[Healeys] DW overdrive piston

[Bob Spidell]

The rings will score the inside of the piston housing, though not badly 
(photo at 205K miles). Looks like there's a side load on the piston, 
probably from the spring.

I donated this accumulator to another owner; never heard how they 
worked. Moss shows the rings available (but who knows?).


On 8/3/2022 12:36 PM, Henry G Leach via Healeys wrote:
> I assemble ODs using the original metal rings and have not had any 
> issues with pressure or engagement/disengagement.
>
> When Mr. DeNormanville stayed up in the middle of the night to 
> engineer the operation of the unit,  I think he decided that the use 
> of softer rings (sacrificial metal) against a hardened casing was the 
> best solution for control and wear.  If a rubber o-ring was a better 
> solution, he would have used one with the proper buna rating.
>
> I think the bigger problem, now-a-days, is the availability of the 
> metal piston rings.  Rubber O rings are a dime-a-dozen. If you contact 
> Overdrive Spares in the UK, they should be able to supply the proper 
> rings.  If they too, have decided to go with rubber, then plan on a 
> breakdown/rebuild in a shorter period of time than units equipped with 
> the original parts that last a long, long time. Hank
>
> -----------------------------------------
>
> From: "Michael Salter"
> To: "healeys at autox.team.net"
> Cc:
> Sent: Wednesday August 3 2022 9:38:15AM
> Subject: Re: [Healeys] DW overdrive piston
>
> I have a question about the "O" ring type of accumulator.
> The way the accumulator works is that when it is fully charged the 
> piston moves against the spring until the rings reach the radial holes 
> in the wall of the housing which acts to relieve any excess pressure.
> My concern is that at 3 - 400 p.s.i. oil will obviously get behind the 
> "O" ring and force the material of the "O" ring into those radial 
> holes and then, as the piston moves back over them, a piece of the 
> ring will shear off.
> I'm guessing that Laycock-DeNormanville used the complex cast iron 
> rings rather than "O" rings because they recognized the possibility of 
> this happening.
> I'm sure that tiny pieces of the "O" ring would be found in the filter 
> if this was a problem. Anyone found them or noticed damage to their 
> accumulator "O" ring upon disassembly?
>
> M
>
>
> On Wed, Aug 3, 2022 at 9:08 AM Bob Spidell <bspidell at comcast.net> wrote:
>
>     I put one in my BJ8's O/D. It's subjective*--O/Ds seem to work a
>     little
>     quicker with cold, thick oil than hot oil--but it cuts maybe a
>     third off
>     engagement time on average. I had the O/D on the bench and
>     disassembled,
>     and the current one had a scored barrel so, why not? Engagement isn't
>     much, if any, harsher than before which, I believe is the reason DMH
>     wanted the weaker, smaller spring. If I'd known about it, I might have
>     bought AHSpares' with an O-ring instead.
>
>     * I've never really 'timed' O/D functioning, it would be a bit
>     awkward;
>     anyone done it? I usually tap the clutch pedal when engaging O/D, and
>     give a little throttle when disengaging. I thought mine engaged a
>     little
>     quicker when I switched to synthetic fluid from engine oil, but in all
>     cases confirmation bias may be involved.
>
>
>
>     On 8/2/2022 8:09 PM, Joseph Costa wrote:
>     > Has anyone installed their upgraded overdrive piston?  If so, is it
>     > worth the trouble ?
>     >
>     > Joe
>     > BN1 #923
>     >
>
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