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Borg Warner Velvet Drive - Dipstick keeps blowing out


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Having problems with my Borg Warner Velvet drive (71C) with the dipstick blowing out during running. Thought I'd cracked it when I realised the oil level has to be checked when at temperature but did this and is still doing it. There is a breather located nearby, can't see in the manual if this is related to the dipstick cavity (?). Does anyone know if this could be the cause of the issue if this was blocked ?

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The breather should vent the gearbox housing volume above the oil so if it is blocked the dipstick could blow out BUT all the 71Cs U have seen had a crude screw in plug with dip stick attached. I can't see how those would blow out, the oil seals would probably blow.. But that was years ago so it may have changed.

 

 

PS - the boxes I knew may have been 72Cs so maybe the 71C did have a push in dipstick that tended to blow out.

Edited by Tony Brooks
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23 hours ago, Tony Brooks said:

The breather should vent the gearbox housing volume above the oil so if it is blocked the dipstick could blow out BUT all the 71Cs U have seen had a crude screw in plug with dip stick attached. I can't see how those would blow out, the oil seals would probably blow.. But that was years ago so it may have changed.

 

 

PS - the boxes I knew may have been 72Cs so maybe the 71C did have a push in dipstick that tended to blow out.

Thanks Tony, the breather doesn't look too difficult to remove so will have a go at it next time I'm on the boat. 

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Managed to remove the breather, it was a bit chewed so looks as if some else has had a go at it in the past. 

 

Cleaned it down and tried to blow through it but couldn't.

 

I've read that some breathers only allow air to pass at a certain pressure, but the dipstick isn't locked in place so can't see this being the case for a 71C as any pressure would be possible to lift the dipstick which is what is happening

 

ASAP do a replacement breather for a 71C for £31 so I'm going to order one and see how it goes.

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Before you do that is there any chance that you could fit a small tube into the fitting and route it to well above "its sunk" bilge water level and turn the top end over into an inverted U. I have seen many gearboxes with broken/missing breathers that have run years without problems so don't see why yours would not. Many have a ball valve in them that is supposed to stop water getting in but they should allow you to blow air from the box side outwards. I managed to knock a little push on cap off mine and lost the spring &ball in the bilge. It gave no problem for over 15 years.

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9 hours ago, Tony Brooks said:

Thinking about it a bit more: if you have a push in dipstick then its not likely to be waterproof so any pipe on the breather only needs to be higher than the dipstick. It will save you £30

Thanks Tony, that sounds like a better idea, I've got some plastic tubing that may fit so will give it a try. 

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  • 3 weeks later...

Update - Resolved , the problem turned out to be the dipstick itself.

 

The dipstick has a mechanism that expands a plastic taper that is used to hold it in place. It is expanded by turning the dipstick handle whilst holding the dipstick body still and there is a screw thread that pulls the plastic taper closer to the top of the dipstick forcing it to expand and lock it in place.

 

On my dipstick the taper was expanded but not enough to hold it in place so a turn on the handle has now locked it so shouldn't now pop out during running.

 

It does actually mention this in the manual which is a bit annoying, must remember to read the manual properly next time.

 

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On 22/06/2020 at 14:59, Tony Brooks said:

The breather should vent the gearbox housing volume above the oil so if it is blocked the dipstick could blow out BUT all the 71Cs U have seen had a crude screw in plug with dip stick attached. I can't see how those would blow out, the oil seals would probably blow.. But that was years ago so it may have changed.

 

 

PS - the boxes I knew may have been 72Cs so maybe the 71C did have a push in dipstick that tended to blow out.

Borg Warner seemed to use both types of filler cap/dipstick. Some were screw in, some were push in with an expanding rubber to hold in place.

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