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  1. #1
    PolarisNut's Avatar
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    Who has actually "twisted" their non welded crank?

    I know "T&W" is a buzzword when talking 2 stroke performance. I have been running high performance PWCs and snowmobiles for years, and have NEVER had a crank welded...trued and phased, yes...I guess I'm just missing the point. If the crank wheels and pins press tightly together, they should never slip under normal operation (some crank models are loose, but I'm not talking about those here). I've hard seized pistons, blown belts (snowmobiles), drinking coolant, etc, and never had one knocked out of phase. I see more welded cranks that break, due to too much heat, which makes the pins brittle. Once they are welded, they are obviously next to impossible to rebuild. Sure, a welded crank may stop a hydrolock situation from twisting it out of phase, but you now have a bent rod or flattened rod bearings on a crank that cannot be rebuilt. Anybody else see my point on this? Do more people do this just because they think it makes it better/stronger? I've spoken with a few well known crank builders, and more than one agreed with me. One said they do it just because their customers request it.


  2. #2
    Hydrotoys's Avatar
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    twisted a 785fuji quite a bit. It was due to a locked bearing, so does it really count? You have to rebuild the crank to get the bearing out, so.... chicken or egg? The fuji crank runs an oil pump from the middle. I've often wondered if this had anything to do with them losing index more than others or was it a weak case design?

    Twisted a 1050domestic. No reason found, but Phil at crankworks thinks it was an initial press-together issue.

    Wobbled a 1050domested...assume it was like that from the start as well. Learned a lot about leaky seals, burned driveshafts and lots of alignment stuff.

    Yami 12r crank ate the middle lower bearing at 40hours... no idea why, but crank has lost index on one hole.

  3. #3
    Pistonwash's Avatar
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    Have no idea who you've been talking to...ask me. I have seen more than my share of twisted cranks, broken journals etc especially on the triples..from the 65u to 66v.
    Crank snouts galore have snapped off.

    Go to RIVA.com and do a search on the Yamaha forums with the words "crank" or "snouts" or"vibration"...yes, it is a must for a modified engine on our jetskis to be true and welded. Anyone says otherwise is foolish.

    Anyone reading this, take this advice...if you are running a modified/ported engine in your ski..especially after a re-build..get the crank trued/welded and you will double the life of your ski.

  4. #4
    Happily Self-Employed WFO's Avatar
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    seems like we just had this discussion a few months back...

    I have seen a couple 13r cranks where the front journal started walking forward, and several 12r cranks with broken snouts (they usually come loose at the front rod journal)

    I ran an unwelded crank for a couple years in my non-ported 13r, but after tear down the ft. journal was almost hitting the cases.

  5. #5

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    Quote Originally Posted by Pistonwash View Post
    Have no idea who you've been talking to...ask me. I have seen more than my share of twisted cranks, broken journals etc especially on the triples..from the 65u to 66v.
    Crank snouts galore have snapped off.

    Go to RIVA.com and do a search on the Yamaha forums with the words "crank" or "snouts" or"vibration"...yes, it is a must for a modified engine on our jetskis to be true and welded. Anyone says otherwise is foolish.

    Anyone reading this, take this advice...if you are running a modified/ported engine in your ski..especially after a re-build..get the crank trued/welded and you will double the life of your ski.

  6. #6
    Mpeavler's Avatar
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    I had one twisted on my Raider 1100 that had the group K kit installed. It was pretty far out of "phase" when you compared it to the new one I bought!

    M

  7. #7

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    Cool

    I had my 1200r walk foward

    cd

  8. #8
    PolarisNut's Avatar
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    Well I am fairly new to the Yami end of things, but I've never had a Polaris crank walk or twist (excluding the Fuji triples...you could knock some of these apart with a mallet-not enough interference in the press fit)...Don't get me wrong, I'm not questioning the need to make sure the crank has no run out and is in phase (the truing part)...But I can't see using, say, the snout breaking as a good reason to weld the crank, as I've seen plenty of welded 66v cranks with broken snouts around here. I've also seen quite a few shoddy weld jobs that over heat the crank, and actually promote failure. I've seen it plenty of times on sled cranks. The Polaris 800 twin is a prime example...get the PTO rod pin too hot and it will break every time. These motors too break the crank snout, but instead its the PTO end. People try to weld them to make them live, but they still fail. I have found that if the cases fit tight (couple thou crush fit) and there is little to no runout, the crank will live a long time. However, if the cases are loose, it ain't going to last, not matter if its welded or not. On the Polaris twins, if the case is loose, it is decked, then the bearing bores are line honed back to spec. The crank lives a happy life after this.

    Some have issues with the webs walking off the pins? Wonder what is making that happen? When you have a 15 ton press fit, that shouldn't be happening...especially on the MAG end where there is essentially no load. Makes me think it has to be a harmonics issue of some type?

    So...Anybody check the bearing to case clearance on these motors (failed or not)? What about the snout runout when they've had the flywheel off of a non-failed crank, after putting some heavy use on the boat?

  9. #9
    PolarisNut's Avatar
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    Nobody? Questions, comments, etc?

  10. #10
    Old Ski Insanity w/rpm500's Avatar
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    I have had two W/R's walk forward on the mag end.. I'm thinking harmonics,as this is a little motor and it took almost hanging on a 20 tons lever to press them back in.. yes a tighter case would enable the harmonics to tranfer better to the block..Yami like to use pins for spin, but i also use a bit of bearing set to just add a bit more pressure and holding power..

    NOTE:the wr doesnt even have the lightened flywheel other than the protec cut o/e available. the tripples with the aluminum wheels tear up the mag end or split at the keyway more than the steel o/e units do... lapping the wheel in, seems to help as it transfers the loads better thru a better fitting surface...some dont prescribe to it.. their choice..

    .

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