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Old 01-11-2014, 07:11 PM   #1
D.T. OP
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Piston ring Q...

I pulled the cylinder off my snowmobile today. Noticed some blow by and was going to replace the rings. But I got the whole piston.

Anyway, the ring gaps were at 7 o'clock and 5 o'clock intake side reference. This does not seem right. I was thinking they should be at 3 o'clock and 9 o'clock or parallel to the crank shaft.

It's a parts unlimited 2 ring cheapo piston. What position should they be at?

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Holland is about the most expensive country in Europe when it comes to bikes and fuel..Stop whining and go riding It's just money and you only live once...
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Old 01-11-2014, 07:20 PM   #2
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Are the ring ends located by pins?
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Old 01-11-2014, 07:30 PM   #3
stainlesscycle
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Quote:
Originally Posted by D.T. View Post
I pulled the cylinder off my snowmobile today. Noticed some blow by and was going to replace the rings. But I got the whole piston.

Anyway, the ring gaps were at 7 o'clock and 5 o'clock intake side reference. This does not seem right. I was thinking they should be at 3 o'clock and 9 o'clock or parallel to the crank shaft.

It's a parts unlimited 2 ring cheapo piston. What position should they be at?

3 and 9 sounds funny - that would put them in line with the piston pin? 5 and 7 puts the gaps between the intake and transfer ports that sounds right. i can't think of a piston with gaps at 3 and 9 - but i don't do snowmobiles... 3 and 9 would place them right in the transfers?- 2 strokes almost always between the transfer and intake. sometimes smack dab in the middle of the intake...
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Old 01-11-2014, 08:04 PM   #4
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Are the ring ends located by pins?


I can get a picture if I get the damn piston pin out. F#$ker won't come out! I heated the piston and no dice. I need to get some threaded rod...



Alright, never mind. I got the pin out with some threaded rod. The piston has 2 locating pins at 7 and 5 o'clock. Now I understand.

Here is a pic of the piston anyway (exhaust side). I need to get a hone for the cylinder now.

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D.T. screwed with this post 01-11-2014 at 08:57 PM
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Old 01-12-2014, 05:06 AM   #5
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Here is a pic of the piston anyway (exhaust side). I need to get a hone for the cylinder now.
that's a lot of blowby. can't tell how worn the rings are, but if i saw that piston come out of a bike, i would measure the bore and find that it's probably outta spec and needs the next bore. a hone could make it worse...a hone will take maybe another .0005" off the bore. if it's ovalled or loose already you're fighting a losing battle.
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Old 01-12-2014, 06:47 AM   #6
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I checked the ring end gap and it's around .024" so it's on the high side of .008" to .030". This is already an .020" oversize piston. Maybe I will just use some 240 grit and lightly hone myself to remove as little as possible. I ran the piston up and down in the cylinder with out rings. It's not really tight or loose.

I just don't want to throw a bunch of money at this thing.
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Old 01-12-2014, 07:32 AM   #7
stainlesscycle
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Originally Posted by D.T. View Post
I checked the ring end gap and it's around .024" so it's on the high side of .008" to .030". This is already an .020" oversize piston. Maybe I will just use some 240 grit and lightly hone myself to remove as little as possible. I ran the piston up and down in the cylinder with out rings. It's not really tight or loose.

I just don't want to throw a bunch of money at this thing.
i don't know bore size, so i don't know what the specs are, but that's a pretty big gap for any piston under 70mm... think about this way, if perfect is .008" and you're at .024" that's 3 times the best gap, and only 25% away from worst gap... what's the gap of the rings that were in there and leaking badly?



i wouldn't try honing with sandpaper....... but if you're deadset on doing it that way, move the sandpaper around the bore, and not up and down. any vertical marks/lines will just leak by your new rings. either way if your bore is not round, it'll blowby very shortly..
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Old 01-12-2014, 10:43 AM   #8
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Piston is 72.5mm and the new rings gap is around .020" or less.

I'm skipping the hone, I used some 500 grit paper and used a circular motion for the cylinder. $30 and a week wait time?

Tip #1 Mapp gas and a torch really works well on the top of the piston if you are having trouble installing and removing the piston pin. Expands everything just enough to make it slide in easier.
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Old 01-12-2014, 02:00 PM   #9
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Is it a Nikasil bore? Or cast iron liner? Nikasil just install new rings, NO hone and enjoy. Did you do a compression test before tear down? Is that a Forged WiseGuy piston? or OEM cast? What sled?
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Old 01-12-2014, 02:09 PM   #10
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Is it a Nikasil bore? Or cast iron liner? Nikasil just install new rings, NO hone and enjoy. Did you do a compression test before tear down? Is that a Forged WiseGuy piston? or OEM cast? What sled?
it's not nikasil - he's .020" over so it's gotta be iron.
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Old 01-14-2014, 06:21 AM   #11
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it's not nikasil - he's .020" over so it's gotta be iron.
Well, maybe, I guess. Not to be argumentative, but my RZ350 is 2mm OS, and Nikasil. But, you're PROBABLY right..
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Old 01-14-2014, 06:37 AM   #12
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If you're RZ is Nicasil it's not OEM. The RZ came with cast in iron sleeves.
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Old 01-14-2014, 05:47 PM   #13
concours
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If you're RZ is Nicasil it's not OEM. The RZ came with cast in iron sleeves.
You are correct. I had it done. I just used that as an example of why I asked a bunch of Q's to the OP.

Ever mess with these???










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Old 01-15-2014, 12:04 AM   #14
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Yikes. Is that out of a newer Ski Doo?

I fired up the sled yesterday, ran just fine. So far so good. Non plated cylinder in my old 1987 Yamaha Phazer 492cc.
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Holland is about the most expensive country in Europe when it comes to bikes and fuel..Stop whining and go riding It's just money and you only live once...
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Old 01-15-2014, 05:38 AM   #15
concours
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Yikes. Is that out of a newer Ski Doo?

I fired up the sled yesterday, ran just fine. So far so good. Non plated cylinder in my old 1987 Yamaha Phazer 492cc.
'05 PowerTek 800 143hp. Failed intake boot, known pattern failure. Cylinder was junk, no core allowed.
The Fizures run forever, make sure no mouse nests in the cooling shrouds. Windshield don't last long on those though...
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