Opening cooper s rods out to a plus bearing diameter
Turbo Mini Forums

Having done some calculations to asses the feasability of doing a short stroke k-head engine I have run into a few issues, mainly by using a 70.2mm stroke with a 6 inch rod the piston will sit proud of the block. With the piston choise available the piston needs to sit around 70 thou down the bore to get the desired compression ratio of 9:1

A quick calculation has revealed a 970 cooper s rod is about 3.2mm taller then a standard rod, therefore if the big end could be opened out to allow for it to take an a plus big end bearing this could provide a viable route to go down for the conversion.

Of course the other option would be to grind the crank to s big ends, but I'd prefer to keep the big ends the largest diameter possible by modifing the rods to take the larger bearing, so is it possible to do this?

The hardest thing to achieve by far I fear would be finding a set of 970 s rods for a reasonable price.

Economically, doing a 1293 may make more sense at this rate, but I must say for all the buggering about with mini engines spending a couple on grand on a vtec engine and dumping that in is getting more appealing.

an issue i found when i was looking to do similar (to build a stroked 1400 k-series) was that rods always have the rod bolts pretty close to the bearing diameter, so if you open the big end, you hit the bolts.. not sure if this is an issue on s rods, as its been a LONG time since i owned a set lol.

turbo 16v k-series 11.9@118.9 :)

Denis O'Brien.

^^^ What he said about the bolts

use the 70.2mm stroke crank, 6 inch rods and get some low pistons. Easy and it will work! I have an engine with a SA crank, std 5.75" rods and powermax pistons, and I had to skim the block 7 mm to get them flush. So really the pistons should not sit proud with a 6" rod anyway...

also, running the pistons down the bore is a no no! get the cc's in the head instead!

Edited by miniminor63 on 13th Oct, 2011.

Pistons can be dished out....

I'd call them first mate.

If something is worth doing, it's worth doing half of.

I'll clarify, my rods are forged from blanks then cnc machined.

Jk

If Carling made Mini engines
it would probably be like this one!

If so John, I'd quit writing billet rods. Billet rods are shite, forged ones are what we need :)

PMSL!!

chicken... egg...

Billet is continiuous cast (similar to extrusion).

How is steel forged when it is in its liquid state?