Re-use old rings?

78 KZ750 twin
Should I re-use these rings?
So I bought some oversize pistons with rings, cylinders and head (from the same engine) from a reputable member of kzrider. Everything looks good upon visual inspection. The previous owner bored the cylinders, did a head job, and put new agftermarket pistons and rings in- he drove it 900 miles and disassembled it to part out the bike-- NOT due to any piston/ring/head problems....

Wouldn't it be better (and cheap) to put new rings in? Or is it more important to keep these rings with the cylinders they have been seating in for the last 900 miles? My conventional wisdom tells me brand new is better but I have also heard once rings and cylinders "seat" and run awhile you're better off to leave them working as a set.

Or does it really matter since 900 miles is not that much opportunity for them to wear anyway?

curious...

kz750twin:

Look at the wear pattern on the rings. If they are burnished and look like chrome, they have seated and must be replaced. If they still have the ground finish on part of the surface they might reseat when assembled. It's risky and the only time I did reuse rings they did not seat properly. Probably should get a new set. Sometimes going cheap ends up with more problems. Ride safe, Steve

Assuming you are installing the pistons and rings in the same cylinders they were removed from, then I wouldn't even think of replacing the rings, since they only have 900 miles on them.

steell wrote:

Assuming you are installing the pistons and rings in the same cylinders they were removed from, then I wouldn't even think of replacing the rings, since they only have 900 miles on them.

I think they should work if they are still on the pistons and you don't change them side to side. Just make sure to align the end gaps properly and you should be in business.

If you want to install new rings just for peace of mind, I can give you a source for new rings for $36 a set.

Ok
I will inspect them for burnish and take your advice

also-- I am not sure what "end gap" is on rings....The pistons and rings will mated with their respective cylinders so assuming I reinstall them I am not sure what end gap is...... pls explain

thanks
jim
750twin 1978

I don't have a manual in front of me to give you a measurement, but "end gap" is the measurement between the ends of the rings if you slide just the ring down into the cylinder or up through because it is generally easier if there is still a taper on the bottom of the cylinder.
Use the bare piston and rod to push the ring into the cylinder about half way so it will be straight in the bore. Use some oil while doing this, then measure the gap between the ends of the ring with a feeler gauge and compare it to the limits in your manual.
I hope this helps.
Ride safe.

You could also do this at several locations in the cylinder to check for any taper in the bore itself.

Reuse the rings they are still breaking in. they are like new.if u rering u must rehone.

jammor wrote:

Ok
I will inspect them for burnish and take your advice

also-- I am not sure what "end gap" is on rings.......... pls explain

thanks
jim
750twin 1978

You have to orient the position of the gaps in the rings correctly when you install them: The top and bottom ring gaps must face forward, and the gap on the middle ring must face to the rear.

I see there are a lot who would re use the rings, my fifty cents,, gas price increase, I would replace the rings and hone the cyls, its not that much money and then you know you should not have any problems with it

BSKZ650 wrote:

I see there are a lot who would re use the rings, my fifty cents,, gas price increase, I would replace the rings and hone the cyls, its not that much money and then you know you should not have any problems with it

You mean you wouldn't even check the bore diameter to make sure honing it again wouldn't push it past the service limit and force you into an over bore?

Every time you hone a bore you make it a little bit larger, not a lot, but it was a used standard bore to begin with, and it's already been honed once.

Run them, there should not be any issues.

they only have 900 miles on them! some of the guys on this board have 50,000+ likes on their rings...


Run them.

Hmmm... Ok, maybe it's just me...But it doesn't seem you have the proper measurement tools on hand, maybe I'm wrong so please excuse if I'm miss understanding.

Example: I don't have the bore caliper to accurately measure the cylinder inside diameter either...

Since you obviously have the top end apart and have your cylinder off, wouldn't it be just as easy to take your cylinder and pistons (w/rings attached) to a motorcycle machinist and have the cylinder measured & confirmed to specifications?

NOTE: Some of these would be hard to answer unless you knew this guy and the bikes history....

Same time, was the compression tested before hand and was it within specifications?

Were you blowing smoke prior to taking this apart?

Pistons charred/carbon/scared?

Lacking power?

Do you know the history of this bike... How old are these pistons and rings if known? I realize "He said 900 miles" but... For only 900 miles, they should almost look fairly new...

Maybe it's time for a new top end upgrade... These are all the questions you need to ask/research.

Ok, I'm done now....

If the bike was running fine before you took it apart then you should be ok. Granted no guarantee's here but if compression was good, now excessive ringing noise (broken ring), they rotate on the piston, they're not burnt to a crisp or show signs of FUBAR then you should be ok.

OMR