Shadow Build

[John H]

I wouldn't survive as a teacher. You need to be looking at a clutch while reading this. Come by when you can. Here is an explanation that is better than mine. There are many more articles like this in old Vincent books and magazines.

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[John H]

While I had the parts laid out I decided to rebuild an extra clutch plate carrier. It's easy to put the clutch shoe links on the wrong pin.

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Another important item is getting the primary clutch plate to lift evenly when the clutch lever is pulled. So all 6 springs need to read within a pound of each other. Small shims are added inside the bottom of the thimble to correct the variations.

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[John H]

Measuring the 3 different shoe carriers, it became obvious that only one was usable. Checking closer shows it needs straightened so the clutch shoes set correctly in the drum. Also the thrust bushing surface had to be resurfaces as well as the end of the splined bore.

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The only way I could locate this for machining was to make an expanding mandrel that would fit the splined bore. Just another tool to go in the Vincent tool box.

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[Lotus54]

I like the mandrel you made- I need to keep that in mind.
A pipe thread for expansion?

Did you have to weld up and turn back down for resurfacing? Or perhaps just turn down a bit?

[John H]

Yes, the expander is a pipe plug. The trick to doing this on an old lathe is to drill, thread and saw cut, then turn the diameter required for use without removing from the lathe.
I had to remove only a few thousandth to on all 3 surfaces to get things true again. The chain wheel rides on the the shoe carrier and the running end clearance is set at .006" so I had to keep that in mind when refinishing the surfaces.

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The clutch shoes have new pivot bushings installed and spring pressure set. The 2 driving 'long' drive shoes require more spring pressure than the braking 'short' shoe. Lots of controversy as to just how much pressure the braking shoe should have. Much depends on the type of lining and all around wear.

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When in neutral and the drum is turning, it is the centralizer pins against the post that keeps the shoes from dragging. The plunger in one shoe wasn't making contact so a special counterbore tool was used to deepen the counterbore by .040".
Boy! to think, I could have adapted a modern mulit-plate clutch in less than a day makes me wonder why I have spent so much time restoring this clutch.

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[John H]

Last job on the clutch is to arc the shoes to the drum. I made a special tool by using an old clutch drum. It was bored out and coarse sandpaper was glued around inside. With the shoes mounted on the carrier I can manually force the shoes out against the drum as the lathe slowly turning. This arcs the shoes perfectly. The clutch is FINISHED!

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[Lotus54]

What a great way to arc the shoes. I used to have a show arcing gauge, but darn if I can find it anymore. One of those things I’ve had for 40 years and never needed- until I can’t find it.

[John H]

This is a short video clip of the shoe arcing in progress. https://www.youtube.com/shorts/1gDAuVH8rHg

[John H]

With the clutch complete it's back to the crank. The new oversize crank pin is 1.0675" so the flywheels will get bored to 1.065". The later year flywheels seem to be tougher steel but since I have no way of checking it, .0025" is a safe press fit tolerance. First step is bolt a plate to the mill table and bore a hole to fit the main shaft. A cross drilled hole is for a bolt to pinch the main. This assures that the new bore is parallel to the main shafts.

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The stroke on a stock Vincent is 90mm so moving the mill table 45mm centers the cutter exactly on the old pin bore. Both flywheels will be finished with the same setup. The trick is getting a very smooth bore at exactly 1.065". An old machinist trick is to reverse the rotation of the cutter to smooth the bore. This can change the dimension as much as .0005".

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[Lotus54]

Looking great.
Thanks for the tip on reversing cutter. I can see where that could ‘hone’ it lightly and leave a better finish and slightly increase size.
I can’t do that with my little tiny mill- but I can with my little tiny lathe. I will keep that in mind.