Off topic but kinda stumpimg me

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2mike18
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#1 Post by 2mike18 »

I just finished putting a new top end on a 99 arctic cat zr600 two-stroke snowmobile and the compression reads almost exactly the same as before I replaced the pistons, rings, and honed the cylinders. I am getting 65lbs compression and the sled starts on the 2 pull like the efi motor is supposed to. after the first start only one pull is needed to restart it. when running it revs good and idles fine with no out of place nioses or sounds. The cylinders look good and mic within spec all new gasket, rings, pistons, oil and fuel so have I missed anything?? I also used another compression gage just incase mine was broken but that one had the same readings. as you can imagine i'm a little frustrated and hope this makes sense and someone points out a minor detail I may have missed. wacko.gif

Dude54758
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#2 Post by Dude54758 »

QUOTE (darkknight @ Oct 15 2011, 11:11 PM) <{POST_SNAPBACK}>
I just finished putting a new top end on a 99 arctic cat zr600 two-stroke snowmobile and the compression reads almost exactly the same as before I replaced the pistons, rings, and honed the cylinders. I am getting 65lbs compression and the sled starts on the 2 pull like the efi motor is supposed to. after the first start only one pull is needed to restart it. when running it revs good and idles fine with no out of place nioses or sounds. The cylinders look good and mic within spec all new gasket, rings, pistons, oil and fuel so have I missed anything?? I also used another compression gage just incase mine was broken but that one had the same readings. as you can imagine i'm a little frustrated and hope this makes sense and someone points out a minor detail I may have missed. wacko.gif

Gasket Thickness same on new motor between jug and case? if you raised it compression will lower? Give it time to seat in as well. After about 2 hours it will be higher. If you really had 65psi of comp it wouldnt start. If it did it would run like $hit and surely not fire over right away. Did you do a leak down test on it? heads sealing plug sealing drop a little oil in the cylinder does it go up?

Me thinks your gauge is twacked. Both of them.

Dude54758
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#3 Post by Dude54758 »

wink.gif

rayspeed
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#4 Post by rayspeed »

Are you holding the throttle wide open while pulling? Not everybody knows to do that but on a two stroke it can really make a difference.

2mike18
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#5 Post by 2mike18 »

QUOTE (Dude54758 @ Oct 15 2011, 08:33 PM) <{POST_SNAPBACK}>
Gasket Thickness same on new motor between jug and case? if you raised it compression will lower? Give it time to seat in as well. After about 2 hours it will be higher. If you really had 65psi of comp it wouldnt start. If it did it would run like $hit and surely not fire over right away. Did you do a leak down test on it? heads sealing plug sealing drop a little oil in the cylinder does it go up?

Me thinks your gauge is twacked. Both of them.


Upon thinking (dwelling) on it last night I realized I changed test gauges but not the hose that has the schrader valve in it. So hopefully thats the issue. I didnt measure gasket thickness but eyeballing things while assembling they seemed the same. I also figured a little more run time might help. I just finished assembling it so there was a lot of oil in the cylinders I put it on the pistons, rings, skirts and then oiled the cylinder walls so everything would go together smoothly as it did, then before I put the head on I put oil on top of the pistons and pulled it over slowly. I didnt want a dry start up. so adding a drop of oil or 2 might not change much. the leak down test is a option and that one might be in the future. yeah 65psi shouldnt run at all, so I believe my problem isnt the engine. thanks for the suggestions. I kinda feel foolish cause I rebuilt the motor because the compression read low and now rebuilt it reads exactly the same mad.gif leading me to believe bad test tool. I just bought the sled and it ran fine only did comp test out of couriosity.

2mike18
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Joined: Wed Mar 10, 2021 10:41 pm

#6 Post by 2mike18 »

For anyone wondering the outcome. Yup 2 bad compression gauges. actually the valve in each hose. one doesnt hold pressure and the other not sure but at 60psi it must collapse or something?? I borrowed another gauge and all, ran a test again and 130psi is ths outcome YAY!!!!

cannondale27
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#7 Post by cannondale27 »

Aw man that sucks.Who would have thought.

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