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Thread: Diagnosing Valve Train Noise

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    Default Diagnosing Valve Train Noise

    While slowly reconditioning my early 74 260z, I decided to do a valve lash adjustment.

    After I was done I was able to notice a significant valve train noise somewhere around cylinder 5 or 6. The noise is sharp and follows the RPM. It's the same hot or cold. With a stethoscope it appears to be more loud on the passenger side. It makes the noise regardless if the spark plug wire is plugged in or not.

    I've triple checked the lash both hot and cold. And they're extremely close to perfect at .008 intake / .010 (cold) and .10 intake / .012 (hot).

    My oiling bar is recently cleaned and silver soldered by me, and I visually verified that it is working (what a mess).

    I believe it did make the noise prior to the lash adjustment, but it's definitely louder now.

    The cam looks fine, the wipe pattern between the cam and rocker seems fine, the springs and retainers are all there and not obviously broken.

    I'm not a novice mechanic, but nearly all of my experience is from much newer cars.

    What procedure should I follow to figure out what the problem is exactly?

    Desmond

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    Just a little more info: It runs and idles excellent. The compression is terrific and equal across all six cylinders.

    I do lose a little oil from valve stem seals (slightly at first start up, and under heavy throttle).

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    I have a noise from my #1 cylinder. It's been there for about 20,000 miles, no change. I also adjusted lash, and double-checked. And have excellent compression numbers, a smooth idle and otherwise great performance. I've kind of come to the conclusion that some rocker arms and their associated parts just move differently than others and are noisier. Or I have a loose part somewhere that is just noisy, but okay. I decided that noise is not a problem.

    I've also noticed that I hear odd noises more after I work on the engine.
    1976 280Z, with some minor modifications

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    I know the 2 aren't related but when there is a crack in the seal of the exhaust manifold or header flange it is easy to hear the exhaust valve slap against the valve seat. #1 and #6 are the first break a stud or have the nut back off.
    Chris
    1970 240Z HLS30 01955 March/70

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    On your suggestion I retightened the exhaust studs.

    Number 6 was loose, but it didn't effect the noise.

    Zed Head, I know how you feel. My Land Cruiser is the same way. However, this noise is so loud that it's literally a spectacle. I had one of my non mechanic friends say 'There's something broken in your motor'.

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    One at a time, after you adjust each valve while the lobe is up, try to rock the rocker back and forth......if you find one that feels loose, take a little out of the adjustment. You can usually feel the play in a noisy rocker. Some Z engines just have more valve train noise than others.....but you can usually isolate a loud rocker by doing this procedure. IMO
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    90 300zx and a 1996 Acura NSX.....but who's counting?

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    Different scene then. Before and after seems like where you're at. If it didn't make the noise before, but it does now, then you must have altered something when you were adjusting lash. Did you knock one of the anti-rattle (mouse-trap) springs off or bend it? Easy to do since they're right next to the locknuts. Their purpose is to keep the rocker arm tight on the pivot. So it doesn't make noise.
    1976 280Z, with some minor modifications

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    Quote Originally Posted by Diseazd View Post
    One at a time, after you adjust each valve while the lobe is up, try to rock the rocker back and forth......if you find one that feels loose, take a little out of the adjustment. You can usually feel the play in a noisy rocker. Some Z engines just have more valve train noise than others.....but you can usually isolate a loud rocker by doing this procedure. IMO

    When you say rock the rocker, do you mean front to rear, or drivers side to passenger side?

    Both my 5 & 6 exhaust rockers seem to move a tiny bit more in the front to rear direction than the other ten. And I mean such a tiny amount that it might be placebo effect.

    And do you mean loosen the lash when you say 'take some out'?

    Quote Originally Posted by Zed Head View Post
    Different scene then. Before and after seems like where you're at. If it didn't make the noise before, but it does now, then you must have altered something when you were adjusting lash. Did you knock one of the anti-rattle (mouse-trap) springs off or bend it? Easy to do since they're right next to the locknuts. Their purpose is to keep the rocker arm tight on the pivot. So it doesn't make noise.

    My mouse trap springs are ok. It did make the noise before... but it's more pronounced now (both because the valvetrain is overall less noisy, and the rapping noise became louder.

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    Shake em side to side.......if one or two feel loser than others, tighten the gap from .010 to .008 inches. Sometimes when you torque the lock nuts down, you'll change the lash clearance on that final lock down. Your noise is almost certainly in the valve train....loose is noisy...right?
    Last edited by Diseazd; 04-13-2014 at 06:00 PM.
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    As an update, I got a chance to jump on this a little last night.

    I adjusted the valves in question both much tighter, and way more loose and the noise still persists.

    I'm convinced it's valvetrain noise - but I'm at a loss as to why it's so much noisier all of a sudden.

    I'm going to try to take a video and post it tonight.

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    I was chasing a similar noise over the last month, trying to get my 240Z on the road (L28, SUs, Schneider cam with springs and lash pads, MSA 6-1 header).

    I inspected the valve train (including camshaft, rocker arms, lash pads, springs) and adjusted valve lash. Everything looked good. Started the engine and the noise was still there.

    I next checked all the manifold nuts and they all seemed tight. I inspected the intake and header (MSA 6-1 coated) and could not notice any obvious leaks. I installed the header in ~2005 and noticed some discolouration of the coating where two pipes come close together. Though when I held my hand nearby, I could not feel or see any obvious leaks.

