Piston Rings By prairieman (Read 383 times)

[prairieman]

Hi new to the page it’s not actually in a scooter it’s in a snowmobile but it’s a cn 250 engine. I ordered a complete top end kit from ebay assembled and have some issues first off I was uncertain on the location of the rings on the piston Obviously the oil rings go on the bottom in the manual it says the ring marked “N” goes on top the rings that came were marked “M1” and “M2” so I assumed “M1” would be the top ring and “M2” the second ring from the top took a guess not sure that’s correct. 2nd issue is I believe some how I’m off on timing first off I thought the — mark was tdc lined up the cam as per manual rotated manually to make sure no contact set valves as per manual and seemed I had little to no compression so I messed with the valve adjustment backed them off and seemed to gain some compression and more if I backed them off past the bolt hole for the hold down so I figured valve timing was off downloaded a better manual and showed the timing mark on the flywheel more clear and that the marker goes between the “ “ marks but still seems as though timing is not correct.

[cyborg]

Even a tooth or two off on the cam chain will pretty much throw everything off ,,,I'd be double checking all cam /crank position and are the ring gaps staggered?

[prairieman]

Ring gaps are clocked all to 120 deg. I’m almost positive it’s a valve timing issue for a few reasons (1) with the rocker cover off the valves remain closed and turning it over when the piston comes up you can feel it build compression (2) if I back the valves off all the way lock bolts removed it almost offers to start problem is the there are a few different markings on the flywheel at tdc and when the piston reaches tdc the crank rotates a few deg before it comes of tdc and the manual is as clear as mud so I’ve been trying different marks first I thought the — was a T but no go then I tried between the “ “ and no go

[prairieman]

[img src="i289.photobucket.com/albums/ll227/daddy-dc/CACC9FA7-8314-4236-89D9-42E12ACAE65F.jpg" src="http://" alt=" "] which is the mark I need to line up with the notch in the inspection hole The manual says T but I don’t see a T picture from another manual I downloaded shows a mark but I can’t seem to get it 

[prairieman]

which is the mark I need to line up with the notch in the inspection hole The manual says T but I don’t see a T picture from another manual I downloaded shows a mark but I can’t seem to get it seems no matter which mark I try won’t fire and I only get compression if I let the valve adjusters fall past the min adjustment with the lock bolts out what am I missing 

[cyborg]

I think the cam is 180* out

[prairieman]

I’m not sure how though I’ve done it over and over as per the book and the pictures not sure what I’m missing

[cyborg]

Do it mechanically,,,,pull the plug put a long straw in the plug hole rotate the engine by hand watching the intake rocker when the intake valve gets opened the piston should be on the down stroke,,,keep rotating till the valve closes and the piston should be on the upstroke,,,when it gets to the top (tdc) the rocker follower end should be on the base circle of the cam,,,when you get to that point check all the markings,,,if all is kosher then set rocker / valve clearances and you should be good to go,,,