What causes rocker arms to pop off?

[Force Fed]

Found #2 had 0 compression the other day, pulled the valve cover to look at the valve train and a rocker arm had popped off and was apparently causing both valves to open together. Stuck it back on and check a few others to see how much lash there was. Most had a hair of play, couple more than the rest, but the one that had popped off didn't seem to have any play, I could wiggle it at all by hand. Checked compression again, got 180 psi (as do all the other cylinders). Cranked it up and it ran pretty good, no valvetrain noise.

Started it today a while ago, and not there is a distinct tap coming from the valve cover again. It's kinda intermittent but ticks more than it's quiet. Seems to have a skip again too, so I suspect that rocker has again come off.

Would the lash being set too tight cause it to pop off easier? Or is the rocker arm or lash pad worn out maybe? I don't see it being a seat dropped out or sticking valve, as I wouldn't have good compression if that had happened. It is an N47 head, if it makes any difference. I forgot to really look at it, would it have solid or hyd lifters? It's on an F54 block in my 240Z.

[Nissanman]

As far as I know, all L series engines have solid valve lifters, thus requiring valve lash or clearance to be set manually.

The rockers should all have a Rocker Arm Spring Part #31 to hold the rocker captive on the Rocker Arm Pivot Part #28 hooked into the Rocker Arm Spring Retainer Part#30.

Are yours still there?

Without those little suckers the rocker can wander and pop off the works.

[Arne]

There were a few heads on some ZX Turbos (P90a, but apparently not even all of those) that had hydraulic lifters here in the US, but only those few. All other heads were/are solid.

[ktm]

There were a few heads on some ZX Turbos (P90a, but apparently not even all of those) that had hydraulic lifters here in the US, but only those few. All other heads were/are solid.

Primarily the 1983 280zx turbos. Pre-1983, the turbo's came with a P90 head that utilized solid lifters. Some P90as on the 1983 turbo came with solid lifters, but most of them are hydraulic.

FYI, the P90as do not utilize the rocker arm spring.

Edited October 16, 2008 by ktm

[Mr Camouflage]

I thought they were rocker arms.

[carrott]

Sounds to me like a valve is sticking slightly open and allowing the lash pad to pop out then the rocker arm becomes slack .This is common if the car is not frequently driven and there has been a lot of oil leaking past the guides, over time it will harden up and prevent the valve closing properly which is the start of your prob's , If the the bottom end has good compression and oil pressure consider removing the head for a service ,preferably by a z specialist .

Good luck.

[rxsleeper]

Over revving on a down shift can cause the rockers to pop off. I hit about 7400 on a down shift when the red mist got in my eyes at turn 1 Luckily nothing major damaged. Finished the race on 5 cylinders and then recovered the lash pads from the pan later.

[Force Fed]

Yeah the springs are still all there, the rocker was actually still held onto the pivot, it had just hopped off the lash pad and skipped off to the side, and jammed between the valve springs. The car did sit for about 8 years before I got it, and the guy I got it from got it from a kid who apparently had no idea what he was doing. So who knows what the lash is at, I know they are not all right. What are the lash settings for these?

I'm gonna pull the vc off again hopefully today and see if it's popped off again, or if it's another one, or maybe it's just way out of adjustment when cold. I did buy a set of skinny motorcycle feeler gauges yesterday to use on it, as I think the rocker tips are kinda narrow, right? Ran into that problem when trying to set the valves in my Tercel

[Nissanman]

For the 2.4, 2.6 and 2.8 with solid lifters the valve clearance is: -

HOT

Inlet.........0.010"[0.25mm]

Exhaust....0.012"[0.30mm]

COLD

Inlet.........0.008"[0.20mm]

Exhaust....0.010"[0.25mm]

[Force Fed]

Well the rocker arm was still on, but the lash pad had popped out again. Put it back on and started to adjust the lash (searched and found the settings, .010 Int .012 Ex), but the rain stopped me at #2 exhaust valve So far they've only been out a little. The valve seems to pop back up pretty quick on #2 int (the one that keeps messing up), but I didn't push it down very far, just enough to get the lash cap back on.

Edit: Thanks Nissanman, I was setting them cold w/ the hot settings Your post wasn't up when I starting posting, I'll change the lash settings when I work on it again.

Edited October 18, 2008 by Force Fed

[tibZ]

I think carrott is right, at the very least you have a sticky valve. This post may help you.

http://www.classiczcars.com/forums/showthread.php?p=258354&highlight=stuck+valve

I haven't pulled my head yet so i don't know what causes my issue. Like yours, it sat for years.

[enzo250GTO]

Hi, Check the lash pad to see if one of the sides is broken off. If one side is missing the rocker arm will slide off . Regards David.