Does this look like too big of a gap on my old to compression piston ring?

enter image description here

It measures more than 0.04" (I stacked a 0.02 and a 0.021 feeler gauges together) but I could not find a specification for an acceptable range in my Haynes manual for my Toyota Tacoma v6 2007. By searching the web, I found that it should be around 0.004" per inch of bore diameter, which in my case is 3.6", so 3.6 x 0.004 = 0.0144". So I am about three times that much, assuming that threshold is correct.

Q1: Does this explain why my pistons were leaking almost 100% of air pumped in?

Q2: How did the gap widen so much? It started leaking (losing compression) only after moisture/ice got into the cylinders when I had the heads off last winter for a valve grinding job.

RELATED: Likelihood of every piston ring corroding the same rate

  • How did you set the rings square in the bore? Aug 14, 2022 at 19:26
  • 1
    I put the ring in manually, they pushed it down with an upside down piston to balance it
    – amphibient
    Aug 14, 2022 at 19:28

1 Answer 1


The best way to know the end gap clearance is to consult a service manual for your vehicle. But the rule-of-thumb is 0.004 x the bore diameter in inches.

You're way over that and this is a problem.

  1. Check your piston bore to make sure it's within specs.
  2. It's quite possible that your ring is damaged from the earlier event with water/ice.
  • do you think it's possible that the bore somehow expanded?
    – amphibient
    Aug 15, 2022 at 0:18
  • @amphibient - Expanded? No. Bores are very stable until they become worn. In the image there is a ring ridge (circle around the bore near the top of the cylinder). This indicates there is cylinder wear. More than likely, it's a combination of slight cylinder wear and greater ring wear. Aug 15, 2022 at 9:42
  • @Paulster2 so you think replacing the rings should take care of most of the leak?
    – amphibient
    Aug 15, 2022 at 20:38

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