How to repair an eccentric lobe

[ADAM GIBB]

Can anyone suggest a god method for repairing the surface of the eccentric lobe that is found on the propeller shaft gear of a Johnson A? Is there a way to weld up the pitts/wear and have the surface machined. How would this be bet approached?

Adam

[Mumbles]

There’s lots of meat on the cam so it can be turned without building it up. The piston stroke remains the same and resurfacing doesn’t seem to affect the pumps capabilities.

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[Tubs]

Someone told me decades ago that the pits are actually
a beneficial. They increase the amount of lubricant
being carried on the surface. As I don’t have the skills
or the tooling that Mumbles, Richard, T2 and others
have this philosophy has worked well for me over the
years.

A "Boathouse Repair" is one thats done without having tools or the skills to do it properly.

[RICHARD A. WHITE]

Quite simple actually and Tubs, thanks 🙂

You simply machine a cylinder with an ID .001 smaller than the OD of your cam, and an ID closer to what it was originally, heat the sleeve and slide it on. You may have to machine the lobe to bring it back to an actual eccentric, But that in itself it not that great of a task for a decent machinist. It can be done in a lathe or a milling machine.

Get a good chunk of Ampco(sp) Bronze, to make the ring/sleeve, and another to make the disc to attach to the water pump piston, and it should not wear out for at least another 200 years…

http://www.richardsoutboardtools.com
classicomctools@gmail.com

[ADAM GIBB]

Tubs,
My pits look like the photo that mumbles posted. They look to have a health appetite for the bottom of the pump plunger.

Mumbles,
So are you suggesting that the overall diameter of the eccentric can be reduced and the the pump will still operate as it should with the same stroke but the travel will start and end slightly lower (by the amount that was removed)

Richard,
I am not sure I follow your method 100%. Do you make a repair sleeve, or a whole new cam?

In either case, how do you chuck the gear in a lathe so that it rotates around the center of the cam rather than the center of the shaft.

[Mumbles]

Sorry Adam, I had a blonde moment there. I was thinking of something else. The stroke does get shortened, but only by a small amount but it doesn’t seem to make any difference to the pumps output.

To set up the cam, I’m using the four-jaw chuck and a dial indicator.

EDIT: What I meant was, the length of the actual stroke remains the same, but the depth of the piston in its bore isn’t quite as deep as it was.

[RICHARD A. WHITE]

quote Adam1961:

Tubs,
My pits look like the photo that mumbles posted. They look to have a health appetite for the bottom of the pump plunger.

Mumbles,
So are you suggesting that the overall diameter of the eccentric can be reduced and the the pump will still operate as it should with the same stroke but the travel will start and end slightly lower (by the amount that was removed)

Richard,
I am not sure I follow your method 100%. Do you make a repair sleeve, or a whole new cam?

In either case, how do you chuck the gear in a lathe so that it rotates around the center of the cam rather than the center of the shaft.

Either way. I assume the gear in the picture has a hole thru it. It may or may not use a locking screw or pressed in pin to hold it to the shaft.
I will make a video explaining the process.. Gimme a bit

Ugh, by the time I said all that I wanted to say, I was over 700 gigs…LOL
Yes you can go either way really, a sleeve or remake the entire lobe.

http://www.richardsoutboardtools.com
classicomctools@gmail.com

[hotrod]

When a lathe isn’t available, I file the cam down, all around, keeping the file flat. The pump stroke stays the same if you take the same depth off the low side of the cam as you take off the high side of the cam. Finish it with sandpaper.

[ADAM GIBB]

Thanks everyone. I will try to round up a local machinist that will take this on. Hard to find people that will do one off jobs around here.

How much could be removed, before it would be necessary to build it back up? If material is removed from the lobe all around, the pump will operate, but lower in the travel. would .020 be OK, or if that much is removed, should it be built back up to standard?

[RICHARD A. WHITE]

If you have .02 removed from the entire circumference of the lobe you will never know it while running.

http://www.richardsoutboardtools.com
classicomctools@gmail.com

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