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Valve spring installed height.


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The background.  L-16 engine from 1970 521, original engine.  Engine had used up valve clearance adjustment, had an oil leak, and timing chain noise on startup.   Engine started to miss, felt weak, compression was 60, 120, 120, 150.  Engine was pulled, head removed.  Intake valves were sunk, removing one intake valve revealed brass (bronze) valve seats. Had a valve job done on cylinder head.


Valve job was done, and I checked the valve spring installed height.   Nissan service manual L-13, L-16, & L20(a) has specification of 38.9 MM height, other info I have has 40.0 MM height.  I measured 40.3 mm to 40.97 MM.  How critical is valve spring installed height?


I also checked the valve length.  My Nissan FSM had 115.9 mm for intake valves, and 116 mm for the exhaust valves.  Intake valves measured 116.43 mm to 116.92 mm, and exhaust measured 117.24 mm to 117.73 mm.  


There is some correlation between the longer valves, and greater valve spring installed height.   In your experience, do valves stretch much in Datsun engines?  My calculations seem to show that if I had valves with the factory service manual length, valve spring installed height would be much closer to factory specifications.

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40 thou loose is a bit much but it will work. You have some options here. Valve shims come in 15,30,60 thou increments usually.

You could put a 30 in there and be only 10 thou loose which is fine. Or you could put a 60 in there and be 20 tight. Or you can stack a 15 and a 30 and be really close. On a stock rebuild with a stock cam and re-using stock springs id put a 60 in there just to get a little more pressure. If its new springs id stack a 15 and a 30.


Are u measuring with the stock spring shim in place? The springs cannot be placed directly on the aluminum or death will occurr.


Also, how are you measuring this? Those wind up height installers are junk, so are snap guages

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Hardened seats, YES!


This is how I measured the spring installed height.  I used some light springs from Summit Racing, and assembled the valve, shims, retainer and retainer locks.  You can see the lightweight spring in the second picture.


This is an old pair of adjustable calipers I had.i



I carefully adjusted the calipers until there was a very slight drag at one point as I rocked the caliper end points back and forth under the retailer, and on the shim in the head.



then I measured the adjustable caliper with a digital slide caliper.



I know I can make this measurement closer to factory specification by shimming the valve spring.  But I am also wondering if the reason for at least part of this measurement being too big is have the used valves currently in the head stretched slightly?  In other words, would getting new valves be a better option than shimming the valve springs,


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Length (L20B)

Intake...... 114.9-115.2mm

Exhaust... 115.7-116mm


Installed spring height, intake/exhaust




Can't see the valves stretching or everyone would be complaining. Valve seat position would affect this. (how well/accurate the head was rebuilt) Grinding the seats would increase this. Lapping the seats would increase this. (very slightly)  Seat wear would definitely increase this.


It's a small thing. Measure the spring closing pressure at your position and the 'correct' height. Won't be measurably different. No two springs will be the same height or pressure either. You can always throw a shim in there.

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OK, if the valves are not the same height all the way across installed then the wrong valves were bought, or the wrong valve seats were bought/installed.

What I meant was that maybe lash pads could be used to correct the issue of some of the valves being higher than the other valves if one doesn't want to disassemble the head and start over.

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All the valves were used.  I just got done measuring another set of 8 valves, and every one I have is longer than the length posted by Datzenmike.  I am wondering if anyone has a set of new L-valves, to verify the length when new, or has checked the length, and wrote it down.


The head is dissassembled, and sitting on a bench inside my warm house.  So I want to take the time to get it as close to correct as I possibly can.


This head was put together with 38 MM intake valves, and 35 MM exhaust valves.  If I order new valves from Nissan, what engine used this combination of valves.  I know USA L-16s used 38mm and 33 mm valves. 

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  But I am also wondering if the reason for at least part of this measurement being too big is have the used valves currently in the head stretched slightly


If you were talking about early air cooled VWs, I'd say yes.

That was a big problem, and if you didn't check valve clearance regularly, and catch an exhaust that suddenly tightened up, it would drop the head off into the engine, and kill it.


Datsun, I've never seen it happen.

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Different lenght valves will affect the rocker arm geometry aka; Cams wipe pattern on rocker arm. Typically new seats would all be installed same depth and cut same depth same with valves. Then valves installed and a straight edge placed across the tops and all tall valve tips ground to match but only to a point. This helps with using all same thickness lash pads when setting up rocker arm geometry "Wipe Pattern" otherwise your having to use different thickness lash pads which is ok but only up to a point dependent on the valve retainers your using. I don't believe valves stretch that much otherwise they'd be breaking.

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Valves that have been ground will also sit deeper in the seat, causing higher installed spring height.  That's something I forgot to take into consideration on the last engine I spring-balanced (with shims).  If I'd been thinking ahead I would have used the least-ground valves in the most-ground seats and vice-versa.  Since that engine had 24 intake and 24 exhaust valves, I had a lot to choose from...

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You probibly gained some height in the valve face, if they just touched the exhaust seats and didnt replace them, they probibly cut your new intake seats to the same depth so you dont have your valve height all over the place. The valve groove, keepers and retainer could have slightly worn and bumped it up a few thou too.


Slam some shims in and run it! Dont forget to shim the inside and the outside.


Btw your way of checking height is fine.

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