Rod stress analysis

Just got this from Carrillo

STRESS CALCULATIONS shows that the inertia load from the piston/rod reversing direction on a 750cc at 7500RPM is reduced by approx 900 lbs with JS lightweight pistons and JS ultralight longer rods (per side so the total is approx 1800 lbs). The Inertia load from the piston/rod reversing direction on an 850cc at 7500RPM is reduced by approx 750 lbs with JS lightweight pistons and std JS longer rods (per side so the total is approx 1500 lbs).

I remember Brian Slark saying that if the Norton piston cut loose at high RPM (with nothing to stop it) it would travel all the way into the stratosphere.

jseng1 said:

Just got this from Carrillo

STRESS CALCULATIONS shows that the inertia load from the piston/rod reversing direction on a 750cc at 7500RPM is reduced by approx 900 lbs with JS lightweight pistons and JS ultralight longer rods (per side so the total is approx 1800 lbs). The Inertia load from the piston/rod reversing direction on an 850cc at 7500RPM is reduced by approx 750 lbs with JS lightweight pistons and std JS longer rods (per side so the total is approx 1500 lbs).

I remember Brian Slark saying that if the Norton piston cut loose at high RPM (with nothing to stop it) it would travel all the way into the stratosphere.

Click to expand...

Hi Jim, What is the figure for standard rod and piston? Your rod/piston combo reduces inertia load by 900 lbs from what load?

Carrillo has a spread sheet for this (no they won't make it available, but they did me a favor when I asked).


Ultralight bushless rod big end wt 307 gms

Rod small end wt 95 gms

JS 750 lightweight Piston/rings/pin wt 242gms

6.4" rod length with 89mm stroke

Inertia load is 3951 pounds at 7500 RPM




JS bushless rod big end wt 326 gms

Rod small end wt 105 gms

JS 850 lightweight Piston/rings/pin wt 262gms

6.4" rod length with 89mm stroke

Inertia load is 4304 pounds at 7500 RPM


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Stock rod big end wt 344 gms

Rod small end wt 78 gms

Stock 750 Piston/rings/pin wt 340gms

5.875" rod length with 89mm stroke

Inertia load is 4881 pounds at 7500 RPM






Stock rod big end wt 344 gms

Rod small end wt 78 gms

Stock 850 Piston/rings/pin wt 362gms

5.875" rod length with 89mm stroke

Inertia load is 5057 pounds at 7500 RPM