New oil pump guide pins too long!

[Holgs]

My first post after joining the clubs a few months ago…. I am just finishing a 1953 AJS 18 (photos below) after a full four months restoration to join my ‘63 Norton Atlas that I have for thirty years. However, at the very last stage I ran into issues with the oil pump - I might have been just unlucky, but it might be an issue that may effect others…

I was starting the AJS the other day for the first time in almost fifty years. Oil return briefly after a minute, then stopped. When I did not see any further oil returning after two minutes, I started investigating… Stripping the pump again, it turned out that the oil pump plunger gear was severely worn in one spot and the newly fitted guide in the bolt was deeply marked on the top surface. Further investigation revealed that the the new guide pin, when in the bolt, is about 0.65mm (25 thou) longer than the old worn one, a combination of being a little longer and having a different taper at the tailed bottom end: the new one is 31.25mm rather than 30.60mm in total. The friction damaged the plunger gear when the pin hit a ‘tight spot’ in the groove when warmed up after running for a minute or so. A initial turn by hand showed the pump moving, so I checked no further, unfortunately. However, the axle appears to be ok when visually inspected through the oil pump tunnel, possibly saved by the slightly worn gear on the plunger. Two photos attached show the marked pin end and wear on the plunger. After this, a friend checked his new guide pin too (from the same supplier at the same time) and it is too long by a full 1.05mm and movement of the pump and engine is very tight when turning. However, he hasn’t started up his G3 yet, so there was no damage.

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I let the supplier know and now I am after a new or second hand oil pump plunger now to get the bike back on the road for her 70th anniversary as the rest of the bike is ready. I just registered the bike as the third (!) owner and was delighted to be able to keep the original buff log book and get it stamped. The bike was originally registered in Ireland, in Cork in 1953 then sold in 1974, run for a year and then put into a shed for 48 years…

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[Reynard24]

Before you ride it you need to reverse the front wheel, the brake drum should be on the drive side. The brake torque arm is currently in compression and should be in tension. It would be a shame to spoil all your hard work if it failed and caused you to drop the machine.

[Mollbhan]

Agreed, I have a mod 18, the brake drum is on the wrong side which would be an MOT failure.

[SPRIDDLER]

I let the supplier know................... but it might be an issue that may effect others…

Who was the supplier?


Lovely bike. Welcome to the Forums.

[Joker_Bones]

That is a bitter pill to swallow. I hope the axle is okay as you say.

I have a G80 engine apart at the monent. The crankcase where the guide pin bolt screws in was damaged, when I was cleaning it up it it occurred to me I needed to be careful not to deepen the seat for the bolt as the guide pin would sit further in. Having read this I will certainly be checking how far the guide pin is sitting in the plunger bore.

[Holgs]

Spriddler, I got the pins from Steven from AMC Classic Spares, but I guess all the guide pins are from the same source, so it could possibly happen with any new pins? I sent him a message but unfortunately he is not reachable at the moment due to a family bereavement.
Joker-Bones - Measuring and comparing the pin assembly and also ‘inverting’ the plunger in the tunnel with the guide pin in place to check free movement before assembling the pump will show if there is a problem. Grinding the bottom taper end to the right angle and length would avoid damage as the design of the bolt does not allow a spacer or washer to be added.

The front brake is correct for 1953 models, btw: ‘52 brake gear, bracket and lever was on the left, switched in ‘53 to the right before re-design of the whole front brake thereafter. Even under compression there is no chance of buckling - it is fixed both ends, so the effective unsupported length is halved and the area moment of inertia is very high, given the bracket is 4.5mm thick and 7/8” wide. I have little confidence that 7” brake will ever be efficient enough to reach anywhere near critical load on the bracket. The fact that bike was ridden up and down Cork’s steepest hill on a daily commute for twenty years with that set-up is assuring enough…

[clive]

Holger I wonder where you get your information about the change in brake from the left to the right in 1953? I have been in the club for 43 years and never heard of this change nor seen a 53 bike set up in thus way. Its interesting to note that neither the AJS or Matchless factory issued brochures for 1953 show the change to the right hand side. I can see no logical reason for the change for one year only. I would not risk it and you are always likely to be advised you have the wheel the wrong way round. I take it you have found Christian's archives which are a great source of information and well worth a look. http://archives.jampot.dk/

[Joker_Bones]

Yes... I had a look at mine and as you say the pin sits on the chamfer at its reduced end.
I have a different housing screw to yours. It does not have the reduced shoulder under the head, so I could put a spacer under the head. Neither does it have much material remaining at the top of the head, the last photo shows the depth of the drilling.

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[Holgs]

Is it a new guide pin and if so, how does it compare to the old one? Washer will definitely work for you.

Clive, I stand corrected, not sure where I got that info, but let you know if I find the source. Will swap over, so, have plenty of time on my hands till a new pump plunger arrives… thanks for the advice!

[Joker_Bones]

It is the pin that came with the engine, I don't have a new one.