1928 K6 350 Big Port Sturmey Archer Gearbox

Information relating to Matchless and AJS Models built prior to 1939
Posts: 3
Joined: Sat May 02, 2015 2:15 pm
Location: DERBYSHIRE UK

1928 K6 350 Big Port Sturmey Archer Gearbox

Postby Ferring100 » Mon Sep 07, 2015 9:02 pm

Getting to know my recently purchased Big Port which has developed an annoying habit of jumping out of 2nd and mostly 3rd gear in Sturmey Archer gearbox. Initial investigation shows well packed with grease (at least a good handful i dragged out). I have removed the layshaft and all gears look fine. The hand gear shift mechanism is set correctly and moves the mainshaft sliding dog to correct position. No signs of apparent wear on dogs. The mainshaft tightens up nicely with no movement when I try and move the clutch sprocket. I assume the forces that keep the sliding dog gear in chosen position is friction between gear dogs and friction between sliding dog and splined mainshaft ? Vibration overcoming these forces and allowing dogs to slip out of engagement ?. Can you have too much grease ? Any thoughts on what else to look for appreciated.

Committee
User avatar
Posts: 9036
Joined: Mon Jan 01, 1990 12:00 am
Location: ESSEX UK

Re: 1928 K6 350 Big Port Sturmey Archer Gearbox

Postby Rob Harknett » Mon Sep 07, 2015 11:39 pm

A quick reply is, is the grease too heavy. An egg cup full of oil is often used to loosen up the old gear boxes.

Committee
User avatar
Posts: 9036
Joined: Mon Jan 01, 1990 12:00 am
Location: ESSEX UK

Re: 1928 K6 350 Big Port Sturmey Archer Gearbox

Postby Rob Harknett » Tue Sep 08, 2015 8:50 am


Posts: 3
Joined: Sat May 02, 2015 2:15 pm
Location: DERBYSHIRE UK

Re: 1928 K6 350 Big Port Sturmey Archer Gearbox

Postby Ferring100 » Mon Sep 28, 2015 5:15 pm

A quick update on my 'jumping out of gears' problem. I placed a thick plastic washer on the gear lever shaft to make it difficult to Jump out of third gear. I went out for a spin and found out the root of the problem. Turns out the gear disengagement was a symptom of ... Clutch slip ! I had originally ruled this out as I never felt the clutch going, but the clutch slipping and gear disengagement was instantaneous, generally when torque to the back wheel was at its max, i.e in third gear, low speed, things not quite warmed up, chugging up an incline. I had innocently sprayed the chain liberally with lube a while back and some of it had found its way the short distance between the metal clutch plates and clutch sprocket contaminating the cork. Dismantling the 'dry' clutch mechanism, wiping the oil from metal and cork elements with cotton wool and a bit of white spirit seems to have cured about 95% of the problem, and tightening up the clutch spring will hopefully cure the rest. It's going to be tricky preventing chain lube from finding its way to the small radial gap between clutch plate and clutch sprocket, but at least I know what to do next time. On the plus side I have learnt how the gearbox works which is beautifully simple. Anyway I had a great day out today pottering around the back lanes of the beautiful Peak District today and have thoroughly enjoyed getting to know and fettling the Big Port. My 18CS is feeling a bit neglected this year.

Committee
User avatar
Posts: 9036
Joined: Mon Jan 01, 1990 12:00 am
Location: ESSEX UK

Re: 1928 K6 350 Big Port Sturmey Archer Gearbox

Postby Rob Harknett » Mon Sep 28, 2015 7:12 pm

If it happens again, check the gear change linkage allows the lever to be in the correct position in the gate.

Posts: 3
Joined: Sat May 02, 2015 2:15 pm
Location: DERBYSHIRE UK

Re: 1928 K6 350 Big Port Sturmey Archer Gearbox

Postby Ferring100 » Mon Jan 02, 2017 2:25 pm

Decided to get the gear dogs 'undercut' by a local machine shop. A maximum 3 degree undercut on each dog seems to be the perceived wisdom on the driving side of bottom, top and mainshaft sliding gears. The top gear wheel was painful to remove but on closer inspection had some rounding off which would not have helped keeping the gears togeather under load. Seems to have done the job. Gears select nicely with a satisfying 'clunk'. Hopefully you can see the newly machined undercuts from the photos.
You do not have the required permissions to view the files attached to this post.

Return to Prewar

Who is online

Users browsing this forum: No registered users and 3 guests