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Discussion Starter · #1 ·
Mxz 800R 2009

Hi!
I bought a sleed that was broken. The seller said that it got seized on idle.
When tore apart the engine i noticed that the connecting rod were bent. Piston ok.
What causes hydrolock?
I have bought a rebuilded crank, 900$ (in Sweden) So I dont want it to happend again...

It wasn't water that caused it. Fuel or oil were the reason.
Bad main valves carbs?
Oil injectors crank case?

Best regards/ Kalle, Sweden
 

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Well, if it wasn't water that caused it sinking it wouldn't be the case eh?

Fuel or oil huh? Gas from a flooding carb would be possible, it would be obvious I think.

Oil is a lot different issue, inner crank seals is another possibility.

If there's any evidence of coolant, then a broken crankcase is often the cause.
 

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Windsurfnut
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inner crank bearings leaking enough oil into cylinders to hydrolock? Its gravity fed from the oil resi. I've had 2 800 etecs loose those seals, burned oil like crazy. I suppose if enough leaks past it could do that?
 
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SnomoSnob
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We had a 2009 Summit 800r, and it appears during the post mortem, that the fuel pump, which is mounted to the MAG Side, leaked into the crankcase, causing that side to hydro-lock. This went on to tear the cases apart.

The pump had a torn diaphragm and the best guess as the to cause was a large backfire.

These backfires are common with these 800s since the pilot circuit is very lean from the factory.

GutZ
 

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We had a 2009 Summit 800r, and it appears during the post mortem, that the fuel pump, which is mounted to the MAG Side, leaked into the crankcase, causing that side to hydro-lock. This went on to tear the cases apart.

The pump had a torn diaphragm and the best guess as the to cause was a large backfire.

These backfires are common with these 800s since the pilot circuit is very lean from the factory.

GutZ
I didn't think to increase the pilot for the backfire. It was only happening when going into reverse or out of reverse, no sure which one. It was awful and I was worried about the seals.
 

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SnomoSnob
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I didn't think to increase the pilot for the backfire. It was only happening when going into reverse or out of reverse, no sure which one. It was awful and I was worried about the seals.
This was someone else's idea, but I increased the pilot and added a shim under the needle and tadaa no more backfiring.

The backfiring for us was after running hard and coming to a quick stop. Throttle Chop at stop sign.

I think it beat up on the Reeds too.

GutZ
 

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This was someone else's idea, but I increased the pilot and added a shim under the needle and tadaa no more backfiring.

The backfiring for us was after running hard and coming to a quick stop. Throttle Chop at stop sign.

I think it beat up on the Reeds too.

GutZ
I did like the fuel economy lol
 

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O-ring on the carb float assembly will allow a freeflow of fuel into the engine causing hydrolock. See it all the time at my shop.....often enough that I replace the o-rings everytime I clean the carbs on a customer's sled. BRP doesn't offer the o-ring..... just a $130 float assembly!!!!

FYI Arctic cat does sell them $1.70....same o-ring.... part number 6505-875

Better than that, I will have to check on the part number for sure, but the last bag I bought was from amazon, but here they are on ebay....100 of them for $10 plus $5 shipping:

https://www.ebay.com/itm/GRAINGER-APPROVED-1RJA2-O-Ring-Buna-N-10mm-OD-PK100-/313336890433

BTW Same o-ring on all polaris, cat, and Doo, Mikuni carbs with the plastic float setup
 

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Discussion Starter · #12 ·
Thank you for all good advise!

What I know is just second hand information, he saId that when started it, it was on idle then it happend.

The crankcase is ok. If it been swimming I dont know. There were no coolant in the crankcase when I opened it.

I'm gone change the diaphgram in the fuel pump, just in case. I can only find complete fuel pumps, is there no loose diaphgram to this pump?

Then i'll go to arctic cat dealer for the o-rings???????? codooster!

Some other things you think good to change just in case?
 

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If it was flooded with oil enough to hydro lock there should be evidence of the oil in the crankcase and exhaust, whereas fuel would eventually evaporate once stuff was pulled apart. Should be fairly easy to tell which liquid caused it. Aside from the stuff already mentioned, check or replace the oil injector nozzles.
 

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That's assuming it is a fluid .......... lol

What about an integrated seal..... lol
 

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Discussion Starter · #15 ·
If it was flooded with oil enough to hydro lock there should be evidence of the oil in the crankcase and exhaust, whereas fuel would eventually evaporate once stuff was pulled apart. Should be fairly easy to tell which liquid caused it. Aside from the stuff already mentioned, check or replace the oil injector nozzles.
It was a while since I disasembled the engine, my poor memory tells me that were oil in case but not enough for hydrolock. I have tried to check the oil injector nozzles with my mitervac, seems to be allright. But they might seize some other time. Best to replace! ????????
 

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Discussion Starter · #16 ·
That's assuming it is a fluid .......... lol

What about an integrated seal..... lol
It don't have to be, just assumed that. The inner ring of the crank bearing rotated on the crank but now I have rebuild crank.
 

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It don't have to be, just assumed that. The inner ring of the crank bearing rotated on the crank but now I have rebuild crank.
I was just fooling around lol However I have heard of such objects being chewed by the piston and spit out the exhaust, but the seals are metallic and would show evidence as bits and pieces in the tuned pipe as well as gouges in the piston crown and head. I have yet to see this myself, nor participate closely with one, so take it for what it is worth....

However, I have once seen a rod that bent from a hydrolock. It was straightened in a vise with the help of spacers to bend far enough to spring back straight. What is unbelievable is that this 583 is still working today lol I have seen it, did not believe it would work, and ridden the sled for years after, so for me it is first hand information. The cause was an oil flood, but here is the strange part. In future oil floods - because the issue was not solved until years later - I have pulled started that sled more often than any other sleds combined lol I eventually did get smart enough to vacuum the oil with a pump, but for those years that I didn't it never hydrolocked again, even though it would start then foul a plug until most of the oil had gone out the exhaust.

Sooooo, I think that Codooster called it right with the engine that manages to start/fire on the good cylinder, and engine speeds-up until the piston on the flooded cylinder draws enough fuel/oil into the combustion chamber to cause a hydrolock. My endless cranking experience - lol - tells me the conditions to be met for this to happen would be difficult to replicate. In other words it was bad luck lol
 
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