More Technical Esoterica

[ensys]

RE: Distributor mechanical advance weights.

While I cannot name the source (other than noting it was not the FSM), I am led to believe that the total mechanical advance is identified by a stamping on one of the weight pairs; i.e., "8.5" would denote a pair that provides 17deg. of total mechanical advance, etc.

Can anyone confirm or correct? Source?

I thank you for your attention.

 

 

[jonathanrussell]

@ensys.... just seeing this. What you wrote above is how I understand it AND it is consistent with what I figured out while rebuilding a 1972 manual transmission D612-53 distributor this past week. 

For the D612-53, the advance curve is documented in the 1972 FSM on pages EC-12, EC-28, and EC-29. The curves show distributor RPM, not crankshaft RPM so you have to double the number to arrive at the crank advance number.

The manual shows an average curve of 12x2=24. When I rebuilt the distributor, I was able to see that the top weight is stamped with the number 12....indicating 24 degrees of mechanical advance at the crank...consistent with the manual.

FYI, the technical bulletin manual for Jan 1969 through Dec 1972 has a section that shows advance curves for some of the distributor models that Datsun had produced to date at that time. So if your distributor is an early one you might find it listed in this technical bulletin book starting on page 88.

The models listed in the manual for the 240z are D612-52, D613-01, D614-51, and D614-52.

 

In case you have the euro spec distributor, the advance curve works as follows....based on my research and notes (also consistent with my testing using timing light and mityvac).

Initial 17 degrees at 650 rpm

Mechanical is 6 distributor degrees or 12 crankshaft degrees. Starts at 900 rpm and reaches 12 crank degrees by 2,000 rpm. I haven't rebuilt my euro spec distributor but I would expect the weights to have a 6 (or something close) stamped on the top.

Vacuum is 5.5 distributor degrees or 11 crankshaft degrees. Starts at 3.94 inHG and reaches 11 crankshaft degrees by 9.6 inHG.