1998 Speedster 787 Motor Piston Removal

[HighTrim]

All,

I had my 787 motor rebuilt at a shop when I bought it.

While starting it at the dock, the plastic threads that hold the rave valve up tore apart, and the rave valve bounced off of the piston, breaking the ring.

So, now I have to pull the jug to replace the ring, and check the damage to the piston.

I see the 2 exhaust bolts I need to remove. It is the jug closest to the rear of the boat that needs to come out. The bottom bolt looks like it will be tight with the carb there, does the carb HAVE to come off to do this?

Secondly, anything I MUST replace while Im in there? Would the gasket still be ok, or does it need changing?

Appreciate any advice, have never done one before.

 

[HighTrim]

Do I follow torque specs for say the SPX here?

http://www.seadoosource.com/images/TorqueEngine1998.jpg

 

[Danosll]

All,

I had my 787 motor rebuilt at a shop when I bought it.

While starting it at the dock, the plastic threads that hold the rave valve up tore apart, and the rave valve bounced off of the piston, breaking the ring.

having broken a lot of rave valves myself . i can tell you by experience that unless the valve broke below the shaft on the guillotine part. and you have a std. or .25 over bore the valve should not have hit the piston. i suspect that when your motor was rebuilt the shop may have gone over the first oversize and at that point the rave valve clearance to piston has to be looked at.

 

[Danosll]

All,



I see the 2 exhaust bolts I need to remove. It is the jug closest to the rear of the boat that needs to come out. The bottom bolt looks like it will be tight with the carb there, does the carb HAVE to come off to do this?

Secondly, anything I MUST replace while Im in there? Would the gasket still be ok, or does it need changing?

Appreciate any advice, have never done one before.

as you can see in pic there are four bolts holding manifold to cyl. so you should either remove carbs . or both cyls at same time. . and yes change gasket.gasket surfaces have to be spotless.. if yours is oem count holes between cyls to determine the correct thickness you will need.

 

[Danosll]

if yours is oem count holes between cyls to determine the correct thickness you will need
some aftermarket as well

 

[HighTrim]

A ton of great info thanks Danosll!

 

[HighTrim]

I asked the shop, he only went 1 over from standard, so he said that does not require trimming of rave.

Looks to me like the plastic threads just rotted out. What luck!

 

[Danosll]

if piston, valve, and cyl, are within spec. the shoulder of the rave valve makes it impossible for valve to touch piston View attachment IMG_20150802_135413.jpg this is a picture of my worn cyl. if yours is worn like this it could also be an area of concern

 

[HighTrim]

Well I loosened the exhaust, then pulled off both jugs at the same time. Bad news.

Both pistons on the rave valve side are scratched very badly! The rings are surprisingly ok, or so they seem. Motor still seems locked up, I would assume I should be able to rotate crank like this no by pushing or pulling on pistons? They wont budge.

Even the piston that had the intact rave valve was all scratched up. Pistons were in bore correct. 025 on them. Only 1 over, so the rave valves should not have needed trimming?

Im at a loss here.

 

[Danosll]

can you verify that the pistons actually touched the rave valve? is there any aluminum transfer from the piston to the valve.?
could be more along the lines of an oil starvation issue. which would have heated up the cyls enough to melt the plastic rave piston or seize the valve in the housing. at .25 over the valve wont hit the piston , as long as both the valve and the bore the guillotine it slides in is to spec.if you can a bunch of pictures include the spark plugs

 

[HighTrim]

Ok will do. The head on one side was terribly pitted as well! The cylinder where the rave valve broke.