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Shimming Lash Pads


JohnH

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Is it a safe & reliable to shim the lash pads for normal engine use. I have a Nissan billet 530 lift regrind that I checked the rocker wipe pattern on & requires a .300 lash pad. I'm having difficulty finding .300 lash pads. MSA does not have them at the moment, Brian at Z Car customs is on vacation,  Courtesy does not have them, Nissan does not have them & I'm waiting back to hear from others. I have .260 lash pads & Isky retainers so I would only shim them under the pad .040. Any thoughts on this or anyone know where I can get a set of .300 L6 lash pads.

 

Thanks

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Isky has them.

 

Leave out any idea of adding more parts to fly out into everything when you start thinking about the valvetrain. With that much retainer holding it in place, it *might* all stay together, but with the revs you'll be running with that cam profile, I'd want to be *sure*. If you do use shims, they need to be hard...the lash pads are HRC52-55, last batch I checked, which is very hard but can be machined with carbide tooling.

 

Make sure your retainers can handle a 300thou lash pad, there are two heights that isky sells/sold and three heights that Nissan Comp sold (they sold stock, isky shallow, and isky deep, IIRC.)

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Good luck on that one.  Never even heard of ones that thick. Schneider has 220's.  What is your base circle?  Must be like 1.1" or less.  Ensure your retainer pockets are tall enough to support those or they may pop out.  I have shimmed lash pads.  Put the shims on top of the valve stem.

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Base circle measures 1.056".  Ramps look fairly steep too. Maybe too steep. The retainers are .230" deep measured from the top of the retainer to the top of the valve stem & were used with .260" lash pads. With the .260" lash pads & .040" cut worth of feeler gage underneath the lash pad sits about 3/4 in the retainer.

 

dapiper What did you use to shim your pads?  As Xnke mentions Rockwell hardness is a concern of mine. I can get "blue steel" tempered shim stock in .042. sheets but would have to cut shims to shape. I have also been combing the internet for valve shims used on other vehicles & motorcycles but have not found a compatible diameter or thickness yet.

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Total rookie on head work, but would new valves be an option?  If you can't find pads, or they're very expensive.  Maybe the valve tips were dressed to equalize lash and it was overdone.  New valves might get you back to where you need to be.

 

Page 80 of the Honsowetz Modify book says that Nissan Motorpsorts has up to .330" stock lash pads.  Of course, that was in the year 2000.  They might be out there somewhere.

 

Feel free to ignore...

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This is from Mike of MSA.

 

"At this time all of the lash pads are out of stock. I spoke to my buyer yesterday and he is thinking that Nissan is going to discontinue the lash pads in all sizes. It has been getting more difficult to get them from Nissan. We are currently looking to see if there is a manufacture that will and can make them for us.
Mike"
 

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Funny, I called Nissan Comp down in Smyrna and while many sizes are out of stock, there are plenty of stock in selected, thick, sizes.

 

I am considering just buying a few dozen....they're not too expensive compared to getting them from Isky or MSA.

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Wow, that BC is tiny.  Hope you got lots of head, manif and high CR for that cam.  Schneider has 220's.  I used SS feeler gage stock and cut little squares to fit under the lash pads.  Lets see, calc lash pad thickness:

 

Pad = (stock BC - cam BC) / 2 / rocker ratio + stock lash pad = ((1.3 - 1.056) / 2 / 1.5 ) + .117 = .198

 

Something's wrong.  Is your head a P90?  NewZed may be on to something re valves being trimmed too much to equalize.  I NEVER trim my stem tips, cuz of loss of tip hardness.

 

If you can, remove springs and measure inner pocket height (inner spring perch to stem tip without shims.  Should be 1.610 - 1.625 on new N42.  Outer pocket will be .050 more.  Of course depends on if new valves, new seats or how much grinder pocketed valves into head.  Normally, exh valve pocket taller by .020.  Did you use any cam tower shims?

