| Author |
 Topic Search  Topic Options
|
steve(ill) 
Orange Level Access
Joined: 11 Sep 2009
Location: illinois
Points: 85495
|
 Post Options
 Thanks(0)
 Quote  Reply
 Topic: DIstributor centrifigual advance operation
Posted: 05 Jun 2022 at 7:24pm |
I know that most of the MAGNETOs are timed at TOP DEAD CENTER... then when the tractor starts up the IMPULSE kicks in and advances the spark to 30 degrees ( or 20 or 25 depending on what model of mag)... I think that happens at a couple hundred RPM.. goes to FULL ADVANCE.
When a Distributor is put on a CA or WD45, etc.... Do the weights kick in at 500 RPM and go to FULL ADVANCE, or is it a gradual thing ? I would assume it is similar to the magneto that once the motor is running, the weight springs are fairly week and the advance happens quick......... as compared to many old car engines that the advance is somewhat linear from 1000 RPM to 3000 RPM..
Assume it is not a big deal with tractors that run a constant speed and dont need the throttle response ?
|
|
Like them all, but love the "B"s.
|
 |
|
Sponsored Links
|
|
|
DrAllis
Orange Level Access
Joined: 12 Sep 2009
Points: 21360
|
Post Options
Thanks(0)
Quote Reply
Posted: 05 Jun 2022 at 7:27pm |
|
Each distributor is designed to "full advance" by a certain RPM range as designed by the engineers in charge of specific engine performance. D-17 for example is full advanced 30 degrees at 1800 RPM on early models and when they figured out that wasn't working out (center main crank bearing pounding) they changed to 25 degree advance at 1600 RPM's. The important thing to remember is, ALWAYS set the ignition timing at full throttle !! so the advance is (should be) fully advanced. If this is done and the advance is working correctly, then at a very slow idle (400 RPM) the timing will then be close to TDC so as to not kick back against the starter when cranking.
Edited by DrAllis - 05 Jun 2022 at 7:40pm
|
|
PaulB
Orange Level
Joined: 12 Sep 2009
Location: Rocky Ridge Md
Points: 4928
|
Post Options
Thanks(0)
Quote Reply
Posted: 05 Jun 2022 at 7:35pm |
|
The impulse in a Mag allows for the timing to retard at slower speeds and then above impulse it goes to wherever the spark is set for.
|
|
If it was fun to pull in LOW gear, I could have a John Deere.
Real pullers don't have speed limits.
If you can't make it GO... make it SHINY
|
|
steve(ill)
Orange Level Access
Joined: 11 Sep 2009
Location: illinois
Points: 85495
|
Post Options
Thanks(0)
Quote Reply
Posted: 05 Jun 2022 at 8:20pm |
yes, i realize all that........ I know all distributors advance with speed above idle.. I was just wondering if anyone had ever measured the "advance" at 1000 RPM or 1400 RPM and knew if the advance was a big JUMP to 25 ( or 30 degrees) at 1000 RPM, or was somewhat gradual up to 1800 rpm ?
the "MAG" is either ZERO or 30 degrees, right ? Nothing in between... Just wonder if the distributor was doing the same thing, or working linear more like an auto engine.
Edited by steve(ill) - 05 Jun 2022 at 8:22pm
|
|
Like them all, but love the "B"s.
|
|
steve(ill)
Orange Level Access
Joined: 11 Sep 2009
Location: illinois
Points: 85495
|
Post Options
Thanks(0)
Quote Reply
Posted: 05 Jun 2022 at 8:36pm |
The question came up if you had a B or C tractor with a MAG... and wanted to put ELECTRONIC IGNITION on it, you would need a distributor, the drive, the adapter housing, then spend the money to upgrade to the electronics...
The discussion lead to " does it have to be a specific distributor "... how about a 4 cylinder VW setup already for ELECTRONIC .... and that distributor already has some type to TEE drive similar to the MAG drive.....
