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

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,

Yeah, the moment I saw this trimmer to buy it I knew that it had been neglected a bit, like they guy wasn't even using an air filter and I was also half-sure that the head was not supposed to spin when idling, but I got it really cheap.

That's exactly what I thought.

And the carb is a Walbro WYL and doesn't have low and high screws.

I'll create a new thread when I install the clutch.
Thanks

This is my final comment on this thread.

I have installed a new clutch in the line trimmer and after assembly the unit started right away. So the broken clutch was the cause of the hard starting and idling problems. It now takes only about 3 pulls to start and idles without stalling like it did before.

Had I known about this I wouldn't have spent money to purchase other parts so hopefully someone other than me can learn from this: A seized clutch could be the reason for hard starting and idling problems.

I wanted to thank all of you, specially to Grumpy, for all the help, guidance and for running such an excellent site!!

Thank you for coming back with a final report on the problem and solution, Dario. Our archives are much more useful, and interesting, when we finish up knowing the actual answers. Otherwise they are a bit like a murder mystery with the last chapter missing.

I'll close this thread. If anyone needs to post to it, just PM a moderator.