Piston ring gap spacing

Sep 13, 2006 4 Replies
J

What is the current thinking on ring gap spacing around the periphery of the piston?



I learnt the traditional method of 120° (for 3 rings), but am reconsidering. My Toyota Landcruiser book recommends 180°, i.e., gaps in first and third rings in line. Landcruisers routinely run 500,000 km between overhauls.



This makes sense to me when I think about it, giving a longer (more torturous) path for gas to escape down the piston.



On the other hand, there is a school of thought which claims that most blow-by is past (or behind) the rings, not via the gaps, so it doesn't make all that much difference. Do the rings auto-rotate in service?



Comments?



Jack (JW²)


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K

Rings do rotate in service, but its not a good idea to build an engine with all gaps in line though.

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A

Some rings are pegged to prevent rotation so someone thinks gap position is important.

Isn't it more to do with cylinder wear than blow-by? I mean, rings are not a complete circle, so the pressure on the cylinder wall would be more at the point of the gap. 3 in line would produce scoring...

The 180 spacing maybe because of the tendency for bores to wear oval.

What engine are you fitting the rings to?

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T

'thinks' or 'thought'? Didn't that practice go out with the ark? Or are there recent examples?

Some makers say to avoid having the gaps in line with the gudgeon pin. I generally aim for around 120 degree spacing, so there are at least two rings between any in-line gaps.

Cheers Tim

Dutton Dry-Dock Traditional & Modern canal craft repairs Vintage diesel engine service

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A

Definitely still current with piston ported two stroke engines but this is to do with issues of the ring ends getting caught up in the ports rather than blow by.

Andrew Heggie

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