This got me thinking, but i have not looked into the size of the DRIVE or how to build an adapter to go from the governor housing to the distributor.. I did look up the DISTRIBUTOR and it has a variable advance from 1000 - 3000 RPM... that could be changed with springs on the weights..
|
|
Like them all, but love the "B"s.
|
|
DrAllis
Orange Level Access
Joined: 12 Sep 2009
Points: 21360
|
Post Options
Thanks(0)
Quote Reply
Posted: 05 Jun 2022 at 9:09pm |
|
Each Delco distributor built by Delco for A-C was designed to give a certain amount of advance at a certain RPM. Using the actual p/n on the dist tag and finding an old distributor testing machine and its spec books would (years ago) give you the info you seek. Good luck with that. Compression ratio plays a part in how the advance curve looks too.
|
|
steve(ill)
Orange Level Access
Joined: 11 Sep 2009
Location: illinois
Points: 85495
|
Post Options
Thanks(0)
Quote Reply
Posted: 05 Jun 2022 at 9:41pm |
|
YEA.... i guess since the MAG works , and it is basically ON - OFF with the advance, that any distributor would work as long as it has the right advance at rated speed.. What happens at 1000 or 1400 probably not important as the tractor does not normally run much at that speed.
|
|
Like them all, but love the "B"s.
|
|
Les Kerf
Orange Level
Joined: 08 May 2020
Location: Idaho
Points: 1050
|
Post Options
Thanks(0)
Quote Reply
Posted: 06 Jun 2022 at 7:50am |
 steve(ill) wrote:
...The discussion lead to " does it have to be a specific distributor "... how about a 4 cylinder VW setup already for ELECTRONIC .... and that distributor already has some type to TEE drive similar to the MAG drive..... |
The 'TEE' drive on a Type 1 VW distributor is offset from center to prevent it from being installed 180 degrees out of phase, so that would certainly need to be addressed during any conversion attempt. By its very nature any centrifugal advance mechanism is progressive. The inertia of the weights, plus the springs attached to the weights, prevent any advance until sufficient RPM increases the centrifugal force enough to throw the weights outward. The shape of the advance curve will then depend upon the geometric relationship of the weights, fulcrum points, etc. and will be ultimately limited by some sort of physical stop which sets the maximum advance parameter. In theory the curve will be nice and smooth, but friction in the pivot pins and springs will cause it to be a bit herky-jerky; this usually isn't a problem but I have seen rust cause things to bind up and cause issues. The impulse mechanism on a magneto retards the spark by physically holding the armature which causes the spring to wind up, the releases it to whip the armature past the magnets at a higher speed; electrical theory tell us that this induces a higher current and voltage through the coil, thus producing a better spark. As the engine speeds up the impulse mechanism is disabled for normal running at the preset advance. The old Caterpillar starting engines (AKA Pony Motors) did not have this impulse mechanism in their magnetos and required a mighty yank on the pull rope to get enough speed to make a good spark. Yes, yes, yes, I know that when they are in good shape they start quite well, but my Dad's old D2 was most definitely NOT in good shape, and I wasted enough of my mis-spent youth wrapping the rope around that flywheel and hearing the disappointing foof-foof-foof of a non-running engine to leave me with a permanent dislike of all things magneto. Your mileage may vary 
|
|
Ed (Ont)
Orange Level
Joined: 08 Nov 2009
Location: New Lowell, Ont
Points: 1410
|
Post Options
Thanks(0)
Quote Reply
Posted: 06 Jun 2022 at 8:13am |
Years ago on our stock cars we locked our chevy distributors at 36 degrees. Start and run at 36. Had to have good gear reduction starter to do that. As technology got better then we used MSD ignition with mechanical advance only with very light advance springs. All in by 2200 rpm or so. Have a nice street engine now. Again MSD and mechanical advance only. Full advance at just over 2000 and 36 to 38 degrees timing. Timed at 2500 rpm. You can do a lot with engine timing. Small changes make huge difference on dyno.
