Orphaned Rocker Arm

[Candide]

Newbie warning, and first post.

Am original owner of a 77 Pickup that I have been trying to get running well for longer than I care to admit. Finally caved and took to nearby shop. They fiddled with the usual suspects and then did a compression check and discovered zero compression on number 2. Mechanic called to inform me that engine needed serious work, and the kind they will not do on something so old. Owner later informed me that rings were the problem and just not worth the cost on something so, well, worthless.

 

So I quizzed him some, and discovered they had performed a leak-down test, and air was audible through the exhaust pipe, thus rings. So I get home, and proceeded on the premise that my devoted truck deserved a second opinion on their terminal diagnosis. After a few minutes on the internet I knew it was probably exhaust valve. So, swinging over here, you all said check valve lash. I found rocker arm on #2 exhaust valve was laying in the ditch. My heart filled with relief, and some hate.

 

So, how does one get rocker back on the valve stem? I expect the spring must be compressed, and if so can anyone point me to the proper tool for this engine?

[datzenmike]

Welcome to Ratsun Candide.... and good on you for working this out yourself. However... If the rocker was off, the exhaust valve should be permanently closed and the cylinder sealed during the compression test. Possibly the valve seat has popped out and jammed the valve open. This would produce a monstrous amount of rocker arm clearance and it flew off. See what happens once the rocker is back on.

 

Easily enough to get back on. But first... if the rocker came off, the lash pad that is pinched between it and the valve tip must certainly have flown off too. Look on the top of the head around the springs, it may still be laying there. Also the small wire 'mouse trap' spring on the pivot... where is it?

 

 

Get a large screwdriver or suitable pry bar and slip under the cam from the opposite side of the spring. Place the tip beside where the rocker arm will sit on the spring's lash pad. The other end must be under the cam but clear of the cam lobe. You don't want to damage a lobe. Have the rocker handy and lift up on the pry bar. This will compress the spring and you can slip the rocker back onto it and the pivot on your side.

 

Take note that you are opening a valve and this is an interference engine. If the piston just happens to be up, the valve will bump against it. If you can't pry the valve open far enough to compress the spring you'll have to turn the engine some more to move the piston, hopefully downwards and out of the way.. 

[Candide]

Good news here. Mouse trap spring was still in place, lash pad was laying in plain sight. Rocker arm laying in ditch was just my way of saying I found it laying down between two adjacent springs.

 

I was able to get back in place as you described. Fired it up, and for about 20-30 seconds (seemed longer), clattering and not so smooth running. Then, like one through a switch, no clatter, and purring like a kitten. Took for brief drive on property, and it all held.

 

Still probably should drain the couple gallons of non-ethanol supreme I recently put in. Smells bad from tank having been dormant. From what I have read hereabouts, filling it with some seafoam additive would be advisable.

 

Many thanks to Vancouver Island. Stayed at Victoria Empress just last summer.

[distributorguy]

Do another leak down test if you have the means.  You could still have an issue that's inexpensive to repair, as opposed to putting a valve through a piston if it all goes wrong.  Or it could all be great, but why risk it?   

[datzenmike]

I'm curious why the rocker flew out.

[Candide]

Being an advocate of risk/reward analysis myself, I will order a test kit. Do appreciate the advice.

[Candide]

I have no credible hypothesis on why it bailed. Structurally, it looks sound. Your compromised valve seat theory made sense. But it has to be firing on all four now. I did not hear any valve chatter before, nor do I now. I have only touched the adjustment on #4 exhaust, and I did that cold for now just to see where we were.

I will report on my own leak-down test after I have a kit. Until then, I am scratching my head.

 

170k on original engine. Changed oil every 2-3k. Can a valve spring get weak? Felt strong when I was asking for some purchase to get the rocker back in place.

[Grahem]

ive had that happen on a 78 620 L20b, put everything back together and adjusted the valves and its been fine for years. that being said the valves were way out of adjustment.

[datsunaholic]

My 78 510 chucked a rocker the same way.  I put it back on, it came off less than 3 miles later.  Put it back on, adjusted the valves (duh) and that was 100,000 miles ago.

 

BTW, had taken it to a shop when it started missing and their diag was "Needed a full valve job".

 

Oh, and a leakdown test with air coming out the exhaust would NOT be rings, so the shop was full of BS.  Bad rings would blow air out the oil breathers.

 

Check your valve lash again, because it's possible you had something caught between the valve and seat, holding the valve partially open.

[banzai510(hainz)]

HRH on here is in Spokane maybe he can help you.

 

Rocker lash fall out all the time when they get loose. Happen to me also.

 

First off the mecahnic is a Moron he should have notice it running on 3 cylinders.

Take that fucker back and show him.

 

Run 2 fuel filters unteill you know the tank is OK. as rust will kill the idle jets.

 

I run old gas all the time 2 yrs old but not where its smelly old. Drain it or siphone it out for the lawn mowers then pull the plugg and drain it.

 

 

I would not run seafoam myself might unclog to much shit and ruin something.

 

if it running good buy a book and slowly read everything. Dont be changing shit to just change it.

 

if it running and you want to put better stuff on there then ask us first and well get the best parts for you and instructions.

 

 

olddatsuns.com

[Candide]

Datsunaholic, I'm not driving her until I personally see all four cylinders pass the leak-down test. And I will check valve lash again.

 

banzai, I was thinking of two gas filters, but questioned adding additional drag on suction side of electrical pump (3psi for Weber). But I will do it, and will pass on the seafoam too. I have no experience with it, and as you say, it is running pretty good at the moment.

[distributorguy]

You can toss a rocker arm by over revving it on decel pretty easy (missed shift).  Its the one thing I fear on the Bonneville engine with well over .600" lift at the valve.  If the valve didn't need to rotate, I'd suggest loctiting the lash cap to the valve, but that's not a good idea.  

