HarleyTechTalk

Hey guys , Ive done about 5 rebuild and I'm finding sometimes the piston rings have rotated and ring gaps are almost lined up. Now I know that they well rotate a little but 180 degrees? I'm doing a 110 kit on my street glide and after 20,000 miles the rear compression rings gaps where almost perfectly lined up and that's from the factory meaning I  have been in the motor yet and I bought it new.  I checked the top ring cap and its 0.15  bottom is 0.23. Just was wondering if this is normal. Thanks Mike

They can always rotate. Check the roundness of the cylinder.

Rule of thumb for ring gaps is 4 thou per inch of bore.

Rings *can* rotate but shouldn't, if there are defects in piston / bore etc they will eventually tend to line up the gaps, two strokes and ported engines you can usually inch them around a bit without stripping the motor, our engines you don't even know until you strip the engine.

Quote from: jbexeter on December 23, 2016, 11:53:27 AM
Rule of thumb for ring gaps is 4 thou per inch of bore.

Rings *can* rotate but shouldn't, if there are defects in piston / bore etc they will eventually tend to line up the gaps, two strokes and ported engines you can usually inch them around a bit without stripping the motor, our engines you don't even know until you strip the engine.

2 stroke pistons have pin locators for the rings. They better NOT rotate........ever, in a 2 stroke or you are hanging a ring in a port!

Quote from: Ratman1640 on December 23, 2016, 08:39:46 AM
Hey guys , Ive done about 5 rebuild and I'm finding sometimes the piston rings have rotated and ring gaps are almost lined up. Now I know that they well rotate a little but 180 degrees? I'm doing a 110 kit on my street glide and after 20,000 miles the rear compression rings gaps where almost perfectly lined up and that's from the factory meaning I  have been in the motor yet and I bought it new.  I checked the top ring cap and its 0.15  bottom is 0.23. Just was wondering if this is normal. Thanks Mike

It is common to find all the piston ring gaps lined up on cylinder that has been run hot.

Quote from: qtrracer on December 23, 2016, 12:02:12 PM
]2 stroke pistons have pin locators for the rings. They better NOT rotate........ever, in a 2 stroke or you are hanging a ring in a port!

You may wish to tell Detroit, Villiers, lots of Yams, etc about that.

Rings rotate from directional blowby gasses acting on one of the end gap faces. The shorter distance in the ring gap initial stagger will have the most push effect on the ring below. This will try and line the gaps up. I know, somewhat confusing but I'm sure someone understands me.
Another reason is from an uneven bore. Ring pressure is not exactly even around the circle so they try to line up to the out of round condition.
Ron

Quote from: jbexeter on December 23, 2016, 12:34:19 PM

Quote from: qtrracer on December 23, 2016, 12:02:12 PM
]2 stroke pistons have pin locators for the rings. They better NOT rotate........ever, in a 2 stroke or you are hanging a ring in a port!

You may wish to tell Detroit, Villiers, lots of Yams, etc about that.

If it has open ports on the cylinder walls, it has to have the ring end located on an uninterrupted section of cylinder wall, yes? I have never taken one apart in 40 years that didn't have pins in the ring grooves to facillitate this.

All of the 2-Stroke Yams I rode/raced in the 70's had pin locators for the rings.

Quote from: qtrracer on December 23, 2016, 01:03:09 PM

Quote from: jbexeter on December 23, 2016, 12:34:19 PM

Quote from: qtrracer on December 23, 2016, 12:02:12 PM
]2 stroke pistons have pin locators for the rings. They better NOT rotate........ever, in a 2 stroke or you are hanging a ring in a port!

You may wish to tell Detroit, Villiers, lots of Yams, etc about that.

If it has open ports on the cylinder walls, it has to have the ring end located on an uninterrupted section of cylinder wall, yes? I have never taken one apart in 40 years that didn't have pins in the ring grooves to facillitate this.

An EMD is 2 stroke and has ports. The piston spins on a crown.

Quote from: rbabos on December 23, 2016, 12:38:24 PM
Rings rotate from directional blowby gasses acting on one of the end gap faces. The shorter distance in the ring gap initial stagger will have the most push effect on the ring below. This will try and line the gaps up. I know, somewhat confusing but I'm sure someone understands me.
Another reason is from an uneven bore. Ring pressure is not exactly even around the circle so they try to line up to the out of round condition.
Ron

This makes some sense as to why they line up in an otherwise good Harley engine that gets run too hot.
These cylinders are unstable at best because of their fin shape but once over heated they become ovals.

I always swam upstream when installing rings. I never liked the ring gap being on a thrust surface so put them 180* apart in line with the piston pin. Never a problem, but then I never got to check them for rotation on disassembly because they never failed. Consequently I still do it.  Ron's explanation makes sense. I always felt it was cross hatch angle, cylinder out of round and taper that contributed to ring rotation.

Somewhere in some proper engineering book 40 years ago I read that piston rings rotate at 1,000th of the rpm, might have been 100th, it was a long time ago.

I've never known a 2-stroke that doesn't have the rings pinned to stop rotatation.

Degree of cross-hatch plays into it. 
John

I understand what you guys are saying and even Ron's post, but with the gaps lined up would you not loose some compression and have blow by. my buddies and I where talking last night about it and one buddy brought up the cross hatching just like jsachs1 said.  I did a top end rebuild for a customer that had a 82 roadster that had oil coming out of the front drag pipe and when I got into I found the rings where lined up and the ring gap was 125 thou !!! come to find out the cylinders and pistons were 30 thou over after I checked the piston and bore,the last guy that rebuilt it which was a year earlier must have put stock rings in it or the wrong rings. after I finished it the compression was good and I had a happy customer. 

