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Discussion Starter #1
.. Good morning gents and ladies ,here is my problem :
I am a pretty decent wrench and i took my mouth to full when i promised that i could get a good friends polaris to run ..
.. well i think i checked about all i can check and i am stumped .
And about to loose face !
Scenario:
The culprit is a '400 Sport' made in '96 or so ,to the best of my knowledge all stock .

What i have done so far:
1. Pulled the spark plug , stuck it on the end of the plug wire and grounded it .. hit the starter . result plenty of spark !!
2. Stuck my finger on the sparkplug hole and hit the starter ... Got compression !!
3. Pulled the flyweel and checked if the key is sheered or other funny stuff happened .. well couldnt find anything humerous .. iaw flyweelkey all looks good .. reassembled.
4. On a wild guess replaced CDI unit ( ep380 i think) .. still got spark still no go ..
5. removed breather sparyed gas in the throat while cranking ... not a pop not a thing !!!!!!!!!

So thats where i am at ... all one needs is fuel spark and compression and it should at least pop !!!!!!!!!!! or something !!!!!!!
Thanks for any input
Mark
 

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get a compession gauge , the old 2 strokes need around 100 psi to run, maybe reeds are broken in intake too
 

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x2 on Russ' suggestion, should be at least 100 psi but more in the 130 psi range to be good.
 

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To find out year model it should be a tag on the frame. Near the air box. It will start with the letter "w" followed by numbers. The 2 nummbers after the w is the year model. Compression needs to be above 115 psi. If not more than that you have a problem.
 

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Discussion Starter #6
get a compession gauge , the old 2 strokes need around 100 psi to run, maybe reeds are broken in intake too
Great idea didnt think to check how much compression ,just did the 'thumb on the plug hole thing' , should have done it while i had all the plastic off !


To find out year model it should be a tag on the frame. Near the air box. It will start with the letter "w" followed by numbers. The 2 nummbers after the w is the year model. Compression needs to be above 115 psi. If not more than that you have a problem.
I got the year part just cant remeber , have to start writing everything down getting old ;)

Thanks keep 'em coming i appreciate it , wont get to tearing into things again till after the holidays , however its nice to have something to go on !
 

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Discussion Starter #7
Well i had a few minutes yesterday and checked compression .. hmm i think 25 pounds is anyway you look at it not enough .. guess i gonna tear the beast down and see what went on .. thanks for the input !
 

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Hahaha thanks ... but i think it wont be all that bad .. will know more after i strip all that darn plastic off so i can actually get to the motor .. ( thats why i ride a chopper no plastic to remove for anything !!! :D )
 

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So i think i continue on this thread .. finally had some time to tear into this beast ..

And there it is ... in all its glory



Already a few plastic bits removed

And some more bits gone



First 'oh shit' moment as i looked into the header pipe



I dont think there should be antifreeze in the pipe !!!!!

OFF WITH HIS HEAD !!



There was the next UH-OH moment !!!



Well that explains the 25 ponds of compression !!!!

Ran a hohne through the bore ... and it doesnt look too bad .. pisten is roached cylinder appears good to go ..
( i cheated a bit on the pic thats actually hohning my shovel jugs was just too lazy to make anoyher pic you get the idea ! )



So we ordered a piston rings and a gasket set ... wont be in till wednesday next week ... i will update the thread as i go along ... if it bores let me know otherwise i keep going !!
 

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How do you know the cyl. wall isn't egg-shaped? Usually when there's a chunk missing out of the piston,it mean it got hot> Just don't want you to waste your money, on a pston and rings you can't use.
 

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I would think it needs bopresd and an oversize piston, needet mic out cylinder to tell, usually worn more towards bottom of cylinder
 

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How do you know the cyl. wall isn't egg-shaped? Usually when there's a chunk missing out of the piston,it mean it got hot> Just don't want you to waste your money, on a pston and rings you can't use.
We use a Sunnen hohne an egg-shaped cylinder would show with this procedure . and yes it got hot but the scars on the piston would indicate detonation , now considering the timing is pretty well fixed on this set-up general consenses here is that it was running very lean. also the chunk missing on the piston rim is located on the exhaust port further solidifying this theory.
Thanks for the input , a very valid point!


I would think it needs bopresd and an oversize piston, needet mic out cylinder to tell, usually worn more towards bottom of cylinder
Yes the cylinder is worn more on the bottom we pre-hohned to the point where it cleaned up and then measured , considering pistons available and clearance applied we will have to go to the largest (85 mm) oversized piston available .As soon as the new piston is here and we know the excat physical size we will hohne the cylinder to propper clearance . Slap it back together and see what happens .
Not sure what you mean by 'bopresd' please elaborate.
Thanks for the input

Mark
 
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