classic motorcycle forum
Motorcycle Discussions => British Bikes => Topic started by: dynamic on July 17, 2025, 05:31:22 PM
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I have an oil leak from the lower oil pump / timing case (lower slot screw ) I need to replace the gasket
also is this chain in need of replacement ?
I notice there are no timing marks on crank / magneto do I just centre punch each sprocket and mark chain cover casing
all input gratefully recieved
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pic 2
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No, you can't just centre pop the gears as you need to synchronise the position of the piston on the firing stroke with the position of the mag points.
Simple enough if you have a manual. FW Neill is a good one.
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Since the sprockets look to be in excellent condition, the chain may not be worn ?
Can you just pack the magneto up a bit higher on its platform ?
Or is the platform adjustable even, with slotted holes on one side ??
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Loose enough to wear away the case ............I d replace the chain.......you could pack up the mag ,its base mounted
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thanks all for posting I will post my progress soon.
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I have one of these models. The magneto chain is adjustable by moving the magneto platform which is designed for that purpose. The sprockets are not keyed, they just have a tapered fit and if you use a puller to get them off the taper you will have to re time the ignition.
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Also, as you have to remove the sprockets in order remove the timing case to change the gasket I would try just removing the bottom screw, cleaning it and coating it with silicone jointing compound and replacing it and see if that slows the leak.
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thanks for the info esoracer bike is losing approx. 300ml each time engine is run, I will keep all posted on progress
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That screw also possibly needs a fibre washer under it/them ?
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thanks R will fit fibre washers to all screw and post results .
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oil weep problem found I think bottom screw hole on gasket slight left ?
now cannot get it to start , when I removed the timing/magneto case I was very careful to keep the inlet/exhaust cams in situ,
all went back together no problem maybe timing has slipped ,I have points just opening at 7/16 BTDC then full open at 12 thou , I have a strong spark, what have I missed
all input gratefully recieved
PS I started bike this morning ran no problems
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Is that a particle of debris ye refer to ?
Good that its sorted then.
PS I started bike this morning ran no problems
Its not clear if this comment supercedes the non-starting issue.
Good if its all good again but ...
Have fun !
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yes a piece of "debris" inpregnated into the gasket , now I have a non starting machine, before I took the cover off I marked mag /crank sprockets lining up to the marks I put on the timing case
I feel sure I put back both sprockets as they were when the bike ran earlier in the day before I removed the sprockets /casing
I have checked many times the points just starting to open at 7/16 /12mm BTDC then fully open at 12thou just before TDC if anybody could post re timing engine /magneto I would be very grateful thank you
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Is it possible the crank moved while working on the gasket?
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I was carefull not to disturb crank or timing/cam sprockets ,I did wipe the mag shaft before replacing the sprocket maybe I disturbed the timing then ,
I have set the piston full advance (lever slack cable) at TDC then back 7/16 BTDC watching for the points to just start opening before replacing mag sprocket ,
I am getting a bang back through the carb ,I have the advance /retard at mid way point
if anyone could help me to re time motor I would be very gratefull
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Grandma's eggs here, but you should wind the engine backwards a lot further, then winD forward until the timing point is reached. otherwise the lash in the gears will throw your timing out.
I usually start my bikes on just a little retard (rather than half) but all bikes are different and yours might need more retard.
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then WIND forward
Aye, if all ye backlashes accumulate, then you may be in no mans land....
Lightly tapping the sprocket onto its taper is highly recommended,
or it may slip or move while you are tightening up the nut.
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Double check that you have set the spark on the firing stroke, when both valves are closed.
Leon
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Good call. ?
On a twin, you'd just swap the plug leads over.
But 4 stroke singles don't work like that.
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FINALLY STARTED before I was not allowing for gear backlash only setting to 7/16 BTDC, going further back then coming up to my gauge mark made all the difference
thanks to all who posted sound advice .
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kickstart has now decided to jam in upright position will not engage its solid just about an inch movement down before going solid ,it does spring back to resting position
anyone experiensed this at vall ?
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Have you tried turning the engine/gearbox over, via the back wheel. ?
And seeing if that makes any difference.
It sounds like the kickstarter is not meshed or located correctly.