Quote from: Ratman1640 on December 23, 2016, 04:21:45 PM
I understand what you guys are saying and even Ron's post, but with the gaps lined up would you not loose some compression and have blow by. my buddies and I where talking last night about it and one buddy brought up the cross hatching just like jsachs1 said.  I did a top end rebuild for a customer that had a 82 roadster that had oil coming out of the front drag pipe and when I got into I found the rings where lined up and the ring gap was 125 thou !!! come to find out the cylinders and pistons were 30 thou over after I checked the piston and bore,the last guy that rebuilt it which was a year earlier must have put stock rings in it or the wrong rings. after I finished it the compression was good and I had a happy customer.

The rings in a healthy engine will all turn the same speed so if the gaps are spaced to begin with they will still be spaced at 100 thousand miles. It is the properly spaced rings that become perfectly aligned during operation that are a sign of trouble.

Quote from: 1FSTRK on December 23, 2016, 04:35:15 PM

Quote from: Ratman1640 on December 23, 2016, 04:21:45 PM
I understand what you guys are saying and even Ron's post, but with the gaps lined up would you not loose some compression and have blow by. my buddies and I where talking last night about it and one buddy brought up the cross hatching just like jsachs1 said.  I did a top end rebuild for a customer that had a 82 roadster that had oil coming out of the front drag pipe and when I got into I found the rings where lined up and the ring gap was 125 thou !!! come to find out the cylinders and pistons were 30 thou over after I checked the piston and bore,the last guy that rebuilt it which was a year earlier must have put stock rings in it or the wrong rings. after I finished it the compression was good and I had a happy customer.

The rings in a healthy engine will all turn the same speed so if the gaps are spaced to begin with they will still be spaced at 100 thousand miles. It is the properly spaced rings that become perfectly aligned during operation that are a sign of trouble.

How do you know that?

I owned a 99 Dyna with a 107 all bore motor built by Hot Shot Motorworks.  I'm the second owner and the work was done on the bike before I purchased it.  The bike was a monster and would lift the wheel pretty easily, even with a lardo like me in the seat.  Started smoking a bit so when winter hit pulled the top end down and found the rings all lined up on both cylinders.  The cylinders had no uneven wear patterns so called the builder and asked his opinion.  The first words out of his mouth were have you been using synthetic oil which was a yes.  Told me you can't use synthetic oil in this motor or that will happen every time.     Honed and reringed and used regular oil and worked fine till I sold the bike that year.  Brother rode it for two years and sold it and it was still working fine.

Quote from: Snowyone on December 24, 2016, 08:11:15 AM
I owned a 99 Dyna with a 107 all bore motor built by Hot Shot Motorworks.  I'm the second owner and the work was done on the bike before I purchased it.  The bike was a monster and would lift the wheel pretty easily, even with a lardo like me in the seat.  Started smoking a bit so when winter hit pulled the top end down and found the rings all lined up on both cylinders.  The cylinders had no uneven wear patterns so called the builder and asked his opinion.  The first words out of his mouth were have you been using synthetic oil which was a yes.  Told me you can't use synthetic oil in this motor or that will happen every time.     Honed and reringed and used regular oil and worked fine till I sold the bike that year.  Brother rode it for two years and sold it and it was still working fine.

In that case there would be a lot of HD engines with rings lined up and a nice line worn in the cyls from the compression ring gaps always remaining lined up. Just about all the real reasons rings rotate have been covered but the oil one is a bit far fetched. No, it's really really out to lunch.
Ron

Yep
The cross hatch is a helix.
Look at the stripe on ring 2 for a better idea of what may be an out of round condition.

  The first words out of his mouth were have you been using synthetic oil which was a yes.  Told me you can't use synthetic oil in this motor or that will happen every time.    
[/quote] I wonder if he had a 2nd excuse if you had said no to the syn oil?

Quote from: HD Street Performance on December 24, 2016, 09:14:44 AM
Yep
The cross hatch is a helix.
Look at the stripe on ring 2 for a better idea of what may be an out of round condition.

You raise a very important point. Cross hatch needs to be uniform around the bore and the correct angle. This tends to cancel out oil channeling variations around the bore. Channeling this oil at an angle, this angular direction of moving fluid acts against the ring that can promote rotation if one area of the hatch is moving more oil then the other side. Rotation is not a bad thing unless it stops and the rings stay lined up at the gaps. That is almost always from the bore distortion. It's not unusual for rings to line up for brief periods and then move along to another positon. When they stop and will not move from that point , then there's a problem. I've always said if you do a leakdown test and it's marginal with most air entering the case , put another hour on the engine and retest, exactly for this occaisional gap line up deal.
Ron

Oh,  now I understand how a 2 stroke without ring gap locating pins keep from rotating....ya gotta stay away from that synthetic oil.   

Also make sure to use an oil that will facilitate equal rotation of all rings in a cylinder....should state that on the back of the bottle,  right?

Quote from: 04 SE DEUCE on December 24, 2016, 10:16:59 AM
Oh,  now I understand how a 2 stroke without ring gap locating pins keep from rotating....ya gotta stay away from that synthetic oil.   

Also make sure to use an oil that will facilitate equal rotation of all rings in a cylinder....should state that on the back of the bottle,  right?

Doesn't Liquid Moly do that?
Ron

Quote from: kd on December 23, 2016, 02:30:43 PM
I always swam upstream when installing rings. I never liked the ring gap being on a thrust surface so put them 180* apart in line with the piston pin. Never a problem, but then I never got to check them for rotation on disassembly because they never failed. Consequently I still do it.  Ron's explanation makes sense. I always felt it was cross hatch angle, cylinder out of round and taper that contributed to ring rotation.

2 nd that on gap placement.Been loading them like that for over 35 yrs with no issues!!