Harley 45 Engine Teardown and Inspection

Text and Pictures by Mark Trotta

Purchased as "parts only, non-running", this Harley 45 flathead engine was locked solid with no flywheel movement at all. But the VIN number was unmolested and belly numbers matched, so if it came apart cleanly and without damage, it would be worth the effort.

Typically, the teardown process includes removing the generator and ignition timer before taking off the gear cover and separating the engine cases. But those pieces were missing, as were the intake manifold, carburetor, cylinders and heads.

Visual inspection of the cases revealed no cracks or broken bolts. Overall, what was left of the engine was in good shape considering it's now 70 years old.

It's always nice to find unstripped factory screw heads - something not very common on vintage motorcycle engines.

According to the previous owner, the motor "sat outside for awhile".

As a precaution before starting disassembly, the entire engine was placed into a tub of motor oil. This would allow every nut and bolt to come off as easily as possible.

After removing the Military-style breather tube, I scrounged up a plastic tub that the motor would fit into, and filled it with four gallons of automotive engine oil.

Harley flathead engine teardown and inspection

The motor soaked for over a month before being pulled out. It was placed on a flat drain pan and given time for the oil to drain off.

The next part of cleaning was done with shop towels, brake parts cleaner, and compressed air.

Oil Pump Removal

On a Harley 45 engine, the generator, oil feed pump and ignition timer need to be removed before the gear cover can be removed. One bolt and three nuts hold the feed pump on.

The gear cover is set onto dowel pins and is secured by ten screw-head bolts.

A little coaxing with a gasket scraper and light hammer helped.

motorcycle engine teardown and inspection

As is evident from the pictures, the motor collected a lot of dirt and debris from sitting outside with no top end.

A two-jaw gear puller helped remove the pinion gear.

The scavenger oil pump is mounted with four studs and nuts. Removal required light tapping with a small hammer and punch.

The breather valve is an integral part of the scavenger pump. The small screen between the breather valve and crankcase port will be cleaned or replaced.

Separating The Cases

Harley 45 cases are held together with two bolts that thread into the case, and five studs with nuts on either end.

After the nuts were removed, the studs can be driven out with a flat-ended punch and hammer.

With the help of a gasket scraper and light hammer, the right case separated from the left case.

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Remove Flywheel Assembly From Case

The flywheel assembly needs to be pressed out of the case. The best way to do this is with a hydraulic press.

The roller bearings and cages were solid from years (perhaps decades) of non-use.

The reason for the frozen flywheel was now apparent!

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Remove Tappet and Tappet Blocks

Even after the long soaking, the valve tappets and blocks wouldn't budge.

I decided to stop and put the the right-side engine case back into the tub of oil, where it soaked for another two weeks. But even after the second soaking, three of the four valve tappets and blocks wouldn't budge.

Next, the engine case was placed in an oil drain pan, then sprayed down with penetrant. The next few mornings, I'd spray them down again, and then again in the evening.

After a week's time, they still wouldn't budge.