Cone Knuckle Part 1

Knuckle heads on a cone style Shovel bottom end. Most have seen one, so there is not much debate as to whether it can be done, but there is much disagreement as to whether it should ever be done. Those who say it shouldn't be done generally fall into one of two camps. The purist, who believes that it is sacrilege to desecrate a set of Knuckle heads by running them on anything but a set of Knuckle cases, and the quasi engineers who see nothing but disaster when a part does not work exactly as the designer envisioned.

On the other side of the issue are two likewise divergent camps. On the one hand you have the less-than-a-shade-tree mechanic who will throw together nearly any combination of parts that will physically fit together and leave the "making it work" for the next owner. On the other is the wrench who does his best to weigh the issues and address them in such a way that the finished product is functional as well as unique.

Having raced a Knuckle top/ Cone bottom drag bike for a number of years, I can attest to the fact that those who say that there are too many cam/rocker arm/geometry problems for a motor like that to run well are wrong. Two AMRA National Championships would suggest that they are very wrong. In fact, performance is easily addressed by standard methods. Making the motor streetable in regards to the oiling system is a much more difficult proposition.

There are a number of things to consider before building a Cone Knuckle. In no particular order, they are:

1. Different rocker arm ratio. Knuckle rockers are 1:1. Shovel rockers are 1.43:1. That means that a cam that lifts the valve .450 in a Shovel will lift it .315 in a Knuck. (.450 divided by 1.43)

2. Knuckle lifter blocks don't bolt onto Cone cases. Some of the bolt holes are close, but no cigar, and there is no oil port in the case to match the one in the Knuckle lifter blocks.

3. A Knuckle cam will not fit in a Cone cam cover (at least without major modifications).

4. The angle of the pushrod tubes is different between a Knuckle and a Shovel or Pan making it difficult to seal the bottom of the pushrod tube to a Shovel/Pan lifter block.

5. The oil return system from the heads is completely different between a Knuckle and a Shovel, Pan, or Evo.

Looking at the rocker arm ratios first, there are a number of ways to approach this. One is to have a cam custom ground with Knuckle profile lobes for use with Shovel lifter blocks. This solves any and all valve timing and lift discrepancies, but will be expensive and time consuming.

The second method would be to select a high lift Shovelhead cam. Stock and mild performance Knuckle cams are from .350 to .370" lift. Taking into account the Shovelhead rocker ratio of 1.43:1, you can see that a Shovel cam that is advertised as .500 to .530 lift will open the valve .350 to .370 in a Knuck. If you consider the S&S 514 Shovelhead cam, its .514 lift translates to .359' lift with the Knuck's 1:1 rocker ratio. Compare its other specs with two Andrews Knuckle cams; the N is considered a stock replacement and the S a performance cam.

S&S 514 - IO 23/IC 43 (246 duration) and EO 43/EC 23 (246 duration)
Andrews N - IO 13/IC 41 (234 duration) and EO 44/EC 16 (240 duration)
Andrews S - IO 27/IC 55 (262 duration) and EO 55/EC 27 (262 duration)

As you can see, the S&S 514 falls nicely between the specs of a stock and a performance Knuck cam. Seems like a no brainer to me that this (or a similar cam grind) would be a viable choice.

Using Knuckle lifter blocks on a Cone lower end, while possible, would require quite a bit of welding and machining as well as a custom ground cam (or even more machining to fit a Knuck cam to a Cone cam cover). Not really practical unless you are a machinist by trade and just want to show off.

If you have by now settled on using Shovel lifter blocks, the next issue is the angle at which the pushrod tube meets the block. Now back when I was racing, this was a non issue, since I ran no oil to the top end, and no pushrod tubes. This lack of pushrod tubes did, however leave me with a couple memories that will give a clue as to the solution to the problem of sealing them up. On my Cone Knuckle drag bike the pushrods appeared to be perfectly in line with the lifters. I mean straight as an arrow (at least to the naked eye).This was especially noticeable in comparison to the Shovel dragbikes which were its contemporarys. The pushrods on a Shovel were at a fairly drastic angle coming off the top of the lifters. One might never notice that if they have never looked at a Shovel motor with pushrods installed, but no covers. The reason is because the Knuckle has four different lengths of rocker arm so each one aligns with its corresponding lifter. Not so on a Shovel (or Pan, or Evo, or even Twin Cam). The misalignment on these "modern" motors is compensated for by the ball and socket arrangement on each end of the pushrod.

If you look at a Shovel lifter block, you will notice that the "seating surface" for the cork seal is NOT perpendicular to the bore for the lifter. Well, one of them is probably perpendicular, but the other three are canted to line the tube up with the rocker/box. I have not had a chance to try this, but I suspect that aligning the pushrod tubes on a Cone Knuck may be as simple as remachining the seating surface in the blocks so that they are perpendicular to the lifter bore.

Finally, we come to the oil return system from the heads. Oil return from the heads is the biggest obstacle in making the Cone Knuckle streetable. Since it is fairly involved, it will have to wait for another post - coming soon in part 2.