Rebuilding an F-head Engine

Page 2: Plugging Oil Passage Holes

by Eric Lawson

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Before installing the oil passage plugs use a flashlight and lookthrough each oil passage to verify that it is clean. A riflebore brush, soaked in kerosene, on the end of a rifle cleaning rodmakes an excellent tool to clean oil passages. If you have to brushout any oil passages use compressed air to blow out anything you mayhave dislodged and check all of the passages again.

For those unfamiliar with firearms, rifle bore brushes are availablein sizes from about .25 inch (6mm) to about .5 inch (12mm) diameter.A gunsmith or firearms shop will have both the cleaning rods and thebrushes. Use the cheapest rod and the best brushes you can get. Hoppe's #9 (rifle) bore cleaner or mineral spirits will work well if you don't want to purchase kerosene.

Holes to be plugged
This photo shows two of the holes in the oil passages that must be plugged. The one pointed to by the green line gets a standard 1/8 inch NPT plug. The one pointed to by the red line gets the slotted head 1/8 inch NPT plug. After the crankshaft is installed, check that the crankshaft counterweight will not strike this plug.

Cam bore to be plugged
The large hole is the rear cam bore. A "freeze plug", well it looks like one anyway, fills the large hole.

The "medium sized" hole at the 7 o'clock position from the cam bore is another oil passage hole. The plug that fits into this hole is the same type as shown in the cam bearing photo below. Make sure the head of this plug is below the surface of the crankcase.

Oil line holes
The two holes on either side of the oil pump flange (driver's side of the block) get square head1/8 inch NPT plugs. The head of the plug on the hole to the right has a small hole drilled in it. This is where the throttlereturn spring will be attached. The hole to the far left, under the fuelpump, is where a flexible oil line connects. This oil line goes to theside of the oil filter.

The two holes to the far right: the upper one is where a rigid oil line connects, which supplies oil to the rocker arms in the cylinder head. The lower hole is for the oil pressure sender. Both are 1/8 inch NPT holes.

Cam bearing
The cam bearing. This was installed at the machine shop. Note the pipe plug at the 5 o'clock position from the cam bore. The square hole in the pipe plug is 5/16 inch and required a special tool to remove and replace it. Make sure the head of the pipe plug is below the surface of the crankcase.

Engine front plate
The engine's front plate. Behind the plate is a gasket. To help prevent leaks, use a gasket sealer on the gasket and on the bolt's threads. -- Eric Lawson
Continue to Page 3: Valves and Camshaft

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Last updated 6 February 1998 by Derek Redmond redmond@cj3b.info
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