Chinese piston/cylinder kit total annihilation.

[SoopermanLuva]

Good evening, gentlemen!
So I had this chinese top end for a 036 that I popped in there for testing purposes. And here's the result after about 2 tanks, half of which was really adjusting and playing around with different settings. In the pictures you can see that the spot where the circlip is supposed to sit had a thin edge to begin with and it just broke off. What happened next is pretty much self evident. The clip came out, the wrist pin came loose and as soon as I moved my finger off the trigger... Boom, baby! Luckily, the impact wasn't super violent and the crank shaft seems fine. This is just a little story for people who want to pop a cheap chinese piston in place of a worn OEM one. These things can ruin your day. The cylinder is actually chromed, so there's some marks just from wearing in, but there were no sharp edges, the ports are chamfered, even if sloppily, but at that price point there's nothing wrong with that. Maybe I just got a lemon, but these things do happen.

 

[Dieseldash]

Ouch!! Were those the China Circlips? They’re junk always use new OEM Stihl or re-use your old clips. How was it running before it came apart?

 

[SoopermanLuva]

Ouch!! Were those the China Circlips? They’re junk always use new OEM Stihl or re-use your old clips. How was it running before it came apart?

The saw was running well actually. Cold started with 3 pulls, failry smooth idle at 2600 rpm. The problem is not even the quality of the clips. the part of the piston holding them in place just popped off. Probably a casting issue. You can see that in the pictures. Gives me a warm feeling, because in this case it's not my fault.

 

[s sidewall]

Cheap casting, you can see the casting flaws in machine surfaces. Looks like cracks.

Steve

 

[Dieseldash]

I should of looked closer at your pic. I see that now. Had to get my readers out, turned 42 and I can't see crap up close.

 

[brandonstc6]

Yikes! That’s a mega crappy looking piston


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[a. palmer jr.]

Those Chinese pistons have always had a trouble with circlips. On some of them it's not wise to use OEM circlips because the groove is bigger and the OEM doesn't seat too well and just barely holds the wrist pin in. Probably best to get a different piston, Chinese stuff is always a crap shoot..

 

[SoopermanLuva]

Those Chinese pistons have always had a trouble with circlips. On some of them it's not wise to use OEM circlips because the groove is bigger and the OEM doesn't seat too well and just barely holds the wrist pin in. Probably best to get a different piston, Chinese stuff is always a crap shoot..

Chinese circlips can be improved. They can be bent apart slightly and heat treated to make them more springy. I came to the realization, that a piston replacement can ruin your top end. If that was an OEM cylinder I'd be pissed off. Now I just have to clean the metal shavings out of the crankcase and put on the OEM I cleaned up.

 

[SoopermanLuva]

I should of looked closer at your pic. I see that now. Had to get my readers out, turned 42 and I can't see crap up close.

Don't worry about it, we'll all get there eventually.

 

[SoopermanLuva]

Oh yeah... Here is the circlip. Almost completely straightened out by the impact.

 

[a. palmer jr.]

Oh yeah... Here is the circlip. Almost completely straightened out by the impact.
View attachment 618640

A pair of long nose pliers will take care of that...

 

[SoopermanLuva]

A pair of long nose pliers will take care of that...

Nothing a little duct tape couldn't fix.

 

[67L36Driver]

Yikes! That’s a mega crappy looking piston


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Offhand it looks like the mold and material were diecast at a lower than ideal temperature.

 

[a. palmer jr.]

Still say that chainsaw makers should be able to figure out a more positive way to retain those clips. Dragsters use teflon buttons on the end of their wrist pins..

 

[SoopermanLuva]

Still say that chainsaw makers should be able to figure out a more positive way to retain those clips. Dragsters use teflon buttons on the end of their wrist pins..

Absolutely. This right here is just not a secure connection. Even on OEM pistons this tends to happen sometimes, depending on the position of the opening of the circlip.

 

[ericm979]

Buttons would catch on the transfer ports. And interfere with flow into the ports on Stihls with the funky short transfers and cutaway pistons.

Yamaha had circlips figured out in the '70s as did a lot of other two stroke motorcycle manufacturers. Quality wire, no tangs, good grooves in the piston and small reliefs in the piston to make it easier to install and remove the clips. Dunno why everyone hasn't copied them. You only need a small screwdriver or needlenose to install or remove them, not a 14-piece tool like Stihl has.

I rotate the clips to where the opening faces up or down. If it's to the side then piston acceleration/decelleration at the ends of the stroke could make the clip compress and come out. Probably superstition but it doesn't hurt.