Wossner Pistons For KLR650, 1987-2007 - Kawasaki KLR 650 Forum
1987 to 2007 Wrenching & Mods For maintaining, repair or modifications of Generation 1 KLR's. 2007 and earlier.

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post #1 of 12 Old 06-14-2014, 05:38 AM Thread Starter
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Wossner Pistons For KLR650, 1987-2007

FYI:

http://www.wossneronline.com/product...ai-1987-04.htm

Quote:
The numbering system after the first 4 numbers shows a “D” followed by a letter or some numbers:

“A” would indicate a piston for the stock size bore.

“B” would indicate a 0.01mm larger bore

“C” would indicate a 0.02mm larger bore

“050” would indicate 0.5mm larger than stock diameter

“100” would indicate 1.0mm larger than stock diameter

“200” would indicate 2.0mm larger than stock diameter
Possible alternatives to Kawasaki pistons and rings. Wossner may be a more stable source, given Kawasaki's revision and obsolescence policy regarding part applications.

During a rebuild, an oversize piston and ring set may be preferable and less expensive than a "big-bore" installation, for some.
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post #2 of 12 Old 06-14-2014, 07:00 PM
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Damocles,
Thank you for that info!
Now can anybody tell us about various compression ratios and octane requirements of the Wossner pistons?

pdwestman
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Still riding my 1987 KL650-A1. 85,000+ miles & counting
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post #3 of 12 Old 06-15-2014, 07:16 AM Thread Starter
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Originally Posted by pdwestman View Post
Damocles,
Thank you for that info!
Now can anybody tell us about various compression ratios and octane requirements of the Wossner pistons?
Not I, but manufacturer/vendor contact information is accessible from the link provided.

I'd assume that these standard catalogued items, sold as replacement parts for the KLR650 engine, would have similar compression ratios and octane requirements to stock pistons.

------------------

BTW; while elaborate hop-up techniques have been tried and mentioned by KLR650 aficionados, I've wondered: Why have SO FEW approached increasing the compression ratio (e.g., by "trick" pistons/thin gaskets/shaving heads/etc.)?

Increasing compression ratio is a sure-fire certain technique for increasing power output, but . . . NO! Tuners will go big-bore (admittedly, increasing CR to some extent), aftermarket cams, porting-and-polishing, big valves, intake and exhaust enhancement, trick valve timing, exotic carburetor jetting, maybe even indexing spark plugs, etc., to get more HP, but . . . one seldom hears about the relatively simple expedient of raising compression ratio.

Why? Is raising the compression ratio somehow forbidden, for KLR650s?

-------------------------------

Just wondering!
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post #4 of 12 Old 06-16-2014, 06:00 PM Thread Starter
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WAIT!!!!!!!!!!! hIGH-COMPRESSION PISTONS OFF-THE-SHELF!

My assumption, Wossner pistons result in the same compression ratio as stock Kawasaki KLR650 pistons, is in error!! (NOT the first time my assumptions have been found so.)

Here, direct from the US distributor, is this information:
Quote:
The CR is 11.0:1.
So, sports fans, if you're serious about hopping up your KLR650, here's one proven path to additional power and increased fuel mileage: Raise the compression ratio.

No, I haven't done it . . . YET! (I'm tempted.)

US stock of Wossner pistons in various sizes (stock to oversize) is varied but small; additional sizes are available from Germany with an attendant delay.

Now, would the higher compression ratio suggest higher octane fuel? Reckon so!

Would a higher compression ration increase the heat load of the engine? You bet, but . . . this conservative increase ought to be within the stock cooling system's capability, I'd imagine. Verwah reports, on this forum, operation within safe limits with a Wossner 11:1 piston on his KLR650, with stock cooling system.

Will durability and reliability suffer with a higher compression ratio? Certainly, components will be stressed more fully, but . . . so would they with any other hop-up techniques and procedures ('cept maybe the PCV valve mod! (I'm kidding.)).

No, I haven't done it (as stated); no, I have no dynamometer "before" and "after" runs, but . . . conventional wisdom states, increasing the compression ratio on an engine increases its power output. Know of no reason why an exception should occur here.

Stock compression ratio: 9.5:1. Wossner piston compression ratio: 11:1. "Delta," or difference: > 15 %. How much power increase probable from raising the compression ratio over 15 %? Don't know, but . . . the popular "685" big-bore kit raises displacement by about 5 %; GREAT increases in power are reported by some who have performed this mod.

Last edited by Damocles; 06-16-2014 at 07:06 PM.
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post #5 of 12 Old 06-16-2014, 07:11 PM
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This is interesting.

