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1980 GS 850G pistons

  • Thread starter Thread starter BigDaddyD1971
  • Start date Start date
B

BigDaddyD1971

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Does anyone have a clue as to where I can find piston kits for a 1980 GS 850G? I have looked on line as well as locally. I have talked to the dealers as well as the salvage yards. Wiseco doesn't make them for the 850. I'm looking for everything that comes in the Wiseco kits: the pistons, rings, clips, etc. HELP!!!!!
 
I can get them made for you. Kind of pricey though. What bore diameter do you want? Ray.
 
Pistons for GS1000 will NOT work due to wrist pin size. 16mm vs. 18mm. Contact MTC engineering and ask if they have any more GS750 piston kits in 70mm(870cc) or 72mm(920cc). Both will bore into a GS850 block with stock sleeves. Dar
http://www.mtceng.com/
 
All three suggestions are great. I'm asking if there isn't something that is already out there that will work. I know some of you guys out there have these bikes, and they are getting up in miles. At least they should be if you guys are riding them. How are you handling this issue? I can find everything for my bike except these parts. Are you boring them out? Getting them custom made? Surely somewhere out there still makes parts that will work. Once again, pistons, rings, pins, and clips. Surely someone else has had this problem and knows where to get these items.
 
The amount of mileage you can get on a set if there are well looked after I suspect not too many have faced this problem so far...!

Dan :)
 
Why not just order some factory oversize pistons and rings? Suzuki pistons are top quality and will be cheaper than aftermarket.
 
If the stock Suzuki overbore pistons are available I can get you "SMOKIN" prices on Suzuki stuff. Ray.
 
You can get stock, +0.5mm, and +1.0mm pistons and rings from Suzuki for around $25 - $30 each. Why fart around with aftermarket?

I will say that the online fiches on most parts site are completely screwed up in their piston listings, so please don't order without double-checking the parts numbers here.
 
Because "farting" around with aftermarket gets you BETTER parts that make MORE power! Why use 40 year old technology when you can use NOW technology?!!! Ray.
 
I fitted custom JE pistons to mine. They are 71mm and 10.5-1 CR. As Ray says, custom are a little dearer than Wiseco kits. I offered to do a bulk deal for GSR members some 12 months back, but not enough takers.
It's a shame, because they really do wake up a stock 850.
 
In what way are aftermarket pistons better? You can make more power but there are tradeoffs in terms of durability and cost.
 
Nessism said:
In what way are aftermarket pistons better? You can make more power but there are tradeoffs in terms of durability and cost.
Click to expand...

The cost is relative to what you expect from the end product. If they're not available in stock form and you really believe in the benefits, then you need to go custom.
As for durability, my custom pistons will outlast the kms that I will run up on the bike, before I won't be able to keep riding it. I doubt that they will see 200,000 kms on them, but I'll bet that they will still be serviceable in 100,000 kms time. I expect they will need re-ringing in 40 -50,000 kms.
If I was to run the engine no higher than 6000 rpm, they would last even longer, but that would be defeating the purpose that I fitted them in the first place. They get regular trips into the red line.

Modern piston designs allow tuners to lighten up with safety, retaining minimal crown thicknesses and ideal squish bands.

IMO, controlling heat dissapation and the burn off rate are keys to good tuning and engine reliability.
 
rapidray said:
Because "farting" around with aftermarket gets you BETTER parts that make MORE power! Why use 40 year old technology when you can use NOW technology?!!! Ray.
Click to expand...

Depends on your goals, I suppose.

If, like most people on this site, you're just looking to keep a neat old bike on the road without going to a lot of trouble and expense, then the easily available stock pistons are the way to go.

If you really want to extract more power and performance from your GS and don't mind the added trouble and extra expense, then by all means look into a set of custom pistons and the associated modifications needed to take advantage of them. Custom pistons are actually less expensive than you might think, and, of course, they are just as reliable

49er, I remember seeing your posts a while back when you had your pistons made. Can you go into a little more detail about what other modifications you needed to make the best use of the higher compression ratio? I assume you need to use higher-octane gas.

