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55 hours on this top end...your thoughts

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So, like the title says, I've got 55 hours on my Wiseco forged piston and rings (2 ring set up), and I am still getting over 200 psi on a cold compression test. The only oil I use is Castor 927 at 32:1 and it's jetted nice and clean with a #8 slide, Suzuki needle, and RB Designs machined head. It sees mostly woods, lots of mid- and low-RPM time and as much WOT as I have the balls for thru the trees, but also some longer wide open transfer sections (fire road-ish).

My question is, am I pushing it on these rings with the hours? It runs great, starts first or second kick every time, still makes great power, and as mentioned still makes good compression. But I wonder if I need to just go ahead and replace the rings as a preventative measure. I'd hope to get a warning of reduced compression and power that it was time, but what do you think?

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My rule is 50-75 hours is coming up on new piston. What "can" happen is the skirt wear and or small fracture cracks not noticeable. Cheap insurance, new piston, size per bore test. If you said OEM, I would say 75-100 hours. Many have different results, so yours may vary. 

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At 50hrs, it is time to start planning on a top end.

As yzdoc stated, the skirt will start to collapse & eventually crack.

Preventative maintenance.

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For woods riding I'd go to 100 hrs and check compression again and replace if there is 15-20% loss.

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I feel you're are being way too cautious.  I now routinely exceed 90 hours on wiseco pistons in yz 125s flogged mercilessly in the woods.  I do change the ring at 50ish hours.  This thread provides details and pictures.  I have more piston pictures and results I will post at some point, but this should certainly be of interest to you:

https://www.thumpertalk.com/forums/topic/1128226-955-hour-yz-125-piston/

 

Edited by rpt50
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I measure the piston ring end gap inside the cylinder. If it's out of spec or close, replace the whole top end since the the rings and the skirt wear.

Edited by mikeylikesit
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Thanks for the help, everybody. I figured since it's a forged piston it would be good for awhile but I will take a very close look at it while it's apart. I will order up a set of rings this weekend.
I'm honestly pretty impressed it's still running this great after this many hours. Hey, if it grenades, I'll have a wonderful excuse to finally go after that YZ300WR set up I've been lusting after.

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4 hours ago, RockerYZWR said:

Thanks for the help, everybody. I figured since it's a forged piston it would be good for awhile but I will take a very close look at it while it's apart. I will order up a set of rings this weekend.
I'm honestly pretty impressed it's still running this great after this many hours. Hey, if it grenades, I'll have a wonderful excuse to finally go after that YZ300WR set up I've been lusting after.

As a piston ages the skirts start to collapse. (they actually lose a bit the first ten hours in most cases I have measured).   If you measured this one before installation take a look and measure again if you replace the rings and give Wiseco a call.  Then call back a few days later and ask someone else.  I got told (years ago) that anything over .001" was an automatic replacement to people who said as long as it meets the clearance specs.   Usually since I have it down I put in a new one.  You should see the backup collection I have going. 

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9 minutes ago, Texasxcrider said:

Here's my OEM piston with 72 hours on it. Way overdue for rings as you can see with the blowby. I'll do my next top end at the 50 hour mark.

~Air filter cleaner religiously.

~Motul 710 @ 40:1

~one gallon of c12 race gas mixed with 4 gallons of ethanol free 91 octane pump gas.

IMG_1711.JPGIMG_1712.JPG

Runs very cool.

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2 minutes ago, ossagp said:

Runs very cool.

Do you mean by the lack of scorching inside the piston? That is what I thought also as I have had pistons before that have been pretty black inside there. The old wrist pin bearing was not distinguishable from the new one.

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Called and talked to Wiseco to get their opinion. His take was that if it's still making good compression, keep running it, and said depending on how I run it, 55 hours is not all that much for the piston itself but to inspect closely on teardown. He told me about a CR500 piston a customer sent back to them with over 700 hours on it...not typical, obviously, or recommended at all, but that's what that guy did and got away with it.

So I got some new rings and a gasket kit in and had every intention of doing the job this weekend. Decided to do one more compression test and got almost 240 psi (cold engine, WOT, kicking until pressure stops increasing). I have lost zero compression since I did this top end 55 hrs ago (same gauge), and it's actually a few pounds more than when I checked it at around 30 hours. I guess I ride like a complete Sally, I need to work on that...

I told the Wiseco tech guy I'll keep running it, but will check pressure every 10 hours or so in the next 50 hours, and just replace it at 100 no matter what because it seems like the right thing to do.

0402171200a_HDR.jpg

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I had 101 hours worth of woods racing (30+ B) on my 295. A crack in the reed block boot allowed water in at the last race and forced me to rebuild it. It was still running very strong and I was planning on replacing at that time anyways.

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To the original poster.. What jetting did you settle on for woods riding with 8 slide zuk needle and RB head?... thanks!

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To the original poster.. What jetting did you settle on for woods riding with 8 slide zuk needle and RB head?... thanks!

Right now with temps in the 70s and 80s for the most part, I'm at 168/42 NECJ-3 with airscrew somewhere around 1.5 turns out (tuned as required for that day). I do get a very slight rich part-throttle burble at cruise, so perhaps the NEDJ would be better for me, but I haven't tried it yet. But it feels right on everywhere else and runs very strong.
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I've been doing rings at 50h and the Wiseco piston at 100h on my 250 but it doesn't really need the rings. On my new piston/rings I am thinking of just going to 100h without taking it apart, except I noticed one of the head o-rings was kind of toasted. Trail riding only BTW.

 

My previous Wiseco at 100h had the same compression as when new and ring end gaps well within spec.

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