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Discussion Starter #1
I know we've discussed this before, but I don't remember what the consensus was. What's the proper orientation of the rear piston? Kawie manual says F mark forward no matter which cylinder. Wiseco says dimple (mark) ALWAYS goes towards the exhaust. That of course makes a mirror image on a v twin, and backwards from what Kawie says on their stock pistons.
I just looked at my rear Wiseco, and it's got the dimple by the exhaust. It's run perfect for over 12,000 miles that way. Wrist pin is still snug, and everything about it feels good.
So if I put another Wiseco in now, I'm tempted to do it the same again.
 

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In most stock engines, the Wrist pin is not in the exact center of the piston and the mark indicates the proper direction for stroke lead-in. That's why Kawasaki has the "F" on theirs indicating both point forward or to the front. Some aftermarket piston manufacturers center their wrist pins and focus on the combustion chambers and valve reliefs are more important. For those it will be important to have say.. the exhaust valve reliefs under the larger exhaust valves. I'm guessing this might be the case with Wiseco. I say whatever the piston maker says to do for your application...do. :)
 

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Discussion Starter #3 (Edited)
Well, I got the Wiseco piston today. I was surprised to see they don't really say much about how to install the mark anymore. What little they do say is mainly under the 2 stroke section, and it's basically "follow your service manual".
So I get to looking at and measuring the piston. It's tough to do properly with just a regular caliper, but I do get a difference in measurement from one side to the other to the edge of the wrist pin hole, though I can'tget it to repeat the same numbers consistently. Looking at it, the hump cut above the wristpin hole does look to be slightly off center. If that's true, then the piston must be designed to go a certain way.
 

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Discussion Starter #4
75425
 

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Discussion Starter #5
If you draw a centerline through the wristpin hole, does the peak of the cut above the hole look right of center to you?
 

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Discussion Starter #7
To me it does. How about from the edge of the wrist pin hole to the outside of the piston?
That's the dimension I was trying to measure, but said it was tough to get a repeatable measurement. I assume if it's off center, it won't be by much?
 

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Discussion Starter #10 (Edited)
So I found the box for my original set of Wisecos. The sku number is the exact same as the one I just got. So, it's highly likely that the piston in my rear cylinder is exactly the same as my new one. That means that the idiot who installed it put in backwards! He probably never even thought about looking at the manual, and just put the dimple above the exhaust on both cylinders because that's what he was used to. Or he read the original directions and that confirmed what he knew, being a single cylinder mechanic. Either way, it's been in there wrong for 12,000 miles. 😡
But the new one is going in RIGHT!
 

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Discussion Starter #11
A couple of good reads:


That pic in that article is exactly like mine, and Wiseco said that most of their pistons are offset wristpins. So, that helps a lot. The Wiseco pistons made for Kawies are offset just like the OEMs. Fwd mark is going forward.😉👍
 

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Discussion Starter #12
Yep, the piston was the same as the new one. It was installed backwards the whole time. The wrong skirt was taking the thrust. Wore a wider wear mark than it should have. The wrist pin was snug coming out, but there's no ovaling of the hole, and no damage to the conn rod or bearing.
Still waiting to hear what this did to the cylinder.
75430
 

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Discussion Starter #13
75431
 

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Wow...well if that's the case prepare for it to run different...smoother and quieter for sure. Maybe a hint more power too.

At least it didn't look like this one...which I think was in backwards for a very long time...which also took out the rod bearing.

 

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Discussion Starter #15
Wow...well if that's the case prepare for it to run different...smoother and quieter for sure. Maybe a hint more power too.

At least it didn't look like this one...which I think was in backwards for a very long time...which also took out the rod bearing.

I'm looking forward to a smoother, quieter engine, for sure. It will also be nice not having to add oil every ride.
 

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Discussion Starter #16
Yikes! Is that piston on a Kawie?
 

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Yikes! Is that piston on a Kawie?
Yep..05 BF 750. The complete thread is over on BC. I feel bad for these people..they just bought it and was told it had all this great stuff in it...and it "went" before they even had a chance to ride it. When apart they found none of what the seller claimed and now it's a full rebuild. At least it didn't through the rod which it was about to.
 

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Discussion Starter #18
Yep..05 BF 750. The complete thread is over on BC. I feel bad for these people..they just bought it and was told it had all this great stuff in it...and it "went" before they even had a chance to ride it. When apart they found none of what the seller claimed and now it's a full rebuild. At least it didn't through the rod which it was about to.
Wow. That's too bad. Dishonest sellers suck. With the market the way it is right now, they probably figured it was a great time to unload their problem.
 

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Wow. That's too bad. Dishonest sellers suck. With the market the way it is right now, they probably figured it was a great time to unload their problem.
Yeah and the thing that really gets me it was just a sweet lady looking for something for herself to ride with her better half. I hate it when people do that to other ...and nice people. Now she has a full rebuild to do on an old machine that really isn't worth the 28-3K it will take to do. Who knows what else this thing will cost her in the future. Diffs probably...and axles...bearings...a-arm bushings...
 

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So you are saying that on the rear piston that the dimple on the weisco piston should be forward and not pointing towards the exhaust outlet ?
 
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