Question about replacing rings in my G1

[1989Marathon]

Definitely check the bore size. Usually a piston skirt will break because the bore is worn oversize or the piston is worn undersize.
Likely, those pieces are in the bottom of the engine.

[sontag1]

Here are the pictures of the pins in the ring grooves. The first picture is of the bottom groove. You can see that the pin is still round and can do its job. The second picture is the top groove. It is hard to tell, but this pin is worn flat with the top of the groove. The bottom ring was stuck in the bottom groove due to the damage from yesterdays short drive. This piston is a goner!

Hopefully someone can learn from my mistakes....

[sontag1]

OK....now I need a little more help so I buy the correct piston / rings. Here are the specs:

Cylinder Bore is 68.25 mm (This is from top and bottom of the cylinder)
(I used a good steel straight edge and the walls of the cylinder are parallel)

Piston diameter is 68 mm (measured as per my SM)

I have standard rings and the ring end gap is supposed to fall between .2 mm and .4 mm

I very carefully measured (with some very nice German made calipers, AND I had my grannie glasses on too) my ring end gap on the standard ring and it was 3 mm! Not 0.3 mm but 3 mm!

So....What do I do now?

Do I need to order a new oversize piston / rings?

I figure if I get a 68.25 piston with rings, I can file the rings down so I will have an end gap that will fall into specs.

http://www.lvssales.com/store/produc...cat=135&page=1

Any advice will be greatly appreciated.
Here are the specs from my SM:

[sontag1]

Originally Posted by 1989Marathon

Definitely check the bore size. Usually a piston skirt will break because the bore is worn oversize or the piston is worn undersize.
Likely, those pieces are in the bottom of the engine.

I thought about that. I used my shop vac and rigged up a small tip to slip down into the crank case. I did not find any chunks of aluminum, hopefully I wont get a nasty surprise one day. What I am hoping is that they chipped off a tiny bit at a time and I was able to suck them out with the vac.

[1989Marathon]

You may have a .25mm oversize jug. It could have been bored. The specs on the standard jug are:

Standard is 68.00-68.02mm(2.677-2.678in) wear limit 68.05mm(2.679 in).

Either way, you have about .010" piston clearance which is way too much.

[sontag1]

Originally Posted by 1989Marathon

You may have a .25mm oversize jug. It could have been bored. The specs on the standard jug are:

Standard is 68.00-68.02mm(2.677-2.678in) wear limit 68.05mm(2.679 in).

Either way, you have about .010" piston clearance which is way too much.

Maybe I honed that cylinder more than I realized.

So do I need to order the .25 oversize piston with rings?

[1989Marathon]

If you can hone off .010" without knowing it, bless you. Honing is usually for taking off .0001" at a time.
A 68.25mm piston won't fit into a 68.25mm hole. I think you need to get some really accurate measurements and see where you are before you decide what to do next.

[lakehopper]

Take it and have it bored at a good cycle shop in your area . Take your new piston with you when you do . Doing this will put every thing true again and you shouldnt have to worry about it for a long time

[sontag1]

Originally Posted by 1989Marathon

If you can hone off .010" without knowing it, bless you. Honing is usually for taking off .0001" at a time.
A 68.25mm piston won't fit into a 68.25mm hole. I think you need to get some really accurate measurements and see where you are before you decide what to do next.

I have to confess that it was the first time I had ever honed anything other than a knife. I really thought I was taking it easy, but obviously I did not really know what I was doing.

I will make some calls around town tomorrow and see if I can find a shop to help me.

[sontag1]

What kind of a ballpark cost am I looking at to have the Cylinder bored, and how much should I have it bored?

I am a fair hand with a wrench, but I am a little beyond my skill set here.

I found a new cylinder / piston assembly for $200 (shipping included). Would that be the best option?

I can always set that old cylinder on my desk at work to put pens in.