Harley 45 Cylinder Assembly
Text and Pictures by Mark Trotta
After the oil pumps were rebuilt and installed, cylinder assembly was up next on the Harley 45 engine build.
Valve Guide Inspection
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.
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.
Valve Lapping
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.
Read: How To Lap Valves
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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.
Valve Installation
Before slipping the valves into the guides, lubricate stems with a dab of engine oil.
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Pistons And Pins
There are two styles of piston pins found on Harley 45 flatheads. The early-style pin used an L-clip and was seen until the mid 1950s. The later style was the more common E-clip seen from the mid 50's up until the end of flathead production in 1973.
Pictured are the less common early-style piston pins.
Piston Lock-Ring Tool
The factory part number for this lock-ring tool is 12052-32. It's primary use is 1932-1956 Harley-Davidson 45 models.
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Harley 45 Engine Specs
Cylinder standard bore: 2.7445" to 2.7455"
Piston clearance in cylinder, measuring piston at bottom of skirt front to rear: .001" to .002"
Piston pin in piston is a light press fit
Piston pin in connecting rod upper bushing: .001" clearance
Piston ring side clearance in grooves: .004"
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Prior to re-assembling, the outside of the cylinders were cleaned and scuffed with a Scotchbrite pad, then painted semi-gloss engine black.
Ring gap is .010" to .020" and can be checked with a feeler gauge.
When installing, avoid having ring gaps near exhaust ports, as ring ends may overheat and burn.
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James Gasket offers a complete gasket set for 45ci Flatheads from 1936 through 1973. It replaces OEM 17026-40.
Shop: Harley 45 Engine Gasket Set
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Install Cylinder Assemblies
Lubricate cylinder walls, pistons, pins, and rod upper bushings generously with engine oil. Pour some oil onto the rod lower ends as well.
Install cylinder base gasket, and work cylinders carefully over pistons and rings.
Install rear cylinder first. As the cylinder seats, turn engine so that the tappets are at their lowest position.
You should now be able to thread on the base nuts, but don't tighten yet. After the front cylinder is installed, both front and rear may need to be shifted slightly to fit the intake manifold.
Harley 45 Heads
Most Harley 45 cylinder heads are cast-iron. If yours are cracked or have broken fins, finding good used replacements is easy.
Compression Ratio
There is usually a number stamp on the 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 (6.0:1).
Here in the 21st century, it's hard to believe that 6.0:1 was once considered high compression, but the reader must remember that high-octane fuel and high compression engines came after (and were actually by-products) of World-War-Two.
Aluminum Heads
A set of aluminium heads not only bump up compression, they dissipate heat better and are lighter than cast-iron heads.
Finding a set of original Harley 45 aluminum heads is difficult. V-Twin Manufacturing now offers aftermarket replacements.
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