engine and drivetrain The 0.490" Conspiracy

[Healey3000]

Hi,

 

When I was messing around with my '67 Austin Healey 3000 distributor, as I designed a cam sensor for that engine, I noted that the diameter of the shaft was an oddball dimension.  0.490" does not equate to anything standard that I could think of.  I chalked it up to British eccentricity.  Then I found that some Chevy distributors of that vintage also had .490" shafts.  Hmm.

 

The plot thickens.  I pulled some relatively recent Nissan optical CAS units off Maxima's and Villager's and found that they too used the same diameter shafts.  Keep in mind that these are on new engine designs and therefore have no reason to carry over  a legacy dimension.  This makes it nearly impossible to find standard bushings or bearings, if you want to use the shafts.

 

I just measured a 2002 distributor gear that a fellow forum member was kind enough to provide, and, you guessed it, 0.490".  Et tu, BMW??

 

It's a conspiracy, I tell you!

[roadhog0]

My guess for the reason of that is that when they cast the dizzy housings they cast that part to .500 inches +/- some then they have a little meet to turn down to .490. That's my guess at least....

[TobyB]

Yeah, I was gonna guess to fit a 0.500 housing diameter, but .010 is a pretty loose fit...

 

t

[xferboy]

or 12.5mm

 

.490" = 12.446mm

.054mm tolerance (.0021")

 

.5" = 12.7

Edited March 15, 2015 by xferboy

[Healey3000]

or 12.5mm

 

.490" = 12.446mm

.054mm tolerance (.0021")

 

.5" = 12.7

Highly doubtful it was metric since both the Brits and Yanks used this.

 

There's probably some arcane reason that goes back years, like the gauge of railway tracks based on a horse carriage.

[Mike Self]

 

 

There's probably some arcane reason that goes back years, like the gauge of railway tracks based on a horse carriage.

Actually railway standard gauge (4' 8 1/2") goes back to Imperial Rome--it was the decreed and standardized track for all wagons and carts in the Empire, so designed due to the stepping stones placed at intersections in Roman cities so citizens could cross the streets (which had open drains) without getting either shoes or togas wet or messy.  (Take a look at pictures of streets in Pompeii) This same standard was used on carts in English coal mines, which ran on tracks, and since the first railroads-and their cars and locomotives--were built in England, they adapted the track that mine cart builders were already using (and no, I'm not making this up!)

 

Off topic trivia for today!

 

mike

[Healey3000]

Actually railway standard gauge (4' 8 1/2") goes back to Imperial Rome--it was the decreed and standardized track for all wagons and carts in the Empire, so designed due to the stepping stones placed at intersections in Roman cities so citizens could cross the streets (which had open drains) without getting either shoes or togas wet or messy.  (Take a look at pictures of streets in Pompeii) This same standard was used on carts in English coal mines, which ran on tracks, and since the first railroads-and their cars and locomotives--were built in England, they adapted the track that mine cart builders were already using (and no, I'm not making this up!)

 

Off topic trivia for today!

 

mike

I do remember reading this at one point.  Now, why did the Brits drive on the left and the Continent on the right?

[02Les]

I do remember reading this at one point.  Now, why did the Brits drive on the left and the Continent on the right?

I believe it's another Roman time thing. To do with the sword hand (mostly right) to fend off the bandits coming in the opposite direction. So they kept to the left on their horses. No clue why us Brits kept it up and the Romans swapped over. Maybe there was a lot of lefties in later years.

I think we drive boats on the right....not sure.

[xferboy]

According to a show I saw on one of the smart channels (H2 or the such), the Continent started driving on the left, but then the Conestoga wagon came along with the seat and brake lever low and on left (rather than front center).  http://en.wikipedia.org/wiki/Conestoga_wagon%C2'> That's when the switch came.

 

These wagons were named for the area they came from, Conestoga.  Also cigars were produced in that area, and the slang for stogie was born.

 

All this because I don't have a heated garage and cold winters   Any errors in fact can be blamed on that show.

 

Also, other slang explained, freeways, turn pikes and hiways.