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  1. #1

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    Piston Pin Retainers: CirClip VS Snap Ring

    OK, I've decided to draw on the collective knowledge of this site to help me answer a question that is really bugging me:

    When I rebuilt the motor for my 99 XPL last year, I bought SBT pistons 'cause I heard good things about their design and they were available in the next over-bore size I needed (.5mm). When they arrived, I was surprised to see they used standard Snap Ring retainers for the piston pins. OK, I can do this, I used my SR retaining ring pliers and installed them into the grooves of the pin boss. After installation, I used a sharp pointed tool to rotate the ring in it's groove to be sure it was inserted correctly. All 4 turned and were seated. (Note: A little background - I am a machinist and have spent the last 38+ years working in everything from CNC shops to fab shops. I know how to install snap rings and use a set of snap ring pliers).

    This year: I have about 15 hours on the motor and 4th of July weekend, it started to cut out at idle and run rough. Pulled the motor out this past weekend and tore it down Monday night. Found that the MAG side piston is destroyed and the cylinder sleeve will have to be pulled and replaced. Culprit: Snap Ring popped out and did it's best to beat the heck out of the piston, cylinder wall and head dome.

    Question: I can get the cylinder re-sleeved in .5mm (friend has a spare sitting on the shelf) and just get a new SBT piston, but then I'm running the chance that I'll loose another hole at some point if the Snap Ring lets go again. I looked into using standard Rotax CirClips, but the design of the groove on the SBT's doesn't seem right for the CirClips.

    What would you suggest?

    Re-Sleeve both holes back to standard and go with OEM Rotax pistons?

    Re-Sleeve the MAG hole and keep my fingers crossed?

    Try to use CirClips on the SBT's and hope they'll stay in place?
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  2. #2
    mibunkerking's Avatar
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    SBT does not have the best reputation for many reasons. this is one. but to answer your question, yes you can resleeve. however, you being a mahineist should know that if you want to reuse that old sleeve, you have to make sure its not out of round. also that the piston to wall clearence will be in spec. as the old sleeve could be worn. the only way to know that is to buy the new piston first and see if it will work. if the sleeve truely is trashed and cant be bored out, then the safest option is it resleeve back to stock and get better pistons (OEM, PRO-X, WISECO).that or pick up a new stock bore block on ebay and bore it out to matched pistons.

  3. #3
    Deanrw3's Avatar
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    When I rebuilt the motor for my 99 XPL last year, I bought SBT pistons 'cause I heard good things about their design and they were available in the next over-bore size I needed (.5mm). When they arrived, I was surprised to see they used standard Snap Ring retainers for the piston pins. OK, I can do this, I used my SR retaining ring pliers and installed them into the grooves of the pin boss. After installation, I used a sharp pointed tool to rotate the ring in it's groove to be sure it was inserted correctly. All 4 turned and were seated. (Note: A little background - I am a machinist and have spent the last 38+ years working in everything from CNC shops to fab shops. I know how to install snap rings and use a set of snap ring pliers).
    As far as i have ever seen, sbt, pro x, weisco, wsm all use the same style retaining clip.

    Am I missing something? I guess i don't see why this was the retaining clip design issue. All the ones i have seen are just the C clip that goes into a groove and then you spin it. what else is there?

    I wouldn't jump to the conclusion that it is a piston issue.
    dean

  4. #4

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    Quote Originally Posted by Deanrw3 View Post
    As far as i have ever seen, sbt, pro x, weisco, wsm all use the same style retaining clip.

    Am I missing something? I guess i don't see why this was the retaining clip design issue. All the ones i have seen are just the C clip that goes into a groove and then you spin it. what else is there?

    I wouldn't jump to the conclusion that it is a piston issue.
    dean
    It was probably a mis-installation issue. This was the first motor where I put the top-end together myself and even though I thought I got the snap rings in correctly, I must have goofed. I was just trying to get some feedback as to whether or not others have run into this issue. All of the other motors I've put into the ski, have been completely assembled by others, so to save a few bucks I thought I had the skills to do it myself. I guess I'll just have to learn how to do it properly and hopefully, not loose another cylinder and piston set.

