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Testing crank seal

D

Dylan Mackay

New Member
Hey guys,

I just purchased a 95 xp 717. Nothing has been tampered with it looks like ( still has the grey fuel lines) so I’m going to have to do the whole go through of it. Compression is a little less then 145 on both.One of my seadoo mechanics told first thing to do before anything is to check the crank seals or crank case or a leak or whatever before starting anything because the 717 was known for bad seals? I remember he mentioned something about just spraying brake cleaner on the case and then hit the starter to see any bubbles ? I’m guessing spray around the case at the seam ? Thanks guys
 
If it were mine I would take the plugs out, ground the plug wires and crank it over to see if any or much oil blows out the plug holes, , change out the grey fuel lines with continental black automotive 1/4” fuel hose, clean the micro filters in the carbs, either change out the square o ring in the fuel filter or vacuum test it and see if it holds 4 pounds of pressure, either change out the fuel selector valve or pressure test it with 4 pounds of vacuum in ON and RES position, if your completely invested in making this machine work I would then give it a try. Is there a reason you think the outer crank seals are leaking? Or are you only concerned because someone told you they leak regularly? If you want to know if the outer seals are leaking before putting any money in at all for fuel lines then you can do a leak down test by removing the carbs and head pipe, sandwiching in some inner tube between carbs and intake and between head pipe and exhaust manifold and pressurize crankcase to 6 pounds through the pulse fitting. If you don’t know what oil was used you will need to empty the tank and clean or replace the oil filter before adding new oil to the tank as different brands of oil can congeal. Once you get it running correctly ride it with the seat off for a minute to look for any possible water leaks.
 
If it starts and idles at least somekind of half normal,
You can also test to spray "starter spray" really near or close to the crank, usually if it is a leak it fill suck that ga sinto engine and it revs up
Same procedure when you seek for leaks at the inlet on a car engine...., I dont know how easy it is to get it into the Magneto side on that motor, but if there are some openings maybe for stator leads or other "vent" there..
You can add a bit of 2 stroke oil to the gasoline, to be sure it have good lubrication,
 
Okay so I just made my own pressure tester for the carbs and jet pump. Am I able to use that for a “vaccum tester”? I’m guessing I’ll need a gauge with negative pressure hooked on a device that will suck in.
 
burtshaver2021 said:
If it were mine I would take the plugs out, ground the plug wires and crank it over to see if any or much oil blows out the plug holes, , change out the grey fuel lines with continental black automotive 1/4” fuel hose, clean the micro filters in the carbs, either change out the square o ring in the fuel filter or vacuum test it and see if it holds 4 pounds of pressure, either change out the fuel selector valve or pressure test it with 4 pounds of vacuum in ON and RES position, if your completely invested in making this machine work I would then give it a try. Is there a reason you think the outer crank seals are leaking? Or are you only concerned because someone told you they leak regularly? If you want to know if the outer seals are leaking before putting any money in at all for fuel lines then you can do a leak down test by removing the carbs and head pipe, sandwiching in some inner tube between carbs and intake and between head pipe and exhaust manifold and pressurize crankcase to 6 pounds through the pulse fitting. If you don’t know what oil was used you will need to empty the tank and clean or replace the oil filter before adding new oil to the tank as different brands of oil can congeal. Once you get it running correctly ride it with the seat off for a minute to look for any possible water leaks.
Click to expand...
No reason yet. When I went to look at it it was not spraying oil out when starting with the plugs out , nor did it have a pool of oil at the bottom of the hull which is a good sign. I guess my guy just said the crank seals tend to go bad and this machine has been sitting for a while …
 
Your "guy" is wrong, these outer seals don't just go bad.

Burt is correct, the most common seal leak on these are the inner crank seals and if they are leaking the cylinders will be full of oil when you crank it over with the spark plugs out.

If you have an actual air leak the ski will start and rev up to the moon and pulling the lanyard will do nothing so pull the choke and it will kill the engine.

The only correct way to verify all gaskets and seals are bad is to do a leak down test as burt explained. You block off the intake at the carbs and the exhaust at the head pipe and pump 8 psi into the pulse fitting. It should hold 8 psi for at least 10 minutes.

If it was mine I would see if it starts with a little premix and go from there.
 
Dylan Mackay said:
Okay so I just made my own pressure tester for the carbs and jet pump. Am I able to use that for a “vaccum tester”? I’m guessing I’ll need a gauge with negative pressure hooked on a device that will suck in.
Click to expand...
You can use pressure to test the filter and selector valve, I use vacuum because it’s under vacuum in the system but pressure will be fine. Yes, you will need a gauge for all testing to see if pressure is lost. Don’t use a compressor to add your pressure, buy or make one with a hand pump. You don’t want to over pressurize carb, engine or anything.
 
mikidymac said:
Your "guy" is wrong, these outer seals don't just go bad.

