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.

It is important to oil the piston rings before you install the piston in the bore, and to oil the needle roller bearing. You must oil the crankshaft bearing before you assemble the connecting rod to it. Aside from those points the most important assembly issue is putting the connecting rod bearing cap on straight and squeezing it into place with your fingers, to be sure it sits down properly: many of them are capable of jamming because of the complex machining which ensures that the cap is installed square and on-center. Once you have the cap on properly, install the screws and hand-tighten them. Check that there is no gap between the cap and the connecting rod, at the sides of the cap. Then tighten both screws to just a couple of foot-pounds. Finally, tighten the screws with a short-handled socket wrench. On an 8" wrench, apply about 15 pounds force to the handle. After tightening both screws, recheck the first one, then recheck the second one, but don't apply greater force than you did the first time.

After closing the crankcase, rotate the engine a few times with your hand on the flywheel. If it is difficult to turn or the feel is uneven, you have to open it up again and see what has gone wrong.

From what you have said I take it you are not replacing the piston rings. If that is correct there is no real break-in procedure. As long as the engine turns smoothly, just let it warm up for one or two minutes, then put it to work.

Hi grumpy,

I'm going to oil all the bearings but fortunately I won't have to reassemble the connecting rod because I never touched it; I just took out the piston, gudgeon pin and the needle roller bearing (shown in previous pic) which goes at the end of the connecting rod. The gudgeon pin goes inside that same needle roller bearing.

I am replacing the piston rings. Basically it will be all the same old parts except for the new piston, piston rings, circlips and gasket (all these are new parts). So what is the break in procedure? The cylinder will still be the old one. You mentioned to clean all the alluminum shavings from the bore; I put some carb cleaner and flushed and wiped with a rag, is that enough?

As I recall your old piston showed some scoring on its outside. That means some aluminium from the piston will have stuck to the bore of the cylinder. The bore needs to be extremely smooth, for the piston and rings to run up and down it without damage. It needs to be honed just enough to remove any rough spots. This can be done with some wet-and-dry automobile paint-rubbing abrasive, or with metal-polishing abrasive (either cloth or paper backed). Around 220 grit would be OK, if there is anything to be removed. If you are confident there is no aluminium stuck on there, up to 400 grit could be used. My preferred way to do it is to use a round piece of wood of just a touch less than bore diameter, drill a hole through it lengthwise so you can put a rod through it to spin it in an electric drill, and make a fairly shallow saw-cut radially into the wood along the full length. Feed the end of the sheet of abrasive paper into the saw cut, then wrap it around the wood. Cut the paper so it just makes one turn around the wood, without overlapping. Feed it into the cylinder, with some kerosene for lubrication. As you start the drill running, start pumping the lap up and down in the cylinder so you are polishing the bore with helical motion, not rotary motion. Keep trickling kerosene into the bore to carry away the grinding dust, or it will cut grooves in your bore.

So I finally reassembled the machine and tried to start it but it's not working.

Grumpy, I ended up sanding the cylinder by hand with a 400 grit wet and dry. I didn't really have tools nor the expertise to try the wood cylinder trick. I think it should be OK with the brief sanding I gave it though.

Now the problem I have is that when I try to start the engine it starts for like 1-2 seconds (that is if it starts at all). I've seen a couple things that I'm not sure they're right: when I crank the engine the line spool rotates (even if the engine doesn;t start), is this normal in cylinders or do I have a clutch problem? The spool also rotates even at idle for the 1-2 secons (if the engine starts) that the engine runs.

The second thing I noticed is that the breather valve/ vent cap line is full of gas. Is this normal?

First, the trimmer head should not rotate when you pull the starter. You may not have correctly assembled the engine back onto the drive shaft. The centrifugal clutch is in between the two. It usually consists of a pressed steel drum on the shaft, and a centrifugal mechanism on the engine.

Second, there are several versions of how to vent the fuel tank. Essentially you either have a vent in the tank cap, or a tube extending from the tank. If you have the tube system, it should not have fuel in it but you may have made this happen by overfilling or something of that nature. It is probably not the source of your starts-and-then-stops problem.

Third, the normal and recommended technique for cold-starting brushcutters or chainsaws that have a choke and no primer, is to pull them over with the choke closed until they start and then immediately stop, then open the choke to about two thirds closed, and pull the starter again. Unless there is something wrong, they will then start first pull and run through warm-up, during which process you open the choke the rest of the way. Those engines cannot run with the choke closed: they do not have an "unloader" on the choke, so they are simply strangled to death immediately. In the process of strangling and dying, they pull fuel into the crankcase so they are then able to start very easily on the next pull.

After trying different throttle and choke positions I was able to start it for about 20 seconds but it doesn't idle on its own. I have to keep revving it up to about 1/3 or 1/2 throttle for it to keep running.

The trimmer head keeps rotating at all times even at low idle and I wonder if that's the reason why it can't idle? Maybe it's offering resistance to the engine? I couldn't have messed it up because when I disassembled the engine I never took out the crankshaft, clutch or anything (the furthest I went was to take out the piston and gudgeon pin). I now remember that even before I overhauled the engine it had the exact same problem. The head rotated at all times, even when pulling the start cord and it was very difficult to start. This is why I disassembled the engine on the first place- to find out what it was...

It can't run slowly while driving the output shaft. Realistically, most small bent-shaft trimmers can't idle slowly enough to disengage the clutch anyway, though the more expensive and larger machines can. I don't recall you mentioning the brand or model, or posting pictures of it.

We need to know what kind of machine it is, and how fast it has to be going to keep running steadily. If the output shaft is rotating when you pull the starter, though, the clutch is certainly not working, and will have to be fixed. When we see the pictures, we'll try to work out how to dismantle the clutch and find out what is wrong. It sounds as if it may have a broken clutch-spring.

So I managed to turn it on and warm it up. It's really finicky to start but it managed to rev up to max and idle without stopping for like 7 minutes with trimming included (I ended up turning the engine off myself). I'm still not happy with how hard it is to start and I suspect there's something wrong but I'll deal w/ it later.

But the head keept turning at all times, so I opened it up and the clutch spring was broken and the grip material of the shoes was all faded. What would have caused this? It was like that when I bought it. So I guess I'm ordering a new clutch assembly?





The grass trimmer is a straight shaft Shindaiwa T230. I'm quoting the manual: "engine idle speed should be final adjusted to 2,750 (�250) RPM (min-1)". Maximum speed: 7,500 rpm. Carburetor does not have a low or high adjustment screws.

The broken clutch spring would be the reason the clutch has been engaged all the time. The worn out clutch shoes may have happened by overloading the clutch, for example by running the engine with a toothed cutting blade stuck in a tree or whatever, or with a seized up gearbox at the bottom of the shaft.

You appear to need a new spring and a pair of new clutch shoes. These should all be standard service parts. It would seem that someone sold it to you because the clutch had been trashed by abuse.

When the clutch works properly it should be easier to start, since it won't have to turn the drive shaft when you pull the starter. However I'm not clear on how the carburetor would have been made without tuning adjustments for high and low speed mixture. It is possible, of course, that those adjustments would be covered and sealed for emissions control reasons.

Hi Guys, Just a gentle heads-up, this thread has wandered way off topic. To keep our archives happy, can you please start a new thread.
Thanks guys,