Wrist Pin Buttons

[dkirk]

Have any of the professional 911 engine builders here considered using wrist pin buttons instead of retaining rings? This method of pin retention has been standard practice for air-cooled aircraft engines and has proven to be very reliable. Only possible issue I could see would be the compatability of an aluminum button on a Nikasil or Alusil bore surface. Virtually all of the aircraft engines employ steel cylinders.

Using buttons in the 911 engine would make the assembly process much easier.

[Lapkritis]

Bob, HawgRyder (RIP) was a proponent of teflon buttons for these.

[Rufian]

I will think it will introduce more unnesesary friction.....

[Walt Fricke]

Dave - I think the buttons used in drag race hot rod motors are Teflon. For me, the issue there would be longevity. The top of the line drag motors get torn down how often? Between every pass, so that would not really be an issue with them.

Interesting to learn that air cooled aircraft engines use aluminum buttons.

Me, I don't understand why circlips aren't adequate, and we have to break one of the Ten Commandments in order to install - or remove - the clips J&E chose to use.

[Lapkritis]

The titanic wouldn't have sunk if they just had used the JE clips.

[chris_seven]

The forces on teflon buttons is very low so I would imagine that changes in friction are very low and not something to worry about.

If the engine uses a full skirt piston they are good solution and we used them extensively in early Coventry Climax 4 Cylinder engines that had bad rod ratios and poor clip designs.

With a slipper piston the button becomes very long and probably weighs more than the typical round wire clip.

For very high performance Smalley's Spirolox Double Clips are becoming more common as they have excellent strength to weight capability.

Aluminium buttons running on steel would tend to be an issue at high speeds and would certainly gall on Alusil and I wouldn't like them on Nikasil either.

Are you sure the liners are steel and not cast iron?

[cgarr]

I would just use the clips: The buttons can let some oil collect inside the pin at least that's what we find on the aircraft engines that use them

[RedCoupe]

Chris, my father is a retired aerospace engineer who also happened to have his FAA A&P license so he could do his own work on his own hobby airplanes. In his shop, I found a service manual for a Continental C125 & C145 flat six airplane engine. I looked up cylinder construction and they're forged steel cylinders with individual heat-treated aluminum alloy heads screwed and shrunk on. Yes, it uses the aluminum plugs pressed into the ends of the piston pins.

[chris_seven]

I have also found several articles describing the use of forged steel cylinders.

It seems they used 4140 alloys in a through hardened condition. Some cylinders appear to have also been nitrided and chrome plating appears to be common.

I can't find any references why steel replaced cast iron but is must be to do with inconsistencies in casting and certification.

[safe]

I've not built many engines, but it only took me 3 cylinders util I got the hang of it with just pliers and my thumb and if you have access to the proper installation tool its dead easy.

[Walt Fricke]

Well, the Porsche stock (for aircooled) clips aren't that hard. But J&E's are, at least for me, and I bought an insertion tool. Tough in, and tough to get out. Only installed and removed for one engine to date. Maybe next time easier, but I don't expect that.

[Lapkritis]

Walt - agreed. The task of removal of JE clips is not a fun afternoon. I was bending my pick tools trying to get underneath during the job. Finally sacrificed a screw driver and ground it down to fit into the space and even then you have to be careful not to slip and paint the garage red on your way to the first aid kit.

[safe]

OK, so the JEs are more difficult. How are they different compared to stock?

[Walt Fricke]

The stock clips have that 90 degree bend with a stub sticking in, radially so to speak. The J&E lacks that. I've repressed the rest, but there is a bit more to it.

To insert, the "easy" way is to make or purchase an injector - put the clip into the injector with about half of it peeking out at a small angle, insert so the outer barrel of the injector sockets into the wrist pin hole surround, push the plunger in so the clip is squeezed out of the injector and into the piston without "unsqueezing" before that happens. Done right, it goes right into place.

Worked better for me when I lubricated the barrel part of the tool.

Better, go to Steve Stomski's website, where he explains how to use his tool. I recall a picture of the clip.

But then there is removing the devils.

[safe]

Originally Posted by Walt Fricke

The stock clips have that 90 degree bend with a stub sticking in, radially so to speak.

Hmm, not in my 3.6 and don't think my 3.2 had it either. They were just a C-shape.

A small grove in the pistons so that you can stick in a small screw driver to bend the clips free, keeping your thumb over it so it doesn't hit either your eye or straight into the crank case.
For installation I have used pliers with a 45 degree bend. Grab one end of the clip, insert the other end in the groove and twist it in while you, again, use your thumb to hold it in.
Its actually faster than the injector tool.