OutdoorKing Repair Forum Forums Restoring, Customising and Modifying Tech Talk How do I install circlips on my 2 stroke?

I am trying to install new circlips to my 2 stroke piston but it's way too hard.

The circlips are quite large for the hole in which they should fit, they are also very strong so I can't insert them w/ my hands. Even if I use needle pliers it's still hard and I have ruined the old circlips that way.

If I over-stress the new circlips then they will loose their spring and elasticity qualities and eventually break after using the engine; it would destroy the engine.

Please look at my video on vimeo:
How do I install circlips on my 2 stroke?

Here I'm showing how large the new ring is and how small the hole.



I'll keep uploading pics but please watch my video above.

Please let me know if I should start from the top side and then push in with pliers. What do you think?

Hi Dario, I can only tell you my method - perhaps others will offer alternatives.

The circlips I am used to tend to be for cars, and they have one end of the circlip turned inward. You can grip the turned-in end in the pliers, which makes inserting them very quick and easy. You can also easily rotate the circlip in its groove, after installing it, by just gripping the turned in bit and rotating the ring toward it, which reduces the ring tension and allows the circlip to slip and rotate. You always rotate the clip in the groove as the final step in installing it, because that verifies that it is fully in the groove all the way around.

With the "value analysed, low cost" design of circlips you have, I would position the clip with its gap adjacent to the cut-away in the circlip groove at the side of the gudgeon pin bore of the piston. Put one end of the clip into the groove, level with the bottom of the cutaway and extending right across the cutaway, while holding the opposite end of the clip in the pliers. Twist the clip moderately with the pliers, which will use its springiness to reduce its diameter so you can start to ease it into the groove. Because you haven't had practice at this, you will need to use something like a piece of brass to help push the clip into the groove, starting near the first end of the clip that you began by putting into the groove, maintaining the twist on the ring with the pliers so that the clip has sprung down to a reduced diameter. Gradually move the piece of brass around the clip as you put more of it into the groove.

When you finish installing the clip, one end of it will run across the cutaway on one side. To remove it, you just grip that part of it, and twist it slightly in the contracting direction while lifting it out of the groove. It is quite easy to do.

g.day Dario,
just a suggestion , you could try using a hose clip of the right diameter, insert your c'clip & tighten to the desired size . Then with a drift of roughly the same size as the gudgeon pin( the drift could be a wooden dowel )lightly tap the c/clip home , mentally ithink this method could work,
cheers john.

Hey Grumpy,

Yes, I dislike these circlips very much. I didn't understand your method. But I just finished installing one of the circlips.

The way I did it was pretty much like the extraction method you mentioned but in reverse order: Basically I inserted one end of the circlip at about the 11 o'clock mark inside the groove, then sustained the circlip at 7 o'clock pressing against the piston, then with my needle nose pliers I gripped the circlip at the 4 o'clock mark and pushed towards the centre of the piston and towards the left at the same time and by that time I was able to push the pliers inside the 3 o'clock cut-away and finally insert the other end of the circlip inside the groove.

It was really difficult, I know it seems easy but it was my first time and the piston is about the size of my thumb and the pliers were large.

Hi ozzyjohn,

So for future reference, you think that it's OK to use circlips that are not original? I think I'd be skeptical to put something like that in an engine...

Bugger! there goes my 4lb hammer thought! You did good by the sounds of it, just make sure the little so and so's are seated in the groove tight and all should be well

I JUST RUINED MY PISTON!! I was trying to put the piston pin inside the first hole before installing the piston and I ruined it. There seemed to be no way that the pin could go inside that thing and could not go straight, no matter how I placed it it would lay on a side and start to fit in crooked. I was careful. I tried. But the piston is made of alluminum or some really soft metal and the pin deformed the area of the groove and it's just useless now. I'll have to buy a new piston.

How do you install the pin??? I put the piston on top of a piece of wood and then hammered the pin with a piece of wood in between the pin and the hammer.

Yeah, I'm new but I should have thought of that one. It also occurred to me that on top of heating the piston I can put the pin in the freezer to reduce its size.