IIRC, a stock GS850 has a CR around 8.5:1, part of the reason it runs fine on low-octane gas, but this low CR certainly places a limit on power.

I also wonder what the effect of higher compression pistons might be on a later CV carb GS850 -- the intakes are significantly larger than on the '79 model, so perhaps they would have an even greater effect.
 
bwringer said:
49er, I remember seeing your posts a while back when you had your pistons made. Can you go into a little more detail about what other modifications you needed to make the best use of the higher compression ratio? I assume you need to use higher-octane gas.

IIRC, a stock GS850 has a CR around 8.5:1, part of the reason it runs fine on low-octane gas, but this low CR certainly places a limit on power.

I also wonder what the effect of higher compression pistons might be on a later CV carb GS850 -- the intakes are significantly larger than on the '79 model, so perhaps they would have an even greater effect.
Click to expand...

Brian, I did a few extra mods when installing the custom pistons. The aim was to keep the new pistons at the stock weight (196 -200 grams)
The new pistons all weighed in at 209 grams. Don't you just love the accuracy of CNC machining?

I machined some extra metal off the inside of their crowns and also off the crown end of the gudgeon support posts. A minimum crown thickness of 3 mm was maintained. I managed to bring all pistons down to 198 grams. The gudgeon/wrist pins were 9 grams heavier than the stock ones. They would have been sturdy enough to fit to diesel pistons. I bought new stock pins and ground them back 0.060" (1.5 mm) to match the custom circlip positions. This resulted in a set of pistons and pins that were the same weight as the lightest of the old stock combination.

The '79 850 cams are the same grind as the 1000. I was that impressed with their range of torque that I didn't change them. Consequently, the valve pockets remain the same depth as the stock ones, as is the squish band depth. The squish area has slightly increased as a result of the extra 2 mm of piston diameter.

No porting or chamber mods were done to the head, only casting clean ups and blueprinting.

Prior to completing the camshaft endfloat mods, a gave the camshafts a minor clean up grind to correct some slight lobe wear/tappering. This wear had occured through the camshafts flexing at higher rpms. The 8 valve engines don't have enough bearing support for the cams, to prevent this wear.

I originally tuned to 98 octane fuel, which I used when the dyno session was done. Since then, I have run 95 and 91 octane fuels without any detonation issues. I was surprised that I could go as low as 91, from my previous experiences with high CR auto engines. This engine does make more torque in the lower/midranges on 91, than when running on 98 at the same spark advance. There is a very slight trade off in top end power though.
I have found the ideal solution to be a mix of 91 and 95, especially in the hotter parts of summer. There is no need to run an oil cooler on this set up.

I have a set of Keihin 31CR's that would go well on the larger ported CV 850's. Mine runs so well on the VM26's that I haven't bothered to try them with the smaller ports. Saving them for the 1100 rebuild.
 
If I remember correctly, your octane numbers run higher than ours. :-k

I forget which is which, but our numbers are an average of the research method and the motor method.
Your numbers are only the higher of the two.

.
 
Steve said:
If I remember correctly, your octane numbers run higher than ours. :-k

I forget which is which, but our numbers are an average of the research method and the motor method.
Your numbers are only the higher of the two.

.
Click to expand...

That's right Steve. Our ratings are Research Octane Number (RON) which is higher than Motor Octane Number (MON). Your ratings are an average of both, called Pump Octane Number (PON).

Your PON rating of 87 is equivilant to our RON 91. So I guess that I have been running your 87 octane in my 10.5-1 engine without too much drama!! We really do need to compare "apples with apples".;)
 
In the UK they have 95, 97 & now 98 & even 102 I think :D

Used to be 2 star or 4 star :lol:
 
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