Hello Everyone,
New to the forum and happy I joined. I am helping my little nephew with his atv. I am replacing the top end with new parts and was curious about a few things. What is the ring gap spec? I have read anywhere between .006 and .018. Should I reassemble piston and cylinder lubed up or dry? I have noticed articles on both and not sure which way to go. And last but not least what is the break in procedure when I get it running. I am trying not to be long winded on my first post
Thanks guys

 

Most of the little youth machines manuals just show maximum ring end gap on the 50 and 90 (0.30) which imo I don't see how they'd even run with that clearance. .008-.016 would be a good setting clearance. If you bought the complete piston/ cylinder kit,they're ready to go.Torque the head nuts to 14 foot pounds only.Manual just says no wide open throttle for the first hour or so. Just vary your speed.

 

Ok, so I put in the new cylinder and piston, I put the piston in with the arrow pointed to the exhaust, I torqued the head down to 14 ft pounds and I am only getting 60 psi and obviously it's not starting. When he got it back from the local dealer they said it was only 60 psi and probably needed a new top end which is what we bought. So am I missing something here?
I cleaned all the mating surfaces and removed completely old gasket material and I am at a loss here. I only have experience in 4 stroke engines,so again am I missing something?
Thanks guys

 

As long as the rings are installed right,letters/numbers facing up,ring ends against locating pins properly,should have way more compression than that.Possible you may have gotten a mismatched piston and cylinder kit.Sounds like you need to tear it down and check your work along with the piston to cylinder clearance.

 

"As long as the rings are installed right,letters/numbers facing up"

I did not notice any numbers or id marks. Only that the ends were not squared off but at angles

 

You have to look close at the ring ends. Should be a faint marked "R" or "N" indicating top side of ring. With these aftermarket kits who knows, may not be marked. If that is the case you have to look closely at the ring for the flared out/bevel of the ring. This is the scraper side that contacts the cylinder walls.Plus again check the bottom of the piston skirt to bottom of the cylinder as to what clearance it shows.

 

Thank you. I'm about to go back in soon

 

Well, I just ripped it apart again and the rings are installed correctly. I compared the new cylinder to the old and also noticed that the ports on the new one are also slightly smaller than the original. Is that crutial?

 

Port timing could possibly be altered with smaller ports,but still doesn't really explain the 60 psi compression you showed with a new cylinder and piston kit.I'd still check the clearance on the piston to cylinder. Plus you may even pull the exhaust pipe to see if it's plugged up.

 

Could you please explain the clearance between piston and cylinder. I dont quit understand.