K series pistons

[p.mole1]

When fitting forged pistons I noticed that the gudgeon pins are fully floating, what stops the gudgeon pins from contacting the cylinder bores?

I am trying to build a 1.8 on a budget and have found a set of VVC pistons but I have been told you cannot re-use the con rods with the interference fit. Can these be used with a fully floating gudgeon pin.

[Wrightpayne]

Forged can be interference fit but DVA recommends against this. You can refit 160 pistons to rods but the quality of the 'interference' may vary. No personal experience purely reading blatchat / discussions I've had with a couple of experts - DVA and McMillan.

As I mentioned previously, I think your best bet is a set of 160 pistons and rods.

Ian

[simon_h]

How do you mean fully floating? The gudgeon pin is always floating in the piston and is held by the rod in interference. This is normal for all K Series.

If you have rods that have been modified to have bushed little ends then you need either to get pistons with circlips to locate the pin or have them modified to take circlips. I think DVA can do this. I wouldnt reuse the rod as interference if the pin has been pushed out, if the old piston and pin have been machined away then you may get away with it, or maybe not.

Getting a set of built up VVC 160 piston/rod assys is the easiest route.

 

[p.mole1]

I can get a new set of 160 VVC pistons with rings for £150 but I have yet to find any with rods other than knackered second hand stuff.

[elie boone]

If you don't have the budget to do it properly you might end up in tears.

[oilyhands]

Don’t EVER try to reuse the interference fit on a rod, it will end in tears. If you want to fit TF160 pistons then they will need to have the pins shortened and circlip grooves machined. The rods will need bushing with oil ingress hole on the top, or they can be honed to the correct size with a top ingress hole and the pin can run in the rod.

If you have trouble getting this work done then by all means drop me a mail to discuss.

Be aware that an awful lot of ‘Turbo’ and ‘TF160’  pistons sold on fleabay and similar are just regular stock pistons. VVC pistons and rods are just standard 1800 K series unless they are TF160. AFAIK all current K pistons from Omega have circlip grooves and circlips, no TF160 pistons do.

Oily

[Wrightpayne]

Simon,

The interference fit holds the gudgeon pin in the right place by effectively fixing it to the rod, so the pin cannot creep sideways and gouge the liner. This is effectively what can happen when interference rods have a second set of pins/pistons fitted

Fully floating gudgeon pins have the same bore in the rod little end as is used in the piston, so the pin is completely free to move laterally, therefore needing circlips to stop the pin escaping.

Hope that makes sense.

Ian

[simon_h]

Ian, I am aware of all that thanks ;)

I was querying what he was meaning as it sounded like he had normal pistons i.e. no circlip and bushed rods as he was asking how they pins didn't hit the liners. Sounded like a problem may have been looming.

Cheers Simon

[Wrightpayne]

Would have helped if I'd read all of your post :-)

Ian

[CharlesElliott]

It’s a shame that the Caterham regulations for K series Race engines allowed forged pistons but did not allow anything other than standard rods so you had to reuse the interference fit. And sometimes you did get pin migration. 

[p.mole1]

Thanks for the information, more to think about!