Let me find the Ajay booklet to refresh the grey cells, if someone doesn't chime in sooner.
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Hi R yes tried rocking in gear still no joy
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If you google this problem, its exceedingly common with Burman boxes. !
The solution is to grind down the 1st tooth on the quadrant, and the 2nd tooth a bit.
Assuming you haven't reversed it from its original fitting.
Which can also be a fix.
Pulling the clutch in when this happens can also sometimes free things off.
(https://encrypted-tbn0.gstatic.com/images?q=tbn:ANd9GcQdX6mU14jFcCBPXf3_Zf5COfIHkqsRe7j_2A&s)
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thanks for the input R I took the outer case off & and all looks in order ,HOWEVER now when I wheel the bike along I get a click click click from the g/box area ?
this happens in both forward backward motion .............rather confused ?
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So can you now kickstart it OK ?
Is that a fast click click, or slow
The chain contacting something could be a slow click,
but a fast one needs further investigation.
Even the tyre contacting something
Don't recall, is this bike new to you.
Some fettling is to be expected....
P.S That box is later than the CP expected for 1951 ?
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here are more photos dident load with previous post
PS. kickstart still solid .
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Can you turn the box over at this point, using the back wheel.
The leading 2 teeth on that quadrant are not ground down at all.
This gives a rather brutal initial engagement, and they can jam.
Ground down a bit, they lead into the others, and swing into action. !
If that were mine, I'd get out the angle grinder with a thin blade,
and shave a bit off the 1st 2 teeth. Keep the same basic tooth shape,
just shaved a bit, and no sharp edges left. Easy does it....
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Hi All
When the outer cover is taken off the indent plunger and spring behind the selector drum pushes the drum outwards so partially engaging a gear inside the box hence the clicking !! It will be ok when the cover is put back on..
Make sure the ratchet gear on the gearbox shaft is working correctly and not worn out or broken.
John
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We are assuming there is nothing untoward going on here,
like a case full of broken teeth jamming up the works. !
Without a full inspection, its a bit of a lottery if this will be good.
Draining the oil and inspecting what comes out is a useful diagnostic tool.
If its nice and clean (and new) it can go back in ?
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Pull the gearbox to bits .....the whole joy of old bikes is pulling them to bits and putting them back together again.
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small metal fragments found in g/box oil so an inspection will be the next move
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The CP Burman boxes dont normally chip gears ,as the gears are quite soft to avoid breakage ........the worst can happen is tooth breakage caused by worn layshaft bushes..........good news is millions of these boxes were made in WW2 ,and NOS parts are cheaply available .........be aware though there are several changes in the whole gearset made in WW2 to meet criticism of too wide gaps in the ratios............In general ,there are prewar trials ratios,post war trials ratios,and standard road gears.
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Or is it timed on the compression stroke?
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Most likely cause of jamming is burred first tooth on the starter quadrant .......first meshing tooth should have a sharp point .....when it gets burred ,the traditional cure was to grind it off and sharpen the next tooth...........ditto the mainshaft ratchet gear ...it should have pointed teeth ..........I d also add ,you never stab at the pedal,mesh the gears first before applying pressure ...........The 1956 on AMC box has the Norton style kickstart with a sprag engaging an internal rack ......reliable and near abuse proof.
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thanks all for posting I will update on prognosis
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As you know, your AJS is essentially a re-badged Matchless. By far the best owners workshop guide for you is the “MotorCycling” Maintenance Series covering Matchless 350 & 500 cc Heavyweight Singles 1939-1955.
Republished by Bruce Main-Smith Ltd in 1976 and as they say “intended for Matchless but good for AJS too.”
It contains every bit of technical information you’ll ever want to know plus all the technical differences from year to year and lots of clear illustrations. You’ll love it.
A4 landscape size, published by Bruce Main-Smith Ltd and edited by Reg Hide. Get a copy.
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Far better, in my experience, is the little Pitmans manuals for most makes, in this case written by the AMC service manager FW Neill.
Usually these books are on Ebay for a tenner at most.
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Buy both! You can’t have too much info.
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True enough. Both books and even better still, find on-line forums for more real world 70 years on solutions.