The ThreeBond Knucklehead—Part #III

WE HAVE now reached the final stage of our ThreeBond Knucklehead buildup. We left the engine at the end of Part II complete to the top of the cylinders and it is now ready to have the cylinder heads and their relative parts installed.

Sealing the top end of a Knucklehead is a tall order; the sealants we used are various ThreeBond products. A little known fact is that the very first Knuckleheads produced in 1936 did not have their rocker gear completely encased, and the beautifully crafted tin covers, unique to Knuckleheads, were installed from 1937 onwards due to complaints from customers being covered in oil.

Gaskets are all James and the hardware for holding everything in place is by Colony.

Although the heads are brand new we decided to remove the factory black paint and finish the heads in Standox silver to give them a fresh lighter look and to blend them into the rest of the engine where all the cast iron parts are similarly finished.

The first thing to do when assembling a set of heads is to check the valve stem clearances in the guides. The factory figure for this is .004” to .006” for both inlets and exhaust. We would like to see the inlets on the minimum @ .004”; and the exhausts midrange at around .005”. To check this we use a Go/No Go gauge that is .001” smaller than the desired figure on one end and .001” larger on the other. The theory is that the small end will slide in easily and the other end will not fit, guaranteeing the correct size.

With the correct clearances confirmed and a quick check of the valve spring tensions and the valves, the springs and collets can be assembled. This is exactly the same procedure with any Harley engine including Twin Cams, although Knuckles and some other early engines don’t run valve stem seals.

Rocker arms and shafts are assembled and brought up to final tensions without any of the stiff seals installed; this is a good opportunity to check that everything is moving smoothly and freely with the specified amount of end float. With everything passing the various tests with flying colours, the heads are now assembled with the seals installed.

With the heads bolted onto the engine the remainder of the work can be carried out on the engine stand. High quality head bolts by Colony duplicate the original fasteners in every way. Heads initially are left slightly loose to ensure an optimum fit at the inlet manifold; this is an important step and allows the early style threaded manifold nuts to be drawn up evenly ensuring perfect seal and manifold vacuum.

The final stage of the cylinder heads is to install the seals necessary to keep the whole assembly oil tight. We used ThreeBond products for this chore for their outstanding sealing qualities in conjunction with James gaskets and seals.

That completes our ThreeBond Knucklehead project. Using modern parts, gaskets and sealants, we have created a reliable classic engine of considerable beauty.

If you require more information on quality engine re-builds, give me a call at Redgrave Motorcycles: 02-9484-9955.

Feature by Richard Nicolls at Redgrave Motorcycles.