[Healeys] DW overdrive piston

Bob Haskell rchaskell at earthlink.net
Thu Aug 4 15:27:55 MDT 2022


Might be something here that would work: 
https://www.lislecorp.com/oem-products-division/magnetic-plugs/pipe-thread/

Cheers,

Bob Haskell
Austin Healey 3000 BN7/BT7 registrar

On 8/4/22 1:12 PM, Bob Spidell wrote:
> 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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