1998 sportster 1800 compression

[beanz2166]

Hey guys, new to the forum and hopefully new to the concept of seadoo boats. Any how Im looking at buying a 1998 sportster 1800, the boat is in real nice shape and hes got it for a nice price. Now heres my question I have seen two different schools of thought regarding the compression test numbers. the first being 150 is a new boat and anything in the 130 range means a rebuild in the near future. Then I seen the numbers dont really matter as long as they are within a few PSI of each other. hes numbers are Port 133 and 132 SB are 137 and 135. whats so the experts think about these? Am I looking at a rebuild soon? Thanks

 

[Guest_User]

Hey guys, new to the forum and hopefully new to the concept of seadoo boats. Any how Im looking at buying a 1998 sportster 1800, the boat is in real nice shape and hes got it for a nice price. Now heres my question I have seen two different schools of thought regarding the compression test numbers. the first being 150 is a new boat and anything in the 130 range means a rebuild in the near future. Then I seen the numbers dont really matter as long as they are within a few PSI of each other. hes numbers are Port 133 and 132 SB are 137 and 135. whats so the experts think about these? Am I looking at a rebuild soon? Thanks

was the compression test done with the throttle fully open and cranked for at least 5 revolutions?

to be certain, try another gauge, unless you are already using a quality gauge...
while you have the plugs out, shine a small LED flexible wand light down in the cylinders to see any signs of scoring and you can also view the piston wash...

Did you water test this boat? I would absolutely recommend that... that will show the health of the engines/exhaust water leaks, carbon seal water leaks, and reveal any pump/impeller/wear ring issues...
good luck...

 

[Dr Honda]

The spec compression on that engine is 150 psi. (+- 5psi)

As above... the test is done, with the throttle open, and crank for max pressure. (about 5 revolutions)


If the compression is VERY high... that coudl be a sign that the center seals are leaking oil into the engien. In that case... start the engine for about 30 seconds... let it cool for a few minutes... and check it again. (That will help purge extra oil)

If it's getting down to 130 psi... it's tired, and will need a rebuild. If you wait much longer... it will melt down.


The "Old school" saying about.... "It's ok as long as it's 5% of each other" is really for car engines. There is some truth to it. If you see 150, and 135... something is wrong.... but with a high performance 2 stroke... when the rings start to leak (low compression is the sign) the hot combustion gasses will push past the rings... displace oil... overheat the piston skirts... and melt the engine.


So:


150 psi = GREAT

140 PSI = good, and has life left in it

<135 psi = time to replace the top end, before a melt-down takes out the entire engine.


The above is the Gospel according to Dr Honda. (lol) FYI: this is for 800 and smaller Rotax. The 951 engine has lower compression from the factory (135~140 is good on that engine)

 

[Seadoobuddy]

to beanz2166,
Welcome to the forum.
The Dr knows his stuff, I would follow it to the letter.

 

[howie099]

Sounds like to me you can a good deal on that baby now that you know the engines are on the last leg. If the price is right you should buy and replace or redo the enignes. For bargin sake you can take about $1000 an engine to take off of the deal. If the guy won't just walk away. I have the same boat and I trusted the guy I bought it from he was right on the hours when he sold it to me 124 on it whne I hooked up the machine.

 

[Guest_User]

Sounds like to me you can a good deal on that baby now that you know the engines are on the last leg. If the price is right you should buy and replace or redo the enignes. For bargin sake you can take about $1000 an engine to take off of the deal. If the guy won't just walk away. I have the same boat and I trusted the guy I bought it from he was right on the hours when he sold it to me 124 on it whne I hooked up the machine.

me too! I trusted the friend and look at the POS I wound up with... and friends no more. never received on dime back and the tool was supposed to pay for at least one engine... That is a complete doosh bag in my book...

OP, don`t get burned, work the best deal knowing your going to spend money on something!

 

[howie099]

The guy I bought it from didn't lie about the use. The boat was used 3 times a year since 1998. Only Memorial Day, 4 of July and Labor day weeks. They never pulled a person ever with the boat. Garage kept its whole life and still is in a heated garage. They did run it once in to shallow of water and messed up the bottom and 1 impeller. So they put a depth finder in after that. The hours showed on the scanner like 120 for a boat is good. A ski that is normal in Chicago for that year or a little more since we only have like 4-5 good months for skis.