[Healeys] Ring Choice - closing the loop

[Bob Spidell]

I'm curious as to why both 4- and 5-ring pistons are offered (by Moss). 
Does it vary by year or model, or just builder preference? As far as I 
can tell, cars came from the factory with 4 ring pistons.

FWIW, I have a DWM 3-ring Omega set in my BJ8, and I haven't noticed any 
piston slap.

Bob

On 4/19/2021 5:14 AM, m.g.sharp--- via Healeys wrote:
>
> Many thanks to everyone who responded to my question about the rings.  
> Seems that there are examples of people fitting that fifth ring and 
> leaving it off, and no-one reported a problem or bad experience either 
> way.  It also seems there is no hard knowledge on why that bottom ring 
> was fitted, but several of us, me included, think it may have been 
> aesthetic: simply to reduce the noise from piston slap.  I thought 
> Earl’s response was most telling in that he had been through a 
> complete engine cycle (i.e. he is on his second rebuild after 140,000 
> miles on the first) with a 5-ring piston and there were no issues 
> noted on the strip-down and good performance.
>
> While I have no doubt that extra ring may result in extra friction and 
> rob the engine of a horsepower or two, no-one has measured it, so we 
> do not know if that is significant in any way.  The only other 
> potential down-side is that the bottom ring will scrape the oil from 
> the cylinder wall on the down-stroke, reducing lubrication on any 
> piston-cylinder wall contact between the two oil control rings.  
> However, the bottom ring may also prevent the piston from making 
> contact with wall, or at least _reduce_ the friction, so maybe that is 
> not an issue.
>
> My goal is a well-built, reliable, original car with factory-level 
> performance. Given that, and some concerns about the unknown 
> consequences of an empty ring groove, I am electing to install the 
> 5^th ring.  Also, I think there is wisdom in Hank’s comment that as a 
> general rule parts should be installed as the manufacturer intended – 
> who are we to second guess the engineers who thought it necessary to 
> add that ring?
>
> Interesting discussion, and if anyone ever turns up hard engineering 
> evidence as to why that extra ring was added, I would be very happy if 
> they would share it.
>
> As always, this list is amazing for providing a forum for providing a 
> forum for discussion on the things we find interesting – as arcane 
> they may be!
>
> With thanks, Mirek
>
>

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