Sunken valve with no lash adjustment left.

Engine, Transmission and related drivetrain.
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datzenmike
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Sunken valve with no lash adjustment left.

Post by datzenmike » 30 Mar 2016 20:14

I know this happens but not often. But say you have your rocker arm post turned all the way down and can't get your lash above 0.004" AND you don't have a spare 210 head, not soon getting one and you're broke so it isn't getting new seats soon either. Well there is an easy enough fix that will help you get another few months out of it, maybe more, until you can source a replacement. It's not intended to be permanent, hell in the long run it might not even be good for it but it will allow you to set your lash and keep it running.

Remove the rocker pivot. I also removed the sleeve it fits into. When I was done I found you probably don't need to.
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I used a second lock nut to jam against this one so it was easier to hold while grinding the nut down to 2/3s it's original thickness. From 0.320" to 0.215"
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This is the post bottomed out, before. Note the lip that secures the mousetrap spring clip just above the sleeve nut.
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Note the lip has been ground down also by half at least but still holds the mousetrap spring clip..
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I wasn't sure how much I would get so probably went overboard. The posts on either side were bottomed out and a straight edge placed across them. The shaved nut and sleeve adds 0.110" of adjustment. That's 2.75mm, way more than anyone could need but it shows it's easily done. I checked and the pivot post does not bottom out either. Now you can easily adjust and get that extra 0.010" valve clearance you need.
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I suppose as the valve rises up into the seat the cam lobe wipe pattern changes?
"Nissan 'shit the bed' when they made these, plain and simple." McShagger510 on flattop SUs

Three B's Racing
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Re: Sunken valve with no lash adjustment left.

Post by Three B's Racing » 31 Mar 2016 08:07

Yes!!!! I did this around `75 for the exact same reason, living on my own and broke. But shortly there after I got another head at the Ecology when heads were a dime a dozen.
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datzenmike
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Re: Sunken valve with no lash adjustment left.

Post by datzenmike » 31 Mar 2016 17:15

Necessity is the mother of invention.

Was wondering what 1 mm of pivot post adjustment works out to at the valve lash end. If the rocker ratio is 1.48 would 1mm = 1.48mm??? If so that's like 0.060" Holy crap that's tons.
"Nissan 'shit the bed' when they made these, plain and simple." McShagger510 on flattop SUs

510rob
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Re: Sunken valve with no lash adjustment left.

Post by 510rob » 31 Mar 2016 18:11

I want to see the head when it eventually comes off :)

One of my valves is slowly sinking too...

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zKars
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Re: Sunken valve with no lash adjustment left.

Post by zKars » 01 Apr 2016 06:17

Interesting idea. As long as the cam wipe contact patch stays ON the rocker pad, then it's likely not going to cause any serious issues. Get the Sharpie out, color the rocker pad and rotate that cam once and see where the black remains. If you can't see a black bit on either end, that lobe is running off that pad. Not good for lobe life!

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Re: Sunken valve with no lash adjustment left.

Post by 510rob » 01 Apr 2016 11:14

I suppose that another potential issue to keep an eye on is that as the seat sinks, the valve spring becomes less loaded when the valve is in its 'seated' position.

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RMS
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Re: Sunken valve with no lash adjustment left.

Post by RMS » 01 Apr 2016 13:03

I too have a head that ate up a seat and clearance on no 3 intake within 1500km.
this is great to keep ya rolling but what is the underlying cause of valve sinking ?
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James
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Re: Sunken valve with no lash adjustment left.

Post by James » 01 Apr 2016 14:46

RMS wrote:I too have a head that ate up a seat and clearance on no 3 intake within 1500km.
this is great to keep ya rolling but what is the underlying cause of valve sinking ?
Most of the time - it is from a head that doesn't have steel seats for the valves (they used to be bronze - worked well with leaded gas). With our current gas, they get beat up, and the valve pounds the seat away.
Finished is better than perfect......

datzenmike
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Re: Sunken valve with no lash adjustment left.

Post by datzenmike » 01 Apr 2016 16:52

Not sure when Nissan switched to hardened seats. '72? or later L20B?
"Nissan 'shit the bed' when they made these, plain and simple." McShagger510 on flattop SUs

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