1998 seadoo jet boat sportster 1800 engine rebuild questions and oil injection

[Black creek cruzin]

I have had my 1998 seadoo jet boat now for a few years. The right motor rear cyinder is reading no compression. I ordered the manual and plan to take a swing at rebuilding my self. I just need a few pointers getting started. One, how do I identify what engines are in the boat, I know there the 85hp models but I think theres more then 1 style. Also The oil injection has been blocked off by previous owner but they left the tank and lines in the boat. Can I just yank the oil tank out of there and have no worries? Im very handy with tools, and have been a mechanic on cars and jets for about 10 years now.. Im pretty confident I can rebuild the top end on this thing. Just looking for any pointers or reccommendations from someone with more experience. Thanks for all the help in advance.

 

[racerxxx]

It should have 717's in it (also called the 720). You have to leave the oil tank to keep the oil to the rotary valve shaft lubed. Some guys loop it from one side to the other, but I'd say leave it you won't benefit form the weight loss.

Your engines should look like this. The top of the head should be parallel with the ground.

 

[Black creek cruzin]

Yes they look just like that as far as I can tell from the top. Those bolts that hold the top plate down around the spark plugs, I tried removing it just so I can inspect the pistons and rings but everyone of those bolts feel like there gonna snap as I try to loosen them. Is this a common problem? I wasn't looking for weight loss or anything , just figured id clean it up a little bit. I just thought it would be easier with it out, less lines and shit running around. But ill just leave it alone. Thanks.

 

[racerxxx]

No problem. Depending on how the boat was taken care of will dictate how the engine comes apart. I ride in both salt water and fresh water and my top ends on my Speedster have came apart no problems, but am very anal on flushing the boat after every ride--fresh or salt. I have broken an exhaust bolt or two. So if you break the bolts you'll need to get them to a machine shop that can get rid of the broken bolt. We do them at my father in laws machine shop in the milling machine, no way would I attempt to do it with a hand drill. We drill to the minor diameter of the bolts threads then slowly and carefully chase the threads with a tap to clean out the remaining threads of the bolt. I would assume who ever bores the cylinders will be able to remove any broken bolts for an extra fee.

 

[Black creek cruzin]

Does motor have to come completely out for top end only ? or is there a way to pull just the pistons and rings?

 

[jhjesse]

Does motor have to come completely out for top end only ? or is there a way to pull just the pistons and rings?

Yes but it is a pain leaning over the engine compartment with you feet in the air. You are better off pulling the engine out.

Just a thought,
Have you thought about getting a reman engine from SBT. most probably by the time you get through doing a top end with new pistons and machined jugs you will have $500 plus into it. Usually it is not long until a 15yr old crank lets go under the increased pressure from a new top end build. For $245 more you have a complete rebuilt engine with a no fault warranty. JMHO

 

[Black creek cruzin]

Im intending on less then 150 $ pistons, rings and gaskets. I have my own honing kit I will use to clean up the cylinders. Not to interested in swapping motors right now . Can you tell me how to pull just the top end without motor. I have become used to working upside down over the years lol. Im only thinking I can use my honing kit because it worked on my 4 wheeler pretty well . boat aint much different is it ?Thanks

 

[jhjesse]

Im intending on less then 150 $ pistons, rings and gaskets. I have my own honing kit I will use to clean up the cylinders. Not to interested in swapping motors right now . Can you tell me how to pull just the top end without motor. I have become used to working upside down over the years lol. Im only thinking I can use my honing kit because it worked on my 4 wheeler pretty well . boat aint much different is it ?Thanks

Tuned pipe, air breather, carbs, rave valves etc. will have to be removed to get down to the cylinders. Then on to the head and cylinders and that's where your problems could start.
As you mentioned in post #3 there is a good probability that some of the bolts are going to be stuck and could break. Especially the bolts inside the water jacket that hold the cylinders to the crankcase. In that case you will need to remove the engine and extract the broken bolts. Hand drilling broken bolts could be a nightmare. I personally wouldn't do it especially since it is not very difficult to remove the engine.

In any case once you remove the head then remove the cylinders exposing the pistons. Take a couple of rags and cover the crankcase so that nothing (retaining rings) fall into the crankcase. Now you are ready to remove the pistons and wrist pins. You will need new wrist pin hardware and needle bearings for the rods. When replacing the pistons make sure to put the pistons back facing the right direction. Arrow should point to the rave valve, rotary valve, side.
I use a piece of thin sheet metal to squeeze the rings while installing the cylinder over the rings.

