The Harley Davidson "F" head engine

* The "F"-head H-D
Relatively modern for their day, with chain drive, three speed countershaft gearbox, rear drum brake and lubrication by an engine driven oil pump, the "F" and "J" H-D motorbikes are interesting restoration objects because of their high quality and because they still can be used on the road without too many problems from the Ministry of Transport. Until recently France was a primary source of these bikes where many of the about 15,000 military H-D bikes delivered in the First World War had survived.Restoration of the "F"-head models is not an easy job - some of the essential spare parts are very difficult to get - and requires a good knowledge of the underlying technical principles applied in these engines. Great help is to be found in the following books, which are a "must" for the "F"-head restorer.

* Literature
For details of the evolution of this model during its years of production, the book "Inside Harley Davidson, an Engineering History of the Motor Company from F-heads to Knuckleheads 1903-1945" by Jerry Hatfield, ISBN 0-87938-388-7 (A) can be recommended; the "Motor Repair Manual for the Guidance of the Motorcycle Repairman" by Harley Davidson (B), is indispensable as regards the engine overhaul. Unfortunately reprints are difficult to find nowadays.
 Mr J.W. Boon  Meppelerweg 3, 7963 RV Ruinen (tel: NL (0)522-471177 - fax. -473433) Netherlands, just (end 1998) publised a new catalog of parts for Pocket-Valve Models 1915-1929, which he has available .

* Engine restoration
While restoring complete 1916 and 1918 bikes and a further 1920 engine, and talking to other owners and restorers about the problems they encountered, many hints and tips were exchanged and solutions were found which might be of interest both to other H-D owners and to restorers of other bikes. Most of the work described in the following recommendations can be done yourself and, when the use of machine tools is necessary, it is at least possible to prepare the parts for machining, so that the costs will be lower compared with having all the work done by a specialist. Moreover when you carry out assembly yourself, you have a final possibility to check on what has been done by others; sadly this proves necessary nowadays.

Let us start with the engine overhaul, which is very well described in book (B). The engine design will be clear from figures 1 to 3 (1917 and later models).When comparing the pre-1916 and later engines, it was found that until 1916 the sprocket side of the crankshaft was journalled in a self-aligning double row ball bearing (figure 4a) which, peculiarly for an American bike, is a millimetre sized bearing (1305-25x62x17mm, max load: Cr=13800N, Cor=6000N).After 1916 a double row roller bearing of H-D manufacture was used (see figure 3). According to book (A) the earlier crank cases, whose left half (sprocket side) has a large diameter bore because of the large bore of the ball bearing race, were used for so-called "fast" motors even after 1916, perhaps because the self-aligning bearing allows the crankshaft to swing or bend at high speeds.For restoration, it was decided to replace the 1916 self-aligning double row ball bearing by a double row spherical roller bearing (see figure 4b) (21305-25x62x17mm, max load Cr=39100N, Cor=25700N), dimensioned to be on the safe side under operating loads and retaining the self-aligning function.

* Adaptations
The self-aligning bearing arrangement stimulated me also to adapt the later crankcases to such an arrangement, not only because of the better support for the crankshaft but also because of its easier assembly with the crankcases; not the least consideration was the easier availability and lower cost of bearing assemblies compared to the loose parts of the original double row roller bearing arrangement. Looking through the pages of a bearing catalogue, a double row spherical roller bearing of the size 25x52x18mm was found (22205CC max load: Cr=30500N, Cor=21600N).Since the sprocket shaft has a diameter of 1" (25.4mm) and the original outer bearing ring in the crankcase has an outer diameter of 2" (50.8mm), only very little material needed to be removed from the shaft (from 25.4 to 25mm) and from the crankcase bore (from 50.8 to 52mm) to fit this spherical roller bearing! The selected double row spherical roller bearing is not cheap (about 100 DM in Germany) but, since in most restorations a new bearing ring and sprocket shaft would otherwise have to be manufactured, because these are usually either rusted or worn, the proposed adaptation to fit a standard roller bearing proves cheaper overall.The work on the sprocket shaft (grinding it down to 25mm) and on the crankcase (enlarging the bore to 52mm) is relatively straightforward and, when the work is done in a machining workshop, is not very expensive (picture 6) . When pressing the bearing into the crankcase it is advisable to insert a steel washer of 52mm outer diameter behind the bearing in order to allow the bearing to be pressed out again, in the same way as the original bearing outer race, if necessary. This washer ring should be of sufficient thickness so that the bearing when pressed into the crankcase is flush with the inside of the crankcase.

