Thought I would hi jack this thread as rods always interest me and had just got an interesting email.
I have been considering options for some new rods for my race bike and had never seriously considered steel rods as I had assumed they would cause vibration due to their greater weight. However a mixture of seeing a utube clip of some heavy duty modern alloy rods and also seeing a reference to Carillo's being lighter than many OEM rods set me thinking.
My existing std BSA rods weigh (according to my scale) 370 grams being 150g reciprocating weight (stops-and changes direction each stroke so implicates inertia) and 220g rotating weight (affects balance but primarily just spins).
I sent out inquiries to several supplier and both Thunder Engineering and BritCycle kindly got back to me with corresponding weights for their Alloy and Steel rods.
The weights make interesting reading:
Std Rod 370g, 150/220 split
Thunder Eng 440g 125/312 split
Carillo 479g 130/349 split
So there is little difference in reciprocating weight between a replacement alloy or steel rod
.
I havent done any maths on the implication of the additional rotating weight of both rods but am assuming it will simply move the vibration up or down the rev range slightly
or the crank could be rebalanced if necessary.
My current thinking is that with no effective weight disadvantage, a steel rod will retain oil pressure better due to lower expansion rates, so be superior in a performance engine.
Now just need to save up enough money...
Tim