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2010 GSX 550F Rebuild Won't Start? HELP

GSX 550F Rebuild Wont Start HELP

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#1 wheels_17

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Posted 09 October 2019 - 01:53 PM

Back ground - 2010 Ski-doo GSX 550F, 7000 miles lost PTO side piston,  Replaced top-end sled started and ran my son drove 20 miles sled locked up turns out lost crankshaft didn't know Rev XP need new isoflex grease after time.

 

Current State - Pulled motor took it down split crankcase replaced crankshaft & isoflex :D, pistons, 1 - cylinder sleeve, gaskets, and starter. Put motor back in double checked magneto and lined trigger coils, verified spark, cleaned carbs, new plugs, sled turns over like a champ but won't start.

 

Next step went old school and put fuel directly down cylinders still won't fire.

 

Next test I have an extra Calibrated Module I even swapped that both allowed spark plugs to show spark, last test was a compression test notice 1 cylinder was slightly less it should still fire.....right? I'm stumped did I miss something? If anyone suggestions let me know.

 

Thanks,



#2 brutus503

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Posted 09 October 2019 - 10:09 PM

Welcome to DOOTalk. Great sled (I might be a little biased). :)

Sounds like you have done everything right, especially if you have spark. Even with a finnicky calibrated module mine would kick over and run (albeit not well). When trying to start the sled with fuel in the cylinders, were you cranking it over by hand or with the starter? My dad’s ‘96 Touring 440 used to act dead during the first start of the year when cranking with the starter, but would fire right up with a few pulls of the cord. It’s worth a try to pull it over by hand and see if that makes a difference. I have no idea why but it worked on that old 440 fanner.

Silly question but did you make sure the exhaust and intake were both clear of any debris, rags, etc.? I’m sure you did but it’s always good to double check.

What numbers are you seeing for compression? You noted one seemed a little low. Even with one lower in compression it should try to fire as long as it’s not way low like with a popped piston. You should be seeing 110-120 psi on both sides. A few psi difference from one side to the other is not unusual. 10+ psi difference would not be ideal though.

Also, when installing the new pistons did you make sure to gap the new rings to specs? They usually need to be filed down a bit. That shouldn’t affect initial kick over though. Just another thing to make sure was done.

You made sure the pick-ups were in the correct positions? The reason I ask is because if they were swapped inadvertently you could be getting spark but with the wrong timing.

Were the plugs wet when you tried to start it the first time (i.e. before you poured gas in the cylinders)? If you definitely have spark and the pick-ups are correct, then the only other place to look is fuel supply.

I’ll keep an eye on this thread. I’m also available to chat via PM if need be. We should be able to get this figured out for you. I rebuilt my 550 from the crank up the season before last. My mag side got ground up badly when a piston retainer circlip grenaded. I didn’t need a new crank but I had to replace the two outer PTO side bearings (the inner bearing had lost its seal and was washing away my Isoflex). I replaced a cylinder and head and put in two new pistons. It’s been running like a top the past 1-1/2 seasons since the rebuild. :righton

#3 TheBearAk

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Posted 10 October 2019 - 03:26 PM

I would hope that after a rebuild the compression would be at least 120-120 and hopefully 125-125 or better.    After warm up and break in, that should rise a little and put it at around 130-130.

 

110 is low, in the hard to start area.

 

 

Something you can try is removing the spark plug from one cylinder and see if it will start on a single.   If not, do the same for the other side.

 

3 things:   Fuel, Compression, Spark.    If spark plug is wet, then it is getting fuel.   Compression 120 or better, then the last thing it can be is spark.

 

Change plugs?   Had a spark plug that would work fine when not in the hole, but once tightened into the hole it would not spark.  (darn NGKs)



#4 mbret2004

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Posted 10 October 2019 - 05:02 PM

Check the pick-ups. Were you aware they went in specific positions? If not, verify they are installed correctly.
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#5 brutus503

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Posted 11 October 2019 - 06:11 PM

I would hope that after a rebuild the compression would be at least 120-120 and hopefully 125-125 or better.    After warm up and break in, that should rise a little and put it at around 130-130.
 
