In between various customer projects, I have slowly been making progress on my engine. The Heads are twin cam 88 originally, but have been modified. I reshaped the majority of the fins, rounding them around many of the sharp edges. Here is an overall view of the cylinder, head, and rocker box mocked up.
A typical twin cam has aluminum cylinders with an iron sleeve pressed into it. I had Randy at Hyperformance make me billet iron cylinders. The advantage being that there is no way for the iron sleeve to become loose in the aluminum cylinder, because it is all iron! These are secured by a “head and base” stud setup, much like a knuckle, pan, or shovelhead would have been. Here a set of 4 studs hold the cylinder to the crankcase, and another set of 4 hold the head to the cylinder.
An evo or twin cam, traditionally, used a set of 4 studs that ran all the way through the head, cylinder, and into the case. This is a simpler way to attach all the parts, but not as strong.
In addition to the stud conversion, I have adapted the heads to use a superior head gasket method, the metal o-ring. On a stock twin cam (or any other harley) a composite flat gasket was used, sandwiched between the head and cylinder. They work fine, but can blow out if extreme cylinder pressures are achieved. The metal o-ring setup eliminates the flat gasket, instead using a series of steps machined into both the head and cylinder, with a copper ring integrated into it. All of the mating surfaces make contact with each other at the exact same time. This requires extremely precise machining, but results in a nearly indestructible union. I can only assume, too, that heat transfer between the head and cylinder will be improved, due to the metal to metal contact.
Here is the top of the cylinder. The surface rust inside the bore will be gone when the final honing happens.
You may have noticed that there are no oil drain passages in the cylinder. This is because I have re-routed them to the outside of the head and cylinder. This is good for 2 reasons. One is it keeps the oil cooler, since it is not touching the approx 300 degree cylinder walls. The second is that there is no chance of oil weeping between the head and cylinder surfaces, since it bypasses that area completely.
I had to machine a passage through the fins of each cylinder, through the wall, and into the oil drain passage inside the head. This was then tapped for a custom made fitting. Obviously, the original hole underneath has to be plugged as well.
Here is the stainless drain fitting coming out of the head. It has a 6 AN fitting on the end for hose attachment…
I have also added compression releases to the heads. Compression releases are simply tiny valves that allow the cylinder pressure to be bled off as the starter motor rotates the engine. This takes a huge strain off the starter motor and battery, and they simply pop shut when the first combustion occurs, allowing the engine to start. It is unusual to see them on motors with small displacement, but there is no downside to using them. Also, my compression ratio and the resulting cylinder pressures are far higher than either a stock evo or twin cam, so despite the small displacement, the starter will still need all the help it can get.
Installing compression releases is easy with the right tools. It requires a precise hole to be drilled and tapped, which enters the combustion chamber between the exhaust valve and the spark plug hole. More to come…