kens986

yesterday I went to pick up a sxr800 for my daughter which was represented as having a stock motor. the owner then told us he only had the ski for 2 months prior to selling. checking the compression the ski has 225 psi. What parts or combination would produce that kind of compression. Milled head, thinner head gasket, high compression pistons? We were really looking for a stock ski to run pump gas. It's not a problem to have a modified ski but wold like to know something about it. we have no experience with the sxr800 product. Used to ride js550s when dinosaurs roamed the earth.
Ideas?
thanks,
ken

topbloke

wow 225 psi that is high not to sure what its got to be. to get that compresion it must of been worked but i dont no what. may be pistions head or some one poured oil down the head to seal the rings so he can sell it. fire it up and warm engine do another test but use a different gauge
it cought me out a while ago i presure checked my 900 zxi and read 80 psi i rebiult the engine from bottom to top added .5 over size pistons did another check and still reading 80 psi took it to the shop used there comp gauge and said 128 psi

kens986

I didn't suspect the guage was an issue as it's a snap on gauge and the guy takes really good care of his stuff and the readings I did on our sea doos came out spot on. Since I've never ridden an 800 before I have no comparison on how it should feel power wise but weather the gauge is wrong or right this boat is fast. I haven't ridden a stand up for a good 10 years and used to ride a nicely modified 550. I couldn't believe how different stand ups are now. Wow! Since then we've run a few tanks of gas through the ski with no problems. We'll try again next time the ski comes out, I think the ski is put away for a few months for now. Only problem is now we need to run race gas in the machine. We usually have race gas around as my son needs it for his motorcycle but the $10 a gal sure has a sting.

topbloke

higher compresion normally needs better octane fuel and at wot for long periods puts more stress on bottom end ie crank rods bearings ... but i would still try once with another gauge. even though its a snap on gauge your only paying for the brand name {SNAP OFF}
ive been a diesel meckanic for over 17 years {working with road trains } i have alot of snap on tools and they do have their faults { AND OVER PRICED ] or over rated .
but i would still double check.....i allways got told measure twice cut once.... but then again if your happy and its still running run the thing to the ground and have fun
im glad my 900 dont need race fuel the triples love to drink the gas i wish i could convert to diesel as as i could just take it out the work car

kens986

Well, I guess the reality is that I probably wouldn't spend the money to unmodify the engine. Just saying I would have preferred to get a stock engine. I'll spend the extra money to run the expensive gas to lengthen the life of the engine as is and probably retest the compression after we've run a few more tanks of gas. that's a good point that someone could have put oil in the engine to up the compression. I wonder how many minutes that would last before it burns out. I'll keep that in mind. Next test will show.

topbloke

when i winterize my ski or even my boat engine i allways pour some oil down the pistons and crank it over with no leads atached to lube the top end as it will be sitting for long periods specially the boat ive not had it out for over a year now maybe even 14 months or so.... the ski is different i do allot of 4wd and beach work so the jetski comes in handy.
i can tell you that when starting my jetski with oil poured down the pots it starts up normal as long as i prime the fuel. it will idle perfect and very little smoke but if you go to snap the throttle its as if the engine took on a bad habit it will smoke 20 cigeretts a day LOL but after 3 to 4 min it will burn off..... but normally when some one buys a used ski its normally a quick start up an shut off on their drive way
to be honest sounds like you got a good deal. even putting oil down the pots will only raise the compresion around 20 to 25 psi