|
|
Steve in NJ
Orange Level Access
Joined: 12 Sep 2009
Location: Andover, NJ
Points: 11925
|
Post Options
Thanks(0)
Quote Reply
Posted: 06 Jun 2022 at 8:56pm |
Steve, Coming in on this pretty late I guess, but as the Doc mentioned, the advance comes in at different spots on each Distributor. The 1111411 Distributor comes in a little sooner than the 1111745 or 1111735. That's why when a customer is in need of a rebuilt Distributor, I ask them what the P/N on the tag is, and match the same Distributor to what the customer has. This way it keeps the same timing in the engine, and the engine performs as it should. I set up the Distributor's centrifical advance differently on Tractor pulling engines mainly due to compression ratio and camshaft used. I can play with that on one my 504 sun machines. It's a game of springs n' weights... HTH Steve@B&B
|
|
39'RC, 43'WC, 48'B, 49'G, 50'WF, 65 Big 10, 67'B-110, 75'716H, 2-620's, & a Motorhead wife
|
|
steve(ill)
Orange Level Access
Joined: 11 Sep 2009
Location: illinois
Points: 85495
|
Post Options
Thanks(0)
Quote Reply
Posted: 06 Jun 2022 at 9:40pm |
|
Thanks for all the data guys.... Was just thinking out loud about ELECTRONIC ignition retrofit in an old MAG tractor.... I dont need right now... but i see very few DISTRIBUTORS ( original) as replacements on the CE125 motors with MAGS.... Just wondering what the possibilities were, some day in the future !
|
|
Like them all, but love the "B"s.
|
|
DaveKamp
Orange Level Access
Joined: 12 Apr 2010
Location: LeClaire, Ia
Points: 5958
|
Post Options
Thanks(1)
Quote Reply
Posted: 07 Jun 2022 at 5:21am |
Looking at advance from a historical standpoint, the purpose of ignition timing control wasn't for RUNNING the engine, it was for STARTING and idling.
On a Model A, you retard the spark to start it, so that it won't kick back and break your arm. This same concept prevents your starter bendix and motor from taking an incredible beating.
The magneto has it's impulse coupling to do the same AS WELL AS provide the hot spark of fast armature fling.
IF you move the spark event to a point AFTER TDC, all you NEED to do to make it start, is get it past the peak of compression, and it will effectively start itself.
It won't run with any considerable power, at any considerable speed, with that late of an ignition event, because the fuel doesn't burn instantly- when you touch off the charge at say... 5 degrees AFTER TDC, the expansion pressure of the fuel will occur at mebbie 10 degrees AFTER, at idle speed... but if you add more throttle, the burn SPEED of that fuel actually occurs SLOWER (there's more fuel and air, but the flame front hasn't made it all the way through until well after piston has reached bottom). If you try to speed the engine up, but you're still starting that fuel at 10deg AFTER, you'll reach a point where it simply cannot spin any faster, as you'll have raw fuel/air going out the exhaust, and the new cylinder charge will be limited by spent gases that haven't cleared in the exhaust stroke.
So we advance the ignition event to get the cylinder pressure to occur EARLIER, and let the crankshaft inertia resolve whatever pressure occurs BEFORE crossing TDC, at which point, the engine spins right up.
The concept of 'advance curve' is not really all that relevant to an industrial/agricultural operation, because an industrial/ag motor is not constantly spinning up and down through it's powerband- that's an automotive/motorcycle type situation. We don't rev up hay bailer and shift through gears with silage blowers. Industrial/ag motors are also NOT a 'wide bandwidth' motor- their torque curve starts AT OR BELOW 'low idle' (which is a speed higher than cranking speed, but basically closed-throttle) to full governed speed, and that range may go from 500 to 2500rpm... that's a 5:1 change. An automotive/motorcycle/motorsports application is a 'wide bandwidth', where it might idle at 650, and spin to 6500rpm... a 10:1 range, or in case of say, motorcycle, you're seeing 900rpm to 13,000rpm
The ignition is fully retarded (after TDC) for starting, and once it's running above a certain speed, it can go to full advance.
The reason why we have all the fancy electronic advance now, is for 2 reasons: 1) reliability (no moving parts) 2) Knock and emmissions control.
The advance weights of any distributor wear... the pins wear, the springs get saggy, brittle and break... the rubbing surfaces get dry and corroded... and the result is poor performance. The shaft bushings get worn, the shaft doesn't run true, causing the poitns to not open and close consistently, which causes spark timing to wander around aimlessly.
Fuel is generally lousy nowdays, with all sorts of hygroscopic blends, the burn characteristics vary wildly. Grabbing the distributor and backing off timing to prevent detonation means you don't get the power output, and the exhaust products just aren't that consistent. A computer watching an O2 sensor can constantly adjust to try to get better output of both power, and low emmissions.