* Pinion shaft bearing
The pinion gear shaft is journalled in a large bronze bearing bush. If a new one is required do not forget to regrind the shaft which is normally worn unevenly (thick in the middle, small at either end) from bending of the crankshaft under load. According to instructions in the above referred to H-D manual (B), a clearance of 0.002 to 0.003 inch (0.05 to 0.07mm) should be allowed for the pinion shaft bearing. Experience teaches (fortunately not mine!) that preferably 0.07mm should be given, to avoid any seizing of the shaft in the bushing: a perfect alignment of these build-up type crankshafts can rarely be achieved and therefore more clearance is required.The original bushing has spiralled oil grooves but, in view of better insight into lubrication of plain bearings nowadays, it is possible to omit these grooves and recommended to ensure instead that the lubricating oil supplied from the holes in the upper part of the bushing is distributed over the entire width of the bushing.

* Crankpin bearings
Let us now turn to the crankpin bearings, which have required full replacement in all my engines. The big end comprises a 1" diameter crankpin, four rows of 12-1/4" rollers in open ended cages, and bearing rings pressed into the connecting rods. New crankpins are still available (J.W. Boon) at reasonable cost, but a supplier for new bearing rings of the correct size could not be found. (I just see that J.W. Boon has the rod races in his new 1998 catalog too! ) It is possible to use H-D "Liberator" bearing rings, intended for the forked conrod, and to use two of those side by side for the middle conrod. Because "Liberator" bearing rings are normally sold in sets comprising two narrow rings for the forked conrod and one wide ring for the middle conrod, two sets are therefore necessary to rebuild one "F"-head crankshaft. When measuring the ring diameters it was realized with relief that obviously millimetre size bearing rings had been used here too. The outer diameter of the rings is exactly 43mm and corresponds to the outer diameter of needle bearing inner rings of the size 38x43x20mm (1) and 38x43x30xmm (2), which are readily available and relatively cheap. The size (1) was used for the single eyed middle (rear) conrod and size (2) was used to part off the required width of 9.5mm each for the forked (front) conrod bearing rings (pictures 7 and 8).

Pressing the bearing rings into the single eyed conrod is quite straightforward and can be done with a vice. The forked conrod needs more attention, since all sideward load on the fork should be avoided. A simple "pressing-tool-set" (see figure 5, a ring and brass or steel arbor) was manufactured on a lathe so that the new bearing rings could be pressed into the forked ends from the inside to the outside of the fork (see pictures 9 and 10 for pressing out the bearing ring and picture 11 for pressing in the bearing ring, picture 12 shows the finished job and the tools used). Leave enough side clearance for the single-eyed conrod bearing ring so that oil can reach the rollers when the big-end bearing is assembled!

In order to keep sufficient clearance for lubrication it is advised firstly to measure the total width between the flywheels with the new crank pin in place and then to calculate the width of the rings to be parted off such that the side clearance of the middle conrod is about .02" (0.5mm) in the fork and the side clearance of the fork between the flywheels is 0.006" to 0.012" (0.15 to 0.30mm).

The inner diameter of the rings becomes slightly smaller than 38mm after the rings have been pressed in but these must be lapped anyway to achieve the correct inner size of about 38.1mm - crankpin diameter of 25.4mm + 2x roller diameter of 6.35mm (1/4" rollers) adds up to 38.1mm.You can do the lapping of the inside of the rings yourself if you have an H-D lapping tool (see picture 13), or you can leave this to a specialist at reasonable cost.When lapping I used the old rollers to check whether the correct diameter was almost achieved. Then by lapping with the finest grinding paste and lapping only very slightly each time, the fitting diameter for the new rollers was reached.This last lapping sequence must be done with great care in order not to lap away so much that after the rollers have been inserted the conrods show sideplay (see also the H-D lapping instructions in book (B). Altough the use of the HD lapping tool for lapping 0.1 mm from the big-end roller bushes is not the correct use of a lapping tool, the necessary grinding equipment is normally not available for the restorer and it was found that with some care it is very well possible to achieve good results.

The advantage of using the original 1/4 x 3/8" size rollers - which are still available, as also are oversize rollers - is that the original retainers (cages) can still be used; this sometimes proves problematical when bigger, oversize rollers are used.The retainers must be checked to avoid any clamping on the rollers, as this would lead to premature failure of the big-end bearings. This was also found out by H-D themselves when they changed the heat treatment of the retainers in 1935, which caused slight warping of the retainer ends and failure of many a 1935 model big-end.

* Aligning and assembly
Aligment of the crankshaft should preferably be carried out in the manner described by Mr JonathanJones in the December 1991 issue of "The Classic Motorcycle" or in a large and accurate lathe. In book (B) H-D advises that alignment be done in a special jig between centre points. However not only are the centre holes of old crankshafts usually not suitable for accurate support, the axial pressure applied by the centres to support the crankshaft assembly also leads to distortion of these rather flexible crankshafts, so that accurate measurement is not possible. When assembling the crankshaft in the casings, end-clearance can be adjusted by inserting readily available spring-steel washers of 25mm inner diameter, which fit onto the now 25mm diameter sprocket shaft within a mere 0.05mm.

