It would be fair to say that most attempts at engine reworking infact does not improve the engine. Using the correct tools carefully and be conservative in what you do and all should be well. Take care that no sharp edges are left behind. A piece of fine wet and dry sandpaper rolled up to resemble a small round file is a very useful tool for de-burring port edges.

To check engine timings, mount the engine on a bench etc, and bolt a circular protractor to the crankshaft. Use a pointed needle attached to the engine or bench and arrange the pointer and protractor to read 0 degrees at bottom dead centre (BDC). It may be necessary to take an average reading of the BDC, for left and right hand rotation. It is notoriously difficult to find an exact BDC or TDC (top dead centre).

The following are the areas of modification that will improve most engines.

Improve the flow of the mixture by blending and flowing the inlet and outlet to the shaft. Check for wear marks between the ballraces, if present relieve the crankcase. For racing the shaft timing may be changed to close at 60 - 65 degrees ABDC (after bottom dead centre).

The bottom of the transfer ports can be rounded to improve gas flow into the ports. It is rarely worth adjusting transfer timings or shape.

Most liners become glazed and smooth with use. For the best oil retention etc a fine cross hatch pattern is best. Good manufacturers do this from new. To duplicate this wrap a finger with 240 grit wet and dry and score the bore in a cross hatched pattern. Take care to not work vertically.

A major modification that can improve an engine is the size and shape of the exhaust port. See below

A) is the standard shape port, say at 170 degrees timing, which is a high ‘normale’ type timing.

B) is often used to give an extra boost for pipes, at say 180 degrees timing.

C) to increase the overall timings, the port is simply raised, at say 180 degrees.

D) is going to the max. Not only is the port raised but increased in width to extend almost over the transfer ports.

Almost all pistons can be improved slightly by lightening the lower skirt, checking for a good barrel shape and / or providing a small cut away to improve gas flow to the boost port.

Most non racing pistons have little or no barrelling, and can be improved by very carefully modifying the top of the piston crown edge by turning the piston several times against (oiled). # 240 wet and dry sandpaper Hold the sandpaper in a V shape between the thumb and fore finger. The effect of this is to take the very sharp edge of the piston crown and provide for an oil wedge.

Almost all conrods can be improved by lightening. Take off the square edges of the traditional rectangular conrod to create an oval shape. Be very careful to not introduce scratches etc.

Most engines are supplied with a carby / venturi set-up for easy use. It is rare that more power can’t be gained by using a bigger one. The down side is that fuel draw etc may suffer. For racing models with large venturi, crankcase or pipe pressure will be needed. If using crankcase pressure it will often be necessary to use a restrictor in the pressure line of .008" to .015" (.2 to .4mm) to prevent excess pressure and the resultant tuning problems.

The head is vital to performance. It should always be a snug fit into the liner. The shape is dependent on the fuel and end use.

Just about every shape imaginable has been used at some time, however they tend to fall into 2 distinct categories or variations.

High rpm, small props and standard fuel set-ups tend to use the smaller, wide flat squish head.

High nitro / bigger prop set-ups will tend to use a bigger head volume.

Check that the plug is flush with the bottom of the threaded section. There are big variations in plug thread lengths and head thread lengths.

The modern racing engines are often using the flat coil element ‘Glo Bee’ set-up, which has a specially designed tapered seat plug (no threads), which fits to a corresponding tapered seat head, held in place by a special clamp ring.

There are also versions of the tapered seat plug which use a ‘normal’ fully threaded plug. Some of these use the flat coil element, but most have a conventional element. These plugs are often referred to as the ‘Nelson’ plug.

In racing, the use of the flat coil style is the most common. Of interest is that the coil is generally ‘pulled’ out, away from the plug, into the combustion chamber. When operated like this, the compression can generally be increased, and more power is the result.

Please note, these descriptions and names etc may vary from county to country. It must also be noted that the thread (common between the full plug and insert types) is much larger than the common plug.

Crankcase’s should be checked for clearance between the ball races. It is rare that this area needs to be relieved in a modern engine, as almost all manufacturers now relieve material between the bearings. The tell tale sign of insufficient clearance is wear marks on the crankshaft. It is surprising how far a crankshaft can move and bend in operation. An oil hole or slot from the venturi / shaft junction to front bearing is also necessary to keep the front bearing cooler and oiled.

Transfer passages should be in reasonable alignment to the transfer ports. If the case blankets a portion of the transfer passages etc, it needs to be corrected.

Use a ‘Dremel’ and carbide cutters (do not use grindstones on aluminium) for this work ... carefully.

Good bearings are vital. If you are not sure of the bearings (a shaft should spin very easily, and the bearings feel smooth), remove the bearings and thoroughly wash in methanol or similar. Oil with a light oil and check. For racing engines, phenolic cage C3 bearings are a must.

It is vital that components be thoroughly cleaned (methanol is good), before assembly. A box of facial tissues is very handy. When assembling the engine remember to properly oil every component.

Take care to properly tighten all bolts, that is by first a finger tightening, and then firmly, in a pattern that evenly distributes the forces. In a 4 bolt pattern, tighten in a sequence of 1,3,2,4. And for a 6 bolt head tighten in a sequence of 1, 4, 2, 5, 3, 6 or similar.

Flick the engine over by hand for a few dozen times, remove the head and clean out the oily residue, chances are the tissue will be black from the initial wear process. Time to now run the engine.