BJ8 Distributor Question

[stever]

I have a good condition distributor marked as follows:
25D 40966 J
6 73
My question: Is this the correct distributor for a 1965 BJ8 with VIN 65HBJ8L28308? I ask this because the vacuum advance fitting is not a threaded connection but a smooth small pipe that one would connect via a hose and clamp not the threaded connection that is on the car. The MOSS catalogue gives 25D6 40966 as the part number. Is this one the "same" thing??? Thanks in advance!

 

[Keoke]

Stever, that is the correct series distributor for BJ8's. However, there are a series of numbers on the nose of the vac advance unit that define its suitability for a given engine.These numbers should be checked against the original specification.-FWIW---Keoke

 

[Keoke]

Hi Andrew, The advance curve is inscribed on the nose of the vac advance unit and is not encoded on the body of the distributor.-Regards Keoke /ubbthreads/images/graemlins/yesnod.gif

 

[AndrewMawson]

[ QUOTE ]
I have a good condition distributor marked as follows:
25D 40966 J
6 73
My question: Is this the correct distributor for a 1965 BJ8 with VIN 65HBJ8L28308? I ask this because the vacuum advance fitting is not a threaded connection but a smooth small pipe that one would connect via a hose and clamp not the threaded connection that is on the car. The MOSS catalogue gives 25D6 40966 as the part number. Is this one the "same" thing??? Thanks in advance!

[/ QUOTE ]

The '40966' defines the advance curve - apparantly the early ones had screw vac connections (mine was screw and went down the line in Sept 1964) and later ones had the push on fitting.

Your distributor was made ' 6/73' ie June 1973 so obviously isn't the original one on a 1965 BJ8, but then again my Sept '64 made vehicle is chassis no 28730 so yours is actually earlier than that ! 1965 must be when it was registered in the States.

/ubbthreads/images/graemlins/england.gif /ubbthreads/images/graemlins/thirsty.gif /ubbthreads/images/graemlins/thirsty.gif /ubbthreads/images/graemlins/england.gif

 

[Rick60]

Keoke, AFAIK the 40966 describes (encoded) the mechanical advance curve, while the numbers on the vacuum unit decribe the vacuum advance curve.

Regards

 

[piman]

Hello all,

Rick is quite correct, for the 40966 the correct vacuum unit is a 5/12/8. The first two figures are inches of mercury, start to funtion and maximum advance respectively, with the last being the maximum vacuum advance in degrees.
Interestingly the data I have gives a mechanical maximum advance of 17 - 19 degrees at 3,200 rpm. This equates to an egine speed of 6,400 which I would have thought an unlikely figure?

Alec

 

[AndrewMawson]

[ QUOTE ]

Hi Andrew, The advance curve is inscribed on the nose of the vac advance unit and is not encoded on the body of the distributor.-Regards Keoke /ubbthreads/images/graemlins/yesnod.gif

[/ QUOTE ]

Sorry Keoke but I have to disagree with you. The 40966 describes the advance at various revs as per:

https://www.telusplanet.net/~chichm/tech/lucas.pdf

This document describes the spec of many Lucas distributors and part of the '40966' spec calls up a vacuum advance unit of 5/12/8 specification.

The KEY spec is 40966 which gives the full component makeup of the complete distributir including the vac advance unit, weights, cams, and springs.

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[Keoke]

I Will Buy that, all I was saying is you can have the correct main assy,and the number quoted was correct, but have the wrong vac unit installed.---Keoke /ubbthreads/images/graemlins/patriot.gif




/ubbthreads/images/graemlins/patriot.gif

 

[Rick60]

@Alec: You're right in doubling the engine revs in relation to the dis revs, but not without doubling the advance degrees as well. That would come out to 36 crankshaft degrees @ 6,400 crankshaft revs. Does this make more sense to you?

@Andrew: Thanks for the link. I knew I had seen it anywhere but couldn't remember the site.

@Keoke: You're completely right, I just wanted to point out the difference between mechanical and vacuum advance and the relating numbers.

 

[piman]

Hello Rick,
I didn't make myself too clear, I understand the double advance, what surprised me was the 6,400 revs, surely a Healeys red line is way below that?

Alec

 

[Rick60]

Alec, I understand what you mean. I see it as a theoretical number (because never reached by engine revving). That would mean you'll never have the full mechanical advance even with engine revving at red line. The only explanation I have is that this dis with the same advance characteristics was set up for more than one engine.

Maybe DMH was far ahead of his time and planning on implanting one of those high revving japanese engines in our 3000s. Sometimes it's good history stops at a certain point. /ubbthreads/images/graemlins/jester.gif

 

[piman]

Hello Rick,
a bit strange, but as far as I know each Lucas disributor was unique to each engine, and in many cases more than one type for a particular engine as that engine developed. Certainly many are very similar but they were dyno tuned to get the best set up.

Alec

 

[healeys4me]

All very interesting. How does a Mallory or other aftermarket supplier account for these unique settings by engine type?

John

 

[piman]

Hello John,
If they are supplying for a specific engine I would guess that they copy the distributor settings that they replace?

Alec

 

[stever]

Thanks, guys! As usual, I have learned a great deal from the members of this forum. It appears that it might be OK for my car. I need to check the vacuum unit numbers, though. Thanks!!

 

[Dave Russell]

[ QUOTE ]
All very interesting. How does a Mallory or other aftermarket supplier account for these unique settings by engine type?
John

[/ QUOTE ]
Aftermarket distributors have advance curves which are almost infinitely adjustable. As are Lucas. By changing advance springs, & weight stops, the distributor can be made to give a great number of different curves & ranges. The same applies to the vacuum advance. Various spring tensions & movement stops can be used to give any desired specs.

A little perspective:
There are a great number of different distributor advance settings as determined by the factory. These settings are based on adequate driveability, fuel economy, & not allowing damage to the engine under the worst cases of fuel selection, temperature, altitude, & driver abuse.

It takes experience, a distributor machine, & possibly a dyno to get a distributor adjusted to perfection on any given engine. If it is really important to you, there are dyno tune shops that can set up your distributor for optimum results.

This having been said, the actual advance characteristics of a distributor are NOT terribly critical as long as the maximum total advance under load does not exceed an amount that will damage the engine. This setting can easily be measured with a timing light & usually varies between 30 & 40 degrees total advance (centrifugal plus initial advance setting), vacuum advance is out of the picture when determining advance at full load. There will be minor differences in fuel milage, throttle response, & power output, which often requires a dyno to tell the difference. The seat of the pants differences will be very small to the average driver with the average engine.
D

 

[healeys4me]

Thanks Dave, good info.

John