Classic Motorcycle Build

Harley 45 Cylinders

After the oil pumps were rebuilt and installed, cylinder assembly was next up on the Harley 45 flathead build. The cylinders and pistons were .030" over-size and reusable as is. The cast iron valve guides in the cylinders had been previously replaced and were in good shape.

assemble Harley-Davidson 45 flathead cylinders

Valve Guide Wear

Valve guide wear refers to clearance between valve stem and valve guide. As the guide wears from mileage, the valves will gradually get play side to side as they open and close. This side to side movement can cause valves to seat improperly. For this reason, valve guides must be checked, and replaced or repaired if beyond manufacturer's specifications.

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If you need valve guides, aftermarket ones are still available for most classic bikes. Worn guides are usually pressed out and pressed in. The ones in the cylinders pictured were manufactured by a company called Rowe, who are no longer in business.

assemble Harley-Davidson 45 flathead cylinders

Since the inside diameter of guide will change when pressed in, replacement guides are made with inside diameters slightly smaller than required. After installing, the guide needs to be reamed out to increase inside diameter until the correct size is obtained.

Harley 45 Cylinder Assembly

Prior to re-assembling the Harley 45 cylinders, they were cleaned and painted semi-gloss black. I sprayed them with automotive engine paint.

Install Harley 45 cylinders

Measuring Valve Guide Wear

Valve guide wear can be measured several different ways. The easiest way to tell if your guides are worn is, after you compress the valve spring and take off the keepers, pull the valve out of its guide and jiggle the valve back and forth, or up and down. Actual movement can be measured with dial indicator or other precision instrument and compared with specifications in a service manual.

Checking Valve Seats

When closed, valves need to be air and liquid tight. If your heads were rebuilt at an engine shop, the valves will have a precise bevel, made by a machine, on the valve and seat surfaces. However, a good seal is not guaranteed. The purpose of grinding is to have the valve and valve seat make an air-tight fit. The purpose of lapping valves is to verify that the grinding was done correctly.

How To Lap Valves

If the valve seat and face were ground correctly, the lapping process should take a minute or less for each valve. It actually takes longer to clean, prepare, and round up the supplies than to actually lap the valves. You'll need a tube of valve-grinding compound and a valve lapping tool, which is basically a wooden dowel with a suction-cup on the end.

Harley-Davidson flathead cylinders

Place the cylinder so the head of the valve is facing up. I used a couple pieces of wooden 2x4's for this. The next step is to wet the suction cup on the lapping tool and stick it on the valve face. Once the lapper is grabbing the valve, begin the lapping process. Place the lapper in between both hands, and using light pressure, rotate the tool back and forth at a moderate pace. The motion is similar to starting a fire with two sticks.

Lift the valve up periodically and rotate it 180 degrees to ensure the grinding compound is getting evenly spread. You'll want to watch the progress - you're looking for a consistent grey ring on the valve and valve seat with no breaks or high spots. It is not necessary or good to over-lap the valves.

Harley-Davidson 45 valve assembly

When you can feel and hear the compound losing its cutting ability, wipe off and check. Both faces should be a dull grey when you're done, with an even width across both faces. It does not have to be in the middle of the valve, just an even ring around the valve. You will see the same consistent gray line on the valve and the seat.

Harley 45 Valves

The intake valves, exhaust valves, and valve guides for Harley 45 cylinders are same from 1930 through 1973, as are the retainers, keepers, and bases. Valve size is 1.625" on both intake and exhaust, but they are not interchangeable. Exhaust valves are different in that they are heat-treated.

Harley 45 cylinders

Install Valves

Although bigger than needed, my automotive valve spring compressor worked on the Harley 45 cylinders. Before slipping the valves into the guides, lubricate the stem with a dab of engine oil. I use 5/30W, but it shouldn't matter.

Harley-Davidson flathead cylinder assembly

Harley 45 Cylinder Heads

Most Harley 45 cylinder heads are cast iron. Aluminium heads are lighter and give a higher compression ratio. Finding good used cast iron heads is cheap and easy. Original aluminum heads are rare and expensive, which opened up a demand for aftermarket replacements. Several manufacturers offer these.

Harley-Davidson flathead 45 cylinder heads

There is usually a number stamped into each cylinder head to indicate compression ratio. Heads marked 5.0 are low compression (5.0:1). If it reads 6.0 it is considered high compression (5.6:1).

Harley 45 engine rebuild

read Harley 45 Flatheads

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