    This is a higher than stock RPM motor that spins up to 7260 regularly (well, used to at this point), I just wasn't sure if I was exceeding the design capability of the snap ring set-up for a high-compression, re-mapped MPEM, ported motor, running a stock pipe (that really isn't stock). Heck, even with a wounded hole, the ski still went 68.1 on GPS.

    How does that saying go? 2-Strokes run best right before they grenade......

  5. #5
    retro jet's Avatar
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    I had two 951's with Mag sleeves that needed to be bored and PTO sleeves that were broken. Local shops wanted to sell me new short block, a 2010 GTX, or remanned BRP & SBT. I looked at SBT's cylinder replacement and forget why I didn't use it, size cost or was it a whole kit... I ended up sending them to Group-K. They initially were going to re-sleeve the PTO's and bore all 4 holes to to match at +.25mm for OEM 1st over. After getting the engines, they decided to push out the Mag sleeve out of 1 block and install into the PTO hole of the other. So I ended up with one engine +.25mm and the other STD with OEM pistons. I thought that was a great idea. I think Group-K reccomends using OEM, but I didn't discuss this much. I think it was $80 labor to resleeve, but the costs are on their site.

    If it were mine, I had a new sleeve from a buddy, and since I think it is a shame to overbore a new sleeve, I would buy a 2nd sleeve, go back to STD with OEM pistons and keep the +.5mm sleeve and piston on my shelf for the next time. IMHO from my limited experience in this hobby.

    There was no debris in the crank? It was great when I saved the cost of a crank during a rebuild, just to spend it 30 hours later plus the cost of a new piston and all the trimmings.

    Did you post pics of this at SBT and ask them about it? Not that they would say it was anything but your fault, but...

    post what you decide.

  6. #6
    retro jet's Avatar
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    post a pic of the clips, are they something new SBT justed started using?

  7. #7

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    May 2006
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    Hey Robert-

    I forgot I even registered here at greenhulk... Its been forever since I have been on a watercraft board and other than this summer a few years since I had the skis in the water. Anyhoo...

    firstly, snap rings are not the "C" clips many are used to seeing. Snap rings *shouldnt* be an issue but wouldnt be my first choice. Robert the only way you could have screwed the install is to have left the opening of the clip near 9:00 or 3:00 instead of 12:00 or 6:00. If the snap rings were able to move freely in the grove I wouldnt use it. Dont know why they would opt for the snap rings over the C clips???

  8. #8

    Join Date
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    Quote Originally Posted by 2strok4fun View Post
    Hey Robert-

    I forgot I even registered here at greenhulk... Its been forever since I have been on a watercraft board and other than this summer a few years since I had the skis in the water. Anyhoo...

    firstly, snap rings are not the "C" clips many are used to seeing. Snap rings *shouldnt* be an issue but wouldnt be my first choice. Robert the only way you could have screwed the install is to have left the opening of the clip near 9:00 or 3:00 instead of 12:00 or 6:00. If the snap rings were able to move freely in the grove I wouldnt use it. Dont know why they would opt for the snap rings over the C clips???
    I was thinking the same thing. 7200+ RPM may have caused the clip to loosen in its grove if they were turned to the 3:00 or 9:00 position.

  9. #9

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    Thanks for the tips guys.....talked to a friend over the weekend who has done a lot of these and he asked which way I was installing the snap rings, I answered 'shiny side' out - he said wrong way, they are stamped rings and the 'burr' or dull side should face out. He said that the slight 'burr' side will encourage the rings to stay in the groove, so installing them, dull side out will tend to keep them in the groove. Sounds like a '70's disco song, but, after I hung up with him and thought about it, I think he is right....

    The rings that were still in place, were at the 5:30 position, lined up with the relief notch in the piston. Hmmmm...........When I install the next set, I will use a minimum of tension on them (so as not to distort the ring) and 'snap' them into the groove, with the open end at the 6 - 5:30 position, should encourage them to stay in place.

  10. #10

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    I will go back to standard on the cylinder set that got crunched and I thoroughly checked the crank and cases. I guess I must be the luckiest person when it comes to failure. There is no evidence that the pieces made it to the crank. No marks what-so-ever on the journals, counter-balance weights and I fished around in the swamp-like black stuff in the bottom of the cases and came up with nothing.

    I didn't post pics at SBT, they will deny any wrong doing. I did call them and asked if they offer a 'premium' snap ring. The guy I spoke to didn't have a sense of humor....

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