One of their "200" pistons will give you a 686, which is a 5% increase in displacement. Some folks have said that the 685 results in a small increase in horsepower; I've heard both 5% and 5hp. Let's assume 5% is right, as it tracks with displacement. I was unable to find a calculator that would estimate horsepower increase due to displacement.

If that piston is available as a pop-top that gives 11:1 compression, the calculator here says that's worth another 2%.

Compounded, that's almost a 7.5% increase in horsepower. On a published 35hp, that's an additional 3ish hp which, along with a boost in torque, should certainly be noticeable.

If one is thinking about a big-bore then a higher compression piston is a good find.

I would note that I've removed the KACR from my engine and it cranks over with no problem, so the increased compression ratio should be fine for starting.

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post #6 of 12 Old 06-16-2014, 07:23 PM Thread Starter
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Originally Posted by Tom Schmitz View Post
I would note that I've removed the KACR from my engine and it cranks over with no problem, so the increased compression ratio should be fine for starting.

Tom
Just as an aside as to stressing the engine: While the comparison is not exactly, "apples to apples," the mighty KLR250 boasts an 11:1 compression ratio, as promised from the Wossner pistons. The 250s have proven themselves rather reliable and durable.

DISCLAIMER: I have no personal experience with Wossner pistons. The paper analysis suggests to me, however, there may be some gold in them thar hills.
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post #7 of 12 Old 06-17-2014, 09:26 PM
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Originally Posted by Damocles View Post
Just as an aside as to stressing the engine: While the comparison is not exactly, "apples to apples," the mighty KLR250 boasts an 11:1 compression ratio, as promised from the Wossner pistons. The 250s have proven themselves rather reliable and durable.

DISCLAIMER: I have no personal experience with Wossner pistons. The paper analysis suggests to me, however, there may be some gold in them thar hills.
Damocles,
Mechanical fact, the smaller the bore Diameter, the less susceptible to 'pre-ignition', detonation!
Who among us has 'lugged' an old mid-'70's 318 Dodge, 350 Chevy into the drive-way in THIRD gear, instead of shifting down into 2nd, like we should have?

Not Pretty, if Detonation takes place at 6000RPM, 4th gear climbing a mountain pass on 85-87 octane fuel!!!!!

But, I used to run Premium fuel all the time anyways. Maybe I could go to a Wossner 11:0-1 piston????? If I decide my rings are WORN-OUT!!!!!

pdwestman
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post #8 of 12 Old 07-01-2014, 08:08 AM
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Search under Wossner under my username on .net and you will find all you need to know about my +1mm Wossie. Short story is that it's a beast, requires 91 US pump gas and is less expensive than other alternatives assuming you have a machinist to do the head and cylinder work.
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post #9 of 12 Old 07-01-2014, 01:18 PM Thread Starter
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Originally Posted by Sandstone View Post
Search under Wossner under my username on .net and you will find all you need to know about my +1mm Wossie. Short story is that it's a beast, requires 91 US pump gas and is less expensive than other alternatives assuming you have a machinist to do the head and cylinder work.
Thanks for sharing your direct personal experience, Sandstone! This alternative provides both a compression ratio boost and a displacement increase, at a favorable cost.

Raising the compression ration a point-and-a-half should increase power and fuel economy. Maybe Pemex (Mexican) regular isn't the best fuel for a Wossnerized engine, but higher-octane gasoline is available in most areas, where the KLR650s roam.

As Tom Schmitz posted above, a + 2 Wossner will yield around 685 cc; however, don't know of any this size in stock. + 1s are available off-the-shelf both here and in Germany, according to the US distributor.

Here is Sandstone's thread link:

http://www.klr650.net/forums/showthread.php?t=116019

Last edited by Damocles; 07-01-2014 at 01:34 PM.
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post #10 of 12 Old 07-01-2014, 04:28 PM
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No problem and thanks for posting the link. The 685 KoolAid is so strong that it really forced me to try the Wossie. I learned a lot in the process, especially from a few others who went before me, so I'm more than happy to share the knowledge.

FWIW, I went with the +1 so I could have a bore or two or three left in the cylinder. Whatever (small?) difference in power the larger bores could provide wasn't worth taking the liner out to the max diameter. After all, I was only trying to cure the oil burning.

She really pulls between 4500 and 6500 rpm and has more than enough passing ability at 70 -75 mph so I'm very happy with my Wossie. She won't toast a Porsche (haven't tried) but I'm definitely NOT getting run over.
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