note that there was a small piece of metal missing on the #4 piston when he had it apart, but the rings looks good and nothing was scorched so he put it back.  You think the next step is bearings?  Can those be accessed from underneath?  

 

I guess I should have skipped all this and had someone rebuild the thing, but sadly it's out of my skill level and I only have a sloped driveway to work in myself (and not much experience).  Now maybe I'm stuck till it really blows up?

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  Well if it blows up might as well throw away, the damage will be extensive. There may be a broken ring if the piston is damaged. It won't heal itself and only gets worse. True...it may take a long time. 

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Take a wooden broom handle and start the engine and use the broom handle as a syethiscope and listen to various spots on the head, block, and timing cover to idetify where the noise is loudest.  This will help identify the are of the source of the noise. 

 

How is the oil pressure?

 

Common problem when doing a head the ting chain tesioner comes out and then the chain make all kinds of noise.

 

Look at the cam lobes to see if one looks damaged.

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https://www.youtube.com/watch?v=golIMaf3YP8

 

It does sound like chain links rubbing the guides. Well easy check, take the valve cover off and look down below the cam sprocket in the V the chain makes. There is a 'rubber-ised' guide on each side. See anything shiny?

 

TPKjY2V.jpg

 

 

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Thanks guys, I really appreciate your help and tips!  As you can tell, I'm generally only knowledgeable enough to cause trouble for myself!

 

I ended up following the instructions in "How to Keep your Datsun Alive" to adjust valve lash cold (and rechecked when warmed up).  I went two by two based on which cam lobes were pointed down, and then I didn't have to worry about TDC (although your tips and a vid from Hainz helped me do that).

 

Good news is that the noise improved and is pretty much gone at idle when warmed up.  However there is still a pretty good ticking when I rev it.  I posted a second vid here: 

 

I did look down at the timing chain guide area and did not see any shiny bits and the guides look ok (as much as I can see).  The noise seems to be coming more from the back of the engine around cylinder #4 with my $3 harbor freight stethoscope, but it is harder to pinpoint to there after the lash adjustment.

 

Could this be exhaust leak noise?  I also had the downpipe/muffler/tailipe replaced a bit ago and the gasket between the exhause manifold and downpipe leaks.  I took it back to that shop twice and they replaced the gasket but said they couldn't do anything else because the manifold mating surface isn't flat enough.  Not sure what else to do to seal that up.  Could that be causing this ticking?

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It doesn't seem to get louder, just faster until it kind of blends together to a loud metallic whir.  I can't really check the piston easily though can I?  What happens if it keeps running that way?  I drove it about a hundred miles last week to go camping and it seemed to run fine other than the noise.  Noise gets better at idle when warm but doesn't go away when revved.  Didn't change after the weekend trip.  I know I shouldn't drive it, but figure I can try to take it back under warranty if something different happens than the noise it had when I picked it up.  Although I'd rather figure it out and not have to deal with that mechanic again.

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I decided to pull a couple plugs just to look and the plug  (new NGKs about 300 miles ago when the head gasket was done) for the exhaust side of #4 (where it seems noisier) was noticeably sootier and smelled like gas while the plug from Exhaust #1 looked just right.  So that means I have incomplete combustion in that cylinder?

 

https://photos.app.goo.gl/4hV2ggVNsQrdBCrQA  https://photos.app.goo.gl/4hV2ggVNsQrdBCrQA

 

 

 

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Well you can start by examining anything that might affect #4s running.

 

Check/set the #4 valve lash

Spark plug wire for #4. Maybe swap with another cylinder and see if the problem moves. Are the plug wires securely on the plugs and into the cap? or damaged?

Check the distributor cap for cracks or carbon tracking on the #4 plug terminals.

 

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