Super Jet 1996 701 engine 1mm over OK?

[Zero Client]

I believe the engine in my 1996 SJ is all original. Its has got good compression thus far but am seriously thinking of doing a top-end to freshen it up. The cyl walls have slight scratches and theres a small area of aluminum piston deposits on one of the jug walls. The piston tops look fine - though a little lean for me. Images are before I changed jets by +5.

Images attached. First pic shows some aluminum on the cyl wall. Only one jug is like this.

Stock Bore/Stroke is 81/68, and would like to bring it to 82/68 which would make it 718cc. I'm not looking for anything really major as I'm still basically learning this ski which is currently way to fast for my ability. You could say I'm looknig for the best-easiest least expensive way out hopefully without having to resleeve cyls, modify block, change heads, or change out carbs. I'd buy some Pro-X pistons and gasket kits to suite and then get the cyls bored to accomodate the pistons. Can the stock sleeves and block handle this? What about my ADA Girdled head?

Thank you

 

[yamanube]

You will be fine going up to 82mm, unless you need to go a full 1mm overbore to get rid of the scratches or somehow got a good deal on +1mm pistons, there is no reason not to just go +.5mm.

 

[CRJ]

you can go to 83mm before you need to re-sleeve it. 82mm is fine.

 

[BruceSki]

Pretty sure thy make 81.25 pistons as well.

No reason to jump way up unless the cylinder wall scratches require it. If you think boring it out is good to get more power then you may as well go right to 83-84, or big bore sleeves and start at 85.

 

[Zero Client]

Naa not too interesting in making more power at this exact point in time though I may consider it if 2mm is a reliable option. I really didnt want to upgrade just to mess with other things like carbs, sleeves and such. Plus I dont know 100% what the crank of this motor looks like, nor do I know if the compression

 

[BruceSki]

Then I would suggest sending it to a reputable builder who knows these things. Sometimes the local machine shop isn't as good as you think.

Have them measure it and then bore and supply pistons. Put it back together yourself and run the balls off it.

 

[MADMAT]

Me personally....from what I read....I would mill the head and get to 190psi...bolt it back together and rip it. Spend money on a 13/16-3mm prop and a 85mm exit nozzle bore if you want...then when this engine blows (God only knows when that might be!!!)...go with some fresh Pro-X pistons and bearings and a mild bore/hone.... with no porting.....from jetmaniac....and a maniac crank if needed... That is just me maybe though...

 

[Zero Client]

No one commented on the pics of the jugs. They're not perfect but the engine does run very well. Maybe the 701 engine wasn't a dud like the newer Powervalve motors? I've only put about 5-6 hours on this ski and it's been a hoot, no reason other than to proceed with caution I guess?

 

[Jhucke]

Me personally....from what I read....I would mill the head and get to 190psi...bolt it back together and rip it. Spend money on a 13/16-3mm prop and a 85mm exit nozzle bore if you want...then when this engine blows (God only knows when that might be!!!)...go with some fresh Pro-X pistons and bearings and a mild bore/hone.... with no porting.....from jetmaniac....and a maniac crank if needed... That is just me maybe though...

Why -3mm cut back? never understood this.

 

[Fro Diesel]

Why -3mm cut back? never understood this.

It brings the prop closer to the pump vanes. Too much space between the prop and vanes will create lag. Not all props are just plug and play. If you don't want to mess with cutback, get a Hooker prop or 08+ sj prop.

 

[Jhucke]

It brings the prop closer to the pump vanes. Too much space between the prop and vanes will create lag. Not all props are just plug and play. If you don't want to mess with cutback, get a Hooker prop or 08+ sj prop.

I thought cutbacks took material off the prop blades themselves? Seems like that would be the opposite of what you want.

 

[yamanube]

I thought cutbacks took material off the prop blades themselves? Seems like that would be the opposite of what you want.

No, the hub is stepped on the side nearest the stator to keep the blades properly spaced from the stator veins. My understanding is that many manufacturers want to error on the safe side so this dimension is often larger than optimal.

Zero client, it never hurts to do preventative maintenance but if your motor feels/sounds healthy and has good compression there isn't much reason to rebuild (unless you know for a fact it has been neglected). Just running it till it blows up however is bad advice.

 

[JT_Freeride]

Here's some good advice. If it ain't broken don't fix it

 

[wanderer1]

Here's some good advice. If it ain't broken don't fix it

That advice will cost ya big money down the road. New rings periodically will increase life expectancy of your bore, crankseal inspection/ replacement can save you from a catastrophic failure, crank bearing inspection can save you from a catastrophic failure. A little time and some fresh gaskets can save you money in the long run imo

 

[OCD Solutions]

X2, the 701 in my first SN looked like that and it was till running strong. The only reason I tore into it was to find a lost reed petal and then I found the scores and a not so fresh crank. I rebuilt mine but I probably could have finished off the season on it. I had a huge toy budget and other skis to ride though.

 

[iangdesign]

If the scratches are light enough then just re-ring, and new gaskets, and hone it out. Don't spend more money then you need to especially of you are still learning on the ski. Take the money you would have spent on a top end, get the rings, gaskets, and hone, and shelve the rest for mods in the future.

 

[yamanube]

Spend the money you save on side exhaust.

 

[d_moss]

ask the machine shop to hone one and see what it did. takes two seconds to hone it. if it takes most the scratches out just do rings. if it doesnt bore it up. they prob wont charge you for a hone if you have to bore up .010

 

[JT_Freeride]

That advice will cost ya big money down the road. New rings periodically will increase life expectancy of your bore, crankseal inspection/ replacement can save you from a catastrophic failure, crank bearing inspection can save you from a catastrophic failure. A little time and some fresh gaskets can save you money in the long run imo

That saying doesn't apply to preventative maintenance. What I mean by it is if everything is within spec there is no need to change it.

 

[wanderer1]

I somewhat agree. We each have our own ideas on what preventive maintenance is. Mine is just replace certain parts at given intervals regardless. Yours may differ and that's kool. We both obviously differ on what/when to replace. Hope ya have fun and a good weekend.