|
By MoonShadow - 7 Years Ago
|
Guys I have a Y-Block Mallory dual point up on EBAY. It has a vacuum port on the side and some sort of contact pad behind it. I've never seen one of these before. I was told that some of the Mallory's had a vacuum advance system. I'm wondering if it delays the mechanical advance until vacuum is up enough to pull the pad away from the advance plate. Total guess! Anyway take a look at my listing. I'd prefer to sell to one of the Y's guys if possible. Chuck http://www.ebay.com/itm/332155733571?ssPageName=STRK:MESELX:IT&_trksid=p3984.m1555.l2649 |
|
By Ted - 7 Years Ago
|
Chuck.
That ‘brake’ on the Mallory distributor you have is similar to what’s found on the ’48 and earlier Flathead crab distributors. It works by limiting the amount of mechanical advance of the vacuum signal is removed. On the early flattie, the distributor hooks up to the manifold vacuum and simply allows the amount of ignition advance to back up when the engine vacuum drops at full throttle. It does that by putting spring pressure on the centrifugal advance mechanism and limiting the amount of advance the distributor can supply. It also helps with the starting as the distributor would be at full retard during cranking. Once started, the engine’s manifold vacuum would permit a given amount of additional advance under normal driving and cruising while any reduction in manifold vacuum would put pressure on the distributor and limit the amount of advance. I trust that makes sense.
|
|
By MoonShadow - 7 Years Ago
|
|
Thanks Ted, It does make sense. I didn't want to completely disassemble the unit to figure it out. I find it a bit puzzling that I'd never seen or even heard of this before. Chuck
|
|
By DANIEL TINDER - 4 Years Ago
|
Ted (3/20/2017)
Chuck.
That ‘brake’ on the Mallory distributor you have is similar to what’s found on the ’48 and earlier Flathead crab distributors. It works by limiting the amount of mechanical advance of the vacuum signal is removed. On the early flattie, the distributor hooks up to the manifold vacuum and simply allows the amount of ignition advance to back up when the engine vacuum drops at full throttle. It does that by putting spring pressure on the centrifugal advance mechanism and limiting the amount of advance the distributor can supply. It also helps with the starting as the distributor would be at full retard during cranking. Once started, the engine’s manifold vacuum would permit a given amount of additional advance under normal driving and cruising while any reduction in manifold vacuum would put pressure on the distributor and limit the amount of advance. I trust that makes sense.
Ted,
I recently acquired a late 50s NOS ‘ZC’ unit, designed to replace a Loadomatic distributor. It’s vacuum connection hooks directly into the Holley 4000’s spark control valve position. Would you know if that intended vacuum signal strength (way weaker than manifold vacuum?) will likely rule out the practicality of using the Mallory’s vacuum advance brake when paired with a modern carb?
BTW: I also wonder if my 55’s tach cable will work with this model? I know the modern (discontinued) Mallory dual point units require a special cable.
There are virtually no exploded diagrams & instructions online for lube/maintenance or advance adjustment of this vintage distributor. It’s NOS operation manual left that out. If anyone has relevant experience/advice to offer, I would appreciate it. I do have a Sun distributor machine, so I CAN check advance operation/curve, but recurving would require special springs/knowledge I don’t possess. The unit should also be disassembled and cleaned, since the 62 year old factory lube has likely turned to varnish. So, I’m thinking it should probably be sent to someone who specializes in rebuilding/adjusting vintage Mallory distributors (?). Recommendation?
I am tempted to just drop it in and see how it’s factory settings would work with my original motor, but installing it requires cutting the ends off my plug wires. I also wouldn’t want to mess with the spark control (currently functioning perfectly) setup on my Pony teapot, unless I was actually needing to replace the OEM distributor (only bought the Mallory since I want to stay 6V after eventual carb/manifold upgrade).
Regards.
Dan
|
|
By DANIEL TINDER - 4 Years Ago
|
Still looking for a vintage Mallory service recommendation (?).
BTW: Looks like orig. OEM tach cable should work. Also, though not experiencing any engine misfires, my Motorcraft plug wires ARE over 15 yrs. old. Not so much the expense of replacement concerning as the labor involved (just to test the Mallory). I might buy a new set though to cut the ends off of, and jerry rig their temporary installation (leaving the old ones in position), then put them away along with the Mallory until bigger carb/manifold combo finally gets installed.
|
|
By DANIEL TINDER - 3 Years Ago
|
Ted (3/20/2017)
Chuck.
That ‘brake’ on the Mallory distributor you have is similar to what’s found on the ’48 and earlier Flathead crab distributors. It works by limiting the amount of mechanical advance of the vacuum signal is removed. On the early flattie, the distributor hooks up to the manifold vacuum and simply allows the amount of ignition advance to back up when the engine vacuum drops at full throttle. It does that by putting spring pressure on the centrifugal advance mechanism and limiting the amount of advance the distributor can supply. It also helps with the starting as the distributor would be at full retard during cranking. Once started, the engine’s manifold vacuum would permit a given amount of additional advance under normal driving and cruising while any reduction in manifold vacuum would put pressure on the distributor and limit the amount of advance. I trust that makes sense.
Just curious, but the Mallory ‘HP’ (high performance) version without the vacuum brake has often been praised here for street use, I understand the ‘brake’ mechanism likely wouldn’t be needed for racing applications (revs always kept high), but, other than the goal of simplicity/cost-saving, why wouldn’t it’s absence be seriously problematic on a daily driver/street-rod car? Even the ready availability of 50s era leaded 100-plus octane gasoline would still probably not prevent knock on a seriously high-compression/hopped-up motor under low rpm load, especially if the initial advance was set high enough to maximize performance (?). Or, maybe if the distributor’s set performance curve brings max advance in quickly, and your cam is so hot that your idle has to be super high anyway, then at full throttle load it doesn’t knock? What am I missing?
|