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  1. #1

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    Jul 2008
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    rod bearing failure

    I know there are probably a number of things that could cause a rod bearing failure, but what would most likely cause the front rod bearing on my 95 spx 657x to fail only a few hours after a top end rebuild.

    I checked for play in the rod bearings while assembling the top end and they seemed fine.
    The topend was redone due to stuck rings. Crank was removed, cleaned and oiled and all bearings looked good and spun freely. I dont know the history of this motor. Is it possible that the ski ingested water in the past causing the stuck pistons, and now causing the crank to fail?

    OR is a carb problem, or air leak causing a lean condition more likely to blame?

    Rear piston still looks brand new. Front is pitted from bearing material along with the head, but the cylinder walls dont look damaged.

    Running premix btw.

    Any help would be greatly appreciated.


  2. #2

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    Jul 2008
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    I found a motor from a 93 xp 650 that has a supposedly good crank. Are these cranks a direct replacement? What would be involved in swapping in teh 93 xp motor, could I install the 93 xp motor without switching out all the electronics?

  3. #3
    steach's Avatar
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    Welcome to GH

    Any pics of the carnage?

    Are you sure the crank bearing went and not the wrist pin/rings?

  4. #4

    Join Date
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    ill post pics later tonight.

    Yea its definitely the big end of the rod. I Can rock the rod back and forth, and its moves almost and inch at the small end. Wrist pins + cage bearings were new w/ the top end and still look perfect.

  5. #5

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    Here are some pics.
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  6. #6
    I think you will have to do some more digging dude. There's a retaining ring that mounts up in the middle of the crankshaft. It's possible that it failed. I noticed two little things when looking at the pics...assuming the pistons were still connected to the rods, the arrow on the clean one is pointing to the rotary vavle and the other it is pointing to the exhaust. Both should be pointing to the exhaust. It may not have any bearing here but it does suggest the kind of attention to detail invested by whom ever assembled it.

    The other thing I noticed, the brass shim on the one side of the connecting rod (at the crank end) looks alright. The pic is fairly blurry though so I could be just not seeing it correctly but the other brass shim appears to be quite thin in comparison. If that is the case, check to see if there is any heavy wear into the crankcase on that side or the connecting rod, it will give you a good idea of how much crank runout has been happening. Or there could be too thick of a shim on one side offsetting your crank too far. Did you happen to notice any brass filings inside anywhere?
    Last edited by Schwarzenegger; 07-22-2008 at 09:33 PM.

  7. #7

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    I appreciate the response.

    As for the piston arrow orientation, I was holding the pto piston there for the pic. Arrows were def toward the exhaust when assembled.

    brass shims/thrust washers or whatever they're called are even on each side, not much brass shavings in the cases- the shavings are definitely bearing material. Without moving the crank, the rod moves about 1/4" up and down, it is completely loose on the big end.

    As for the retaining ring, I will be splitting the cases soon, but I believe the crank is pretty well centered.

    I know I need to purchase a crank reguardless, but my real question is... WHY DID THIS CRANK FAIL.

    Keep the responses comming guys, thanks in advance.

  8. #8
    96XPSS's Avatar
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    Normally the big-end rod bearing failure is a result of a previous hydrolock. Or, if not ever hydrolocked, the engine sat in an environment that allowed the bearings to rust. Then when started the rust ground away the finish, then the clearance is excessive, then it eventually fails.

    It wasn't lack of lubrication, as the piston will always seize first.

  9. #9

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    Thanks 96xpss, Thats exactly what I wanted to hear. As long as it was not a lubrication prob I can replace the crank w/o the worry of it burning up again.

    Now where can I find a cheap used crank? My spx is just a side project, and I have 2 other ski's to ride, so I have some time to wait for a deal. However, I am skeptical of buying used engine parts online, without being able to inspect them.

    Anyone know of any jetski salvage yards in Long Island, NY?

  10. #10
    Master of the Dooniverse
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    I agree with Robert. Any big end failure I've seen was accompanied by evidence or s story of "it got water in it at such and such time". most of the time it's water. water in cases or even milky oil in bearings for a couple minutes or even few hours won't hurt, but a couple days or week and it's doomed.

    W

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