110 is low, in the hard to start area.
 
 
Something you can try is removing the spark plug from one cylinder and see if it will start on a single.   If not, do the same for the other side.
 
3 things:   Fuel, Compression, Spark.    If spark plug is wet, then it is getting fuel.   Compression 120 or better, then the last thing it can be is spark.
 
Change plugs?   Had a spark plug that would work fine when not in the hole, but once tightened into the hole it would not spark.  (darn NGKs)


Mine were both reading 118-120 cold on a fresh rebuild (didn’t even have the plastics on yet).

#6 wheels_17

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Posted 11 October 2019 - 07:57 PM

Quick update changed plugs got a few backfires I'm 95 % sure I got the trigger coils in right order but these backfires got me thinking. Right now pulled plugs little wet letting it air out want to ensure its not flooded. Checked compression again 110 and 100 not perfect I'm wondering if that's the culprit but it should start.....taking a break stay tuned.

#7 Mill

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Posted 11 October 2019 - 08:03 PM

Quick update changed plugs got a few backfires I'm 95 % sure I got the trigger coils in right order but these backfires got me thinking. Right now pulled plugs little wet letting it air out want to ensure its not flooded. Checked compression again 110 and 100 not perfect I'm wondering if that's the culprit but it should start.....taking a break stay tuned.

Just rebuilt and only 100psi? Something doesn't sound right. Even after they seat it's going to be low. Rer probably won't work.

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#8 TheBearAk

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Posted 12 October 2019 - 11:46 PM

I've done quite a few rebuilds and the only one that I've ever had test lower than 120-120 after the rebuild was one that had worn cylinders that I didn't catch when I did the rebuild.   It lasted about 300 miles before the compression dropped so low that it was impossible to start when warm.    Rebuilt the motor again, but this time replaced the cylinders (nikacil plating, couldn't bore).    After rebuild:  125-125.   After 50 miles of running it, 130-130  cold or hot.



#9 wheels_17

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Posted 13 October 2019 - 11:39 AM

Thanks everyone I think new cylinders is the plan anyone have a recommendation on a site for parts? I'm in this far with a new crank.

#10 mbret2004

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Posted 13 October 2019 - 01:53 PM

Before you pop for new cylinders, measure the piston to cylinder wall clearance. How about ring gap? You could also put a splash of two stroke oil into one cylinder and see if compression increases when pulled over. If so, the above tests will help point you in the right direction. Repeat for other cylinder.
Pull the engine down slowly and inspect everything closely. I don’t believe this will require rocket science to diagnose.
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#11 Mill

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Posted 13 October 2019 - 07:00 PM

Before you pop for new cylinders, measure the piston to cylinder wall clearance. How about ring gap? You could also put a splash of two stroke oil into one cylinder and see if compression increases when pulled over. If so, the above tests will help point you in the right direction. Repeat for other cylinder.
Pull the engine down slowly and inspect everything closely. I don’t believe this will require rocket science to diagnose.

This.
Don't buy new cylinders yet. You probably won't need them.

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#12 wheels_17

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Posted 14 October 2019 - 02:15 PM

Quick update put 2cycle oil in cylinder and performed another compression test it defiantly increase almost broke my hand when I pulled it over I also got another backfire neighborhood dogs are loving me.... I'm going to take cylinder head off and take measurements stay tuned. 



#13 stealth bomber

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Posted 14 October 2019 - 02:25 PM

I think you need to re visit the trigger coils. On a liquid it won’t spark if they’re installed in the wrong spots, but I believe on a fanner it will. Would explain the backfire.

#14 Mill

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Posted 14 October 2019 - 02:26 PM

How many miles on the engine?

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#15 TheBearAk

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Posted 14 October 2019 - 03:24 PM

How many miles on the engine?
 

 

Not trying to be rude or smart-A, but if you read the first post, the answer to that is there.







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