Electronics take the moving-part wear out of the equation, and grant a capacity to 'do other things' to alter that timing. For an industrial engine application, though, the benefit of electronic adjustability of timing doesn't offer the return of what's found in a wide-bandwidth application.
|
|
Ten Amendments, Ten Commandments, and one Golden Rule solve most every problem. Citrus hand-cleaner with Pumice does the rest.
|
|
DrAllis
Orange Level Access
Joined: 12 Sep 2009
Points: 21360
|
Post Options
Thanks(1)
Quote Reply
Posted: 07 Jun 2022 at 8:08pm |
|
If you pick a certain model of tractor, and google Nebraska Test A-C XXXX gas, you'll get the official testing for that particular tractor. Down from the top (depends on what year it was tested) you'll find a test for lugging the engine to the "peak torque" RPM of the engine. A One-Seventy gas for example gets lugged clear down to 900 RPM before it hits full ft lbs of torque. Now, I will guarantee the ignition timing isn't at 25 degrees BTDC like it was at 1700 RPM and higher !! My guess would be it may only be about 8 to 10 degrees BTDC at that slow speed, because at 400 RPM slow idle, it will be at TDC timing. So, my point is the distributor advance is tailored to meet what the engine manufacturer wants it to do.
|
|
steve(ill)
Orange Level Access
Joined: 11 Sep 2009
Location: illinois
Points: 85495
|
Post Options
Thanks(0)
Quote Reply
Posted: 07 Jun 2022 at 8:16pm |
|
Yea, i think your right Dr... I was thinking of a MAG tractor that has basically STATIC timing... but after 1950 i think distributors / variable timing / more HP / was the name of the game.
|
|
Like them all, but love the "B"s.
|
|
Ed (Ont)
Orange Level
Joined: 08 Nov 2009
Location: New Lowell, Ont
Points: 1410
|
Post Options
Thanks(0)
Quote Reply
Posted: 07 Jun 2022 at 8:21pm |
|
Yes exactly right Doc. On the newer cars you can watch the timing on your diagnostic computer. That is an interesting exercise! Of course no distributor. But the timing acts much the same as the older engines with distributors.
Edited by Ed (Ont) - 07 Jun 2022 at 8:28pm
|
|
DaveKamp
Orange Level Access
Joined: 12 Apr 2010
Location: LeClaire, Ia
Points: 5958
|
Post Options
Thanks(0)
Quote Reply
Posted: 07 Jun 2022 at 9:42pm |
When it comes to REALLY sorting out magneto or distributor ignitions, the appropriate test unit is really the only way to do it.
There's many brands and models, The commercially-made 'kings' include the Allen E35 magneto test bench... and for distributors, the SUN 600.... and a clever guy can build one too... the whole point, is to be able to accurately measure every aspect.
On a modern computerized engine management system, there's basically nothing that CAN'T be done with the ignition timing maps... it can be varied with ANY input (coolant temp, throttle position, Exhaust Gas Oxygen, knock sensor, crankshaft RPM, manifold absolute pressure... on my hotrod boat, I've got the ECM's 'park neutral' switch input connected to the shifter's neutral-start switch, so that it will run less advance at idle NEUTRAL, and when shifted into gear, it ADVANCES the ignition timing by 4 degrees... because the static drag of clunking the prop into gear drags the idle rpm down low enough to kill the engine... but if I leave the timing advanced to survive that, it idles way-too-high to safely shift the drive into gear. I hand-entered all the values into the timing maps SPECIFICALLY for that circumstance. Doing it with a mechanical distributor with vacuum advance or retard would've been darned-near impossible to get right.
While Doc may be right that the ignition timing is changing, I wouldn't be inclined to bet that they HAD to do that... in an undersquare engine, the smaller bore naturally limits flame speed and pressure rise, and the long stroke means expansion rate is FAR from linear. Expanding burning gases naturally keep cylinder pressures in check by virtue of simple geometry. They can run full advance timing a long way down, and not have a fit, because they don't need crazy advance to produce incredible torque at very low speed.
|
|
Ten Amendments, Ten Commandments, and one Golden Rule solve most every problem. Citrus hand-cleaner with Pumice does the rest.
