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18S Gearbox #768026
03/13/19 7:35 pm
03/13/19 7:35 pm
Joined: Nov 2013
Posts: 20
Lincoln, England
K
klektermaniac Offline OP
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klektermaniac  Offline OP
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K

Joined: Nov 2013
Posts: 20
Lincoln, England
Hello All,
Re-commissioning my 1954 AJS Model 18S.
Obviously changing all the oils but when I took the gearbox drain plug out nothing came out - not a good sign! Anyway I continued and put in the recommended one pint of oil, and it has since been leaking from above/behind somewhere.

What I need to know from the experts is where is it most likely to be coming from? I currently have the outer primary case and clutch plates out as the clutch was slipping. Will I need to continue and remove all the clutch, shock absorber, and inner chain case to get to whatever is leaking?


RogerH.


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Re: 18S Gearbox [Re: klektermaniac] #768076
03/14/19 6:34 am
03/14/19 6:34 am
Joined: Aug 2001
Posts: 2,519
Oztralia
R
Rohan Offline
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Rohan  Offline
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R

Joined: Aug 2001
Posts: 2,519
Oztralia
Your gearbox should be the Burman B52 type.

Its likely to be the seal on the mainshaft that is leaking.
Although the drain plug is the only possible source of leaks down low enough that could explain the total lack of oil in the box.

You probably need to remove the clutch and extract the gearbox out the timing side to get a good go at everything.
(But I've only played with the earlier CP type box, so maybe the B52 is better to service ?)
hopethishelpsabit.

Re: 18S Gearbox [Re: klektermaniac] #768078
03/14/19 7:54 am
03/14/19 7:54 am
Joined: Oct 2017
Posts: 222
England
G
George Kaplan Online content
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George Kaplan  Online Content
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Joined: Oct 2017
Posts: 222
England

Re: 18S Gearbox [Re: klektermaniac] #768082
03/14/19 9:25 am
03/14/19 9:25 am
Joined: Nov 2013
Posts: 20
Lincoln, England
K
klektermaniac Offline OP
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klektermaniac  Offline OP
BritBike Forum member
K

Joined: Nov 2013
Posts: 20
Lincoln, England
Thanks for the replies, I will continue at the weekend.

My 1954 bike has the later Monobloc carb for the 55 year on, and (I believe) a 350 clutch as it only has four each plain and friction plates, although I have seen this mentioned more then once on the forums.

Not sure if mine is a bit of a bodge/hybrid, but a lot of things can get changed in 65 years.


RogerH.

Re: 18S Gearbox [Re: klektermaniac] #768265
03/16/19 3:12 pm
03/16/19 3:12 pm
Joined: Nov 2013
Posts: 20
Lincoln, England
K
klektermaniac Offline OP
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klektermaniac  Offline OP
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K

Joined: Nov 2013
Posts: 20
Lincoln, England

Well all dismantled and inner chain case off, and the mainshaft oil seal is not leaking, although the collar that fits inside it is a little worn on it's outer edge.

While it is all off I have Gunked and washed the bike and engine etc and now have a better view of things.
The leak appears to be between the kick start cover and kick start case so will need to remove the cover - any problems likely when I remove this? Taking the rest of the bikes state into consideration there may not be a gasket fitted by the last owner anyway. I have tightened the five screws and it is now only weeping, but I might as well check it out and do the job properly.


RogerH.

Re: 18S Gearbox [Re: klektermaniac] #768277
03/16/19 5:52 pm
03/16/19 5:52 pm
Joined: Feb 2014
Posts: 543
Cork Ireland
C
chaterlea25 Offline
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chaterlea25  Offline
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C

Joined: Feb 2014
Posts: 543
Cork Ireland
Hi Roger,
On the B52 box at the end of the layshaft below the gearbox sprocket there is a flat metal disc like a frost plug
closing off the end of the bush housing
These can and do leak ! so while you have access to it degrease and seal over the area
I have used araldite on a box by laying the bike on its side until it sets, or "Dirko" which I find great
It is helpful to use some sealer on the gearbox sprocket splines as well, oil can weep out along the inside of the sleeve
If the sleeve is worn, you can polish up the outer end and reverse the sleeve

John

Re: 18S Gearbox [Re: klektermaniac] #768895
03/22/19 3:52 pm
03/22/19 3:52 pm
Joined: Nov 2013
Posts: 20
Lincoln, England
K
klektermaniac Offline OP
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klektermaniac  Offline OP
BritBike Forum member
K

Joined: Nov 2013
Posts: 20
Lincoln, England
Hello John,
Yes I can see what you mean but it appears to be oil tight. Used to call these "core plugs" back in the day.
RogerH.

Re: 18S Gearbox [Re: klektermaniac] #768920
03/22/19 10:50 pm
03/22/19 10:50 pm
Joined: Feb 2014
Posts: 543
Cork Ireland
C
chaterlea25 Offline
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chaterlea25  Offline
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C

Joined: Feb 2014
Posts: 543
Cork Ireland
Hi Roger,
Yes I'm old enough to have used the term "core plugs" but thought the readers would understand "frost plugs " more easily
Coincidentally at the moment I have a 1924 Baby Austin engine in the workshop and marvelled at the way they cast the cylinder block
There's an opening on one side of the block where the water connection manifold bolts on, inside you can see the individual cylinders
with water spaces between and all around them. At each end there are large screw in plugs maybe 2inch diameter
The valve spring/ tappet chamber occupies the opposite side of the block but there is no access to the water jacket on this side
making me wonder how they removed the core material after casting the block ???

John

Re: 18S Gearbox [Re: klektermaniac] #768959
03/23/19 10:35 am
03/23/19 10:35 am
Joined: Dec 2004
Posts: 9,846
Scotland
kommando Online content
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kommando  Online Content
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Joined: Dec 2004
Posts: 9,846
Scotland
Sand with a resin used as a core and then after casting it can be broken up with an air chisel and removed.

Re: 18S Gearbox [Re: kommando] #769586
03/29/19 10:42 pm
03/29/19 10:42 pm
Joined: Feb 2014
Posts: 543
Cork Ireland
C
chaterlea25 Offline
BritBike Forum member
chaterlea25  Offline
BritBike Forum member
C

Joined: Feb 2014
Posts: 543
Cork Ireland
kommando

Quote
but there is no access to the water jacket on this side


????? WIth only about 3/16in between the cylinders theres not much room for chisels

Today I went to fit the pistons to the rods, the small ends of the rods have a clamping bolt to hold the pin
The pins have a groove cut in them so the bolt also acts as a cotter blocking any possible sideways movement
I found the bolts would not fit past the pins because the groove was not ground deep enough mad mad
I set the pins up in a collet fixture and carefully ground the grooves 15 thou deeper
Is anything straight forward ?? facepalm

John


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