1997 speedster compression results. Good or Bad?

[chadsheffield]

The boat had been sitting for two years and just bought it. with bad gas and oil in it i got 120psi and 125psi on the right engine and then 125 and 125 on the left engine. I really want to get out to the lake and will i be fine with this readings? i read if they arent more then 10percent apart in psi then it will be fine. so am i good?

 

[deepdiver]

I think they are both low. But if it runs it won't hurt, just won't deliver quite the max power. Do give it a run. It needs some exercise. Hope that is only concern. Watch out for fuel line problems, dirty carbs, etc.

 

[JohnZ]

Your compression tester may not be 100% accurate - I say this because your port engine punched out identical numbers or maybe it is, and then you still have some time to play. I second deepdiver on the carbs - 2 years of fuel sitting in the carbs has probably made them a disaster.

IMO w/ that compression I would test it out in some water, don't plan a day event and take some extra plugs and tools. It may react very poorly when you put it in the water and add a load on the motor, hard to tell since the motors run completely different out of water. I was in the same position, badly wanted to get out on the water to end up with a long afternoon limping home. There are a lot of other concerns you should check out - the wear rings, driveline seals, props........ I have similar PSI (on a cheap-o gauge) and thought all was good to just end up with really really bad cavitation caused by bad driveline carbon rings/seals. I rebuilt the carbs, and drivelines and now the boat runs like a champ.

 

[Dr Honda]

what was said above is correct.


Your compression is low, and there is a good chance that the engines won't run in the water. Also, they are low enough that they may just eat themselves after an hour or two.

 

[chadsheffield]

okay well im going to put new piston rings in before i go out then. but looking up online under oem there are three to choose from??? what one do i want. 82.00mm or 82.25 or 82.55. and what does OPT mean cause it says that next to the two bigger ones in the quanity box. thanks!

 

[parrothd]

Get a second compression tester and re-check, 125 on you gauge might be 140 on someone elses..

 

[JohnZ]

those measurements are for a overbore.... You can just buy the OEM sized pistons but odds are the cylinders are scored up. Stock bore is 82mm then to fix your cylinders you would need to machine them out (bore them out) then get matching pistons, this would be the 82.25 - then the 82.55 gives you another chance to bore out the cylinder.

If you are going to still do it there are places, even on ebay, that you ship them your cylinders and they machine them and send you back the whole top end kit ready to install, but its quite a job and you still may have other issues (carbon rings, wear rings)

I have the same compression and they run fine, I would test it out on water before you do all that, or maybe find spare cylinders and send them off to machined to be ready if yours really goes south, OR you can take the head covers off and check them out - there is only rubber o-rings sealing the cylinders up and in my case I had a cracked o-ring.

 

[chadsheffield]

i checked with another gauge and it read the same. but okay ill hold off and see if it runs good first. i just didnt want to cause more serious damage and money by doing that. on ebay will any seadoo 720 top end and piston kit work since the speedster has a 720 or are they differnt?

 

[Dr Honda]

if you are just going to put pistons and rings in the used jugs... then you need to take the head off and measure the piston size, before you buy parts.

 

[JohnZ]

Yes a 720 is a 720, also check out shopsbt.com, I am lucky to live down the street from these guys and they are great! I still suggest if you're going to do the pistons find a machine shop (you'll have to take the cylinders off any way), and have them bored. Tell them your piston size options and they will measure and cut to the next size - The places I've checked into doing it charge about $30 a hole.

Also have a repair manual - there is a few specialty tools you're going to need......