We all know that there are two type of wrist pin retainers :

the spiral or spirolox type


and the wire lock



Both the type are very annoying to install and remove, so my question is : why pistons manufacturer don't use this type of lock?


Here in Italy we call it seeger, isn't it be able to lock properly a wrist pin?
It is VERY simple and fast to install and remove.

 

It's not even all the way around for starters, but otherwise i'm out to lunch on the subject. But i'm sure there is a good reason

 

a lot of small engines (lawnmower type stuff) use the typical internal retaining rings, picture 3, that you call a seeger; they're usually not considered reliable enough to be used on automotive engines. Spirolox, picture 1, are very common and although a PITA to put in and remove they're more reliable than the typical internal retaining ring. There can be an axial load on the wrist pin because the combustion force is not centered and uniform on the piston; because of this axial load, typical internal retaining rings have failed which can destroy the cylinder where that failure occurs. The round cross section rings (pic 3) are easy to install and pretty reliable because under an axial load from the wrist pin they are also radially forced into their groove and not just axially pushed out. I'm sure a google search will give you much more info, but the easy way isn't the most reliable.

 

I think Ross pistons use the phenolic buttons(correct me if I am wrong). They are the hot ticket IMO, they are machined to match the curve of the bore and simply rest at either end of wrist pin. once the piston is in the bore its impossible for them to go anywhere.

 

Buttons (aluminum, teflon, plastic, ...) have been around for many decades. I found them easy to use and very straight-forward (except on long-rod installations where the pin bore fouled the ring land). Don't know why they aren't more popular.

Buttons don't work in applications where the oil ring fouls the pin bore. Additionally they can introduce an assembly failure point that doesn't exist with lock rings/grooves - accidentally leaving one out.

Some early failures were to not give the pin enough end-play when using aluminum buttons (or too much end-play that hammered the buttons into failure). Solved with plastic or teflon buttons though.

 

Ok so the seeger is weaker than spiral lock and wire lock, I imagine that but I cannot find data on the axial load they can support.
I have seen buttons on a venolia piston if I remember correct, I like them.

 

The clips like pic 3 are used in the Subaru motors. I think they prob cst more so they arent used. I know they are easirer than the spiral locks and prob better than the wire locks.

 

SpiroLocs are simple and easy to install/remove with the proper tools. And a total PITA without proper tools.