    Finally, I removed the header to properly inspect it. I clamped a piece of wood over the manifold section of the header, covered it in soapy water and inserted a funnel and my wife's hairdryer in the exhaust end. Bubbles!! Turns out that the header has a leak where the 6 pipes come together, on the inner side, so the hole was not visable as the pipes are very close together. New MSA 6-1 header will be here Thursday, so now I'm cleaning up and painting the driver side of the engine compartment and polising my intake.

    Not sure if you have a manifold or header, but take a really close look for a leak at the manifold (could be warped) or a hole or crack in one of the pipes. If I had not fould the leak in my header, the next step would have been to pull the head, thinking that I must have damaged a valve.

    NOTE: I've had my Z since '91 and replaced a warped exhaust manifold with an uncoated header. I made the mistake of wrapping the header and it only lasted four years before it developed a hole under the wrap (held moisture against the pipes and increased the heat, increasing rate of deterioration). This last coated header has done well, lasting nine years.

    As an aside, now that I have the manifolds off, I can really see gunk / carbon build-up on the valves. Once it's back together, I plan to complete a careful water mist decarbonization through the SUs (been researching this since I noticed the state of my valves). Interestingly the rear valves are cleaner than the front valves. I have a 280Z vented hood and suspect that water dripping through the driver's side vent, has been dripping into the K&N filter on the rear SU and helped to decarbonize those valves.

    Good luck.

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    Thanks for the heads up Sean!

    While I'm running the OEM cast manifold, I'll definitely take more time to inspect the head to manifold bolts for tightness.

    I couldn't see any logical reason why my cast manifold would warp overnight, so I think that's ruled out. From the manifold down is headder wrapped however, so I'll take a close look at that too.

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    Desmond - In my case, I also thought I had a problem in the last two cylinders nearest the firewall. The hole in my header was at the very rear of the engine compartment and I could hear it distinctly on both sides of the car. I guess the sound bounced off the tranmission tunnel to the passenger side.
    Good luck!

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    Attached is the YouTube video.
    260z valve rap: 260z valve rap - YouTube

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    Hmmm, yeah that is pretty loud. It sounds more mechanical than exhaust, but it's still possible it's an exhaust leak.

    The gasket could be blown out and still leaking even though the nuts are tight. Hold a 2 foot long rubber hose to your ear and move the other end around the manifold. You will be able to hear the air rush if the manifold is leaking.

    Just throwing ideas out... What about a dead valve spring??? It's quiet at idle, but gets louder at higher RPM. If a spring is weak it could be floating the valve.
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    Wow, that's jack hammer. Just throwing out ideas, take the tape off the header and see if there is a crack in the pipe.
    It might be time to pull the head and have a look at things.
    1970 240Z HLS30 01955 March/70

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    It sounds like valve train to me. I'd pull the valve cover, start it up and use the prev. mentioned hose to find the source of the sound. I've used the hose for years. AmaZing tool. Works well for checking the carb. balance too.

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    I assume I'd be able to feel a dead valve spring by applying pressure to them? Should it be obvious?

    In my years if screwing with cars I've only ever seen broken valve springs... Do they have the ability yo just loose their tension?

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    Quote Originally Posted by Mark Maras View Post
    It sounds like valve train to me. I'd pull the valve cover, start it up and use the prev. mentioned hose to find the source of the sound. I've used the hose for years. AmaZing tool. Works well for checking the carb. balance too.
    I'll do that tomorrow.

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    As a follow up to this conversation (and hopefully help to anyone with a similar problem).

    I ordered and replaced the exhaust manifold, and it did not correct the problem.

    Grasping at straws, I decided to order two rocker arms, and lash pads. I removed and inspected the rockers and lash pads on cylinders 4, 5, and 6 and discovered that the lash pads on cylinder 6 were worn more than the others. I replaced the rockers and lash pads on cyl 6, and it's quiet as a mouse now.

    I suspect my oiling bar was not properly lubricating cyl 6. I also suspect my cam has wear on cyl 6, but I'm going to leave it for the time being.

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    There's a thread on Hybridz about rockers not being refinished or made square and they don't ride the lash pad square- which causes noise.
    Steve
    71 240z,bw-5sp 2.4-40 over,balanced,e-88,big valves,ported&polished, stage2,header, triple Mikuni's 40's
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    Mixel, that racket sounds like an exhaust leak at the exhaust manifold gasket. It is EXACTLY the same sort of tapping sound (yes, that sounds like knocking/rattling metal parts) as I had on a 318 in our boat. The exhaust risers were fussy to bolt down with the stainless studs, and they would develop leaks every 2 years or so, so I'm very familiar with this noise.

    What I learned with that boat is that leaking exhaust gasses erode gaskets and even metal, so your having tightened the #6 bolts would likely not have fixed the leak. You've got to pull the intake/exhaust manifolds and replace the gasket.

    Anyway, it's an exhaust leak. I'd bet money on it.
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    That's the thread we're talking about on hbz

    Here are the changes we've made to quiet things down.
    The rockers were not sitting straight on top of the lash pads. This solution could work obviously if you don't have stock valvetrain components.

    Before:
    Click image for larger version. 

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    During regrind with a dremel tool:
    Click image for larger version. 

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    After polishing operation, still done with dremel tool:
    Click image for larger version. 

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    Valve train is now quiet on my engine. Some small lash pad adjustments had to be made after the work. After 1000mi. every is now steady.
    Mark Maras likes this.
    Matt - 72' 240z

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