Rebuilding a 1999 Seadoo 787 RFI top end questions?

[ted-hurst]

Took the 1999 GTX RFI out today and was dragging the church youth around and started losing rpm's. Usually pulls 6700+ but after towing for quite a bit could only get 5200 rpm's. Thought at first it might be the rave valves but when I got home decided to do a compression test and cylinder #1 was 120psi and #2 was 150. My question is can I do a top end kit without tearing apart the whole motor? Are the sleeves in the jugs replaceable and are they pressed in? Can the top end be done in the ski or does the engine need to be pulled? Thanks for any help, we love the ski and have had a great time with it and besides the compression issue it's in great shape and we want to keep it.

Thanks
Ted

 

[racerxxx]

You can do it in house if you want. I would do both cylinders at the same time.

 

[ted-hurst]

I was planning to do both, if I didn't as soon as I get it out the other would screw up (Murphy's Law). The sleeves are slip fit or pressed in?

Thanks
Ted

 

[ravens9273]

Ted

Would be easier to bore your current cylinder jugs. Just take to local machine shop and have them done. Usually .25 mm over and order pistons for .25mm over

 

[ted-hurst]

A couple more questions, the stock bore and stroke is 82x74. How much can I bore it out safely? How much can it be bored out before interfering with the rave valves? I asked about the sleeves because when I bought the ski 6 years ago the previous owner had just put a SBT engine in it and don't know how much it is already bored.

Thanks
Ted

 

[FaceDeAce]

You really will not know until you pull the motor, roll up the sleeves, get into it and find out what you have. Will you be doing the work yourself or dropping it at a shop?

 

[Mekanix]

Top end wsm or sbt kits are 200-300$
Boring is 50-70$ per cylinder depending on the shop.
You need the pistons first in order to know what to bore the cylinders to.
Pull the head and measure the cylinders to know what size you need to get.
Stock is 81.89. The kits go in .25mm increments.
You have to clearence the raves if you go anything beyond 82.5mm. Maybe just a little if you use a smaller bore.


If you do it in the machine, you MUST vaccume all the water, sand, and debris out of the bottom of the water jackets.
otherwise when you pull the cylinders. The base gasket will rip and you will have to pull the motor anyways to get it all out.

Might want to replace the injectors. (Likely cause of the failure) 75$ each i think.

 

[ted-hurst]

First off, thanks to everyone with their inputs. This is what I work on for my job, but when it comes to two strokes I worry about screwing it up. I finally put my big boys pants on and dove in. Vacuuming the cylinders worked awesome, I'll also be doing both cylinders and new injectors. The bore measured 82.90 MM on the micrometer, so it's 1mm over stock bore? I'm adding some pics to show what been done so far.

 

[ted-hurst]

Here are the pics of the engine and engine bay. One more question, the engine was a SBT reman before I got it and it ran great. When I do the top end is there a better option like Wiseco or someone else or just stick with what worked last time (6+ years of abuse)? SBT kit is about $260.

Thanks
Ted

P.S. If anyone makes it to Pensacola look me up and I'll give you a tour of the museum restoration area.

 

[Mekanix]

Well what do you know, Another wing nut

I'm Avionics on the Cp140
You will be able to handle everything on these machines! Just get the manual and read through it. All the specs, tolerances, sealants and lubes.
They are very specific on certain things. For example: the head bolts are lubricated on the threads with marine grease and they use locktite 242 under the heads.

Looks like it is 1mm over.

I would bet the piston's were aftermarket. Either WSM or SBT already.


Keep in mind that when you use a whole top end kit that they only include the LARGEST base gasket. So that means you will have the largest squish gap.

The right way to do it is to assemble without a base gasket, measure squish and then order the right gasket for the squish you need.
I think one of them I did a top end on had 2mm+ of squish with their gasket.

 

[Mekanix]

I think the order of which piston to go with is:

OEM
OEM oversize
ProX
I hesitate to say wiseco but they are ok if you don't mind warming them up first.
WSM/ SBT are in the same category. ( I would only get the WSM platinum kit though)


Best option might to trade SBT your cylinders for a new set with a top end kit already bored to fit.

 

[ted-hurst]

I have the manual and the pistons were SBT, head looked good and the cylinder walls weren't gouged so they should bore okay.

 

[Mekanix]

Once honed I wonder what the clearance would be. If you've been using it for the past 6 years that must have had some effect on cylinder wear.

What does the bore measure in different places from top to bottom ?

I know SBT have some options for trading cylinders and getting the kits fitted to them vs the cost of honing and boring if you needed to.


