95 GTS 587 - low compression: what's next

[sgtb]

Hi, I'm pretty new to this forum stuff, but I don't know where else to go with some of these questions... I've been reading a lot but haven't found some of the specifics so here goes.



The ski belongs to a friend of mine (I am pretty new to the whole personal water craft thing also). But, I told him that I'd take a look at it, do some research and try to help him not pay all the labor cost that the shop wanted.



Here are the basics:

1995 Sea Doo GTS with white 587 motor.

He told me that over a year ago it started running poorly, and when he took it to a shop they said that he didn't have any compression. They wanted about $2500 to put in a new motor (or overhaul the one that's in there or something). He didn't have that kind of cash for it then so it's been sitting since.



So now it in my garage with a dead battery, a Clymer manual on top of it, and a bunch of "hmmm, what would be the best thing to do now...?" questions.



I got the battery charged up somewhat, enough to turn the engine over but not enough to get a compression test. So I used a different one and was only able to get 50 in the rear cyl and 70 in the front cyl. When I put some oil in the spark plug hole I got 70 in both. I looked in both of them with a borescope and can't see any physical damage to the walls or to the top of the piston. (I don't have a great compression tester so I may need to get a second one to test with, but I think mine is fairly accurate in that I am definitely not getting the 150- 155 that I've read is what I am looking for.)



I opened the throttle and the choke all the way, as well as had both plugs out for this preliminary test.



One question that I have is will this hurt the engine to keep turning it over with no fuel/oil going in? Also, should this be normal for a cold engine? I don't have a water connector at this point, or any way to put it in water to try to run it to get to a normal operating temp.



I'm not sure how much to trust the "shop's" diagnosis, since my friend isn't very mechanical I'm not sure he really remembers what they told him other than the price...



Should I just assume that I need to tear into the engine further, like disassemble the head and cylinders to check the rings and all, or just consider it junk and do a complete engine swap. I'm thinking that maybe I could just replace the top end and go from there...



Any thoughts or help with how to get started would be greatly appreciated.



Is this ski even worth $2500 if it is running?



I know this is a lot, but I'm trying to be thorough.


MB

[1fastski.com]

Re: 95 GTS 587 - low compression: what's next

for about 700 bucks you could drop a SBT short block in it your self . if the ski is clean its worth doing that , 2500 no .

your going to hurt anything cranking it over . the compression is low you would need to remove the engine take it apart to find out why and what it really needs . between a crank and pistons your close to the cost of a shortblock so it would be better to go with the shortblock and get a warranty :-)

[sgtb]

Re: 95 GTS 587 - low compression: what's next

"your going to hurt anything cranking it over . "
will or won't hurt anything???

ALso, I keep hearing / reading that it is necessary to replace the crank as well as the pistons. Why is that? I used to to work on Avaition engines (four stroke) and we could just top overhaul the pistons rings and cylinders without worrying about the crank or conecting rods for the most part.

Also, is there an easy way to pressurize the case to see if there are problems with that in stead of the cylinders, or would it all result in needing to tear it down anyway?

We were hoping to maybe just replace the topend not the whole thing.

MB

[radiocontrolhead]

Re: 95 GTS 587 - low compression: what's next

you're best bet woudl be to spend about a grand on it. get a new shortblock. the work sbt does to teh engine is something an average person cannot do. w/ all the tools and machinery they have there.

also you should be rebuilding the carbs. tear down teh engine and find out what caused th low compression. most likely the pistons are socred and you cannot see that from the spark plug hole.

[1fastski.com]

Re: 95 GTS 587 - low compression: what's next

after you pull it apart you can inspect and replace just what you need , in many cases the parts to rebuild it out number the cost of a SBT short block considering the warranty but if the warranty does not matter much then save a few bucks and replace just what it needs nomatter what find out what happin so it wont happin again

[sgtb]

Re: 95 GTS 587 - low compression: what's next

1.
So one question that I still have about the compression test is does it matter that much if the engine can't be brought up to the "regular running temp?"
I also got a newer tester guage from autozone (I know it's not a calibrated Snap-on guage, but it's the best I can do for now) so that I can compare with the one that I already had. In the Clymer book it says something like Sea Doo doesn't publish actual specs for compression and that the two cyl's should be with in 10%. with the oil added through the spark plug hole they were nearly exact. I still need to retest with the different guage though.

Also, is it possible that the compression is low because of a blown gasket somewhere. I know that doesn't seem consistant with the fact that if I added oil and it increased and all. Just trying to cover all the options.

2.
How would I test the case for leaks? or would that matter. I guess I need to take off the intake and exh. and block them, then add like 10psi to the case? Right?
Can I add that air through the sparkplug hole or does it have to go in somewhere else?

3.
I guess this really can't be answered until I pull the cylinders off, but might it be possible to just replace the rings and maybe the pistons (if the cyl bores aren't scuffed up, of course)?
Or at that point would it be better to have the cyl's re-sleeved and put new pistons?
what would be the difference between re-sleeving and new cylinders?

Thanks,
Matt

[radiocontrolhead]

Re: 95 GTS 587 - low compression: what's next

1.
So one question that I still have about the compression test is does it matter that much if the engine can't be brought up to the "regular running temp?"
I also got a newer tester guage from autozone (I know it's not a calibrated Snap-on guage, but it's the best I can do for now) so that I can compare with the one that I already had. In the Clymer book it says something like Sea Doo doesn't publish actual specs for compression and that the two cyl's should be with in 10%. with the oil added through the spark plug hole they were nearly exact. I still need to retest with the different guage though.

Also, is it possible that the compression is low because of a blown gasket somewhere. I know that doesn't seem consistant with the fact that if I added oil and it increased and all. Just trying to cover all the options.

2.
How would I test the case for leaks? or would that matter. I guess I need to take off the intake and exh. and block them, then add like 10psi to the case? Right?
Can I add that air through the sparkplug hole or does it have to go in somewhere else?

3.
I guess this really can't be answered until I pull the cylinders off, but might it be possible to just replace the rings and maybe the pistons (if the cyl bores aren't scuffed up, of course)?
Or at that point would it be better to have the cyl's re-sleeved and put new pistons?
what would be the difference between re-sleeving and new cylinders?

Thanks,
Matt

i'm new to this so dont take everythign i say to be correct. or rather. very specific:

1. if you had a blown gasket, your compression would not change. a gasket has nothign to do w/ your compression.

2. i cannot help you w/ that becaue i have no idea how to pressure test a case or if that is even supposed to be tested. (check the clymers book)

3. you would need to pull the cylinders apart. If you are looking for the cheapest way to get around this and just have a great time i would say a top end rebuild kit from sbt would really work well. or if the clyinders are in tact yuo can get them rehoned and just buy new pistons/piston pins/ and circlips. i'm not a pro at this. but you have to see what happneed inside t hat engine first.

[sgtb]

Re: 95 GTS 587 - low compression: what's next

well I just did a forum search and found a nice test procedure by Bill O'Neal2 at

http://www.sbtontheweb.com/forum/sho...+oil+pump+test

Thanks Bill! I'll try it that way, except for the warm part, it doesn't run that well...

MB

Update:
Well I re-tested the compression both with the plugs and with out, since I've found both ways described on the forums:
Results with the newer guage - 1st time:
plugs in Front 85
plugs out Front 100
Plugs in rear 80
Plugs out rear 90


I guess that solves it since the 5% difference is out, as well as if it should test at 140's they are both a long way off...

I guess it's tear down time for sure. Thanks for all the input

Matt