* Not recommended
I have heard of some restorers using more easily available 6.5mm rollers or omitting the retainers and filling the space with more rollers than the 12 intended .Although the use of 6.5mm rollers is possible, this definitely requires new retainers to be made, which is a complicated high-precision job, in particular when the required clearance of the retainers is considered not only relative to the rollers but also relative to the bearing rings. Furthermore, although some motorbike engines do indeed have cageless big-end roller bearings (HRD-VINCENT), this can be very dangerous in V-type engines not relying on pressurized lubrication, such as the "F"-head Harley Davidson; the higher friction of cageless roller bearings and the resulting heat development might lead to premature failure without sufficient cooling being guaranteed by a steady oilflow.

*Technical Specifications
(see figures 1 to 3) Cylinder angle set at 45 ; valves, inlet overhead in cage, operated by push rods (L); exhaust on the side;bore 3 5/16 " x 3 1/2 " stroke; 60.34 cu.inch displacement; valve clearance 0.004" between the exhaust lifter and valve stem (engine cold) on all twin engines prior to 1915. On 1915 and 1916 twin engines, allow 0.004" for rear cylinder and 0.006" for front, and on 1917 to 1924 twin engines, allow 0.008" to 0.010" for exhaust valves. Allow 0.004" clearance between inlet rocker arm and valve stem on all models. Valve timing on the twin cylinder engines: The exhaust valve should start to open about 9/16" before bottom centre (BBDC) and close 1/32" after top (ATDC), after 1917,  3/32" (ATDC). The inlet valves start to open 1/32" before top (BTDC) and close 1/8" past bottom (ABDC), after 1917 5/32" (BTDC) and 3/8" (ABDC).
It was found that although the 1917 and later models have different cams shapes for the front and rear cylinders, the timing is the same for both cylinders. Actually measured values are; exhaust opens 14 mm BBDC and closes 1 mm ATDC. The inlet valve opens 5 mm BTDC and closes 22mm ABDC.
When fitting the gears (A to E), they should be lined up in accordance with the marks shown in figure 1, so that the marks lie in a straight line. (A) is the crank-shaft gear; (B) the cam gear.The exhaust compression relief valve is for easy starting by relieving compression in the cylinder through opening the exhaust valve. When starting, the left-hand handle-bar grip is twisted to the left, which retards ignition, and further turning raises the exhaust valve via rod (G), which acts through cams (1) and (3). Crank-case compression relief: A vent (I) relieves the pressure in the crank-case at every revolution. The gear (F) operates a rotary relief valve, which should open 1/16" to 3/32" when the front piston is on top. This valve port opens gradually when the engine is turned, and closes once the piston has reached bottom. This provides for a vacuum on the upward stroke, which draws oil and oil vapour to all bearings. A pipe leads to the chain cover and, as it delivers a small amount of oil at each revolution, the chain remains lubricated (applies up to 1916, on later models the pipe ends under the engine).
Oiling system: Oil enters from the oil reservoir through pipe connection (H). It is then carried by a rotary valve pump geared to shaft (F) through sight glass (V) into the engine crank case. If there is too much oil, remove screw (X); if oil does not overflow, turn the engine until it does. Replace (X). Remove the plunger-chamber vent screw (Y) until oil flows in the same manner. Then regulate the oil supply by placing three 0.10" washers on the adjusting screw (Z). Drain the engine and fill with 1 1/2 pumpfulls of oil with the handpump. To increase the automatic oil supply add thin washers, one at the time. To decrease, remove the washers. When all washers are removed the oil-pump plunger has no stroke at all.

* timing ignition
All twin engines, magneto equipped, fire 1/4" to 5/16" before top of compression stroke with the spark lever advanced. All twin electrically-equipped engines fire 7/32" to 9/32" before top. Spark occurs when the points are just separating. Separation can be determined in an easy manner by using a digital multimeter with resistance measuring ability: when compared to analogue meters the digital ones show more clearly the relatively small difference in resistance when the points are closed or open.
Berling magneto: The lower cam on the interruptor times for the front cylinder and the upper cam for the rear.
Dixie magneto: No. 2 cam for front, No. 1 cam for rear.
Bosch magneto: interrupter shoe No. 2 for front, No. 1 for rear.
Remy generator interruptor: Small cam for front and large cam for rear. Relation of spark to piston position (see figure 3a). Because the cylinders are 45° apart when cylinder 1 fires, crank pin (A) will travel one revolution to come to (A) again, then 45 more to (B) or 360° and 45° thus 405° in all, before No.2 fires. No.1 will fire again, from point (B) to (A) 360° minus 45° , or after 315° .The armature travels at half the speed of the engine crank shaft and makes a spark every half-revolution. Therefore the armature with its interruptor and collector ring would travel 202.5° when the crank travels 405° after No.1 cylinder fires. When No.2 fires the crank pin on the engine will travel 315° before No.1 would fire again, and the magneto armature would travel 157.5°. Thus we have unequal impulses. 
* timing marks

Cylinder and Piston Oversize information

If you have any additional hints or tips please send me an E-mail !!
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