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Rough running engine

It is also my understanding that rings do rotate. They are certainly free to do so on my engine

I don’t really know why re-hone. Obviously the engine would run fine if you didn’t re-hone. A search suggests a re-hone is required only if the original hone is smoothed off, which mine is in places. Piston rings won’t bed-in in a bore without the hone pattern, apparently, and you get a high oil consumption, and that I am very familiar with from some years ago.

Good view of the rings here:



Administrator
Shoreham EGKA, United Kingdom

Off_Field wrote:

Can you elaborate on the ring position bit? I was of the understanding that rings rotate in all engines

I don’t believe rings rotate after installation in the bore. I could be wrong and engines may vary.

When you align rings in the bore so that the gaps don’t line up, for example three rings/gaps aligned at 120 degrees, in my experience you find them that way when you disassemble the engine after service. That would imply that sealing of rings is disturbed when the rings are removed and then reinstalled with the ring gap in a different circumferential position.

Last Edited by Silvaire at 08 Oct 20:47

I’m curious about this as it’s always been my impression that anything vibrating that is free to rotate, will do so. What keeps the rings from rotating?

EGCW

You can find lots of people who think quite strongly that rings rotate in service, and equally you can find quite elaborate procedures specified by others (including OEMs) on ring gap alignment to minimize blow-by. My own experience (mainly on modern-ish motorcycle engines) is that when you remove the pistons you find the ring gaps spaced as per the OEM recommendation for assembly. Has anybody actually checked it on a Lycoming?

Last Edited by Silvaire at 08 Oct 21:58

This is quite new to me, as I’ve only ever worked on stuff where the rings were ‘pinned’ to prevent rotation.

Private strip, Essex (not mine), United Kingdom

I’ve had serious concerns about something which that video shows around 0:50 onwards, but all opinions thus far are that it is a total non-issue.

Administrator
Shoreham EGKA, United Kingdom

Thanks for the response Silvaire,

I’ve not pulled a motor apart after I’ve rebuilt it. Yet, so haven’t first hand data on that.

If I recall Mike Busch talks about rings moving round on aero engines. I seem to remember it’s one of the reasons he surmises that you can have occasionally low leak down tests which then suddenly improve after.

I did a little looking and found this article Ring rotation interestingly they say on one of the measured engines at 1000rpm the top ring was rotating at 1rpm.

Peter,
Thanks to you and all the contributors on this topic, I have learned a lot. Also poking around EuroGA I came across Lycoming
SB388 is this relevant ? Plus can you comment on buying a new cylinder kit to overhaul of existing?
Phil

Archer2
EGKA, United Kingdom

Peter thanks for posting all this and the videos. lots of good information here.
I wonder how many hours since last overhaul do you have on that cylinder?

EDTG, Germany, Switzerland

Peter,
Why “ No more IFR trips for a while due to need to bed newly honed cylinder in.”

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