787 maximum bore limits

[salmonkiller01]

I need to get my 787 engine bored due to wall scoring. I noticed in the seadoo manual the maximum bore i can go is 82.25, although I can get aftermarket pistons all the way to 1.25 over stock(82.00). Has anyone gone over the maximum specified bore limits with any success?? I am hoping not to re-sleeve but may need to go to 82.50 for my bore.
Any input is appreciated.

 

[Dennis]

Bored

I've had 787 cylinders bored as much as .060 (1.5 mm) over stock with no ill effects. I do open the low and high speed needles 1/4 turn more on the carbs. I'm not sure if it's necessary to do that or not but it makes me feel better LOL. Keep in mind all I use in my rebuilds are PRO X pistons.
Good Luck, DAWG

 

[nswillin]

Rave

Don't forget about the RAVE valves. If you go over the recommended over size in the manual you'll have to rework the RAVE valves so the new bigger pistons do not hit them.

 

[salmonkiller01]

Thanks for the info, i will definetly have the raves done and will try the jet adjustments. I am going with the wiseco pistons which should be comparable to pro-x, I think!!!

 

[Chester]

If I were you, I'd use the Pro-X pistons instead of Wiseco.
salmonkiller01, what's your location?

Chester

 

[salmonkiller01]

I am in Bc Canada, arent the wiseco forged pistons stronger than cast pistons? or are pro-x pistons forged?
Plus the machine shop doing the boring only has wiseco for 2-strokes.

 

[salmonkiller01]

So I started reading about pistons, and now I am confused on which ones to get, cast or forged. I just want something that will hold up and thought the forged were better but now I am not sure. I don't want to start a debate but was wondering if the wiseco are a goood way to go?

 

[Chester]

You're better off to get the Pro-X. They are way more durable for recreational use. What city do you live in? Who is doing the machining for you? I can get the Pro-X pistons for you or even tell you where to buy them if you are in the lower mainland (same price either way).

Chester

 

[salmonkiller01]

well, I ended up getting the wiseco pistons. I got a really good deal on a top end kit, $180. The machine shop in my area(campbell river) recomended the wiseco so hopefully they work out well. I did read to warm up my seadoo before opening it right up with the forged pistons.

 

[nswillin]

Are you talking about normal use? Maybe so, but, if your talking about after your rebuild you must break the engine in properly, forged pistons or not, or it will fail again very soon.

 

[salmonkiller01]

I know about the break in period, but I read lots of info about letting engines with wiseco pistons warm up to operating temp before going full throttle. It seems that the forged pistons warm up and expand quicker than the jugs and then the piston seizes. I don't really know, but I just wanna get my seadoo running again without breaking the bank.lol

 

[12nvy]

I know here in OZ we call them siezco pistons. Pro-X or even WSM platinum
uke:

 

[salmonkiller01]

I am hoping that getting jugs bored properly will make it last. My engine problem arise from the previouse owner getting the engine rebuilt and the pistons put in backwards. Rave caught seperating ring and wammo, broken piston.

I need to replace my head pipe off the exhaust and was wondering how the aftermarket stuff compares, I am looking at an R&D half pipe or factory pipe spec 1. Will they shorten the engine life, I should mention that I am a recreational seadoo rider, just take it to play, wave jumping that sort of stuff.

 

[richardpr]

sorry to revive an old thread but how do you work the rave valve when you go oversize?

 

[Spimothy Leary]

option B.
get a cheap pair of borable cyl's , they should run less than $25 each.
then you won't have to go so big.

 

[richardpr]

I am only going .5mm over

 

[Spimothy Leary]

I am only going .5mm over

you'll still have to file down the rave so plan on doing that.

 

[WhiskeyD]

sorry to revive an old thread but how do you work the rave valve when you go oversize?

You just have to shave them down a little so they dont catch the piston's rings

 

[CReynoldsMIZ]

Here is what I did.

Take the old piston, wrap a piece of fairly gritty sandpaper around it, then take the leading contour of the rave valve and shave it down, you wouldnt believe it but it will file it down pretty fast.

Then, when you still have the head off of the motor, put the rave valve back down the slot and manually turn over then engine and watch when the passes by the valve if the two touch. File down until there is about .020" of clearance between the edge of the piston to the rave valve, a curved feeler gauge will help you there. It really seems scary but isnt that bad...

 

[richardpr]

Tomorrow it's off to the machine shop. Received the pro x pistons today.

 

[Jetskigoodies]

They should be able to shave the rave for you. I just sent out another top end to full bore. It is $20 extra for them to shave the raves for you.

 

[bell99man]

From what I've seen on here, when Chester speaks, LISTEN! Sorry, thought I'd throw that out there even though his part was a few years back.