787 discussion: rave or piston backwards?

[1983]

Been sorting though parts, curious about this 787. The cylinder head has major pitting/detonation lean pitting. I can't remember if it's even mechanically possible to put rave valve in backwards but I know piston could potentially be installed in wrong direction.
Should stamped piston arrow be pointing towards intake or exhaust?

Engine spins fine by hand. No visual damage/scratches to cylinder walls that I can see. But mag cylinder rave blade port is no bueno

I think mag cylinder piston or rave was installed incorrectly during rebuild which cracked mag piston top ring land off.

Either piston in wrong or rave issue as rave blade contacts piston making a very fun noise.

 

[PGHMAN]

Rob - arrow should point towards the exhaust otherwise the open end of the piston will catch on the port.

Rob K

 

[Jetskigoodies]

He is right and the rave can be installed upside down, however they say what side is up on them.

 

[1983]

Well that dang arrow is pointed towards intake on the shiny new mag piston

And I just realized when I bought this engine it came with the factory service manual book. Guess they skipped that section on piston orientation.

If I get another piston and rings can rave port be cleaned, and cylinder/jug reused?

Rob

 

[1983]

 

[1983]

Also is 81.89 an overbore or factory size?



Thanks,
Rob

 

[Jetskigoodies]

That is factory std bore with oem pistons and on reusing, it depends how scarred the cylinder is. Maybe you got luck and the piston is just smoked, but my guess is the cylinder will need to be bored over. Hard to tell with the pictures. Run your finger nail around the walls, if it catches then it needs to be cleaned up.

 

[Ruskeyjdm]

Standard size

 

[1983]

Ok thanks guys.

This will def need new rave, I will check bore upon disassembly




Rob

 

[mikidymac]

On the 787 The intake and exhaust are on the same side so as long as the arrow is pointing to that side you are good to go. It does look like the piston either caught a ring or hit the rave valve. Rave could have been installed upside down or broken causing it to hit the piston or the rings could have been installed wrong. Too bad since they are factory pistons.

 

[racerxxx]

I can see some good rust on those bores and a few decent stripes. I see a bore job in your future.



If that top right is rust I don't think that will clean up too good. Use a ball hone to clean it up, do not use a 3 stone hone, those are BS these days. So much so, I threw mine out. You especially can't use them on cylinders with a chrome or nikasil bore (neither of which a Seadoo has). I just buy a ball hone for every bore size I need to do. http://www.brushresearch.com/brushes.php?c1=2 You will want the 89mm or 3.5", silicone carbide and I think I use 240 grit. I call them Dingle berry hones. Get the part# and look online, but I just order straight from them

 

[1983]

Ok, I will get some pics of bores when I get this beast on the bench. By which direction should arrow point I mean the purple tuned pipe side or intake - carb side...

on this engine the arrow is pointing right at rave...so arrow is in correct orientation, and they put rave in backwards...?

I will get a ball hone.

Rob

 

[racerxxx]

Yes that is correct, that is the intake side and exhaust side on a 787. Was the rave housing still assembled when you got it? That will tell you everything, provided you haven't disassembled it.

Sent from my SGH-T889 using Tapatalk

 

[1983]

Yep raves are still in. The mag cylinder makes awful noise when rotating crank when it hits rave valve blade.

Rob

Yes that is correct, that is the intake side and exhaust side on a 787. Was the rave housing still assembled when you got it? That will tell you everything, provided you haven't disassembled it.

Sent from my SGH-T889 using Tapatalk

 

[racerxxx]

So I just checked, if you install the rave guillotine upside down aka the wrong way. It's no where near the port, so that theory is out the window.

Installed the correct way

Installed the wrong way

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[1983]

Hmmm, so guess I need to get this apart one evening after work.

I'll throw one more guess out, rave shaft broke dropping rave into cylinder.

I'll update this thread with pix when I pull raves and jugs.

Rob

 

[racerxxx]

Could be, pop the rave housing and you'll find out in about 3 seconds.

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[Seadoodoc]

Check your rotary valve for damage! Almost sounds like rings didnt get seated in correctly.