8MM retainers/locks on 5/16 valves: OK or not OK?

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A “bad fit” for a single groove valve is any combination of parts that won’t lock together.

When the parts aren’t locked together, and the tangs are bearing the load, every time the valve closes there’s a little impact load on the tangs when the valve stops moving.
At higher rpms, especially if the valvetrain isn’t in 100% complete control from the spring(which is much of the time), then the tangs on the locks are literally getting hammered every time the valve slams into the seat...... and that’s just what they look like is happening.

When the interfit is correct, the higher the spring pressure, the harder the locks squeeze the valve, relying less and less on the tangs.
This is the rationale behind the “super 7” and “super 8” locks.
A thicker cross section 7 or 8 degree lock to add more area to combat retainer pull through, but utilizing the steeper(than 10*) angle which does a better job of wedging down into the retrainer and squeezing the valve even harder than their 10* counterparts.
 
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Here’s a little thread over on the bullet where someone has a few problems going on.
school me on valve locks/keepers - Yellow Bullet Forums
The one thing that stood out to me from the pics is....... the bead lock grooves in his LS valves look much wider than the grooves in a stock magnum valve.
I can’t see how locks that would fit those valves would possibly fit a stock magnum valve correctly.
And, I have to think that when you buy some 8mm bead lock style locks.......that they’re going to work on an LS valve.

According to Manley, the std bead lock groove is .110”.
My measurement of an OE Magnum lock groove is .085”.

Here’s an easy test.
If you’re in good with a machine shop, if they have any LS heads kicking around....... see if they’ll lend you a valve out of one.
If not, you could shop around and buy whatever is the cheapest stock LS valve you can find(a stock replacement lq4 intake valve is about $5).
Test your Lunati 8mm locks and matching retainer on it.
If it all locks together properly...... then there’s nothing wrong with those parts....... they just don’t work with a Magnum valve.
The oddball part you’re fighting with might just be the valves, not the other stuff.
One more thing, I notice when looking through various catalog listings for 8mm bead lock style locks, they often specify “LS style groove”, which leads me to believe that perhaps they aren’t the same as a “std” bead lock groove.

Another possibility for the problems your having with the Crane or Manley locks and the Lunati retainers is brand incompatibility.
Sometime parts from different manufacturers don’t fit that well together.

The bead/tang of the lock should only contact the very top of the radius groove of the valve, at the very edge of where the groove and stem meet.

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Very interesting.... I had seen that illustration but had not caught that it showed contact of the bead lock only at the top; thank you. Well, RR seems to be saying that he has a lock bead that is about .020" shorter than the lock groove, based on how the lock can slide up and down the stem a bit. Maybe he will chime in and confirm that, but it sounds like that his vertical clearance between lock bead and groove is OK.

So IMHO, that leads back to what the acceptable tolerance in the 2 diameters: lock ID and stem OD.

And RR refers to the locks not falling off the stem but perhaps that is a misinterpretation of this statement from your linked Yellow Bullet thread attributed to Ferrerea: " With the valve sitting on a table you should be able to put the locks on, pull the retainer up into the locks and let go and the retainer shouldn't be able to fall down". So perhaps RR is not checking them correctly.
 
So IMHO, that leads back to what the acceptable tolerance in the 2 diameters: lock ID and stem OD.
Click to expand...

The answer to that is the same as before........ if the pieces won’t lock together, they are outside the usable tolerance.
It’s that simple......not locked = no good.

The valve locks are fundamentally “collets”.
As Chris mentions in the YB thread, the tangs are basically there to locate the locks...... not to bear the load.
If the pieces don’t lock together, they’re not functioning as designed, and will likely cause problems.

Here’s a good blurb on the Texas Speed site:

“It is critically important to make sure valve locks match the valve size. There should always be a small gap between the two halves of the lock when they are properly positioned on the valve stem. If the two halves fit together without a gap, they are too large. If the locks fit tight to the stem and leave a gap between the middle of the lock and the O.D. of the stem, the locks are too small.

Most people believe that the tang inside a valve lock holds the retainer and valve spring in place while the engine is running. This is not the case. The cross-section of material in the tang is not strong enough to withstand open spring loads of 1000 lbs. or more. The sole purpose of the tang is to temporarily locate the lock, retainer and spring relative to the valve until the taper of the retainer can nest around the outside surface of the lock. This creates a “collet” effect that binds the two together. The more spring force exerted on the retainer (as the valve opens), the more force applied by the “collet” effect to keep the retainer and lock in place.
 
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Reading back through the posts...... there was this:
I got the new locks from Summit: Manley #13151-8 (X2 boxes of em), says on the box: "bead loc for .3110" stem valves use 10 deg retainers standard installed" I mocked one up on a valve with the Lunati retainers & everything appears dead on & tight as opposed to the ~.020" back & forth clearance I had with the prior 8MM locks.
Click to expand...

So, the -.050” installed height version of those locks should fit fine, and fix the problem of the valve tip not sitting proud of the retainer.
 
these 5/16 locks (Crane 99121) are giveing me MORE I.H. than the Lunati 77132 (8MM) locks (both useing same Lunati retainers (75740). OK, I went ahead & assembled it with the crane 99121 (5/16) locks/lunati 75740 retainers that lunati say are OK for 8MM or 5/16 valves, with no inner spring. With me haveing ground off the lash cap perimeter & all assembled, the valve tip is just slightly above the raised perimeter of the retainer & there is a concave dip in the retainer from the perimeter inward so I dont think the roller will hit anything unless the rocker goes sideways quite a bit (the OE mag guide plate pushrod slot is wide but I think it will be OK (??). Hopefully soon I am going to fire it up/breakin & this is where I am at now but I will change anything I have posted if you guys think I should do so. (I felt the love on this one, & it is for sure very much appreciated, thank you!) RR
 
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