MD2B gearbox seized: overheated?

UserError
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Re: MD2B gearbox seized: overheated?

Post by UserError » Wed Apr 11, 2018 3:13 pm

I ended up sucking mine out with a vigorous little hand pump, so I would have expected it to get at least some of any debris that might have been in there. I only got about 200ml-ish, but the suction pipe has an angled end. Next time I'm down there, I'll try starting the engine in gear as Brightstar suggested - maybe churn the new oil round a bit & then suck it out again.
Did you ever deduce what the bits of metal were? I think I read on here that it still worked afterwards?
Thanks
Jonathan
Centaur Polly B
Littlehampton

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Re: MD2B gearbox seized: overheated?

Post by TyroSailor » Wed Apr 11, 2018 3:16 pm

I got a bit more out than that, but as I said, repeated several times (with fitering in between) it probably got most of it out.

I shook it up by tipping the boat about, since I couldn't start the engine at the time and, had I thought of it, could have blown bubbles in the oil too.

The bits that came out were all pretty small - generally <1mm long, and a lot were little more than iron filings. Brass/bronze too. I assumed that they were bits worn off the cogs over time, and especially when operating without oil! It did indeed operate more or less correcty afterwards, until I had the engine removed.
gearbox bits 2 colour corected_opt.jpg
gearbox bits 2 colour corected_opt.jpg (33.92 KiB) Viewed 299 times
The filter paper was a sheet of kitchen roll, to give an idea of the size.
Experience: That which would have been most useful five minutes before you acquired it.

Steve
Tyro (Centaur 1361)
at Southampton

UserError
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Re: MD2B gearbox seized: overheated?

Post by UserError » Wed Apr 11, 2018 4:07 pm

Steve,
Thanks for that.
Air bubbles sounds good.
Cheers
Jonathan
Centaur Polly B
Littlehampton

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Re: MD2B gearbox seized: overheated?

Post by UserError » Fri May 25, 2018 11:25 am

Problem solved. The actuator 'pivot rod' had seized in its housing.

I'm posting this as it could be the cause of other gear change or selection problems.

With the gearbox on the bench, I undid the 4 set screws holding the actuator assembly. I think these are 10mm diameter when new-mine were corroded and needed a range of tools to remove. I replaced them with M6 x 20 high tensile bright plated steel set screws.

I dismantled the actuator assembly (align the retaining pin holes with the housing & drift the pin out. I used a pop rivet shaft as a drift, then gently knocked the pivot from the housing. I cleaned it and the bore with wire wool then greased & reassembled it and it's action is now slick.

You could do this without removing the gearbox if you can get the 4 retaining screws out.

BTW, drain the engine oil before disconnecting the gearbox...

Whether this was in any way linked to the overheating, who knows? Maybe the extra heat and low oil in the gearbox caused any last vestiges of lubricant to drain from the pivot? Or pure coincidence.
Centaur Polly B
Littlehampton

BrightStar
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Re: MD2B gearbox seized: overheated?

Post by BrightStar » Fri May 25, 2018 9:21 pm

Great result, just shows how robust these units are. A drop of oil on the actuator mechanism every now and then would prevent this, by the look of it once every 30 years will just about do it. :lol:
Brightstar
Griffon
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Re: MD2B gearbox seized: overheated?

Post by UserError » Mon May 28, 2018 9:53 pm

BrightStar wrote:
Fri May 25, 2018 9:21 pm
Great result, just shows how robust these units are. A drop of oil on the actuator mechanism every now and then would prevent this, by the look of it once every 30 years will just about do it. :lol:
Thanks. Yes. There is an.oil seal at the top,not sure that anything should/would get past it.
Anyway, now it's working, I can see what damage I've done to the engine....
Centaur Polly B
Littlehampton

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