[banzai510(hainz)]

its running already its good enuff to pass the leakdown test

[Candide]

I used to have '70 2000 Roadster that I expect had the same config over the valves. Surprised I did not toss one of its rocker arms. I was young. There may have been one or two missed shifts, arguably at high rpm's.

 

I miss that ride. But got married and wife wanted a house. Wife #1 way gone now. But so is the trusty Roadster. Oh, if we could only replay some moves. Those life-altering big mistakes.

[datzenmike]

Tossing a rocker is extremely rare and almost always a valve seat that fell out from over heating or too much valve lash. (which is totally preventable) The L series properly maintained, you can drop a brick on the gas at rev the shit out of it all day and they won't come off.

[distributorguy]

You missed my point Mike.   Revs are fine.  A quick decel from revs is where the valves can float and do something entirely different from the rocker arm.  How tall are those lips on the lash cap?  .100"?  How much lift is on the stock cam - .375"?  .450?  The fact is that its possible, and it does happen.  It is caused by increased lash, which can happen at least 5-6 different ways including a worn cam lobe, overrev on a missed shift, poor maintenance (out of adjustment), debris in the engine, dropped valve seat, stuck valve (guide problem), etc...  

[datzenmike]

Lift in an L20B is 0.413" at the valve.

 

RPMs is RPMs. 5K accelerating or decelerating how will valves know when float and the rocker to jump of? 

 

Cam wear isn't that fast that you won't hear the racket. I was talking about a properly maintained engine. A stock engine without any special cam, retainers, lash pads. There isn't much that can go wrong with it.

[distributorguy]

There's a huge difference between slowly climbing to 8000 rpm and missing a shift and revving through 8000 rpm with no load.  Slow and steady versus a Jolt.  Rocker arms will follow the path of least resistance and if the cam has a tapered lobe, the rocker will kick to the side if left "unattended" for a split second due to valve float.  Happens all the time in small block fords, and occasionally in Chevys.  That's why guide plates were designed for pushrods.  Unfortunately, I don't think anyone has ever devised any form of "rev kit"  for this engine.  Yet.  

 

Clearly this guy had it happen or he wouldn't have had an issue.  It wasn't a loose seat or he'd have a bent valve and a damaged piston.  We'll know more after a leakdown test.  I'd suspect the inner valve spring is broken.  

[Candide]

I did not examine inner spring on the suspect compression valve, but I will now. My leakdown test kit will arrive in a day or two and I will post results.

 

I am anxious about Mike's observation that with the rocker off, the valve would  be closed so there should not have been any leakage in the absence of a compromised valve. Its what lawyers refer to as bad facts.

[datzenmike]

There's a huge difference between slowly climbing to 8000 rpm and missing a shift and revving through 8000 rpm with no load.  Slow and steady versus a Jolt.  Rocker arms will follow the path of least resistance and if the cam has a tapered lobe, the rocker will kick to the side if left "unattended" for a split second due to valve float.  Happens all the time in small block fords, and occasionally in Chevys.  That's why guide plates were designed for pushrods.  Unfortunately, I don't think anyone has ever devised any form of "rev kit"  for this engine.  Yet.  

 

Clearly this guy had it happen or he wouldn't have had an issue.  It wasn't a loose seat or he'd have a bent valve and a damaged piston.  We'll know more after a leakdown test.  I'd suspect the inner valve spring is broken.  

 

I don't think we're talking about the same thing. A missed shift wasn't mentioned but a broken valve spring will lower the point where the valve will float.

 

I'm talking about a stock L20B and 5K RPM (with a 2bbl it would take forever to hit 8K+ on a miss shift, and I doubt it would ever get that high if you tried).

 

Yes at some point the valves can float but short of floating, they (the valves) have no idea if the engine is slowly revving under load or quickly and freely revving. How can they? Their job is simply to open and close the valves and as the RPMs rise the time to do so gets shorter and shorter. How fast the engine gets up to the valve float point doesn't matter. At some point the time is just too short for the rocker to follow the cam lobe when closing.

 

This might happen on a chevy but they are pushrod engines with tons of lifter and pushrod inertia and worse they are mostly hydraulic. OHC don't have either lifter or pushrods and I don't think they are really true rocker arms, but more a cam follower. Apples and oranges.

[distributorguy]

Mike, I'm done arguing.  This is stupid.  The valve stuck open from not being driven for a long time.  Pitched a rocker arm.  Now he's back on the road.  And yes, there are a bunch of ways this can happen.  Just  because you haven't seen it before doesn't mean it can't happen.

[Candide]

Leakdown test results:

 

#1 - 6%

#2 - 12%

#3 - 5%

#4 - 7%

 

#2 had the rocker off, test had leaked out tailpipe. With this test today, air was coming up through timing chain chamber - valve cover off.

 

Is it possible #2 piston rings (I presume) could now improve with consistent operation?

[banzai510(hainz)]

If the truck is running good just drive it and adjust the valve lash in case rockers might be tight.

 

Build a new motor on the side if you have OCD and those leak down numbers bother you.

 

I drive them till smoking and have spare motor ready to go.

 

run thicker oil see if that helps.

 

Oh its just a Datsun drive it

[distributorguy]

With some miles on the engine, a couple oil changes, and possibly an engine flush, if the issue is actually rings they may have a couple end gaps lined up causing a little higher leak down than normal. The good news is that rings rotate thanks to the cross-hatch (spiral pattern) on the cylinder walls, and eventually this could change.  I don't worry about leak-down losses until they're consistently over 15%, and that's pretty conservative.  Others run engines in the 30% range.  You're in good shape.