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Oil drain plug on a GB 8 laydown gearbox

Submitted by george_arber on Sat, 02/03/2019
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Heavy Twins

Can somebody please identify which is the oil drain plug as fitted to the GB8 suffix laydown gearbox on my 1956 Dominator 99 ?

Should be obvious I know but there is more that one and I do not want to perhaps loosen something inside the box. The plug towards to front  has most of the hexagon turned off and is nigh impossible to get a spanner or socket on it. There is a hex head screw towards the rear which has a screwdriver slot in it and is not directly under the box.

George

 

 

 

Submitted by ian_macdougall on Sat, 02/03/2019

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is the hex head screw low down at the rear of the box.

Ian McD

Hi Ian,

Taking a closer look at the exploded drawing of the laydown gearbox as shown on the Andover Norton website, item 40 shows a screwed plug which has a spring and plunger and I doubt that this is the oil drain plug.

The hex head to which you may be referring to is towards the rear of the box but is horizontally screwed in place and has a slot in the head. Could this be the oil drain ? I am keen not to inadvertently disturb any internals !

George

 

Further to my query and replies, I have taken a flyer and removed the rear slotted hex head plug and I got a small amount of oil out of the box and all seems well. I assume that there was very little oil in the box so a good job that I decided to check it.

Interestingly , the instructions for this box recommends using engine oil. Is EP 90 for the later boxes ?

George

Submitted by philip_ham on Sun, 03/03/2019

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George,

The other bolt head which faces vertically downwards, is the indexing plunger for the cam plate.  It can be taken out to inspect the spring and plunger without any dire consequences.

Engine oil in the gearbox is stipulated in Haycraft "Book of the Norton" for 1955 to 1962 models.

Philip

Submitted by ian_macdougall on Sun, 03/03/2019

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Yes, Norton's recommendation for these boxes was engine oil. EP oils not recommended as the EP additives (sulphur based) can cause corrosion of the plain bushes. Some EP oils are formulated to reduce the likelihood of this happening, and at the low operating temperatures of a separate gearbox may not happen anyway. The straight cut gears in these boxes are not highly stressed and do not need the Extreme Pressure properties. I use Morris Golden Film Classic Gear Oil (does not have EP additives) but other brands offer similar products. Viscosity is another issue: too light and it will escape via the kickstart bush, too heavy and it might not reach the bushes on the mainshaft. 90 grade seems to be a reasonable compromse and is roughly equivalent to a 50 engine oil.

Ian McD

Submitted by adam_davis on Sun, 03/03/2019

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John Day's pics are of the oil level plug. I attach a pic of the oil drain plug (with the red sealant).

You can also see the detente spring plunger plug with the slotted head. Leave that alone!

The drain plug screws in horizontally just above the pivot lug.

Don't use EP 90, it can damage phosphor bronze bushes. I use Castrol Classic ST90. It's the EP bit which is suspect.

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IMG_20190303_102152.jpg

Thank you gentlemen. I appreciate your help.

As I use Chatsworth 40 in the engine, I assume that this will be ok in the gearbox. Or perhaps  Morris 20- 50 engine oil.

George

Submitted by paul_standeven on Sun, 03/03/2019

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I am told that EGL4 oils are safe with our bronze bushes, but GL5 oils are not.  They damage the bronze bushes.  When I was told that, I took a look at the bottle of EP oil I put in my horizontal box.  It's GL4, so it's OK.

Paul

Submitted by mikael_ridderstad on Sun, 03/03/2019

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I have a 5-speed TTI gearbox in my Manx. TTI recommends Motul Gear 300 75W-90 GL-5. The technical data sheet for that oil says " Suitable for any type of seal and yellow material used in gearboxes design. "

Just to add some confusion to the neverending oil discussion.

 


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