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R500 K Pistons - two types, which one do I have?


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Anyone any idea how to identify which type my car has? 

Apparently it's to do with the manner of connection of the conrods to the pistons - one is "pressed" the other is "floating". 

I am going to put a camera down the spark plug hole and take some pics, but only hope against hope this offer some evidence of the piston type - whereas really I would need to see upwards from underneath and I can't think of a way to poke an endoscopic camera in there - oil hose aperture? 


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You can remove the dry sump pan, but even if you do you'll struggle to get evidence. You'd need to see if there's a bushing in the small end of the conrod.

The circlips locking will be on the side of the pistons.

Why is it important to know?

I think Oilyhands can modify your conrods if they are the fixed pin type.

I'm going to modify a (new old stock) set of Omega pistons on Friday, but you are not likely to be able to remove a fixed pin without damaging the pistons.

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It’s highly unlikely that the pistons are fully floating if they are the originals as the Cosworth pistons did not come with circlip grooves and the rods as manufactured by Farndon were not bushed as supplied. A clue can be garnered by looking for blue discoloration at the small end of the conrod which would indicate the rod has been heated to fit the pin with an interference fit. This would require the sump to be off and a powerful torch.

The pistons can be removed without damage given the right equipment, however following removal the rod interference fit is compromised and is not safe to reuse. The rods can be bushed to convert to fully floating and the pistons can be machined in the pin tunnels to allow circlips to be fitted. It is probably easier and not much more expensive to go with new steel rods which are already bushed as these will also have new ARP bolts.

Fully floating is the best way to go when RPM goes over 7500.




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