The BSA A7-A10 Forum
Technical (Descriptive Topic Titles - Stay on Topic) => Gearbox, Clutch, Primary => Topic started by: lawnmowerman on 04.12. 2018 16:21
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I have just noticed a small oil leak on my Super Rocket which is dripping from the lower loop of the speedo cable.
On closer inspection it seems to be leaking between the black plastic cable outer and the aluminium fitting with the nut which screws onto the drive in the gearbox. It looks like the speedo drive is below the gearbox oil level and the oil is seeping into the cable.
Is there some sort of seal in the drive which holds the oil back? If the oil is supposed to be in the cable then I suppose a fix would be some self amalgamating rubber tape around the joint.
It looks like it has been leaking for a while and the wind has carried oil back over the gearbox and frame.
Anyone else had this problem?
Thanks, Jim
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A common and annoying leak.
BSA issued a service sheet posted below.
The oil seeps between the driven gear and its bush, then gets into the cable and drips out of the joint between cable and ferrule.
The cable problem is the hex crimp used by most cables available today. The original Smiths cables used a circular crimp and had less problems. Second photo shows the 2 cable ends.
Some later driven gears were fitted with an O ring which lessens the leak. Third photo.
You can seal the cable to ferrule joint - slide the nut up the cable and use some wiring heat shrink tube over the joint, then carefully slide the nut back, it will be tight to get it over the heat shrink but it does help. Just occasionally check that oil has not worked up the cable towards the instrument head.
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Thanks Julian. I have slid some heat shrink tube over the joint as you suggested.
I could not find speedo drive info on the BSA service sheets but I found a good exploded drawing on the Draganfly site.
When I removed the nut securing the cable, the whole body of the drive turned slightly before I could remove (and replace) the nut. It did not look like I have a nut holding the drive body in the gearbox casing but I did notice on the diagram that there is a securing pin/screw through the gearbox cover which locates in a slot on the drive body. I assume this is what is holding the drive as I remove and replace the nut.
I am wondering whether I have a later version of the drive which has no securing nut and is just held in by the pin.
One last question - can I remove the drive without removing the gearbox cover so I can see whether I have the O ring type. I may get away with just having to replace the O ring.
Thanks
Jim
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The later type bushes or bodies dont have a threaded portion for a nut to hold it in the gearbox cover. The original late type were mazac but the repros are brass. The earlier ones which take securing nut were brass.
You need to remove the cover to remove the speedo drive and replace it.
With cover off and securing pin removed attach a length of old cable to the drive, clamp cable in vice and pull or tap off the cover.
The O ring on the shaft, if fitted , is quite a flimsy item, easily damaged when replacing.
Photo is a new old stock assembly. A sealing ring goes in the goove nearest the thread. Most driven gears dont have provision for an o ring and rely on fit and scroll to keep the oil inside.
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Hi,
As per julians image above you can fit Triumph seal in the groove, not easy though:
https://www.ebay.co.uk/itm/TRIUMPH-PRE-UNIT-SPEEDO-DRIVE-SHAFT-SQUARE-SECTION-O-RING-IN-GEARBOX-57-0948-/262310003777
Best wishes...
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Thanks Julian and Bess. Looks like it could be a can of worms. Hopefully the shrink sleeve over the cable will solve the problem - at least for a while until I have a reason to take the gearbox cover off.
Jim
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When you seal it at the gearbox end with the shrink tubing the oil has no where to go but up to your speedometer.
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When you seal it at the gearbox end with the shrink tubing the oil has no where to go but up to your speedometer.
Not quite.
because of the directio of rotation & lay of the cable oil is pumped away from the speedo head.
Same principle as the scrol on the clutch.
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Just to update this one - I removed the gearbox end of the cable and shrunk about a 2" length of thin wall shrink tube over the crimp in the fitting. It was tight getting the nut back over it but after a month, no oil seems to be leaking.
Hopefully the oil will stay out of the speedo as I have just had it cleaned.
Jim