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Author Topic: Re-Fitting a Ringed Piston : Help Please !  (Read 1853 times)

Offline Robin_Holden

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Re-Fitting a Ringed Piston : Help Please !
« on: January 28, 2011, 01:40:11 PM »
Hlp please fellas !

I had to dismantle one of my engines.

I'm now having trouble re-fitting the ringed piston into the liner !
The ring sit's 'proud' a tad so it won't go into the liner.I can't 'squeeze' it to make it drop in .

Is there a simple solution please ?
This is the first time I've done this , non-ringed engines are so much easier to work on .

Much obliged for any advice please ,

Regards ,

Robin.
 
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Offline Tim Wescott

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Re: Re-Fitting a Ringed Piston : Help Please !
« Reply #1 on: January 28, 2011, 02:35:11 PM »
Did you check to see if the ring fit into the cylinder before you put it in the piston?  In car engine rebuilds its part of the process to double-check the ring gap, and it should be for a model engine rebuild, too.  If the ring is too big to fit at all then nothing you do with it on the piston is going to bring you joy.

Assuming that you know the ring will fit at all, you could put a hose clamp around the piston, gently, to compress the ring.  Then push the piston down into the liner.  Just start with a hose clamp that's roughly the diameter of your piston, and you should be fine.
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Online RandySmith

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Re: Re-Fitting a Ringed Piston : Help Please !
« Reply #2 on: January 28, 2011, 03:33:51 PM »
Robin  what motor is it?

Randy
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Offline Paul Allen

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Re: Re-Fitting a Ringed Piston : Help Please !
« Reply #3 on: January 28, 2011, 11:43:50 PM »
Robin
       Check the ring groove in the piston, it may have a pin to locate the ring.
Do not force anything!
Paul Allen
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Offline Robin_Holden

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Re: Re-Fitting a Ringed Piston : Help Please !
« Reply #4 on: January 29, 2011, 12:06:23 AM »
Quote from: RandySmith on January 28, 2011, 03:33:51 PM
Robin  what motor is it?

Randy



Randy , it's a ST GS 40 . Chinese production.

Thanks a million for your advice,

Robin.
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Offline Robin_Holden

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Re: Re-Fitting a Ringed Piston : Help Please !
« Reply #5 on: January 29, 2011, 03:01:57 AM »
Quote from: paul allen on January 28, 2011, 11:43:50 PM
Robin
       Check the ring groove in the piston, it may have a pin to locate the ring.
Do not force anything!
Paul Allen
OZ

Paul , many thanks.

I have located the pin . May I ask ....What do I do next please ?

Sorry to be a nuisance !

Robin.
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Offline PerttiMe

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Re: Re-Fitting a Ringed Piston : Help Please !
« Reply #6 on: January 29, 2011, 05:48:23 AM »
Place the ring so the gap is at the pin.
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Online Brian Hampton

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Re: Re-Fitting a Ringed Piston : Help Please !
« Reply #7 on: January 29, 2011, 08:07:48 AM »
Ringed engines can be a bit of a hassle to put back together. There should be a taper at the bottom of the liner that compresses the ring into place so long as the pin lines up with the ring gap. The problem there is that usually the piston/rod has to be fitted to the crankpin before the liner is installed, in which case you have to fit the piston/rod then make sure the ring gap is over the locating pin then drop the liner into place until the piston (at BDC) enters the taper at the bottom of the liner. I usually put a finger under the bottom of the piston to put some upward pressure on it and wriggle the piston a little to help the ring start to compress in the taper. Before you fit the rod to the crankpin though, make certain you've got it the right way round.
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Offline Robin_Holden

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Re: Re-Fitting a Ringed Piston : Help Please !
« Reply #8 on: January 29, 2011, 08:24:16 AM »
Thanks a lot fellas.

I now realise how it works !

The ring was broken anyway. Now I have to find a replacement.

Very much obliged for everyone's advice ,

Robin.
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Offline PerttiMe

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Re: Re-Fitting a Ringed Piston : Help Please !
« Reply #9 on: January 29, 2011, 08:29:56 AM »
... do those rings have an "upside" and a "downside"?

(I remember a case where a mountain biker ended up in hospital after rebuilding his fork and putting some C-clips (bit like rings) back in, the wrong way  ~^ )
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Online RandySmith

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Re: Re-Fitting a Ringed Piston : Help Please !
« Reply #10 on: January 29, 2011, 08:38:18 AM »
Quote from: Robin_Holden on January 29, 2011, 08:24:16 AM
Thanks a lot fellas.

I now realise how it works !

The ring was broken anyway. Now I have to find a replacement.

Very much obliged for everyone's advice ,

Robin.

Hi Robin

LOOK at the new ring very carefully, Many of them DO NOT  set with the gap at the pin in the piston. A lot of the rings have a notch ground into the inside of the ring somewhere to set into the pin that is pressed into the top of the piston and goes into the ring groove.
You will have to be careful to line up the ground out part of the ring with the pin. Others will have either one or both ends  of the ring ends ground half moon shape to clear the pin.
The reason the ring is broke is most likely trying to install it without it being orientated correctly, the rings will break almost instantly that way

Regards
Randy
« Last Edit: January 29, 2011, 12:27:45 PM by RandySmith »
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Offline Robin_Holden

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Re: Re-Fitting a Ringed Piston : Help Please !
« Reply #11 on: January 29, 2011, 10:42:27 AM »
Randy , as ever much obliged for your advice.

Kind regards from a chilly S.W.France ,

Robin.
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Offline Steve Helmick

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Re: Re-Fitting a Ringed Piston : Help Please !
« Reply #12 on: January 29, 2011, 06:45:44 PM »
I expect the setup is the same as the G.51, with pin at the ring gap. The tough part is that the cylinder is a shrink fit into the case, so you need to heat the case (heat gun), hold the parts aligned, and carefully slip the cylinder down over the piston and ring. Three or four hands would be handy. Since I only have two, this is not my favorite task, but I didn't break the ring. All in all, I'd avoid complete disassembly if at all possible. Taking the head and backplate off generally allows a good cleaning if dirt is the only problem. If your G.40 has mechanical woes, then you'll have to deal with it best you can. Be patient, borrow some extra hands, etc.

When ST moved to China, I was hoping that they'd bring out the G.51 in ABC form. Dang, they didn't!  DK^ Steve
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Online RandySmith

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Re: Re-Fitting a Ringed Piston : Help Please !
« Reply #13 on: January 29, 2011, 11:32:36 PM »
The G 51 rings I have used, have the notch cut into the ring away from the end gap. it does not use the end gap as a trap for the pin in the piston ring groove.

It is possible that the G40 is the same

Below is a G40 or S40 ST ring you can clearly see that the notch for the ring is not at the end gaps,
If you do not line it up correctly ,you will quickly break the ring

Randy
« Last Edit: January 30, 2011, 10:33:49 AM by RandySmith »
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