Fully floating pistons - what are they?

[Raffles]

I just purchased a brand new mk3.5 MX-5, and this is part of the spiel from a website I am looking at:

http://www.autoincar.com/2009-mazda-mx-5-minorchange said:

The crucial 500 rpm increase in the rev limit is enabled by greater precision in the engine, namely: a forged crankshaft (this ensures the required rigidity at high engine speeds), fully floating pistons and newly designed valve springs.

What are 'fully floating pistons'?

[v8will]

Something to do with the gudgeon pins IIRC, I'd just read that as techno babble to be honest.

[Yuxi]

Probably means crank guided rods, instead of piston guided rods.

[nc107]

It's where the gudgeon pin can rotate in both the rod and the piston.

[Scuffers]

nc107 said:

It's where the gudgeon pin can rotate in both the rod and the piston.

what he said.

[Boosted LS1]

And the benefit of fully floating is that if the pin seizes in either the piston or rod the piston won't snatch in the bore as it can still rotate Downside could be circlips coming out if they weren't fitted correctly. I like fully floating for high performance applications and a pressed pin for the road.

[Herman Toothrot]

I like that the 3.5 has a forged crank shaft so it's a return to forded induction friendly mx5's. The mk3 killed that market with the chocolate crankshaft they have.

[TallPaul]

Boosted LS1 said:

And the benefit of fully floating is that if the pin seizes in either the piston or rod the piston won't snatch in the bore as it can still rotate Downside could be circlips coming out if they weren't fitted correctly. I like fully floating for high performance applications and a pressed pin for the road.

How often do gudgeon pins sieze in the rod?
I'd think the advantage of a fully floating piston is the gudgeon pin load is spread across 3 bearings (1 in the conecting rod, 1 in each side of the piston), instead of just the 1 in the con-rod.

Edited by TallPaul on Saturday 12th June 21:32

[Boosted LS1]

The load will be the same no matter how many bearings you have? If you have a press fit installation the pin can seize in the piston then the piston could jam in the bore causing a seizure.

Edited by Boosted LS1 on Saturday 12th June 23:05

[Raffles]

Thanks all for the replies, interesting info.