I came across this while surfing the internet. I particulary like the recommended method for running in! I apologise for the length of the read, but I certainly found it worthwhie.


GETTING THE BEST OUT OF A SIDE VALVE

Reprinted by the courtesy of “Motor Cycling”. 1936.

Mr. L. W. E. Hartley. who has made an extensive study of side valve motor cycle engines, has achieved some remarkable results with machines of this type and here gives some valuable hints on tuning them.

Quite a deal of fun and no little interest may be had from the ownership of a really fast s.v. machine, as few road users are prepared to credit this type with anything extraordinary in the way of performance. So far as the majority of standard s.v. singles are concerned, such performance is distinctly lacking, and it is my object here to give a few suggestions which, if properly followed, will definitely enable s.v. owners to compete on, at least, something like equal terms with standard o.h.v.s of similar capacity.
It is assumed that the cycle parts, steering, magneto and transmission of the machine are in normally good condition, also that no engine parts are sufficiently worn to require replacement; in the event of this not being so, of course the remedy is obvious. Having satisfied yourself that these provisions have been looked after, you can proceed with the tuning.
Strip the engine completely and clean every part thoroughly. Commencing with the fIywheel assembly, all sharp edges should be removed as these cause oil drag - a streamlined shape being more important than a mirror finish; there should be at least 3/4 in. clearance between crankcases and flywheel in all directions, this also reduces oil drag and, what is of great importance in a wet-sump motor, allows the maintenance of a greater quantity of oil in the sump, thus ensuring that feed variations take longer to affect the running of the engine. Do not reduce flywheel weight any more than is just necessary to satisfy this condition. Lightness here is all wrong, save in exceptional circumstances, in spite of popular belief.
Be satisfied with the condition of the big-end components; a total slackness here of not more than .002 in is permissible. Do not interfere with the connecting rod without expert advice. Most rods can be lightened with advantage, but no general rule can be laid down, and a broken rod can be a very expensive matter.
The flywheel assembly should run true to within .002 in eccentricity on the main- shafts, and greater error than this calls for expert attention. The subject of balance should next be attended to, and this undoubtedly calls for really expert attention. All this may sound very monotonous, but it is obviously absurd to develop power “up top” and throw it away with a bad “downstairs” department, which may very easily be done.
I will now assume that the flywheels have been properly attended to. Next on my list comes the crankcase. Provided that no new parts have to be fitted, this should go together without difficulty.
The flywheel assembly should have .005 in. to .010 in. end play in the crankcase, according to size of engine, and should be so free to revolve that, when the rod, without the piston, is pushed down the balance weights should return it at once.
Now for the cams, about which, in my opinion, much bunk is thought, spoken and written. The average s.v. engine cam is of too low a lift and too short a “dwell” to be of much use in an engine that is being tuned for speed. You can, however, adopt any of three courses—procure an o.h.v. cam, if available; alter the existing cam to suit, if the facilities can be had; or alter existing cam levers, if any.
There is no best timing. but, as a useful basis, the following will be found to be very satisfactory. Arrange the inlet valve so that it opens 20 degrees before t.d.c. and shuts 60 degrees after b.d.c. The exhaust should open 60 degrees before b.d.c. and shut 30 degrees after t.d.c. Use this timing with a valve lift of not less than 5/16 in. on a 500 cc. motor.
The camshaft (or shafts), when assembled, can usefully have .010 in. end play, if carried in plain bearings, and should spin freely when the timing cover is screwed fully home. The rockers and tappets should be just free enough to fall easily with their own weight when dry. Any excess wear between tappets and guides must be remedied, as otherwise inaccuracy will result.
The same test for freedom should apply to the complete crankcase assembly, with the timing gear in position and the timing chest cover fully tightened. If any tight spot exists it must be eliminated before the “downstairs” department can be passed out as correct.
“THE UPPER WORKS”
The piston next comes up for consideration, also, usually, for complete replacement. Use as high a compression ratio as is possible without allowing the piston actually to hit the cylinder head. This involves realisation of the amount of stretch and whip which will occur at speed, and usually necessitates at the least .040 in. clearance between the crown of the piston and the head. Two rings and a scraper is a satisfactory ring arrangement. and a “tapered-section” gudgeon pin, with plain ring circlips. is both safe and light. The gudgeon pin should be an easy push fit in the piston when the latter is cold, and slightly freer in the small end of the rod.
Piston clearances vary so much with different engines that it is impossible to lay down definite figures. However, in the case of a bore of 80 mm. to 85 mm., aluminium piston-skirt clearances of .008 in. tapering to .012 in. have been found generally satisfactory for fast road work; .016 in. on the ring lands and .025 in. above the top ring are other clearances suitable for such pistons. Proportionately smaller clearances on small bores are indicated.
Ample running-in and the removal of any high spots are essential, and this cannot be overstressed. A running-in period of 2.000 miles. with high-spot removals at intervals of 50. 250. 1.000 and 2,000 miles, is usual, with change of oil and a flushing out of the crankcase each time.
Now for the cylinder. If the bore is at all doubtful, have it reground and fit a suitable oversize piston. Ovality with a good surface is just as bad, mechanically speaking, as a score, and is far less easy to detect. A good mechanic with a micrometer will settle this point. The combustion space should have all sharp edges or “outcrops” removed, and, if possible, should be polished. This includes radiusing the edge between the ground bore and the floor of the valve chest. smoothing the edges of the grinding-in slots in the valve heads and the lower end of the sparking plug hole thread. Where valve caps are fitted, the lower threads must have sharp edges removed.