With 0 compression on PTO cylinder you could be looking at more than just honing the cylinders. In that case you will need to bore the cylinders and get new pistons and rings. Download a repair manual from here or google. It will give you step by step instructions on a top end rebuild as well as needed specs for cylinder measurements, ring gap, piston diameters, torque, etc.

Good luck.

http://www.shopsbt.com/mm5/merchant...r=153&findcat=all&SortBy=price-desc&refresh=1

 

[Guest_User]

:lols: sorry to laugh but 150.00 is your budget, then stop right there and save your money. As jesse mentioned, you need to find the root cause of the failure, repair and go from there. there may be more damage revealed once you start tearing it down.
These engines run on the edge to develop the power of such a small displacement and everything needs to be perfect for a reliable running engine or BOOM... and more than likely when you do a top end, the bottom is sure to give out from the restored compression/power.

chicken wire and duct tape doesn`t give you great results when repairing one of these boats.
I suggest getting a service manual for all the important bolt torque specs and how to align everything from the cylinders to the engine itself...

B - break
O - out
A - another
T - thousand

and that`s the truth right there...

good luck, it`s your boat...:cheers:

 

[racerxxx]

If you haven't done it yet, unbolt the hatch (2 struts and 6 screws on the hinges), otherwise you're just gonna be fighting it. I won't do anything but change soak plus and install a battery in a seadoo jet boat with the hatch on. Then you have all the access to the engines. Just wd-40 the screws from the underside, and back them out a few turns, spray (from the top), thread them in, back out, spray, back in, back of, spray until you get them all the way out. It should task 15-20 minutes to get the hatch off and make the job more enjoyable.

Sent from my SGH-T889 using Tapatalk 2

 

[Guest_User]

If you haven't done it yet, unbolt the hatch (2 struts and 6 screws on the hinges), otherwise you're just gonna be fighting it. I won't do anything but change soak plus and install a battery in a seadoo jet boat with the hatch on. Then you have all the access to the engines. Just wd-40 the screws from the underside, and back them out a few turns, spray (from the top), thread them in, back out, spray, back in, back of, spray until you get them all the way out. It should task 15-20 minutes to get the hatch off and make the job more enjoyable.



Sent from my SGH-T889 using Tapatalk 2

excellent advise right there.:thumbsup:

 

[Black creek cruzin]

$150 isn't my budget. Its just what I seen top end kits with gaskets going for on Ebay. I also already ordered the manual. Im willing to spend the money and do it right. I just like to save money at the same time. If I can reuse parts, or do work my self, id rather do that .

Now im gonna start from the beginning of my problems so everyone has the hole story. Took a 10 miles trip, boat was running 40 -50 mph and running perfect. Got to were we turned around and right motor shut down. Tried restarting it multiple times and no luck. Eventually starter quit working probably from cranking it, put a new starter in it. still nothing let it sit and one day it just started and ran perfect for about hours. I was doing about 35 mph in a turn when right motor shut down again. Same shit woundnt restart. Finally get it to restart and it idles. Kind of rough but not terrible. But I cant touch the right motor throttle. Any throttle at all and it shuts down. I alos replaced spark plugs to. So basically my symptoms are its terribly hard to start, idles rough and cant touch the throttle or it shuts down. I put a compression test on it . Fwd cylinder read 110psi I believe , which isn't bad.. Rear cylinder read zero or maybe like 30 psi max I believe. That's why Im at the point of top end kit.

I just opened up the top end plate and removed the spark plugs and finally got all those bolts out. Cylinder walls look perfect, top of both pistons look good. no metal shavings, rub or anything like that. Last time I looked at cylinder walls on a 4 wheeler when the top end went out it was all messed up. However the area around the cylinders were full of water, not in the cylinder but the outer area of it. I read somewhere that all this could be cause by a possible head gasket or carb issues. Anyone of any knowledge on that? Thanks for all the help everyone.

 

[grinditout]

I use a map torch and warm up the thread boss's after I heat it I let the heat soak, then they will pop loose, I would pull the engine, it is not a favorable in frame, pull hatch, take all lines off and make spark plug lifts, pull engine, then dissasemble, you will need to scrounge up or homemake some tools.
crank rebuilds are pricey, wsm is cheap right now.
your going to sink 800 +shipping on this with no short cuts.
Sbt is probably your friend.

Something smoked that back cylinder, probably wear or carbs or crankit seal, seeing as you are premixing,if it is siezeing as you have described, remember these cranks are pressed and will twist off axis.

Last part of the question on the oil tank can be answered easily, in this case, for me I would pull all the oil system and clean it out after an engine smokes, so with that, you are missing so many parts I would loop lines into a T and check b4 every outing, they will stay full 99% of the time.

