Valve Train

Engine, Transmission and related drivetrain.
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CP
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Valve Train

Post by CP » 01 Aug 2018 20:34

So we had this little part appear to jump out of its position between the top of the valve and the rocker. I have no idea why this would happen and wondering if anyone else has experienced this. I don't think the valve adjustment was too loose, If anything I think our valves were adjusted too tight as cannot seem to get a feeler gauge between the cam lobe and the rocker.
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Byron510
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Re: Valve Train

Post by Byron510 » 02 Aug 2018 06:37

The only way this could happen is if the valve itself does not return to the seat, creating a moment where excessive clearance is made, allowing the lash pad to be able to get spit out. Otherwise there wouldn’t be the gap nessesary for the lash pad to be able to fall out.

Other than the possibility that the lash pad had been assembled incorrectly at some point in the past, or and valve keepers were not seated in the valve, there must be another issue.

So one would have to check the valve stem and the guide itself. Could the valve be bent and it’s operation through the guide not as smooth as it could be? Is the a galling issue in the guide? Something not allowing the valve to move unrestricted in the guide.

There’s one more scenario. I once spit out a lash pad, but it’s because the booster venturi in a 32/36 Webber physically broke, falling past the throttle butterfly and into the motor. It got caught under the valve, holding it open for a few cycles, the lash pad was spit out and the rocker actually came off, marking the cam. The valve was bent, and the piston took a hard enough impact that the action on the wrist pin was tighter that the other three when I disassembled the whole thing.

An very odd line of events, but this was a personal experience many years ago.

In summary, you’d need a lot of clearance in order to eject a lash pad, so something must allow for that clearance to take place.

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CP
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Re: Valve Train

Post by CP » 02 Aug 2018 06:46

Thanks Byron, I will have a closer look at the valve operation tonight.

AIShelby
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Re: Valve Train

Post by AIShelby » 02 Aug 2018 16:43

I agree with Byron. Check for a stuck valve either valve guide, bent valve, ingesting something in engine,or drop valve seat. I had a rocker pop off and found dropped valve seat.

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CP
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Re: Valve Train

Post by CP » 02 Aug 2018 18:30

I have pushed on the valve and it seems to travel smoothly, in the same manner as the valves beside it. I am going to get my hands on one of those bore cameras and have a look inside at the valves and see what that looks like. One thing I do notice is that when I put this lash pad in place it seems to sit about 1/32-1/16th of an inch higher. Almost like the valve is sitting a little higher. Cant say I ever noticed that before.

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Re: Valve Train

Post by Three B's Racing » 03 Aug 2018 04:51

CP wrote:
02 Aug 2018 18:30
I have pushed on the valve and it seems to travel smoothly, in the same manner as the valves beside it. I am going to get my hands on one of those bore cameras and have a look inside at the valves and see what that looks like. One thing I do notice is that when I put this lash pad in place it seems to sit about 1/32-1/16th of an inch higher. Almost like the valve is sitting a little higher. Cant say I ever noticed that before.
Has the head ever been rebuilt? If not it's possible it has the original soft brass seats which likely are sinking which at some point that valve will no longer be adjustable raising the valves lash pad. Did you notuice if that valves valve spring retainer is sitting higher than any of the others? and how high above the lash pads pocket in the valve retainer is the rocker arms contact surface on lash pad sitting? Because if it's to high that can cause the lash pad to pop out.
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CP
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Re: Valve Train

Post by CP » 03 Aug 2018 07:28

Thanks for the input. I don't know the history of the head except that it hasn't been redone since we owned the car. It has had work done though because it has a bit of a cam in it and the retainers are not stock. I will try to post pictures this evening.

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CP
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Re: Valve Train

Post by CP » 03 Aug 2018 20:40

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So I looked things over and every thing seems to be in order. The valve moves freely like all the others. I reassemble it and notice the rocker doesn't quite cover the lash pad as completely as the others. All of the others are consistent. Could this be a bent valve or a somehow bent pivot on the other side of the rocker

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Byron510
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Re: Valve Train

Post by Byron510 » 04 Aug 2018 06:58

I see that someone has upgraded to the lighter aluminum retainers. There are different shoulder heights retaining the lash pads on these retainers, and different spring installed heights available.
In the past I’ve had reports that the shallower seat in some of these retainers can allow the keepers to be spit out in high RPM operation. Usually aluminum retainers are use in conjunction with higher lift cams, and they are sometimes chosen when thinner than stock lash pads are utilized. Two factors come together at this point;
-Aftermarket lash pads have a flat bottom, where an OEM Nissan lash pad has a recess where the pad contacts the top of the valve directly.
-Aftermarket aluminum retainers can have shalower shoulder to allow for thinner lash pads (larger base circle on hi lift cams)
These two items combined can leave a significantly smaller shoulder to support the lash pad at the top of the retainer. At higher RPM, the lash pads do start to bounce around quite a bit, and they need the support that the OEM engineers designed in.
Conclusion; Did you notice that the lash pad had a flat bottom and is there an aftermarket cam in place and are the aluminum retainers really nessesary? Is this a continually high reving motor? If the answer is no, I’d simply install the OEM steel retainers, recheck the wipe pattern on the lash pads to make sure the pattern is more less centered and call it done for reliability sake if this problem persists.

Just a thought.

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bertvorgon
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Re: Valve Train

Post by bertvorgon » 04 Aug 2018 07:34

Is it just me or does that one spring retainer look like it has been contacted? The anodizing has some marks on the edge. That rocker is way too far back from the center of the lash pad.
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abisel
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Re: Valve Train

Post by abisel » 04 Aug 2018 18:23

bertvorgon wrote:
04 Aug 2018 07:34
Is it just me or does that one spring retainer look like it has been contacted? The anodizing has some marks on the edge. That rocker is way too far back from the center of the lash pad.
yes and yes. Also, the wear pattern on the cam lobe doesn't look right either. Or is that just a reflection?

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CP
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Re: Valve Train

Post by CP » 04 Aug 2018 20:53

So in answer to all the questions:
Yes the lash pad has a flat bottom
Yes I believe it is a bit of a performance cam although I don't know the specs.
Yes the valve spring retainer was contacted.
The war pattern is fine, just glare from the picture.

My mind is the rocker is too far back on the lash pad although I don't know why. It appears nothing is bent.

My quandry is do I yank the head to see what's going on or try to remove the spings with the head on and see what if anything shows up.

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bertvorgon
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Re: Valve Train

Post by bertvorgon » 04 Aug 2018 22:46

See if the length of the rocker is shorter than the others, you never know what anomaly may have happened.
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CP
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Re: Valve Train

Post by CP » 07 Aug 2018 08:57

So the one rocker in question is shorter. My question now is, I have a stock 210 head. The one presently on the car is a U67. Can I swap the stock rockers, valve spring retainers and lash pads to this engine even though they may be after market springs.

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CP
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Re: Valve Train

Post by CP » 17 Aug 2018 16:42

Well, thought we had this licked. Went back to the stock valve spring retainers and lash pads. Valve operation all seemed fine with everything moving smoothly...for a couple days. On the way home from a show last night it reared it's head again. It appears the #3 intake valve is sticking. Right now it won't close so I am thinking something broke, perhaps the valve seat. Probably going to pop the head off tonight, but I think were done for the season...Rats

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