|
|
DrAllis
Orange Level Access
Joined: 12 Sep 2009
Points: 21360
|
Post Options
Thanks(0)
Quote Reply
Posted: 07 Jun 2022 at 10:23pm |
|
I'm quite sure it needs to be retarded from full advance at slower speeds. Those who have experience with A-C gas engines that are 8.0 to 1 compression ratio have heard detonation before at slow speeds in road gear and cracking the throttle !! (D15-D19-170-175)
|
|
DaveKamp
Orange Level Access
Joined: 12 Apr 2010
Location: LeClaire, Ia
Points: 5958
|
Post Options
Thanks(0)
Quote Reply
Posted: 08 Jun 2022 at 5:08am |
|
Did you mean D15... or D17?
|
|
Ten Amendments, Ten Commandments, and one Golden Rule solve most every problem. Citrus hand-cleaner with Pumice does the rest.
|
|
DrAllis
Orange Level Access
Joined: 12 Sep 2009
Points: 21360
|
Post Options
Thanks(0)
Quote Reply
Posted: 08 Jun 2022 at 6:38am |
|
D-15 series 2, D-19, 170 and 175's are all 8.0 to 1 or greater compression ratio and are kind of known (to the trained ear) that at operating temp and a quick full open of the throttle butterfly from an idle in road gear will quite possibly detonate a bit. Of course the quality of the fuel and actual ignition timing will affect this, but they must have the timing retarded at the slower speeds or the detonation would be even worse. On 175's there was even a service bulletin telling Dealers to retard the ignition timing setting from 25 degrees BTDC down to 23 degrees BTDC if needed. Some certain model blue Fords even had a vacuum advance on them to help with this quick throttle detonate scenario.
|
|
Les Kerf
Orange Level
Joined: 08 May 2020
Location: Idaho
Points: 1050
|
Post Options
Thanks(0)
Quote Reply
Posted: 08 Jun 2022 at 6:44am |
DrAllis wrote:
I'm quite sure it needs to be retarded from full advance at slower speeds. Those who have experience with A-C gas engines that are 8.0 to 1 compression ratio have heard detonation before at slow speeds in road gear and cracking the throttle !! (D15-D19-170-175) |
Yup. The WD's had compression ratio around 4.5:1 and were rated at about 1400 rpm; not much need for fancy stuff like ignition advance mechanisms for such mild performance requirements. The Model B's and C's were similar, but when the manufacturers got into the horsepower race of the 1950's and 60's things naturally got more complicated.
|
|
SteveM C/IL
Orange Level Access
Joined: 12 Sep 2009
Location: Shelbyville IL
Points: 8472
|
Post Options
Thanks(0)
Quote Reply
Posted: 08 Jun 2022 at 9:59am |
|
I was sternly warned not to make/let the WD knock at low speed loads after the M&W's were installed. Timing was set at 25. Was told it could crack the crank.
|
|
DrAllis
Orange Level Access
Joined: 12 Sep 2009
Points: 21360
|
Post Options
Thanks(0)
Quote Reply
Posted: 08 Jun 2022 at 10:11am |
|
Original WD/WD45/early D-17's were 30 degrees BTDC. D-17's were backed down to 25 BTDC after crankshaft center main pounding.
|
|
SteveM C/IL
Orange Level Access
Joined: 12 Sep 2009
Location: Shelbyville IL
Points: 8472
|
Post Options
Thanks(0)
Quote Reply
Posted: 08 Jun 2022 at 1:31pm |
|
the M&W's are 7.25:1....didn't like 30 deg
|
|
DaveKamp
Orange Level Access
Joined: 12 Apr 2010
Location: LeClaire, Ia
Points: 5958
|
Post Options
Thanks(0)
Quote Reply
Posted: 10 Jun 2022 at 5:37am |
Hmmm... okay...
For the last two weeks, I've been making a more-or-less '5 mile commute' from my place down the hill to a friend's place, towing my dump trailer to assist in some demolition/renovation. I've got a Pertronix kit on the 17 (Series 1), and I gave the dist a full going-through when the remains of the points came out. At that time, I did NOT have access to the Sun 600, so I didn't analyze the curve of the advance, and I did NOT do any cross-ref check to see if the distributor was an original spec, or from some OTHER, so I've got no baseline or ref data to presume it's actually 'right'. I do know that I set it up by ear, at WOT, and then idled it down, then stopped and restarted several times, I made a few adjustments, and observed it advancing and retarding with my light. It was quite a while ago, and I don't recall wether I had a degree indication figured out, but I didn't write it on the block (which I often do)... but I haven't been experiencing any detonation. Probably because I set it conservatively at the high end.
