AJS & Matchless Owners Club

Can anyone please tell me what the approximate gap between the end of the aluminium fork slider and the screw thread on the end of the chromed fork cover extension should be. On my so far unmolested 1950 model 18 it is about 1/32" but when I assembled my 1949 forks with new phosphor bronze bush and oil seal the fork cover extension will not screw down properly. There is a gap of at least 3/32" between the shoulder of the chromed fork cover extension and the top of the lower slider with at least two threads still exposed. I do not remember it looking like this before I stripped the forks down. I have measured everything comparing the old oil seal thickness and the shoulder on the old bakelite bush compared to the new oil seal and the shoulder on the phosphor bronze bush . The shoulder on the bushes are the same size and the new oil seal is 0.010" thicker than the old one, but that is not enough to account for the gap that I have. I have measured the depth of the recess in the fork slider and it shows that when everything is assembled there will be a gap of 0.080", which just does not look right. I am considering reducing the height of the phosphor bronze bush to allow the oil seal to fit a little lower, to in turn allow the chromed fork cover extension to screw down closer to the top of the aluminium slider. Before I do this can anyone tell me if such a big gap between these faces is normal. In all of the photographs I have seen , as far as I can tell there is no perceivable gap between the chromed fork cover extension and the lower slider.

Hi

There's no gap on my 61 G3 and there wasn't before restoration - have you confirmed your replacement top bushes are the correct OD at the flange and are sitting fully located against the shoulder in the slider?

Regards Mick

Hi Mick,
Yes the new bushes are the correct size and are down on the shoulder in the slider. Measuring the depth of the shoulder from the top of the slider and then adding the thickness of the flange on the bush. the thickness of the oil seal and the threaded portion of the end of the chromed fork cover extension and comparing the difference, it is clear that the chrome extension is not going to screw all of the way in. Depth of shoulder in slider is 0.870" Thickness of flange on the bush is 0.200" thickness of oil seal is 0.440" and the length of thread on the chrome extension is 0.320" and I have not included the thickness of the paper washer that fits under the oil seal. Total thickness of parts to fit into the 0.870" deep recess is 0.960" That leaves a gap of 0.090" between the top of the slider and the underneath of the chrome extension. It will just look wrong. As the new oil seal is the double lipped type with a thin single outer wall I propose to put a chamfer around the outer diameter of the top of the bush to allow the oil seal to fit lower down into the recess enough to get the chromed extension to screw down properly.
Regards
David

Invicta wrote:There is a gap of at least 3/32" between the shoulder of the chromed fork cover extension and the top of the lower slider with at least two threads still exposed. I do not remember it looking like this before I stripped the forks down.

When I rebuilt my accident-bent forks 7 years ago I fitted new chrome slider extensions and had (still have) exactly the same gap. The oil seals and bushes are fully 'home' in the top of the sliders. Like yours, there wasn't a gap previously. I considered parting a bit off the threaded end or fitting an 'O' ring to fill the gap............I'd forgotten about it before reading your post and the forks work O.K.

Similar situation when I rebuilt my G3 forks last winter. The (double lip) oil seals were the easiest to reduce in height by judicious grinding at the bottom of the exposed steel side walls. If your seals are fully rubberised then probably the bronze bush would be better tackled, as you describe. I assume you are not fitting a paper washer, btw?

Hi

Just measured the thread length on one of my old slider extensions, 0.295" - less than you're seeing but still not enough to remedy the gap.

Do you have the facilities to turn 90 thou off of the bottom surface of the bush shoulder?

Regards Mick

Hi Mick,
No I don't have a lathe , but lots of files. As Ron suggested I could reduce the bottom of the oil seal as it is the thin walled metal type or chamfer the top outside diameter of the bush . Either method will achieve the desired objective.
Regards
David

I used a grinding wheel, making sure to mark the desired finished depth first as grinding is quick! To grip the slider extension and turn the last half turn I used jubilee clips (2) around old inner tube - closed the gap very satisfactorily.