[Healeys] DW overdrive piston
Bob Spidell
bspidell at comcast.net
Thu Aug 4 11:12:30 MDT 2022
OK, who sells magnetic plugs for MOWOG gearboxes? I'd be willing to
order from Canada ;)
I don't remember exactly when I started using MT-90 in my gearbox, but
it was probably around 90-100K miles. I was hoping it would make the O/D
a bit more responsive, but was surprised that shifting seemed smoother
(I wasn't expecting it, so little-no confirmation bias).
On 8/4/2022 9:38 AM, Michael Salter wrote:
> 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 <mailto:bspidell at comcast.net>
> *Sent: *Thursday, August 4, 2022 9:38 AM
> *To: *Warren Dietz <mailto: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 <mailto: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" <mailto: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> <mailto: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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