AJS 1955 350 engine problem

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Re: AJS 1955 350 engine problem

Postby SPRIDDLER » Wed Aug 08, 2018 10:20 am

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

http://archives.jampot.dk/technical/Gen ... e_Dots.pdf

I already gave Richard that link on 6th in my post above........... ;)


My first step would be to fit a new plug since it fired with minimal compression (i.e with the valve lifter operated) but may fail to spark under full compression.
As said, mags don't store well and you don't know its condition. Personally I wouldn't fit an electronic unit though but get the mag sorted (if that is the problem).

The engine has never run and has been built up from box of parts

A lot of unknowns there. Without being on the spot it's impossible to cover all the 'possibles' but if you recheck that you've got the basics right (cams, ign timing, carb settings etc) it's down to perseverance as most engines have preferences for starting - choke, no choke, throttle shut or part open, flood the carb a little, a lot, or not much. Useful to have a spare plug or two to change one that has become soaked in fuel.
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Re: AJS 1955 350 engine problem

Postby r wheat » Wed Aug 08, 2018 8:17 pm

Hi thanks for all the interest, A new plug was fitted, tried with throttle in all positions, Having read the tecky info timing reset and checked, choke on and off, will back fire on valve lifter on, points checked with great spark. Have checked magnets and fitted new condenser, carbs stripped and checked as to the correct one, I think I may well have to look at getting a new mag as I am running out of ideas . I guess this is what old bikes are about cheers Richard

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Re: AJS 1955 350 engine problem

Postby Rob Harknett » Wed Aug 08, 2018 8:52 pm

Do not think big problem like new mag. Its probably a small problem over looked. Have you checked everything in the carb? I was once making up a carb from my box of carb bits. I notice a nice new slide I never knew I had. Put it in. Bike started, would not run at all well. Discovered the nice new slide was the wrong cut a way. 2 1/2 when should have been 2 or what ever? Found a well worn correct one. Slide rattled on ticked over. I just ignored that. Bike ran very well apart from that. No mention of Tappets. Have you checked them? With both valves closed they should spin very freely cold. In fact feel quite loose. If tight, hold a valve open a bit. 55 G3LS has quite a large carb bore. Where the O ring fits, there's a very thin lip on the inside, this can crack or bits brake off. So you get an air leak. Could even be oval. I have a big ball bearing the carb bore dia. If you find one. Take the carb top off complete with cables slides needle. Very gently tap the bearing through the bell end. That will make the bore round again, in particular where the O ring fits, So a better seal there. Have you tensioned the spring on the SR1 Mag cover. First take out the pointed grub screw that pierces the plug lead and holds it in. Use wire plug lead, not fibre. Refit , pull out the spring to tension it so it makes good contact with the button on the coil.

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Re: AJS 1955 350 engine problem

Postby StephenG80 » Thu Aug 09, 2018 6:36 pm

[quote="r wheat"]Hi thanks for all the interest, A new plug was fitted, tried with throttle in all positions, Having read the tecky info timing reset and checked, choke on and off, will back fire on valve lifter on, points checked with great spark. Have checked magnets and fitted new condenser, carbs stripped and checked as to the correct one, I think I may well have to look at getting a new mag as I am running out of ideas . I guess this is what old bikes are about cheers Richard[/quote

When looking at the primary drive side of your bike, what side of the magneto does your advance/retard cable come out of - top left or top right? - if top left, then when setting the ignition timing you need to have the A/R fully pushed in. If on the right hand side you need to have it pulled fully out ie the timing needs to be set with the timing fully advance (hope I have got that the correct way round). So worth while checking this. If the timing is approximately set she should start and run fine - I do mine with a fine blue fag paper in the points and screw drive in the spark plug hole - nothing fancy - good luck.

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Re: AJS 1955 350 engine problem

Postby StephenG80 » Thu Aug 09, 2018 6:59 pm

Ah -just realised you may have auto A/R - in which case ignore my previous post!

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Re: AJS 1955 350 engine problem

Postby SPRIDDLER » Thu Aug 09, 2018 7:37 pm

r wheat wrote:....... will back fire on [with?] valve lifter on, points checked with great spark.

I think I may well have to look at getting a new mag as I am running out of ideas .

For the moment I wouldn't be in too much of a hurry to have the mag refurbished as you're looking at a cost in the region of £250 and you'd be well brassed off if you still couldn't get the engine started.
It is sparking (backfiring) when valve lifter is operated so you know the mag is working to some degree. You should be able to get a spark jump a 1/4" gap at kickstart speeds so try that test by removing the plug and screwing (jamming) a suitable bolt into the terminal inside the plug cap. With care or maybe insulated pliers hold the end of the screw (EDIT: position the screw, not actually HOLD it!) 1/4" away from a clean metal area of the engine or the mag body and kick the engine over. If you don't fancy holding the plug cap you can also fudge up a jig by putting a couple of screws 1/4" apart into to a piece of wood. Remove the plug cap and attach the HT lead to one screw and a wire to metal part of the engine from the other screw.
To eliminate the possibility of a faulty plug cap (it isn't a suppressor type I assume) you can remove it, bare say an inch of the HT lead and connect it direct to the plug top.
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Re: AJS 1955 350 engine problem

Postby 56G80S » Sat Aug 11, 2018 4:48 pm

Reslonded, below using 'phone and maybe fall foul of small screen and missed stuff.

At the risk of an argument, don't condemn the SR1 because someone did a poor job reconditioning one. They are excellent kit. Just get the work done by a competent person such as Tony Cooper (I've no commercial or other relationship except as a satisfied customer, mag and dyno). But worth fitting the little Brightspark condenser, it's way better than the standard aluminium foil types originally fitted which I've had no good straight out of the box.

Johnny B

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Re: AJS 1955 350 engine problem

Postby r wheat » Mon Aug 13, 2018 5:39 pm

Hi, tried to bump start the bike by being pushed with no result, then out of frustration gave it a good kick (on the kick start ) and it fired up and ran and has done ever since. I have no idea what changed, not complaining but it does not make sense. once again thanks for all your in put. cheers Richard

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Re: AJS 1955 350 engine problem

Postby MalcW » Tue Aug 14, 2018 8:02 am

My 650 was the same. rebuilt mag, new carb etc. but apart from the odd cough it didn't want to play. I'd almost stopped thinking of it as a motorcycle and more of a piece of gym equipment. Then it suddenly started, which was one hell of a shock! It's been reliable ever since. Just make a mental note of ignition advance, choke and throttle positions.

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Re: AJS 1955 350 engine problem

Postby Rob Harknett » Tue Aug 14, 2018 8:52 am

r wheat wrote:Hi, tried to bump start the bike by being pushed with no result, then out of frustration gave it a good kick (on the kick start ) and it fired up and ran and has done ever since. I have no idea what changed, not complaining but it does not make sense. once again thanks for all your in put. cheers Richard

It must have been something very simple like blocked carb jet. Or something sticking like float needle. The latter will sometimes only stick when in use, chamber full of fuel. So bike runs a bit then more or less runs out of fuel.

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