Oversize or Standard Piston Kit, 81 GS850G

[mrb302]

Does anyone know of a source for piston kits?

The only thing I can find is standard replacement OEM pistons.
I was hoping to find a 1mm or 2mm oversized piston.

Is there a direct swap, as in a 1000cc piston and machining my cylinder sleeves?

Any help is appreciated.

[tkent02]

GS 1000 std piston is an overbore for the 850.

[mrb302]

GS 1000 std piston is an overbore for the 850.

Sweet!

Anyone have the dimensions?
I'm sure my machine shop can hook me up if there is not any how-to's around.

[chef1366]

Bring him the pistons, rings and he should be able to cut the cylinder.

[Matchless]

Or just resleeve your 850 back to standard?

[mrb302]

Bring him the pistons, rings and he should be able to cut the cylinder.

Yeah. That's exactly what I was thinking I would do.
That's prob a lot safer than just dropping off the sleeves with dimensions on paper.

[mrb302]

Or just resleeve your 850 back to standard?

Honestly, the sleeves are not in bad shape and could be cleaned up and honed. I just figured since I am into the engine I might as well go ahead and upgrade a little. I'm building this bike into a two-up touring bike and it will see plenty of mountain roads next year. A little extra get-up would be nice.

It's still a 50/50 chance that it will end up as a 850 or a 1000. we'll just have to see how things go.

[tkent02]

Drop in an 1100G engine.

Anything is underpowered in the mountains.

[Nessism]

The GS1000 STD rings are the same part number as the 1.0 mm OS 850 rings. The pistons and piston pin are not the same part number though so not sure if it’s a direct fit or what. Regardless, it would not be worth the expense if the goal is extra power since it's only 1mm larger.

[tkent02]

The GS1000 STD rings are the same part number as the 1.0 mm OS 850 rings. The pistons and piston pin are not the same part number though so not sure if it’s a direct fit or what.

Good catch, it was just the rings that were a common part number.
My mistake.

[Steve]

..., it would not be worth the expense if the goal is extra power since it's only 1mm larger.

I just ran through the math:
stock bore = 843cc
1mm overbore = 868cc
2mm overbore = 893cc

You might get a little more "bang" in there, but not that much more. Like tkent suggested, drop in either a 1000G or 1100G engine, they should pretty much just bolt right in.

.

[gmansyz]

850 to 1000/1100?

Just a note here. The 850 wrist pin is much smaller than the 1000 or 1100's pin. As I had an '82 850. My solution was to either swap in a 1000 or 1100 engine or swap internals. I swap the internals. Yes, the crank popped right int. Used the 1000 cylinder and head though you could use the 850 head but may have too much compression. I also used the 850 clutch basket as the ratio was the same and the 850 trans and final drive. Made for a 1000 geared a little short but was a lot of fun. Or you use the 1000 output shaft and transfer case gears to gear it taller like the 1000. Then the numbers match the frame and all is well.
Hope this helps.
G

[tkent02]

Then the numbers match the frame and all is well.

The engine numbers never match the frame, Suzuki didn't do that.

[49er]

Good catch, it was just the rings that were a common part number.
My mistake.

When I looked into doing this, I seem to recall that either the wrist pin heights, or the pin diameters didn't match up!!

[bwringer]

Many fiches are pretty garbled when it comes to pistons and rings.

Here's the data from Alpha-Sports, which happens to be a bit clearer:

24 12111-45110
PISTON (STD)

24 12111-45110-050
PISTON (0S:0.5)

24 12111-45110-100
PISTON (0S:1.0)



25 12140-45120
PISTON RING SET (STD)

25 12140-45120-050
PISTON RING SET (OS:0.5)

25 12140-49001
PISTON RING SET (OS:1.0)


So let's check availability... aargh.

Looks like you can rings in standard and 1.0mm oversizes -- the 0.5mm oversize doesn't appear to be available.

And it appears you can get pistons in standard and 0.5mm oversizes -- the 1.0mm oversize pistons don't appear to be available.


So that's aggravating...


There was a gent recently who had a custom set of high-compression pistons made for his GS850, and they were, surprisingly, not a complete fortune. So don't rule out custom pistons if there's something special you're up to.

But honestly, the GS850 is quite gentle on its bores compared to its bigger brothers. If it has less than 80,000 miles or so, give the bores a light hone, toss in a standard set of rings, and clean up and re-use the old pistons, and go ride. The bores on an 80,000 mile GS850 engine I inspected were still in spec.

If you've actually managed to wear out the bores on a GS850, it's easier and cheaper to just drop in a lower-mileage used engine. They're not that hard to find. Or grab the pistons and cylinder barrels from a lower mileage engine, at least. Or drop in a GS1000G/GL or GS1100G/GL engine.