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Gordon Gray
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#848034 05/04/21 5:06 am
Joined: Dec 2013
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G'day all,
I have a 1953 BSA M21 that leaks a bit of oil from the gearbox.I use straight 50 wt mineral oil in the Engine and gearbox .. ATF in the Primary case .
Just wondering if anyone has used Semi Fluid Grease in their gearboxes of their BSA's (my Norton Big 4 uses it) ..
Could I drain the gearbox oil and replace it with semi fluid grease with out causing any damage ? Would there be any advantage in doing this ? The box is a wee bit noisy,could the grease make things quieter ?..
Of course, the solution would be to attend to the leaks and do the job properly,but at the moment this is not feasible ..
Thanks folks ..just wondering smile ..

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No BSA gear box other than the reduction box used on some stationary engines should ever see grease, semi- fluid or otherwise.
It is too thick to get down into the layshaft bushes.
It is too thick to be flung out of the holes in the gears and draw fresh oil into the non fixed gear bushes.
Many years ago I took the suggestion to use 00 or 000 grease in my M20 box and it worked really well, till the box spat the dummy big time.
Every bush was buggered, the non fixed gears wobbled on the shafts so would not properly engage,,, some times .
Now to be fair the suggester would have been lucky to ride his M20 more han 200 km a year and I was doing 10,000 on mine .
Finally goten around to replacing every bush & bearing and it is a job I don't want to do again.
You can fit a sealed bearing on the sleeve gear which will cut down the oil losses massively
You can also fit a sealed bearing on the other end of the layshaft which will cut the losses through the kick start & gear change but if you do the ratchet pinion will rquire regular lubes which of course requires removal of the front cover on rigid framed M20's
The alternatice is to fit a rigid / plunger B series box complete.
Swap the outer cover if you want to keep the M20 authentic looking.
Miles of B boxes at swap meets usually for 1/2 to 1/3 of the prices on evilpay


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A comprehensive answer mate,much appreciated... certainly has put me off the semi fluid grease idea...I'll stick with the 50wt for the time being and do the proper job when circumstances permit ..
Cheers my fellow New South Welshman ... thanks again for your response ...

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The post war boxes all leak
Very little you can do about it apart from the sealed 6207 sleeve gear bearing
In the day it was quite acceptable
The 49 on boxes don't leak any where near as much & drop strait in apart from the speedo cable mount.
nabic Swap is comingup soon and the Goulburn Swap is just before it but has been moved to Wakefield park.
Maitland is on for the time being and tends to be the best value with the biggest range of BSA stuff.
Best bet is to grab a B series box, drop it in while you get yours sorted


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Trevor

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