Topic: How / What to measure piston end ring gap

[Blasbo]

I'm not sure exactly what is going on in this picture. It's from page 7-6 of the Official Honda Shop Manual CB750 K8 CB750 F3. Do you take the rings off the cylinder, put them in the sleeve and measure the gap between the ends of the ring?
The text with the picture says:
Measure piston ring end gap.
Place the ring in the skirt of the cylinder bore and measure the gap at the end of the ring.

[Gordon]

Do you take the rings off the piston, put them in the sleeve and measure the gap between the ends of the ring?

Yes.

[andrewk]

Measuring ring gap properly is important.  The manual gives good instructions on that, just make sure you put the ring square in the bore to get accurate measurements.  Some people use the piston (if it's off the rod) for this, I have a locking depth gauge that I use.  Measuring the end gap in several different places in the bore will help determine (approximate) if there is any significant taper or barrel-shaping in the bore.

Also, as a side note, and with knowing nothing about the context of the question, if you're checking ring end gap on your old rings, I would recommend replacing the rings (and deglazing the bores) no matter what- it's cheap insurance.

[Ernest T]

I haven't rebuilt a lot of engines and the ones I've rebuilt all had to have new rings installed so the ring end gaps were all within specs when I installed them.  The 400 I'm working on now, my first four cylinder, was running well, but the cam tensioner was buggered. I had to strip it down to replace it.  I measured the bores and the ring end gap and the bores were still well within standard as was the end gap.  The machine shop measured the bores and confirmed my measurements, but recommended a hone.  After the hone, the bores were still in spec for standard rings, but the ring end gap was now out of spec so I ordered new rings.  My machinist, who has a lot of experience, said you can hone and old rings will reseat as long as they are within specs when you start. 

[CycleRanger]

If your ring gap looks like this replace them!