Burt is correct, the most common seal leak on these are the inner crank seals and if they are leaking the cylinders will be full of oil when you crank it over with the spark plugs out.

If you have an actual air leak the ski will start and rev up to the moon and pulling the lanyard will do nothing so pull the choke and it will kill the engine.

The only correct way to verify all gaskets and seals are bad is to do a leak down test as burt explained. You block off the intake at the carbs and the exhaust at the head pipe and pump 8 psi into the pulse fitting. It should hold 8 psi for at least 10 minutes.

If it was mine I would see if it starts with a little premix and go from there.
Click to expand...
Okay so I’m going to do another check when I get it by cranking with the plugs out and see if any oil comes out. 99% sure it should be good since it wasn’t doing that a week ago when I first looked at it. I want to update the fuel system before starting it much.
 
DaddyLoafin said:
can always get the engine running and spary wd40 at the crank seal and listen for the idle speed to change. if it changes than its leaking
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Nope, on these 2-strokes if you have any external air leaks they will runaway from being too lean.
No reason for any fancy sprays you will know when it goes to 8,000 rpm and the kill switch does nothing.
 
mikidymac said:
Nope, on these 2-strokes if you have any external air leaks they will runaway from being too lean.
No reason for any fancy sprays you will know when it goes to 8,000 rpm and the kill switch does nothing.
Click to expand...
I was told to spray wd40 or carb cleaner around the crank seals and carb base gaskets to narrow down where there's an air leak
 
DaddyLoafin said:
I was told to spray wd40 or carb cleaner around the crank seals and carb base gaskets to narrow down where there's an air leak
Click to expand...
What can I san, it sounds like you have a lot of "experts" giving you information that isn't always correct. Works great on 4-strokes, not so much 2-stroke watercraft.

On a 2-stroke if you have an external air leak it will lean out the air/fuel mixture at idle with no load on the engine. This will cause the combustion temperatures to get high enough to cause ignition without spark and the engine will run to full rpm and the kill switch will do nothing. The only way to stop this is to cool the combustion chamber so you simple pull the choke and it will kill the engine.

What I am saying is if you have an external air leak at the intake or crank seals your engine will runaway before you can spray the engine with anything. So if your engine doesn't runaway then you don't have an external air leak and no spray is needed.

On a Seadoo 951 engine, they are so lean from the factory they can runaway even when everything is perfect so we recommend setting the idle to only 1,400 rpm. The only accurate way to check for gasket and seal leaks is a pressure test at 8 psi.
 
DaddyLoafin said:
well i wont pass that information on anymore lol
Click to expand...
The big difference with these is that there is absolutely no load on the engines when out of the water so they are super sensitive to any air leaks.
Even on a 2-stroke motorcycle you have the gearbox, clutch and waterpump all creating a load that can mask the air leak so the carb cleaner or propane spray can help diagnose it as they don't typically runaway.

So the information isn't totally wrong, just wrong for these watercraft.
 
mikidymac said:
The big difference with these is that there is absolutely no load on the engines when out of the water so they are super sensitive to any air leaks.
Even on a 2-stroke motorcycle you have the gearbox, clutch and waterpump all creating a load that can mask the air leak so the carb cleaner or propane spray can help diagnose it as they don't typically runaway.

So the information isn't totally wrong, just wrong for these watercraft.
Click to expand...
Alright I see what your saying.
Just out of curiosity what would cause a 787 to run away after a long ride while the engine is hot? I had this happen to me earlier this year and haven't figured out why and I haven't been able to get it to run away again. The throttle cable has a little slack in it so I assume it wasn't because of that. The only thing I've been able to think off was it being very low on gas when I pulled it out and it was sitting on a like 20 degree angle when it happened.
 
Did it actually runaway, where the kill switch did nothing?

My 1996 XP with the 787 started to runaway the first time I started it after buying it. It has been sitting on a trailer for 10 years. I knew I was going to rebuild it but did a pressure test before taking it apart. It was the rotary valve cover o-ring, it was hard and dry.

Anything that will make it run lean can cause a runaway. Such as running out of fuel, air leak in the fuel system, stuck throttle, not enough slack in the throttle cable, idle set too high or air leak after the carburetor butterfly such as a worn throttle shaft, carb base gasket, intake o-ring, rotary valve cover o-ring, outer crank seal, cylinder base gasket.
 
Yeah it ran away, I pulled the key and it kept going turned fuel valve off and was standing there for idn how long but freaking out trying to figure out how to kill it until I remembered to pull the choke.
I was at the end of breaking the new top end in and was trying to get the fuel as low as possible to dilute whatever oil was left in the gas as much as possible.
Still has full compression
 
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