 

My base circle is 1.25I, 1.23E and I am using 160/140 pads

My SS-56-SS-54-112 RB cam used 200I/175E pads

Edited by dapiper
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Wow, that BC is tiny.  Hope you got lots of head, manif and high CR for that cam.  Schneider has 220's.  I used SS feeler gage stock and cut little squares to fit under the lash pads.  Lets see, calc lash pad thickness:

 

Pad = (stock BC - cam BC) / 2 / rocker ratio + stock lash pad = ((1.3 - 1.056) / 2 / 1.5 ) + .117 = .198

 

Something's wrong.  Is your head a P90?  NewZed may be on to something re valves being trimmed too much to equalize.  I NEVER trim my stem tips, cuz of loss of tip hardness.

 

If you can, remove springs and measure inner pocket height (inner spring perch to stem tip without shims.  Should be 1.610 - 1.625 on new N42.  Outer pocket will be .050 more.  Of course depends on if new valves, new seats or how much grinder pocketed valves into head.  Normally, exh valve pocket taller by .020.  Did you use any cam tower shims?

 

My base circle is 1.25I, 1.23E and I am using 160/140 pads

My SS-56-SS-54-112 RB cam used 200I/175E pads

 

 

Nope. Brand new valves for N42 head. Head has been shaved & ported & will be fueled by triple 45's

 

My calculations. Rounded off to nearest 10th inch

 

(1/2 base circle diameter of stock cam - 1/2 base circle diameter of reground cam) x rocker arm ratio + stock lash pad thickness = new lash pad thickness or X

 

(.5 x 1.30 - .5 x 1.056) x 1.48 + .120 = X

 

(.650 - .528) x 1.48 +.120 = X

 

.122  x 1.48 + .120 = X

 

.180 + .120 = .300         

 

Verified by visual wipe pattern inspection on rocker arms at random exhaust & intake springs.

 

The .300 lash pad is not out of the ordinary for this .530 lift re-grind when considering the recomended lash pad from Isky for the fresh billet new cam is .260 ". Hence where I got the .260 " lash pads. What is out of the ordinary are companies that expound on being Datsun Z specialist's can't keep a relatively inexpensive & common part on the shelves. The amount of common parts that are no longer availble or becoming rarer is enough to question the viability of keeping an L series engine in the Z.

 

 

 

 

Edited by JohnH
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You DIVIDE by rocker ratio.  Do some measurements.  For example, set clearance at cam to 0.010 for intake per stock spec.  Measure at valve is 0.007.

 

According to Racer Brown you have that calculation wrong.

 

"Any material removed from the base circle radius of the cam lobes (1/2 the base circle diameter) must be replaced at the valve stems as a function of rocker arm ratio. The stock cam base circle diameter is 1.300 inches 0 a base circle radius of 0.650-inch. Now assume that the base circle diameter of the new cam is 1.200 inches (0.600-inch base circle radius), 0.050 inches smaller on the radius than stock. The book gives the stock rocker arm ration as 1.5 to 1, but I have found that 1.48 to 1 is a more reliable number, although we may be quibbling. Multiply the 0.050-inch difference in base circle radius by the rocker arm ratio --say 1.5 to 1, and you come up with a number 0.075-inch. This is the amount the calve lash pad must be increased in thickness over and above the stock lash pad thickness for the rocker arm geometry to come out someplace close to stock, assuming nothing else has been changed."

 

datsport.com/racer-brown.html

 

see Rocker Arm Geometry

 

I think you should do some measurements on your heads & all the other peoples heads you have "helped" with your "calculations".

Edited by JohnH
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  • 3 months later...

great thread.. if i may.. i would like to ask a question about the geometry here..

what are the implications of having the wipe pattern closer to the pivot side.. say about 1/16" offset from the middle vs having it in the middle?

i ask because i have heard some shoot for that.. and i don't know why.

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More duration, more lift.

Playing with lash only affects duration and valve timing events.

By selectively altering variables antagonistically or sympathetically you can deduce which direction to go for power, how to optimize torque in a given set of parts, etc.

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