Pressure testing crank case

[Gary pope]

OK here is the deal. I am in the process of tearing down and going through my 97 720 motor off of a Sea-Doo GTS Jetski. I replaced all four outer bearings on the crankshaft along with the other seals, I want to know if I assemble the motor without putting the pistons in can I pressure test the crank case to see if the outer seals are leaking at all?

 

[mikidymac]

The point of pressure testing is to make sure there are not any leaks anywhere. I would wait until you have it all back together because you will just have to test it again when you pull the cylinders to install the pistons and waste a base gasket since you can't reuse them.

 

[Gary pope]

I was just gonna use some permit tax in place of the gasket for pressure testing purposes and then once I find out that it passes I was going to clean them in then install the gaskets. Isn’t it kind a hard to pressure test the bottom part of the crank case with the Pistons installed

 

[mikidymac]

No, it is a 2 stroke so the bottom and top are connected and there is no way to separate them.
You only pressure test once the engine is completely back together.

Don't use silicone inplace of a gasket, just a mess waiting to happen.

 

[Gary pope]

OK answer me this then, how are you supposed to pressurize the crank case with the piston still inside? You can’t put air pass the Pistons with them installed

 

[andrewterri]

Like mikidymac said it is a 2 stoke so the fuel rich air comes in at crank, crank pressurizes the mixture on the down stroke and it is forced though the cylinder jug into the combustion chamber. The port that runs from the case to combustion chamber is always open unless cylinder is blocking it but than other jug will be open. This allows for pressurized case to also pressurize above the pistons at the same time.

 

[Gary pope]

OK thanks for explaining it to me, I am use to regular four stroke motors not these two strokes.How do I pressurize the motor would it be through the spark plug hole?

 

[andrewterri]

No problem Gary that's what we are here for. I am going to let someone else answer that. I don't know what the best way to pressure test your motor is. I don't want to give you wrong information.

 

[mikidymac]

Through the brass pulse nipple that goes to the carb fuel pump.

The engine needs to hold 8 psi for at least 10 minutes. Anything more than 10 psi can blow seals out.

Also the pistons aren’t air tight because you have the ring gap. Trust me air will get through.

 

[IDoSeaDoo]

Yep, what mac said. Also, I like to have a squirt bottle full of soapy water handy to spray all the possible leak sites. Soapy water will almost instantly tell you if you have a leak or not. Trust the bubbles.

 

[Gary pope]

Thanks guys

 

[Gary pope]

Ok but can’t I instead of spending the money on a set of gaskets just use rtv sealant just for the pressure testing, and then once I find out if it passes or not then tear it apart and put the gaskets on?

 

[Shortrun]

No RTV. Make home made gaskets from a Rice Crispies box if you have to .

 

[mikidymac]

I still don't understand why you want to pressure test just the bottom end then tear it all back apart and put the gaskets on? No reason to do it twice. If you used new seals there is a 99.99999% chance it will not leak, so just assemble the engine completely and then pressure test.

You only need 1 set of gaskets. I am not sure why you think you will need another set. It's pretty simple, assemble the engine correctly with all the proper gaskets, sealants and torque specs and it will pass the pressure test. You are only pressure testing to check your work. In 25 years I have only had 2 engines fail the test. One was from a cracked head and one was from being in a hurry late at night and forgetting a head o-ring.

 

[racerxxx]

The shop manual will tell you how to pressure test the engine. Extremely simple.

 

[Gary pope]

Ok here’s another question. I got the rotary valve taken out and I’d like to replace the bearings and seal that the shaft goes in. How do I get the bearing out of the crankcase that the rotary valve goes in and also the bearing that is attached to the rotary shaft so I can get to that seal?

 

[racerxxx]

You need an internal bearing puller kit. Harbor freight. Some guys use a slide hammer. Look at my 95XP 800 or it might be my 98spx build thread. I have pics in there showing the entire process.

 

[Gary pope]

Well I do have a bearing puller kit that I got from Harbor freight. It has a large and a small polar I should be able to use that right

 

[IDoSeaDoo]

Use the bearing pulled on the bearing in the case. As for the shaft, you have to take off one or two C-clips and the whole assembly slides apart. I believe that bearing is pressed onto the shaft, but not very hard to separate. You can probably use some to set up a jig and carefully tap it out with a hammer if you don't have a press. Careful prying off those C-clips, as they sometimes shoot across the shop. They can be pretty tough to find afterwards

 

[Gary pope]

Ok I know the bearing that’s in the case is a different size than the one on the shaft. Does anyone know the part numbers of the 2 different sized bearings?

 

[Greensam]

Case bearing is 420932797 old #290932797
Shaft bearing is 293350051 old #290932032
Or go to your local bearing house and get
6201-2Z/C3 for the case which is double shielded, one shield will have to be removed
6203/C3 for the shaft, both will probably be half the price compared to the dealer.

 

[racerxxx]

Case bearing is 420932797 old #290932797
Shaft bearing is 293350051 old #290932032
Or go to your local bearing house and get
6201-2Z/C3 for the case which is double shielded, one shield will have to be removed
6203/C3 for the shaft, both will probably be half the price compared to the dealer.

You can order it with just one shield. Just drop the 2 in front of the Z and your good to go. Same on the rv side, just get an rs instead of 2rs.

 

[IDoSeaDoo]

Has anyone actually seen these bearings fail?

 

[Minnetonka4me]

In my experience on the 580-720s the oring between the two intake mani plates is usually the culprit on the engine test, and on the cooling test it's usually the head oring between the two halves.