By Fergus Ogilvy:
Assemble the valve locks on a valve and using your thumb and forefinger raise the retainer to its full height. If the assembly defies gravity and remains in place and doesn’t rock, the valve locking assembly is acceptable. If, however, the assembly falls apart, the valve locking mechanism is deficient in one or more of its dimensions.
Even a brief assessment of the valve lock will quickly convince us it’s at the heart of the competition valve train.
If engines are exposed to over-revving—provoking valve springs and sometimes valve retainers to float—we are dependent upon the valve lock to remain locked or else…
Pioneered by the original equipment manufacturers and virtually fail-safe, the ubiquitous 7-degree valve lock has been the standard for decades. Its 7-degree outer tapered shape fits into a similar taper on the valve spring retainer. Some engineers refer to its 7-degree angle as a locking taper.
The outer angle, which might be 7, 8, or 10 degrees, is measured on a sine vice. The narrower angle creates a tighter lock; the wider angle allows easier separation.
But, the shallower the taper, the harder it is to separate and remove, and drag racers constrained by time, understandably, grew impatient. It was infernally tedious, frustratingly tight and thus inconvenient. In their desire for efficiency, the 10-degree taper emerged.
Though the 10-degree valve lock offers faster dismantling, the wider angle, unfortunately, cannot function reliably for sustained periods of valve float as the retainer can become separated from the valve lock, potentially causing the locks to fall out.
The outer diameter of the valve locks is measured at a specific point on the angle. A race engine builder might specify a gauge dimension of, say 0.575in OD at 0.300in high. To check this dimension, he acquires a 0.575in ring gauge, assembles the locks onto the valve, and measures the position on the angle.
The inner diameter of the valve lock must fit the valve stem precisely. If it is too large the locks may have only two points of contact, resulting in a poor connection with the valve stem. If it is too small the locks could spread and break. Case hardened smaller types are more susceptible to breakage.
Thus an 8-degree configuration is often the better compromise for the racer. It offers better retention during valve float than its 10-degree counterpart and remains in unity with the retainer under severe conditions. In addition, the 10-degree design will reveal wear on parts during valve float that don’t usually sustain wear.
The top region of the valve lock is its most important portion. Whether formed with a radius or with a square shoulder, this is where its locking tab interfaces with the keeper groove on the valve stem. Square tabs usually protrude into the keeper groove about 0.011in or 0.012in; radius tabs 0.020in to 0.022in.
Identifying the telling signs of over revving
Engine builder Jon Kaase says, “Sometimes if the valve train gets out of control and it’s bouncing around, the valve locks get chafed on their bead locks or scored on their half-round portion beneath the bead lock—that is, the part that sits on the stem of the valve.”
A common sign of over-revving is often observed in the contrasting appearance of the valve locks: the locks on the exhaust valves look like new while the intakes have a shiny appearance. This is probably explained by the fact that the intake valve is slightly heavier and also the intake cam lobe is more aggressive.
Kaase continues: “Sometimes when you remove the valve covers you can see what appears to be really dark oil on top of the retainer, which is a sign that something is awry. Things are moving around and the retainer is accumulating microscopic particles of metal, causing the oil on top of the retainer to be dark looking.”
Ideally the valve locks should have full engagement with the valve stem, the keeper groove, and the angled interface of the retainer—the fuller the engagement, the stronger the joint. Further, it is preferable that no part of the valve locks should protrude beneath the retainer.
Moreover, valve lock joints are strengthened by the presence of a deeper skirt—a greater clamping area beneath the keeper groove. This directs stresses to the valve stem below the keeper groove. Thus the groove and more importantly the area above it are less threatened.
Finally, the three critical dimensions of the valve lock are as follows: the outer angle, the outer diameter, and the inner diameter.
Could you send info?
I have 10-degree valve locks on my BBC. The heads are cast 049. The top of the valve stem is even with the valve locks, and I’m concerned that the rocker arm will be pushing down on the lock. This is just a street rod. I’m not racing this car. Should I change these to a 7-degree lock so the top of the valve stem will be higher than the lock?
Mike: There’s hardly sufficient information provided to make a meaningful recommendation. Valve locks and spring retainers are selected to create a desired valve spring ‘installed height’. Regarding 10-degree locks, most manufacturers make them in three different dimensional configurations – usually 0.050in intervals. So this may provide a solution, except the manufacturer needs to discern which lock you are referring. If this suggestion suits, send an example of your valve lock to the following address:
Trend Performance
Attn: Andy Anderson
114 Lime Kiln Lane,
Pisgah Forest,
NC 28768
Tel (828) 862-8290
Another option might be to consider a 10-degree lock with a recess and lash cap.
Thanks Andy for the education on this matter. Lunati has a neutral lock that is also recessed. With this I will still be within my valve spec range. As you implied, precision in valve train assembly is essential or trouble will soon follow. In my younger days, we would install a big cam and run it until something broke, which usually didn’t take long. I’ve got a little smarter now and see the mistakes I made then and hope not to repeat them. Technical help is a must to get it all working right. Thank you again.
I am sending a Manley valve to my head builder that Manley lists as 11670B and with a stem diameter of 0.3125in. I’m trying to insure it receives the correct lock to suit my 10Ti retainer (Chet Herbert HER R10-1.437T). I have the Manley catalog but can find none of 0.3125in diameter. Further my builder says the 0.3125in stem spec’d valve in the catalog is, in fact, an 8mm valve. My calculator informs me that 0.3125in is exactly 5/16in and 8mm is 0.3150. I called Manley and they appeared confused, even more than me. Can you help?
Thanks Keith
Keith, It’s an enigma. I’ve tried to reach Andy Anderson both yesterday and today but no joy yet. If he doesn’t respond, please try his mobile number tomorrow (828) 862-8290.
Thank you Vic,
In the meantime I’ve been trying to solve the mystery and just got back to your website today. I’ve called Comp Cams tech help, Summit tech, and Crower, who tried the most to resolve the problem, although they did not have the solution. However, they referred me to an Andy, who I bet is the same guy you are referring to:) Thanks for the numbers will try tomorrow.
Keith,
Andy Anderson has specialized in the development of racing valve train for forty years, and, like me, he may have entered semi-retirement. However, I’ll try to engage another excellent resource, Ray Bohacz.
Keith,
I do not know if I can be of any help. However, all the specifications I have seen claim that the valve stem is 0.312in but does not carry it out to the fourth decimal as you did. Are your valve spring retainers for 10-degree locks? It appears that Manley has part number 13093-16 for a 0.312in valve stem, but it is a 7-degree lock. Did you or the engine builder actually measure and identify the stem diameter on each valve? Let me know please. Comp Cams appears to have some valve locks for 0.3133in diameter valves stems which is probably closer. You may just want to exchange the retainer for a 7-degree version and go with the Manley part number.