How to correctly install rings onto piston, 4 stroke.

[Not2Sure]

Ive just recieved a new 270cc Cylinder Works big bore kit for a KX250F i am rebuilding and am looking for a few opinions on how to correctly install the new rings onto the piston. I am an Automotive Mechanic so i have rebuilt my fair share of car engines as well as 2 stroke dirt bike engines but this is my first 4 stroke mx dirt bike engine and i am interested in a little feed back on how some of you guys go about it.

The piston has no pins to locate the rings so obviously when i put the rings on they can spin around so my first question is where in conjuction to the front and back of the piston should the ring gap be on the compression ring and oil rings and secondly should the oil rings gaps be staggered and away from where the spring ends meet?. I know most people when doing a rebuild using a piston with no ring locating pins just throw the rings on any old where and slap it together but i thought i'd better hear a few of you guys methods to getting a rebuild on one of these new 4 strokes done successfully, especially after spending $1250 on a new crank, rod, cylinder kit and head.

[ubu]

Do what your manual tells you, if it does. My Yamaha manual had a specific placement of the end gaps. I can't remember exactly what it was so I won't speculate right now.

The fact they could spin was nerve wracking. I got the rings in place and put the piston in the cylinder with enough access to the wrist pin bore, then installed it on the crank and slid the cylinder down.

[intensem1rider]

The rings rotate at about 1rpm for every 1000 rpm of the engine. The main concern with 4 stroke pistons is that the proper rings are in the proper ring lands, and they are gapped correctly.

The reason why 2 stroke pistons are pinned is to prevent the rings from spinning and a end gap catching a port. 4 strokes do not have ports so they do not need to be pinned. If they did not rotate you would have no wear where the ring end gaps are,you would have vertical lines where the gaps are in the cylinder.

[ikis86]

i always set the ring gaps north south east west depending on how many rings you have, being careful not to have a gap in line with the wrist pin, which probably wont matter on your engine, just something i like to do. As for the spring gap i set it 180 degrees from the gap on the control ring. Your engine will almost certainly run fine if you just slap it together though, most important thing is getting the rings the right way up.

[Not2Sure]

Not sure which way up the rings go, pretty sure the oil rings go any way up but the compression ring i am putting it writing side up.

[ikis86]

as a general rule writing to the top, i always have a close look at where the chamfered edge is though, very very rare, but sometimes mistakes get made so i've heard. your control rings should be symetrical

[Not2Sure]

Yeah ive looked closely at the compression ring and as far as im concerned it is also symetrical but i will just install it writing side up i think.

Do what your manual tells you, if it does. My Yamaha manual had a specific placement of the end gaps. I can't remember exactly what it was so I won't speculate right now.

The fact they could spin was nerve wracking. I got the rings in place and put the piston in the cylinder with enough access to the wrist pin bore, then installed it on the crank and slid the cylinder down.

If it was a genuine piston and cylinder i would refer to the manual but this is an after market piston (vertex) in an after market cylinder (Cylinder Works), and just to be helpful they do not supply instructions with the cylinder kit

[race250r]

Hey folks sorry to dredge up old topics.

I have a question about the orientation of the oil rings. In the manual is states that the oil ring openings should be 20-30 degrees on either side of the intake side of the piston (bottom oil ring to the left, top oil ring to the right). My question is can I place the openings WITHIN 20-30 degrees of the intake point or MUST I be at 20-30 degrees from center of intake side? Sorry if that is confusing. I am sure those of you who have replaced pistons have gone through this same process.

Thanks.

[nickdawg18]

My new wiseco came with very detailed instructions to where the gaps should be. I went by that. 4t btw.

[Jakeblues]

My new wiseco came with very detailed instructions to where the gaps should be. I went by that. 4t btw.

Hey you stole my answer!

[nickdawg18]

Hey you stole my answer!

Lol.

[Boyeeeeee]

Your full service answer guide. 

 

http://www.cylinder-works.com/TunersTips.aspx?ItemID=64&page=1

[Altune]

Weisco and your manual have different ways to line up the end gaps.

I am not sure if they are different due to the piston or they just have different ideas how they are supposed to be lined up.

 

make sure if there are any markings especially on the compression ring, they go marked side up.