RODS
The piston deck is shorter than stock pistons so they require a longer rod. I have worked with Carrillo to develop a longer lightweight rod (lighter than their standard Norton rod). A Year of research, design and negotiation has gone into them. The .708" diameter pins must be coated for the Steel rods. This is Nascar technology - the bronze bushing in the small end of the rod is eliminated and the Pin has a Diamond like carbon coating (DLC). The extreme loads that Nascar racers subject their engines to (9000 rpm for 600 miles of practice and racing) can deform and wear out the bronze bushings. Coated pins solve this problem and after the race they still look like new. This is the only way to get a more dependable yet lighter weight steel rod.

A stock length (5.875") Carrillo rod with bronze bushing weighs 138 grams on the small end. The new rod only weighs 105 grams on the small end. That's a total pin end savings of about 60 grams compared to Carrillo rods with bronze bushings (about the weight of a stock wrist pin). Big end weight is 326 grams.

MORE POWER, LESS STRESS
The new rods are 6.400 long. That's .525" longer than stock. This increases the length of rod to stroke ratio from 1.67 to 1 (stock) to a more ideal ratio of 1.83 to 1. The advantage of a longer rod is more top end power and less vibration. The increase in power is a result of more dwell time at the top of the compression stroke and that gives more time for the fuel charge to burn and exert force on the piston. So you also get more power for your money. Since there is more dwell time at the top and bottom of the piston strokes - there is less "snap" and the piston does not have to stop and reverse direction as quickly and abruptly at the same RPM with the longer rod. This reduces stress on the crank, cases, etc. This is very important for Nortons as they have a tendency break cranks/cases and vibrate everything to pieces. The longer rod also reduces the side pressure that the piston exerts on the cylinder wall – this reduces friction and helps the engine to run cooler and more efficiently.

PISTONS
The pistons are forged and that makes them stronger than original cast pistons. Note that forged pistons need more cylinder wall clearance (.005") than cast pistons because they expand more. Going tighter than .005" clearance can result in seizure.

Pistons are available in a variety of diameters from 73mm (750cc) to 81mm (920cc). Stock compression 750 pistons will accept stock size as well as 3mm oversize intake & exhaust valves with an intake valve pocket depth of .197" (about .020"deeper than stock). Stock compression 850 pistons have no valve pockets (like the original pistons) but you can make your own pockets .125" deep maximum (or special order 4 pistons). Racing/Hi compression pistons (approx 11:1 CR) have the deck height of the squish band area raised .040" higher than the original 750 piston and .110" higher than the original 850 piston. This means that everything will fit (if your head has not been milled too much). It will leave a squish band clearance of approximately .050" (I do not recommend less). You can mill your head for even higher compression. Milling your head .040" with the Hi compression pistons for approx 12:1 CR may require that you cut an outer ring relief in the top of the piston to give you the necessary squish band clearance. All racing pistons have valve pockets to fit big valve heads (intake and exhaust) - 3mm oversize intake & exhaust valves for the 750 and 5mm oversize intakes with 3mm oversize exhaust for the 850. Stock diameter valves will fit the same valve pockets. Racing piston intake valve pocket depth is .237", exhaust valve pocket depth is .197" and that should be plenty for most racing cams. It is assumed that every race engine builder will have to check piston squish band, dome and valve pocket clearances. Heavily milled heads will require thicker copper base gaskets (see below). Pistons with special 12:1 compression ratios will have to be ordered in sets of four and require a deposit with a 4 week fabrication delay. These pistons have decks .080" higher than stock 750 and .150" higher than stock 850 pistons. Such pistons will require that you machine an outer ring into the crown for squish band clearance. Pistons with increased compression height for short stroke motors (for 6.400" length rods) are also available.

WEIGHT/VIBRATION SAVINGS:
The new forged piston for 750cc weighs approx 185 grams compared to 250 grams for a stock piston.
850 pistons weigh approx 215 grams compared to 317 for a stock piston.
High strength 18mm (.7080" actual) short pins will save about 18 grams each compared to stock pins.
Longer lighter Carrillo rods will save about 30 grams each on the small end compared to an "off the shelf" Norton steel Carrillo rod (the small end is what shakes your bike). Big end weight will be the same as the standard length bushed Carrillo rod and the stock Norton rod.

These are important weight savings that will make your motor run much smoother because vibration and stress is reduced with the reduction of the shaking forces. The weight of those forces can be reduced by approx 1/3 with these high quality parts and that means 1/3 LESS VIBRATION. This is a wonderful improvement for the Norton motor and makes for a much more pleasant ride. The reduction of shaking forces and related stresses help to save your cases, crank and everything else from failing, and that can save you lots of money.

BALANCING
Installation with the Carrillo rods will change a 750 stock commando balance factor from 52% to around 65% which is an excellent figure for racing and hot street bikes. Consider that the factory produced their commando production racers with a 62% balance factor. Solid frames run smoothest with 70% for street and 75% for racing. So you really don't have to rebalance the commando crank for the Carrillo rods unless your crank has already been rebalanced to a higher balance factor with original pistons, if so then you will have to rebalance the crank because the balance factor will be too high with my lightweight pistons. Balance specs and recommendations are provided with each order.

ADJUSTING COMPRESSION
Copper cylinder base gasket thicknesses are now available to adjust compression. Never use anything but a metal base gasket. Note that Hi compression pistons generally require racing fuels. Stock compression can be too high for todays low octane pump gas and you may want to use a .020" or .032" thick base gasket on a street 750 with stock compression pistons.

NORTON RACE MANUALS AVAILABLE.
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