Piston Ring Gaps

[peterdjon]

http://www.diagnosticengineers.org/jour ... 20Gaps.php

I came across this article recently and would be interested to hear what the forum thinks of the conclusions on staggering the gaps.

Peter

[les]

I'll stagger the rings and gap the rings as before, what's the harm. The piece suggests that a large ring gap is ok, it also says rings rotate but by rotating the gaps can like up. What happens then; ---- the gas goes straight through a large ring gap. So maybe the staggering is questionable but not a large gap. Well that's how I see it.

[panky]

Very interesting and I can see where he's coming from - blow-back is mainly caused by wear on the rings (and bores) and not through the ring gaps. The labyrinth explanation is good and I agree with the principal, we used to run big oxygen recips up to over 20 barg on labyrinth machines, not a ring in sight, and minimal blow-back. But as you say nothing wrong with staggering the gaps as it will make the labyrinth effect more efficient. I guess the point of the article is not to get too hung up if the gaps are a bit bigger than you would like on new rings on a re-bored engine.

[philthehill]

An interesting article but contains nothing conclusive to change my mind as regards the piston ring fitted gaps (details of the gaps for the various piston rings can be found in the BMC Minor wksp man General Data section) and as regards staggering the gaps - BMC Section A.A.11. states that piston ring gaps should be set at 180 degrees from each other.

I will carry on doing what I always have done and that is to ensure that the fitted gap is as the piston ring manufacturer specifies and set the piston ring gaps at 180 degree from one another unless the piston ring manufacture specifies otherwise.

Where piston rings are stopped rotating by a peg in the groove - the peg in the main is fitted to stop the ring rotating on a split skirt piston as the piston ring can if not stopped from rotating catch on the edge of the skirt slit and jam which may result in the ring breaking.

An important point to note is that not all piston ring faces that rub against the cylinder wall are square to the faces that fit into the piston groove - the ring may taper towards the top. Most taper piston rings are marked with a 'T' to indicate TOP and must be fitted with the 'T' facing the top of the bore.
The taper allows the ring to scrape oil off the cylinder wall.

[peterdjon]

Thanks guys, your common sense replies confirm - keep doing things in the 'proper' time honoured way!