Classic Motorcycle Build

Harley 45 Engine Build

Text and Pictures by Mark Trotta

With the motor already off the frame, engine tear-down on the Harley 45 flathead was pretty straightforward. The oil was drained, carburetor and intake manifold removed, followed by the spark plugs, timer (distributor), oil feed pump, cylinder heads, barrels, and tappets.

Harley 45 engine build

Feed Pump

There are two separate oil pumps on the Harley 45 flathead, and each has it's own function. The "feed" pump is the one mounted to the right-side of the engine on the cam cover. It is a vane-style pump which is gravity-fed oil from the tank, then delivers it to the engine under pressure.

Scavenger Pump

The lubrication cycle is completed by the "scavenger" oil pump. This is a gear-type pump and mounts to the bottom of the right-side engine case. It's job is to return engine oil back to the oil tank.

Harley flathead 45 oil pump install

There is a speciality tool for removing the tappet blocks, but applying a small amount of heat to them (just warm to the touch), should allow you to wiggle them out.

Piston Removal

The pistons were removed by first stretching the pin-clip out with a pair of internal snap-ring pliers, just enough to get a flat-blade screwdriver under it. The clip was then slowly and carefully pried off. By applying slight heat (warm to the touch), the piston pin will knock out with a few light taps of a hammer and a deep socket.

Remove the timing case cover carefully. Do not try to pry off it with a screwdriver! Use a hammer and a block of wood and tap the case ends lightly.

After the cover is off, notice the thin steel shim washers where the cams fit into the cover. These will be put back in the same places as where they were. The scavenger oil pump on the bottom of the case is held on by four studs and nuts.

Harley 45 engine assembly

Read: Harley 45 Scavenger Oil Pump Repair

A lower end inspection will necessate separating the engine cases. Before you do this, check the up and down play on the crank and side-to-side play. A little movement is OK.

Also check that the crank is centered in the cases.

Harley-Davidson 45 flathead engine assembly

After the engine is stripped down to empty left and right cases, check for cracks and broken edges. Look for stripped threads where the feed and return oil pumps bolt on, and where the timing plug and drain plug are.


Read: Repair Stripped Threads In Aluminum

The flathead 45 flywheel assembly consists of right and left flywheels, sprocket shaft, pinion shaft, male and female connecting rods, roller bearings in cages, and thrust washers.

As you remove the flywheel assembly from the cases, take a note of the size of washers and which side they came off of. Same with the roller bearings, cages, and thrust washers. Blow compressed air into the side of the pinion shaft to make sure the oil passage is not clogged.

After inspecting and cleaning, cylinder bolts should be stored out of the way. Use a tap and a little WD-40 to clean all cylinder head-bolt threads.

Harley 45 Engine Assembly

Check to make sure the two connecting rods have been assembled correctly. On 1939 and later engines, the forked rod is the rear. On engines up to 1939, the forked rod was rotated to be the front rod, to correct oiling problems. With the shorter, threaded shaft to your left, the male con rod should be in front, and the female con rod in rear.

Clean, Measure, Inspect, and Document All Engine Parts

Lay the right-side case flat on it's side. Install the right-side bearing washer (the one with the tab) into the right case, then drop in the right-side roller bearings (the two-piece cage). Next, prop up or hold up the right-side case and carefully install the flywheel assembly into it.

Harley 45 engine repair

The next step is to install the left-side roller bearings (the two one-piece cages) and bearing washer on the left-side (threaded) sprocket At this point you can easily fit the left case on top of the right case.

Trial-fit Engine Cases

Without gasket sealer, join the cases together with two cap screws at the top and two studs with nuts at the bottom. Tighten them up, then check flywheel end-play. The Harley service manual recommends .012" to .014". The crank should rest centered in the cases. It should not run to one side or the other when rotated.

Harley 45 flywheel assembly

The Harley manual also states that the two thrust washers should be "approximately the same thickness". Place one each on both sprocket and pinion shafts. While fitting the flywheel assembly to the cases, you'll probably have to separate the two halves several times to get the clearance right.

Crankshaft Thrust Washer Clearance

Having proper crankshaft end-play is important. Too much play affects the stability of the piston in the cylinder. Not enough crankshaft end play will cause the bearings to overheat. It would be better to have a little more play than too little play.

If you need to purchase thrust washers, you'll find they're only available in a set of 11 (one of each size). When you're satisfied with the fit, it's time to seal the cases.


Harley 45 Engine Stand

Harley engine stand

I welded up an engine stand for this project, which made working on the motor much easier. It also gave me something to mount the dial indicator to check for crankshaft end play. If you don't have an engine stand, you can lay the engine down on a couple of blocks of wood.

Read: DIY Harley Engine Stand

checking thrust clearance Harley 45


Sealing The Cases

There are dozens of good products to seal motorcycle engine cases. For this engine, I used Permatex Ultra Grey.

Before applying the sealant, make sure the engine cases are as clean as possible. A good way to make sure all oil and grease residue is removed is to apply a little heat to the cases.

Harley 45 engine case assembly

After applying sealant to both engine cases, I let the sealant get a little tacky (5-10 minutes) before final assembly. The two bolts and four studs were then tightened to the proper torque specs.

Glyptal Pros and Cons

There are some that swear by this product. I've rebuilt a dozen or so motors and never felt the need for it. Some claim it seals the inside of the block and fills in any open pores, giving the oil less resistance so it drains back to the pan quicker. A common reply is, "I've never heard of an engine locking up because all the oil was stuck to the sides of the block." Another argument in favor is, "it keeps your engine clean", but so does changing your oil on a regular basis.

One particular concern about using Glyptal on motorcycle engine cases is, if gas leaks through the carburetor while your bike is on it's side-stand, the unburned gas would eat away the finish on the inside of the cases.


Related Articles:

Install Harley 45 Cams

Assemble Harley 45 Cylinders

Servi-car Drivetrain

Harley 45 Scavenger Oil Pump Repair

Repair Stripped Threads In Aluminum

Harley 45 Flathead History

digital caliper for engine building

Read: Best Digital Caliper For Engine Building