Piston Pin Retainer Problem

[T. Cotten]

I agree with just about everything that has been posted here, but I gotta add some perspective and a question.

No means of retaining the wristpin (gudgeon) will cure sidethrust from misaligned rods. Buttons just lengthen the fuse a little, as they cannot be kicked out or broken like metal retainers.
If the rods are really straight, the pin should never exert much force on any style of retainer.

Buttons were innovated for racing, but as Tommo points out, they are great for saving exotic or expensive pistons. Racers can occasionally manage to melt them, and sometimes particles of metal can embed to then carve into the cylinder wall, but most vintage machines will not be treated so harshly.

I am considering button retainers for a project where I wish to increase the reciprocating mass considerably. And I have a lot of scrap PEEK on hand, with superior temperature resistance and tensile strength than teflon.

So my questions are...

Shall I cut the buttons with press-fit tangs to hold them within the pin, and thus seal it? (Did that on my Knuck in the '80s, but haven't torn it down for inspection yet!)

How do I cut the radius of the outside of the button without a Holdridge?

Thanks in advance,

....Cotten

[Kojack]

Right Cotton, straight rods are important and should be checked anytime the cylinder is removed. It only takes a little effort and is easy enough for anyone to do. I bet that a lot of clip problems are caused by bent rods.

We used to have one of our small lathes set up with a very simple system to cut large radii. The lathe had a punch mark on the headstock, under the chuck and between the ways. There was a matching punch mark on the cross slide of the carriage. We had a several pointed rods in various lengths and it was easy to make up any length needed. The length of the rod was the same as the radius that needed to be cut. The handwheel of the carriage was used to hold pressure against the rod and keep it between the punchmarks. Then the cross slide was used to cut across the face of the workpiece. The carriage would follow an arc that matched the rod length. (I hope you can visualize all this) This system was a bit cumbersome to set up and the tip of the cutting tool had to be in line with the punch mark at the center of the arc but the cost of the system was hard to beat. You should be able to make up a moveable parallel with a punch mark to fit between the ways if you needed to move the punch mark away from headstock for some reason like a shorter radius, and, although we didn't try it, you should also be able to do the same thing using the tailstock if you want to cut a concave face.

[rousseau]

Garym
Go with your scenerio #3

[Skip]

I have a friend that makes these buttons in his spare time...he swears by them...he wants me to tear my motor back apart this winter and let him make some for it....as much trouble as I has getting different clips this winter I may let him....I finally went to an implement company and purchased some internal clips....bought 6 for under $2...so far so good...Skip

[rick anderson]

I personally do not like snap ring type lock rings, I have seen alot of trashed cylinders from these rings coming out. Also I don't know for sure if it matters witch side of the ring goes against the pin, because if you look close, the outer edge of the lock ring has a chamfer on one side, and a sharp edge on the other side, but I also noticed that if you look at a side view, holding the ring in the position when it is installed, the sharp edge is not square to the face of the ring, at least not the ones Ive seen.

Rick.

[Kojack]

One thing that I just noticed in my big twin service manual, it states that you should not use the 22588-78 retaining ring in early style pistons, it will fit too loose. You should only use it in pistons marked "7" or "77" on top. I'm not sure how this applies to '73-'77 pistons which originally used the spiro-lock retainers. Are the later snap rings considered interchangeable with those? The spiro-locks are hard to work with and I've replaced them with snap rings on a couple of Sportsters but now I'm wondering if this is bad practice.

Rick, the manual doesn't specify which way to install the snap rings but standard practice would be to have the sharp edge facing out.

[rick anderson]

I agree, but as I stated, the clips I've seen that come with the after market pistons are not a square edge to the face of the clip and I also agree that there should not be any presure from the pin pushing on the clip unless there is a bent rod or a crooked bore.

[Garym]

Thanks everyone, for all the info!
Gary

[T. Cotten]

One last note on the bent rod thing:

Lots of straight rods have shucked a clip for no other reason than they were loose as a goose.

...Cotten

[Garym]

Thanks everyone, for all the info!

Gary

[fabercycle]

Jack, I scoffed at teflon buttons, many years ago........until I took apart a flathead 80, with a ton of miles on it, and found teflon buttons that were so virgin looking, you could see the machining ridges on the surface that rode on the cyl. bore. They were the only good pieces in the whole top end!

Well, now, I've been a believer for a long time, and use them in every motor I touch.

The coeffiecient of friction/wear on teflon covered with oil is like a theoretical zero. Providing there is no severe pressure. So make sure to float the pin sufficiently.

[Jack_Hester]

I'm open to try anything good. What is your source for teflon buttons? Or, do you make them yourself? If so, what are the specs to look for in selecting the teflon?

Jack

[fabercycle]

I keep teflon rod on the shelf, and make them as needed. Teflon of any type all has about a 600 degree melt temp. Just don't use glass filled teflon, it's abrasive. Peek would be good too.

I don't subscribe to drilling holes. Just use a slip fit , button to the pin.

Holes in buttons plus tight fit, is a recipe for gathering oil in the pin, (up to hole level) and affecting balance, as well as having the oil boil, possibly making them overheated, expand, and turn your pins blue. (seen that too). Remember, your pin is exposed to lots of oil. (and should be). I also recommend some extra oil grooves in the pistons' wristpin bores.

Having straight rods is a given.

You'll be taking a top end off, and back on in a couple minutes, without pulling your hair out.