> I'm now wondering about the vacuum advance. How freely should the two
> contact breaker base plates move against each other?
A fair amount of drag is normal. Some expensive cars had bearings between
the plates, but not Triumphs.
> Mine take some effort to
> rotate, and I can't imagine the vacuum from the carb being enough
> to move them.
The force of the vacuum is multiplied by the area of the diaphragm. Not
much force when it's only a 1/4" (or smaller) hole, but the diaphragm is
much larger. It's a square law, each doubling of the diameter multiplies
the force by 4.
> By hooking up a tube to the vacuum input, I
> can get the
> plates to move a hair or two (using NAFTA-sized sucking action).
> Should it take this much effort?
I assume you're talking about lung power rather than a MityVac or whatever
... yeah it's normal to not be able to move it much by sucking on the hose.
A MityVac is fairly inexpensive, and a worthwhile investment IMO. Here's a
nice kit on eBay with a buy it now of $50
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=2486548090
The factory service manual has specs for actual vacuum advance for different
levels of vacuum, so with a MityVac, you can check the overall advance
mechanism and make sure it's working properly.
Or if you have an air compressor, HF sells an air-powered vacuum pump that
will do instead. It's worthless for it's stated purpose IMO, but makes a
good vacuum source for testing automotive systems once you add a vacuum
gauge and an adjustable valve on the air inlet.
http://www.harborfreight.com/cpi/ctaf/Displayitem.taf?itemnumber=3952
I see it's priced at $15 now, but it's frequently on sale for $10. Add a
canning jar and some tubing, and it's perfect for changing brake or dashpot
fluif.
Randall
Check out the new British Cars Forum:
http://www.team.net/the-local/tiki-view_forum.php?forumId=8
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