RESTO Picked up my winter project 1996 XP

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Do you have some mics or dial calipers? I buy the WSM kits they come with a few gaskets.
 
The OEM gasket has nothing to do with 6 holes unless your engine came that way from the factory. Seadoo makes 0.3mm to 0.8mm gaskets and which one you need is determined by the clearance between the piston dome and cylinder head known as the "squish" clearance. To do it correctly you need to measure this clearance then choose the correct thickness gasket to get you within the spec clearance.

The aftermarket gasket companies only supply one or two thicknesses to save them money from making and stocking multiple thicknesses. You can probably get by with a 0.5-0.6mm gasket but this is not always the case.
To little squish clearance and you will melt down the piston from detonation and too much clearance an your engine will be a dog.

It is not like a Yamaha where there is only one gasket and it the same from any supplier.
 
The OEM gasket has nothing to do with 6 holes unless your engine came that way from the factory. Seadoo makes 0.3mm to 0.8mm gaskets and which one you need is determined by the clearance between the piston dome and cylinder head known as the "squish" clearance. To do it correctly you need to measure this clearance then choose the correct thickness gasket to get you within the spec clearance.

The aftermarket gasket companies only supply one or two thicknesses to save them money from making and stocking multiple thicknesses. You can probably get by with a 0.5-0.6mm gasket but this is not always the case.
To little squish clearance and you will melt down the piston from detonation and too much clearance an your engine will be a dog.

It is not like a Yamaha where there is only one gasket and it the same from any supplier.

So you're saying Seadoo potentially picked a different gasket thickness off the shelf when doing assembly? They check the squish because manufacturing tolerance varies that much? I'd think they'd all be the same gasket when rolling off a production line.

For the last 2 years+ I've yet to hear of anybody on this forum or the FB forum actually getting a TDC gauge and a burette to inject a liquid in the combustion chamber to measure the CC's. Is it really that necessary? Apparently not, since it's not widely known if people are having issues by not checking it.

But...I'd add, if anybody does an overbore, head milling, or aftermarket head mods, etc, maybe they should check it.
 
Yes the Rotax engines came with different base gasket sizes. Funny that they sold OEM reman engines without heads lol. As Miki said you can use a fatter base gasket and likely be in the safe zone but you might be leaving some HP on the table. The cast parts do vary some but the cut of the machines that make the mating surfaces has a lot to do with it. Where they are cut and how the pieces fit together messes with ignition timing too.

I have seen a few folks check the cc. It's usually done with the head upside down and the spark plugs all the way in.
 
As Miki said you can use a fatter base gasket and likely be in the safe zone but you might be leaving some HP on the table.

It would be interesting to know what CC volume works best with different overbore's and heads, not a lot of info out there to go on. A topic for another thread of course...
 
As Matt said yes, for some reason Rotax had enough manufacturing tolerance they had to measure each engine on the line and pick the correct gasket for that engine just like the service manual tells you to. I have no clue why they couldn’t manufacture them like the Japanese with more consistent tolerances and one gasket but that’s the way it is.

This is easy to do with solder but for some reason they switched to cc measurement once the 951 came out. It is much harder and almost impossible since once you fill the combustion chamber up it is already leaking past the ring grooves. Yes, ask me how I know that.
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Also note to self, don’t get brake cleaner on the burette.

Another good read is on Group K, BASE GASKET THICKNESS “John’s Story” Sea Doo High Performance Personal Watercraft Modification Updates

So to answer your question GGuillot yes you can just slap a .5 or .6mm gasket in and your ski will run and this is exactly what SBT does, one gasket for every engine. This will not however guarantee your engine will have the same power as it left the factory with or what it has the potential to make.
 
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Pulled the cylinders and gonna have to do a top end. I have no idea how the compression was so good and even. Both pistons had some scoring and one of the bottom rings was snapped in half and locked into the groove. I’ll take some pics of the scoring. Here’s some wash pics of the pistons. I have rebuilt the carbs and found that one side of the cylinder drain at the tee was clogged with sand. It was a ticking time bomb if I’d run it.
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The first piston is the one with the most scoring and the broken ring.
 
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I tell ya, the compression test doesn't tell everything. We've discussed this previously. The engine can be in failure mode and you can still get good/decent compression readings. I don't mind doing the top ends, I don't like doing the whole engine. :) Ski is gonna be even cooler when you are done. :D
 
The more I look with these skis, the more I find. Kinda like old airplanes. You are following so many bad mechanics and owners that just gas n go. My gasket kit came in for the 787 for my next XP resto. Engine is sitting there watching me walk by. LOL
 
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Here is the bad scored piston. I had ordered a gasket kit and orings. I have two donor engines that I thought I could just rob their cylinders, pistons and rings. Well they are OEM 82.5 marked on inside skirts of pistons. The pistons that are on my engine are WSM and no marking to determine size but they are larger and won’t fit into the donor cylinders. What size WSM Piston do I need to order to fit my current cylinders?
 
You really shouldn’t just slap pistons in a used cylinder.
You need to have a machine shop measure them with an actual bore gauge to see if they are within spec and aren’t out of round.
 
My original plan was to use the matches pistons to their matched original cylinders from the donor motors. They had no scoring or obvious issues. The aftermarket ones on my current motor are definitely larger and I thought I’d try to go back to that set up. No way I could mix or match any of the donor pistons/cylinders since too small. Yeah I’m kinda in a pickle at the moment.
 
I suggest Group K. They have been doing my cylinders for over 25 years now. They can supply pistons or once they measure the cylinders you can have pistons sent to them for a little less money and his turnaround is about a week.

Another good option is FullBoreonline but his turnaround time varies and can be quite long at times.

I don’t care for the quality of SBT or their parts.
 
Miki, Where would you suggest sending it? I’d like to have it done right and not have to look back.

I used Fullbore twice for cylinder top ends on my two 787 skis, Spring 2018 and Spring 2019, turn around was about 2-3 weeks. Excellent work, it'll be done right. This is a good time to send them in, but I'd call first and check.
 
Instead of doing a top end and not 100% sure of cranks condition, I bought a motor from Westside Powersports. I’m changing it over to premix and from everything I’ve read and watched im supposed to remove a nylon gear from rear of oil pump. Mine only has a steam linking the flywheel and oil pump. I’m assuming I just remove the stem, the oil pump and place my block off kit?
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There is no good reason to convert this to premix. The seadoo system is as reliable as it gets. The only thing you need to replace is the little 3/32" oil lines from the pump to the intake manifold.
 
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