AJS 1955 350 engine problem

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r wheat
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AJS 1955 350 engine problem

Post by r wheat »

Hi Can anybody help. I have a 1955 AJS engine which refuses to fire although has fuel ,good spark set to fire 1/2'' befor TDC at full advance, and good compression. What i need to know is the correct valve timing. Cams marked with H which I take to be high lift. Inlet cam marked with 3 dots 1,2,3 and the exhaust 2 dots 1,2. Inlet cam set to No3 dot aligned to pinion gear dot and exhaust cam set using No2 dot. thanks Richard
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Rob Harknett
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Re: AJS 1955 350 engine problem

Post by Rob Harknett »

Has the bike been running OK , now after being laid up will not start up? Could be sumped oil Fouling the plug after a few attempts trying to start it. Also you have been cleaning the plug, after its fouled, trying to start it. Drain the sump fit a new plug. I have to do that. Even with old fuel, will then start first kick.
SPRIDDLER
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Re: AJS 1955 350 engine problem

Post by SPRIDDLER »

This techy info will be useful to set/check the valve timing:

http://archives.jampot.dk/technical/Gen ... e_Dots.pdf
Last edited by SPRIDDLER on Mon Aug 06, 2018 5:34 pm, edited 1 time in total.
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ajscomboman
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Re: AJS 1955 350 engine problem

Post by ajscomboman »

Cam timing is correct, 3 for inlet and 2 for exhaust. Has the bike been running at all ever? Is it possible it's been timed to the wrong stroke? The spark could be disappearing under compression when the plug is installed, magneto on it's way out possibly?
r wheat
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Re: AJS 1955 350 engine problem

Post by r wheat »

Many thanks for your helpfull suggestions. The engine has never run and has been built up from box of parts . After looking at the techy info wondering if the pinion is in the correct position. will check tomorrow, Hope it is .
thanks Richard
56G80S
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Re: AJS 1955 350 engine problem

Post by 56G80S »

Maybe you put the pinion on but don't forget it's a left hand thread, wind it to the right to loosen it.

Johnny B
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Re: AJS 1955 350 engine problem

Post by SPRIDDLER »

r wheat wrote:After looking at the techy info wondering if the pinion is in the correct position.
The pinion can only fit correctly as it is keyed to the timing side axle.
The axle isn't keyed into the flywheel though and must be aligned correctly in the flywheel to coincide with the crankpin position.
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r wheat
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Re: AJS 1955 350 engine problem

Post by r wheat »

Hi pinion is ok the only thing that has happened had a back fire when the bike was kicked over with the decom open, totally lost at the moment cheers Richard
oldandsmelly
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Re: AJS 1955 350 engine problem

Post by oldandsmelly »

I had a similar problem when I recently replaced the magneto and camshafts and also removed the carb for cleaning. The bike wouldn't start at all and just made an occasional bang in the exhaust. I'd fitted a new BTH mag so suspected the timing or the mag and spent ages faffing with that.

The reason I'd fitted a BTH mag is because starting got worse and worse with the original "reconditioned" magneto and so if your SR1 mag is out of box of bits it's likely to be a problem. With my old mag, the magnets had become weak and although a new coil had been fitted the spark was feeble. If you suspect this and don't want to spend BTH mag money, I'd go for a Thorspark unit as they are good value and work.

To cut a long story short, In this case, I'd messed up the valve timing. I've consoled myself that it's very easy to do with so many dots & different cams over the years and the original owners manual instructions being less than clear. I found a file called 'cams joining the dots' by Ken de Groome to be the most helpful. When I followed these instructions, everything worked as it should. I've tried attaching this file but its twice the 1Mb upload limit. If you can't find it elsewhere and think it might help then drop me a PM with your email and I'll send it.
196016
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Re: AJS 1955 350 engine problem

Post by 196016 »

Locked