How many holes were in the base gasket (between the two cylinders there is a 3-6 dot patern like on dice.)



Just another tid bit of info. When you reinstall the cylinders. Try and mock them up first using the exhaust manifold and head. You will notice that the head and cylinders can move around quite a bit. There are no dowel pins to line everything up.
Just assemble it on the bench and see how it lines up properly and then mark the head to cylinders relation. It will help when reassembling. Also once you have the cylinders installed. Reinstall the exhaust manifold to keep everything aligned and then torque the cylinders down to the base.

 

[ted-hurst]

I found a complete top end kit (cylinders included) with WSM Platinum pistons for $500 and no cores to turn in. Might be the best route. Don't have to worry to much about warming up the ski, It's usually 90-100 down here and water temp is 80+. Just kidding, I run it a bit before winding it up.

Ted

 

[Mekanix]

WSM kits are 2-300$ depending on where you get it and boring is around 60-80$ per cylinder from what I've found.

 

[ted-hurst]

Got it all back together and thanks for the help. It fired right up and idled right at 1600. Let it run checking for leaks and making sure everything was doing what it was supposed to do and then did a compression test. It was 150 psi on each cylinder. I liked the WSM Platinum pistons, they have the guide pin in the ring groove to keep rings from rotating. Going to break it in slowly and then see what she does.

Thanks
Ted

 

[ted-hurst]

Looking for an older 2 stroke Seadoo, any recommendations? XP, GSX, Thanks again, Ted

 

[Nyy23]

Ted

Would be easier to bore your current cylinder jugs. Just take to local machine shop and have them done. Usually .25 mm over and order pistons for .25mm over

Don't forget to trim ur stock rave valve guillotines too. Can do it easily with a Dremel tool.

 

[Mekanix]

Looking for an older 2 stroke Seadoo, any recommendations? XP, GSX, Thanks again, Ted

Xp for lots of fun.
GSX for cruising and fun. stick with carbed.



Yeah i liked the wsm platinum kits too. Only issue is the one base gasket they give. Need to get the right one from the dealer for the right squish. But with the 6 hole gasket they include works just fine.

 

[Mekanix]

Don't forget to trim ur stock rave valve guillotines too. Can do it easily with a Dremel tool.

Wrap old piston in 400 grit sand paper. Use it as a formed sanding block for raves

 

[ted-hurst]

The old pistons were 1.0mm over and the new pistons with cylinders were .5mm over. I double checked clearance while assembling to make sure nothing was going to hit. What about DI models, pro/cons? And what about a 951 pro/cons? I like the 787 RFI's because it seems pretty simple and mine was pretty easy to work on. I've worked on a lot of motorcycles carbs but never any 2 strokes or jet ski 2 strokes. How much different are they?

Thanks
Ted

 

[Mekanix]

If you want a DI, or an RFI you need a computer as well. So you would need a Can-Doo. They are relatively cheap if your only doing your own machines and only have a few of them. But the price triples if you want to unlock the ability to work on more machines. Can-doo is comparable to what a snap-on automotive scanner would be.

For the DI's, general consensus is that when they work its great. When they don't.... Run away! Unless you have the computer and parts and like to troubleshoot. But complicated problems leads to more repair time than play time.

RFI's are better but can be difficult if your not on top of things. Bad injectors are hard to spot and can ruin a day very quickly. Its little things like that. Also hidden fuel filters that are not on the parts lists.... Great machines when your on top of the learning curve.

For Carbs. That's a little different but the good thing is that anyone can do it. Carb kits are available. Testing equipment is available and build-able. All the information for rebuilding and setting them up properly is available from the OEM as well.

787's pretty much my favorite for many reasons.

951's are ok but require more knowledge of their inherent failures.
Counterbalance shafts do not like to stay inside the cases. Rods like to knock holes in the cases. Generally more destructive when they fail.
However if you build it right and keep up the maintenance they are great.
Buying one that you don't know the history of should leave a lump in your throat.



Also, now that you've rebuilt that engine. What about the injectors?
Generally people try to replace them before failure occurs. I think they were $70 each from one post I read. I'm not the RFI expert, I just have seen quite a few post's where they went bad and caused a top end melt down.
Also the filter inside the tank as part of the fuel pump isn't available but there is a part number floating around here for an automotive fuel pump I think and its the same part?

 

[ted-hurst]

Took your word and replaced the injectors, $75 each, didn't want to take a chance. Took it out Saturday and put 20 miles on it (about an hour ride). Ran up the Perdido River and every 5 miles I stopped and pulled the plugs and they looked good, varied rpm's up from 2000-5000.