I called the dealer to order a new piston and he said the same thing: freeze the pin and heat the piston with a hair dryer or soemthing.

It really pissed me off that this happened. The piston metal was super fragile, I saw a video of a pro technician guy on youtube hammering hard a gudgeon pin of a small 2 stroke with a piece of wood and it went in like a charm - it wasn't the same case with mine

Joe, that Holden red motor had the pin restrained by a tight fit in the rod, not in the piston. The workshop manual says you need to heat the little-end of the rod to install the pin. The heating is done either by immersion in hot oil, or putting the set of rods in an ordinary oven. Don't overheat them, obviously - I no longer recall the correct temperature, but it wasn't very high.

Dario, fitting piston pins always requires care, lubrication and cleanliness. Essentially you get pin and piston bore surgically clean, lubricate both with light oil (sewing machine oil, also known as DTE Light, is good), line the pin up with the hole very carefully, and when it has just started under thumb pressure and you have verified that it is exactly straight, you smack the far end of the pin with the side of your hand, not terribly hard, to get it in half an inch or so. After that it is legitimate to push harder if necessary. I have several times watched this being done on a production line, packing service replacement pistons (which are conventionally sold with pins fitted). All of the people doing it were women, and they were by no means strong. If it won't go in that way, you have started it crooked.

Grumpy,
I wish I had come across that information earlier. I am a very careful person and I tried every way possible of fitting that thing straight with my hand first, it was shiny clean and lubed lightly with 2 stroke oil. But it wouldn't go anywhere, it just didn't fit and less straight. I just happened to see a pro technician in a video smacking it with wood so I made the mistake of copying it.

So when I get the new piston and I follow your procedure, if I still can't fit it in with my hand, how should I heat the piston?

BTW would it be a karate-style blow when you mean the side of my hand?

I sometimes rotate pins slightly, just with my fingers, to help start them straight, but I'm not sure it helps. The main thing is to keep holding it up and looking at it to see if it looks straight, until you have it moving.

The piston is made from aluminium and is therefore not all that easily corroded, but the gudgeon pin is steel and corrodes very easily. That means you can't heat the piston with hot water. An ordinary oven at 150 Fahrenheit is good, but wear gloves so you don't burn your hand (150F shouldn't raise a blister, but it is too hot for comfort). Aluminium expands a lot with temperature, so warming up the piston will help considerably. Do not heat the pin, of course, you don't want that to expand.

So far as smacking the pin with the side or heel of your hand is concerned, you won't need to do it if you warm up the piston - the ladies on the production line didn't warm them at all. Imagine the kind of smack a small genteel lady could carry out every few seconds all day without making her hand sore. It is far from being a karate chop. The problem you had was a combination of not having the pin exactly straight, and having raised a burr with your efforts to remove the circlips.

I removed my post, I was only trying to offer a solution I will but out from now on.

Joe, I wish you wouldn't butt out, you are right more often than I am.

MMMMM yeah sorry I should have pointed out the burrs around the circlip groove, you wouldn't have got that pin in with those there (see surface damage in last photo). I made an assumption that they would be removed?, it would be some thing I would have removed without thinking about it.

Those gudeon pins are a transitional fit, which means they would have slipped in & out of the piston with "relative" ease yet with no play (looseness) what so ever. As you were re-using the old piston and pin it "shouldn't" have given you the grief that it did.

When fitting the new piston ONLY attempt to fit the clip ON ONE SIDE ONLY, so you dont damage the OTHER pin bore. Slip the pin through the first piston bore (which you havent touched, hence undamaged), push through the conrod small end (you may have to jiggle this a little to settle the needles if a needle roller bearing fitted) and make sure the pin has gone through far enough before fitting up the last circlip. Check your circlips have seated well in their grooves and your there! The WARM and COOL trick JOE & GRUMPY pointed out will help, but shouldn't be required unless the rod is a shrink fit onto the pin (check first). Remember keep every thing cleaner than clean too....a fiber off a rag will stuff up the transitional fit...
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About the burrs, they look worse in the picture than what they really are. They are only superficial scratches and they are on the outside, they don't even get inside the very center where the pin is supposed to go. In any case, I carefully sanded those scratches and the hole with fine grit sandpaper and oil. I also tried the pin on the other side (which had no burrs/damage) and tried turning it and different things and still didn't go in.