But as I was wobbling along (as tractors do), I came to the realization that engineers faced a fundamental difference in operation RESULTS with respect to magnetos and distributors...
In a magneto, you get ignition retard BELOW the impulse coupling's setpoint, and when you exceed it, you get full monte... and nothing between.
In the distributor, you have that window of variablility... wether you want it, or not.
The inline six I built for my boat loves lots of advance above 2100, and it's raw water cooled, running 160F and atmospheric pressure, it can take lots of advance, as it sheds heat very fast. From 1300 to 1500, the Rhodes lifters pick up, so it sees a massive character change in that window. Below 1300, it needs LOTS of retard in order to operate, and it is VERY sensitive to the 650rpm out-of-gear/600rpm in-gear idle speed, I have it mapped to advance it a few degrees in-gear, to keep it running, and cut it back a few out-of-gear, to keep it from overspeeding at idle (it's a clutchless shift system).
My '70 Jeepster used to be REALLY fussy... it wouldn't idle the same way twice. Odd-fire V6, the point cam lobes are assymetrical, so they don't wear evenly... and the advance weights were always sticking... in different positions every time. I I'm certain many guys' strange running problems... particularly those that points or electronic don't change, can be traced to sticky weights, or erratic advance from the diz bushing being worn out wobbly.
|
|
Ten Amendments, Ten Commandments, and one Golden Rule solve most every problem. Citrus hand-cleaner with Pumice does the rest.
|
|
DrAllis
Orange Level Access
Joined: 12 Sep 2009
Points: 21360
|
Post Options
Thanks(0)
Quote Reply
Posted: 10 Jun 2022 at 6:15am |
|
Stock bore/compression D-17 gassers were 7.25 to 1 compression ratio and did not suffer from detonation like the 8.0 to 1 compression engines. They didn't like 30 degree BTDC timing, but that was crankshaft center main bearing issues, not detonation.
|
|
Ed (Ont)
Orange Level
Joined: 08 Nov 2009
Location: New Lowell, Ont
Points: 1410
|
Post Options
Thanks(0)
Quote Reply
Posted: 10 Jun 2022 at 6:42am |
|
Was that 7.25 ratio a dished piston or flat top?
|
|
DrAllis
Orange Level Access
Joined: 12 Sep 2009
Points: 21360
|
Post Options
Thanks(1)
Quote Reply
Posted: 10 Jun 2022 at 6:45am |
|
Power Crater squared off dish. The 8.0 to 1 and 8.25 to 1 pistons were exactly the same mold/casting but piston pin hole relocated.
|
|
Ed (Ont)
Orange Level
Joined: 08 Nov 2009
Location: New Lowell, Ont
Points: 1410
|
Post Options
Thanks(0)
Quote Reply
Posted: 10 Jun 2022 at 6:54am |
|
Wonder if they are still available?
|
|
DaveKamp
Orange Level Access
Joined: 12 Apr 2010
Location: LeClaire, Ia
Points: 5958
|
Post Options
Thanks(0)
Quote Reply
Posted: 10 Jun 2022 at 5:37pm |
DrAllis wrote:
... that was crankshaft center main bearing issues, not detonation. |
Ah... thank you for that note! Was the crankshaft center main bearing challenged by anything other than timing, and if so, is there any clue of it, aside from traumatic failure or disassembly and inspection (like... was it audible, if so, what does it sound like?)
And what would the timeframe of the compression ratio changes have been... i.e., would ti be from one model-year on, or at the start of Series III?
Edited by DaveKamp - 10 Jun 2022 at 5:39pm
|
|
Ten Amendments, Ten Commandments, and one Golden Rule solve most every problem. Citrus hand-cleaner with Pumice does the rest.
|
|
DrAllis
Orange Level Access
Joined: 12 Sep 2009
Points: 21360
|
Post Options
Thanks(0)
Quote Reply
Posted: 10 Jun 2022 at 9:03pm |
|
ALL D-17's from the factory were 7.25 to 1 compression ratio. From 1957 to 1967. You can actually hear a pounding in the engine light loads to full loads at 30 degree timing versus 25 degrees. Center main carried the load of 2 pistons.
|
|
