[Healeys] DW overdrive piston

Thu Aug 4 10:38:47 MDT 2022

Based upon my observations when the aluminium overdrive accumulator
housings are scored you will invariably find that there are chips out of
the non syncro 1st and reverse gears and usually badly damaged laygear
rollers.
Because these gearboxes were not fitted with chip gathering magnet
originally the tiny hardened steel chips eventually find their way into the
overdrive then through the overdrive pump gauze (because the magnets
originally fitted in the overdrive have been lost by " the lube guy") and
lodge in the accumulator.
Those chips very quickly score the cylinder as the accumulator piston moves.
If you are careful to never grind 1st or reverse no chips will be created,
that will mean that they don't go through the laygear bearings or find
their way into the overdrive.
A magnetic plug in the gearbox is great insurance.

M

On Thu., Aug. 4, 2022, 12:13 p.m. Warren Dietz, <flyhihealey at gmail.com>
wrote:

> Bob,
>
> Interesting observation.
>
> Only 30/40 wt non detergent oil was used from new till 2013  at which time
> I switched
>
> to Redline MT90 @ 181,000 miles.
>
>
>
> Sent from Mail <https://go.microsoft.com/fwlink/?LinkId=550986> for
> Windows
>
>
>
> *From: *Bob Spidell <bspidell at comcast.net>
> *Sent: *Thursday, August 4, 2022 9:38 AM
> *To: *Warren Dietz <flyhihealey at gmail.com>; healeys at autox.team.net
> *Subject: *Re: [Healeys] DW overdrive piston
>
>
>
> Warren,
>
> Your accumulator piston and housing look to have a bit worse scoring than
> mine; I used synthetic fluid for over half the life of mine, I wonder if
> that made a difference?
>
>
>
>
>
>
>
> Sent from Mail <https://go.microsoft.com/fwlink/?LinkId=550986> for
> Windows
>
>
>
> This was the condition of my piston and housing with close to 200,000
> miles. Tranny was well maintained.
>
> The original metal rings lasted 53 years. So I guess with unknown quality
> of either of todays metal vs rubber
>
> O rings, let the experiments begin.
>
>
>
>
>
>
>
> *From: *Bob Spidell <bspidell at comcast.net>
> *Sent: *Wednesday, August 3, 2022 10:12 PM
> *To: *healeys at autox.team.net
> *Subject: *Re: [Healeys] DW overdrive piston
>
>
>
> 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" <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>
> <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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