 

[Sportster-2001-951C-Stock]

110psi is nowhere near where that motor should be, I hope the other motor blows closer to 140psi or more. The thing is, they can run with 100psi, but not for long b/c the oil film on the cylinder walls will break down due to heat of excess blow-by and excessive clearance between cylinder and piston traps heat in the piston.

Three big killers for a 2-stroke engine in good mechanical condition are lack of good fuel, lack of good oil, and improper tune (commonly too lean mixture leads to detonation and lack of fuel also means lack of lubrication b/c fuel carries the lubrication). They will all seize at some point though, even if well maintained, unless they are properly rebuilt (rebulding IS a normal maintenance item) before the end of their normal servicable life. Monitoring compression is one great way to get an idea of your engine's remaining life, worn rings allow too much blow-by and can cause the pistons to overheat, leading to oil film failure.

 

[jhjesse]

$150 isn't my budget. Its just what I seen top end kits with gaskets going for on Ebay. I also already ordered the manual. Im willing to spend the money and do it right. I just like to save money at the same time. If I can reuse parts, or do work my self, id rather do that .

Now im gonna start from the beginning of my problems so everyone has the hole story. Took a 10 miles trip, boat was running 40 -50 mph and running perfect. Got to were we turned around and right motor shut down. Tried restarting it multiple times and no luck. Eventually starter quit working probably from cranking it, put a new starter in it. still nothing let it sit and one day it just started and ran perfect for about hours. I was doing about 35 mph in a turn when right motor shut down again. Same shit woundnt restart. Finally get it to restart and it idles. Kind of rough but not terrible. But I cant touch the right motor throttle. Any throttle at all and it shuts down. I alos replaced spark plugs to. So basically my symptoms are its terribly hard to start, idles rough and cant touch the throttle or it shuts down. I put a compression test on it . Fwd cylinder read 110psi I believe , which isn't bad.. Rear cylinder read zero or maybe like 30 psi max I believe. That's why Im at the point of top end kit.

I just opened up the top end plate and removed the spark plugs and finally got all those bolts out. Cylinder walls look perfect, top of both pistons look good. no metal shavings, rub or anything like that. Last time I looked at cylinder walls on a 4 wheeler when the top end went out it was all messed up. However the area around the cylinders were full of water, not in the cylinder but the outer area of it. I read somewhere that all this could be cause by a possible head gasket or carb issues. Anyone of any knowledge on that? Thanks for all the help everyone.

Sounds like a crank bearing is trying to seize. Might have to dig deeper to find the problem.

 

[Black creek cruzin]

what do you mean by put them into a loop and T? Can you show pictures.
Thanks

 

[racerxxx]

You loop a hose from the inlet of the RV to the outlet of the RV, and put a radiator flush T with a cap in line at the highest point. Guys that race do it, so they can ditch the tank and save weigh from having to carry the extra weight in oil. A moot point in a boat. Also if you happen to get a crank seal that leaks it could drink all the oil in the "loop" and then you roast the rotary valve shaft bearings and brass gear. At least with the oil tank the low oil indicator will go off BEFORE you're out of oil.

 

[jhjesse]

After re reading your #12 post you said that the water jackets were full of water. Could be you were overheating and your temp sensor is malfunctioning. The drain hose is probably plugged up. I would pull the drain hose and blow it out. It's the tee connection at the bottom of the cylinder jugs on the side of the tuned pipe.
Could be the reason you lost compression. At any rate you will still need to do a rebuild of your choosing.

 

[racerxxx]

After re reading your #12 post you said that the water jackets were full of water. Could be you were overheating and your temp sensor is malfunctioning. The drain hose is probably plugged up. I would pull the drain hose and blow it out. It's the tee connection at the bottom of the cylinder jugs on the side of the tuned pipe.
Could be the reason you lost compression. At any rate you will still need to do a rebuild of your choosing.

He has 720's in his boat(see post#2 and 3). They do not drain like a 787 does, there is no lower cylinder drain like a 787, it drains on the bottom of the exhaust manifold--just don't want him looking for something that isn't there. Regardless, he should still check all the cooling lines before putting it back together.

 

[jhjesse]

He has 720's in his boat(see post#2 and 3). They do not drain like a 787 does, there is no lower cylinder drain like a 787, it drains on the bottom of the exhaust manifold--just don't want him looking for something that isn't there. Regardless, he should still check all the cooling lines before putting it back together.

Ahhh...yes your are correct. Tough getting old. :facepalm: