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  1. #1

    Need advice from polaris pros - 1999 Genesis engine with sequential piston failures

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    with a 1999 genesis carbed 1200.

    It came in with rear cylinder seized and had broken ears off rear cylinder, water inlet and exhaust manifold, (these pictures are not from the time it first came in, but from this time approx 1 to 2 hrs according to owner, I put hour on it before I let them take it and was fine)).

    I pulled engine, used new cases (used) rebuilt crankshaft, new pistons, new gaskets,o-rings. I did use the stator,electrics,

    OK while breaking it in ran fine, (carbs cleaned and rebuilt) fresh fuel, then lightly seized rear cylinder. all cylinders were 125 psi on my gauge before seizing,

    I then bored cyl.and replaced rear piston, I changed cdi thinking that might be it.

    After rebuilding it and changing cdi I tested engine running it on one cylinder at a time. it was equal on all, 3 idled well, I then proceeded to break it in, ran great for say an hour, no seize compression fine, tested if it would run on each cylinder one at a time again ,called customer to pick it up.

    After an hour or two of customer running it, rear piston had hole in center of it. I'm sure crankshaft is indexed correctly (this is second crank rear cylinder has gone bad on), correct plugs were used BR8ES and engine ran perfect until it happened, any ideas this one has me stumped.

    please help, These pictures are from the last seizure/holed piston

    THANKS IN ADVANCE>Marvin

    pictures enclosed


  2. #2
    Click avatar for tech links/info, donation request K447's Avatar
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    Re-used the same carburetors?

    Perhaps the PTO carburetor (or the fuel pump in the carb) is simply defective in some way, causing lean burn.

    Is the pulse fitting in the PTO crank case clear? New pulse hoses?

    Intake manifold castings out of true and leaking air?

  3. #3
    Thats first place I looked thinking lean burn causing detonation as it had plenty oil on each piston and cylinder running 50 to 1 premix besides oil pump,I have a extra bank of carbs we keep jetted for same customers wintertime riding on his sltxB that I know work well and are on the fat side in summer.I also changed all fuel lines,cleaned tank,used new gaskets on carbs and intake before this holed piston.FRom my experiance a holed piston in center under spark plug should be caused by pre-ignition,causing detonation ,whether by lean mix or excess heat causing detonation and piston erosion,do you think this could be caused by timing being way early on pto cylinder,or mainly by heat and preignition from lean condition??Thanks

  4. #4
    Click avatar for tech links/info, donation request K447's Avatar
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    You used the same set of carburetors every time, or a different rack of carbs this time?

    New CDI, but the same magneto stator - correct?

    I suppose it is possible the stator has a problem and the PTO Hall Effect trigger timing is not consistent.

    The piston doesn't appear to have any wash pattern. Do the other two pistons have a wash pattern?

    Did you check the wash patterns after your one hour break-in ride?

    It looks a lot like typical lean burn piston hole...

    Rear crank shaft seal still in proper position? Did you do a leak down test on the rebuilt engine?

  5. #5
    Is the crank still have the proper index? If the original failure was caused after ingesting water at high speed... it could twist the crank. (just a thought)

    If the crank is good... I'd say it's a lean run. (bad carb, low fuel pressure, crank seal, base gasket leak)

    Since it failed on the same piston... I would be looking at something that didn't get changed. (crank and or crank seal)


    If that was at my shop... I would do a leak-down before it goes out again.

  6. #6
    It had new crankshaft (rebuilt)different cases,(used,but inspected)new crankshaft seals,I did use the same carb rack,just finished pulling them apart,they look fine ,I even used mag. glass to look for hairline cracks,I am going to change carbs anyway,stator was not changed,engine held leakdown test 30 min.I will do another leakdown test on it,I dont see how the stator could cause early timing on Number3 as stators when they go bad spark gets weaker!!piston wash was perfect on other two,I did not check wash after hour run I did look at piston thru top of plug hole and there was no erosion(hole in piston would have been visible,and compression was fine.I'll change carbs put an hour on it and check wash.if stator was bad why would it run fine on number 1 2 and 3 testing each cylinder one by one?I pulled intake manifold and its fineI'm going to try and rig leak down test to test intaKE MANIFOLD,i HAVE NEVER SEEN A PISTON HOLED UNLESS IT HAD INTAKE LEAK!or bad crankshaft seals,or lean carb.I have never seen a holed piston from ignition problem bad gas yes,base gaskets new,carb base gaskets new,one other question since it has keihins with number 1 and 3 masters(fuel pumps)and number 2 carb slave(no fuel pump)if it was fuel shortage and not air leak wouldnt number 2 cylinder also have run lean?Hey I wouldnt be asking except I was hoping someone else had run into this,I know its just coincedence but I just got a sltx 99 that has no spark number 3 cylinder .it looking like #3 is not a good number for me !Thanks i n advance for the help and suggestions ,sometimes something very simple gets overlooked>Marvin

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    Click avatar for tech links/info, donation request K447's Avatar
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    If the PTO fuel pump is weak or not working properly then the MAG fuel pump would be trying to feed all three carbs - no? Center carb might still get enough fuel, while PTO carb starves...

    I agree that it seems weird to have the stator appear to be advancing timing on only one cylinder. That said, each cylinder has its own Hall Effect sensor in the stator, so I suppose it might be possible in some strange manner for just one Hall Effect sensor to go strange

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    To Me this Sounds like the new crank was not indexed right its throwing the timeing out or you some how twisted the crank I would go back and check crank index to start with

  9. #9

    Smile

    Quote Originally Posted by lovehavenfun View Post
    To Me this Sounds like the new crank was not indexed right its throwing the timeing out or you some how twisted the crank I would go back and check crank index to start with
    thats my sentiments exactly except this is 2nd crankshaft that its trashed #3 piston with,I found out something else after running it today at 3500 rpm under load against the trailer it feels almost like it does when you exceded rpm limiter in reverse it ,I wonder if the crankshaft could have been somehowe different like with the 1050 how some fire 123 and some 132.I found out customer had 2 hours normal use then started pulling wakeboarder when piston went that makes sense now I found out it only runs rough at 3500to4000 rpm under full load if you just ride it it doesnt run rough and takes off like a bat out of H_-_.also is very smooth at top rpm,also if crank was out of index wouldt it not pass the idle on each cylinder by itself test???Is there any way the limiter that limits reverse rpm could be kicking in at 3500rpm under load forward??,what exactly limits the rpm in reverse it has electric reverse on left handle bar? Thanks again my friends in advance I will get it figured out sooner or later,Thanks guys!!

  10. #10
    Click avatar for tech links/info, donation request K447's Avatar
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    Now that you have a reproducible symptom at mid-range RPM you can start diagnosing

    I am still thinking the PTO carb has issues

    The RPM limiter is engaged when the Reverse mechanism (limit switch inside the motor box) is anywhere but in full forward mode, OR when the Tan wire from the temp sender is grounding. When you engage Reverse does the Reverse message appear on screen?

    Unplug the Tan temp sender wire in the electrical box. If no improvement, unplug the gray CDI wire.

    The 1999 Genesis has two LR modules; one for Start/Stop and one for voltage regulation. Try removing and bypassing the LR-502 Start/Stop module. Black/white solenoid wire to Black terminal.

    If that makes no difference then also unplug the LR-31 voltage regulator module. You will not have battery charging but at least you will be eliminating components.

    Next thing is to unplug and bypass the MFI display. You may need to jumper the MFI connector to start the engine. Purple/White to Black.

    Now you are down to just CDI, stator and carburetors.

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