Only after freezing the pin (after ruining the piston) did I manage to insert the pin straight a few milimiters on the other side (which wasn't ruined).

"shouldn't be required unless the rod is a shrink fit onto the pin (check first)." Why would it be a shrink fit?

I remember when I took out than pin for the first time, it was a pain. It was quite stuck in there, maybe cause it's 22 years old.

With the new piston I'll make sure it's a surgical cleaning though; don't want to screw it up again.

Dario, the gudgeon pin has to be strongly located axially. Probably most of us have seen what happens when the pin moves axially: you get a set of neat-looking keyways down the bore, due to contact from the sides of the end of the pin. Even if you catch it very early that will call for a rebore, but often the wear exceeds the rebore limit by the time you find out about the problem.

There have been several ways of locating the pin, used on various engines over the years. Back in the 1930s it was fairly common to have a "little-end bolt", screwed from one side of the connecting rod to the other, and passing through a recess ground in the center of the pin. This was expensive, it weakened the rod in a critical place, and it increased reciprocating weight, so it was a poor solution. Later, circlips took over, except for the odd exception when they put aluminium "slippers" at each end of the gudgeon pin, so the slipper rode against the bore and kept the pin away from it. (The 1960s Simca Aronde was an example of that one.) Car engines normally use either circlips, or a shrink fit between the connecting rod and the gudgeon pin. Before that became fashionable some car engines had a bronze bush in the connecting rod, and circlips at the ends of the pin, so the pin could make its own choices whether it turned in the rod or the piston. That was a particularly poor solution, used in an engine that was famous in Australia (the Holden "grey motor" of 1948-1963). The result was insufficient bearing area in both piston and rod, and a whole lot of engines with "gudgeon knock" due to mechanics reaming the bush in the rod oversize, to make it easy to assemble the engine.

To get a good design, the engineer must provide enough bearing surface either in the rod or the piston, not in both. Shrinking the rod onto the pin is one good solution to this problem: all movement is in the piston, and the rod is reduced in width to maximize the bearing area in the piston. Also, the piston runs a lot hotter than the rod does, and aluminium has a high coefficient of thermal expansion, so it is very difficult to keep the pin from rotating in the piston even if you wanted to. Another good solution, though an expensive one, for very small engines, where bearing area is hard to come by, is to fit a needle roller bearing to the connecting rod, then make the bearing area in the piston considerably smaller than it would otherwise have to be.

I think this engine has a needle roller bearing at the end of the rod (which is where I have to insert the gudgeon pin).

Today I'm picking up the new piston and circlips. I'll be using the same old gudgeon pin. I'll follow the methods you advised here to install the pin and circlips.

Do you have any other recommendations for a newbie before reassembling a small engine (don't want to mess it up)?

I know I have to lube everything, already have a new crankcase gasket and cleaned the surfaces where that gasket will seat (it's a dry install gasket I was told by the dealer), also new piston rings, have to press the rings when installing the cylinder so they don't get caught, know the arrow at top of piston has to face muffler side, cleaned carbon and everything up, etc.

I also want to know when I install the bolts to fasten the cylinder, how far should I go in terms of torque (I guess I don't want to over tight the crankcase gasket)? I don't have a torque wrench.

Also I've cleaned, reassembled the carburator and replaced all gaskets, needle, etc. The only question I have about that one is, the new gaskets are factory coated with some sort of powder, should I clean that up before installing or just install them as they are?

Do I have to use a procedure to seat the new piston rings? I have to consider I'm installing a new piston with an old cylinder (cross hatch pattern not present, so it's probably what you call glazed). Do I have to run the engine in any particular way for the first few minutes?

That's the one.