THE PORTS
The inlet port can usefully be ground out, and here, again, a super-polish is but second to good direction and easy, sweeping curves. Many 500 c.c. to 600 c.c. s.v. engines have very small carburettors and inlet ports. in which case a carburettor with a choke diameter of 1 in. to 1 1/16 ins, can usefully be substituted and the port opened out to blend. The inlet guide should be either cut off level with the floor of the port or else streamlined. Remember however, that its life will be roughly in proportion to its length!
Provided that the exhaust port is of reasonable area and directness, no work is indicated here; but if not, the remedy is obvious. Do not attempt to shorten the exhaust valve guide.
The standard inlet valve is usually of good enough material, but, after tuning, the resultant increase in power output may make it desirable to fit an exhaust valve of KE.965 or similar steel, preferably of the flat-headed type. Experiment with the under side of the inlet valve head will prove interesting and informative, a tulip shape being faster and flat shape giving better “low end” acceleration. A compromise can be arrived at to embody enough of each virtue for the job in hand. In view of the higher lift cams and (hoped for) additional speed, slightly stronger valve springs are desirable. individual circumstances will suggest a means of satisfying this end; also frequent renewals of that on the exhaust are to be recommended if the performance is to be maintained. The best tappet clearances will have to be found experimentally, but .004 in. on the inlet and .006 in. on the exhaust form a good basis on which to start.
The exhaust system must now be taken in hand. This must consist of a rather long pipe and a silencer at the end if power is to be maintained without undue heating. Expansion chambers close to the exhaust port are definitely “out of court” in the case of a fast side-valver, I have no particular preference, but a cylindrical silencer with some sort of spiral baffle allows reasonably good power output coupled with satisfactory silence. When nding on a track a Brook lands-type silencer is the next best to an open pipe from the point of view of performance.
The remaining points calling for attention are the gear ratios, the carburation, the magneto setting and the sparking plug.
The maker’s standard top-gear ratio, for the size of the machine in question, is usually best for road work, unless a set of close ratios is available, in which case an engine sprocket having one tooth more than is standard is helpful, but usually involves, however, a little more gear changing. I am a strong advocate of under, rather than over, gearing for road work, particularly when there is a biggish drop to the next gear.
Carburettor setting can only be achieved by practical experiment, but, as a general principle, use the richest setting that will give the required results. Attempts to obtain fuel economy inevitably result in trouble and lack of performance. Check the air vents in the petrol tank and the flow of petrol to the float chamber at various stages; mysterious losses of power at high throttle openings are frequently caused by insufficient flow and are not easy to detect. Use the highest octane number fuel that can be regularly obtained. An ethyl petrol is good. or, better still, 50/50 ethyl (or No. I petrol) and pure benzole if it can be obtained. Never use straight petrol for full throttle work on a highly tuned job.
If possible, fit the sparking plug over the exhaust valve. In non-detachable-head engines this can be done by changing the valve caps. In types having detachable cylinder heads ,a new plug hole can be drilled and tapped in many cases. In any event, use the “hottest” plug that will stand the oiling propensities of the engine. In the 18-millimetre size, either K.L.G. 583 or Lodge 1+45. and in the 14-millimetre size, K.L.G. L583 or Lodge H.53 can be recommended for fast road work, these standing the heat very well:
they are also reasonably resistant to oil. The gap between the plug points should be between .010 in. and .014 in.
When timing the magneto do not make the mistake of giving too much advance: too little is better than too much. A useful method of setting is to go out on the road with an obviously too far advanced setting (say, the points breaking at 60 degrees before t.d.c. at full advance); get the motor going on two-thirds throttle in second gear (or third, if you have a four-speed box), and find the position of the control lever which gives the best results. Reset the timing by a timing disc so that the number of degrees of advance at this lever position corresponds to the fully advanced position of the contact breaker. This method will be found to provide enough advance for all conditions, but don’t forget to use the control and, of course, see that movement of the control does result in contact breaker ring movement.
Whilst on the subject of the magneto, make sure that the contact points are clean and square, and, in spite of instructions to the contrary, set their gap to between .008 in. and .010 in.
Whilst I do not pretend that following out these hints will enable you to win races at Brooklands, if they are carefully carried out a very useful and unusually efficient side-valve motor cycle will be evolved, and, to those who are that way inclined, some very interesting and instructive hours will be spent both in the workshop and on the road.
END

email (option): pvlietstra@gmail.com

This is an interesting article written by Harley..He achieved very good results applying these techniques..particularly with Ariels which were his chosen marque.
When reading these older articles some consideration must be given to further knowledge which was acquired at a later date, which in some cases will contradict what is written...after all you wouldn't tune a Formula One car using a 1938 tuning book!.
If serious tuning of a sidevalve is contemplated the key point is to read everything available..Late Harley Davidson K Model tuning information and some of the articles written more recently about sidevalve car engine tuning should definitely be on the reading list as well as articles such as this.
From reading everything available and considering all the information a strategy can be defined to (potentially) suit which ever engine is to be tuned. With a few exceptions tuning of sidevalves rapidly ceased with the introduction of OHV engines and the tuning principles are far less clearly defined, so a degree of experimentation is inevitable. Also the type is inherently more difficult to tune because of its design limitations...but that can make good results even more satisfying (eventually!)...Ian