Performance distributor gear installation

[Kevin Johnson]

Hi,

I am starting this thread to act as a resource for people who want to install the distributor gear correctly. I am hoping that people will respond with detailed technical instructions such as how to mark the gears and do trial runs to see if the proper area of the gear is being contacted and so forth.

Why am I bringing this up?

I recently purchased three replacement gears from different sources: they are all different. One gear came with two sets of instructions -- they were both wrong.

I also purchased a vintage factory authorized rebuilt distributor and, separately, a vintage NOS service shaft. The earlier gear on the rebuild was significantly different to all three later gears. Moreover, the rebuild did not conform to the FSM. The width of the earlier gear section itself is greater, .425" versus .415". The total overall length of the gear with bushing is the same but the gear section is closer to the base of the distributor when mounted by ~ .015". There was zero end play included.

The gear teeth on the earlier piece are different in a number of ways from the later ones: the bottom land is deeper and so the flank and fillet are also changed; the earlier gear teeth are much more consistent in shape. The earlier gear has other finishing points as well that indicates it is a more precise product. This extends to the roll pin which looks to be of higher quality steel and the spacer washer which is surfaced on both sides and does not have the sharp edge from being punched out.

If you are serious about tuning your slant six and making sure your spark is getting to the right place at the right time here is the place to outline the technique. I suggest a return to first principles in how the gear should line up with wear marks, how much free play is needed and so forth.

I don't currently own a slant or I would do this for you. I did own a slant at one time and am fond of the engine and car (old Valiant). I was pretty surprised that every gear I measured was different in some way. I suspect that this is a problem with other older Mopar engines as well.

Good luck.

 

[player1up]

I've replaced a dist gear in the last few months, and have also rebuilt a spare dizzy with the new drive gear (Napa, I'll get the part number when I get home).

This reply falls under the "How the gear should line up" part
The first distributor was out of my 73 slant, used the slotted timing adjusting/hold down plate.
The second was from a 79 slant, used the two piece round/fingered hold down.

What I noticed was that the slotted plate was much thinner than the round plate for the 2 piece hold down. While not being a show stopper for a swap, it did make me question why the "new" gears were all drilled different from the one on my car ( and apparently all other slants on .org )
If the thick plate caused the distributor to sit further out in it's hole, then the gear would need to be further toward the end of the shaft to maintain proper alignment with the cam.

The method I used to drill the new gear was to make sure the gear measured up like the old one and drill the new hole accordingly.
1. Top of gear to center of roll pin ( GREEN )
2. Top of sleeve to center of roll pin ( RED )
3. Distance from top of sleeve to top of gear ( Yellow )

The method I believe would be more accurate would be to measure from the bottom of the hold down plate to top of the gear with all shims/washers in place and verify wear pattern ( as the depth of the gear is determined by how far into the block the distributor sits not just where on the shaft it's oriented ).

With all of that said, I have yet to remove the distributor since installing the new gear to verify the contact pattern to see how well I did.
The pic is to illustrate how I measure the gear and show where/how the original failed...When I do I will also compare it to the spare 79 dizzy I have.

 

[Kevin Johnson]

Just so people know, the three gears I purchased were from NAPA, Advance Auto (BWD -- Borg Warner) and a HELP! gear (Motormite/Dorman) pics below. The guide holes in two were located in the same position. On the other, it was located on the opposite side of the gear. This would make a small difference in how much you would have to turn the body to line up with number 1 in the cap. You should be aware of it in case you are one of those people that marks everything before disassembly -- that might cause some consternation.

 

[Kevin Johnson]

The remanufactured distributor that I have here is part number 2875366 which my old Motor manual says is for a 1968 225 with an automatic.

When I measure from what I believe is the step face that sits on the block to the very top face of the vintage mounted gear I come out with 2.000" which seems too even to be coincidental. Adding half the gear width of .425" gives a predicted 2.2125". Predicted in that this would be the distance to allow the distributor gear to mesh centered with the gear on the cam.

This could be compared to the later service gears. When I place one of them hard up against the washer I measure 2.015". Half of that gear width is 2.075" giving a total to the center of the gear at 2.2225".

It is very possible that one of these two figures is the exact theoretical and optimal place to center the gear. This will need to be checked empirically by marking gears and running them in briefly to see wear patterns. One member of another forum brilliantly suggested using a Sharpie to mark the teeth.

The right hand gears generate an axial thrust towards the distributor rotor under acceleration and steady state running. Under heavy deceleration there will be a reversing of this thrust component as the opposite faces of the teeth are loaded.

While I was manipulating the gear I noticed the large amount of free play (.505" - .497" = .008") and how this allowed the gears to rock back and forth using the roll pin as a pivot. If the gear was not hard up against the thrust washer -- and the FSM leads one to believe it should not be -- then a significant amount of spark scatter could be expected: particularly so at operating temperatures when the Nylon expands. This would also tend to accelerate abnormal elliptical wear on the gear teeth with the foci of the ellipse on a line perpendicular to the roll pin. This would further deteriorate accurate spark control.

It would be wise to remember that the engineers who designed this system would be cognizant of this rocking, having designed the tolerances and held the components in their hands. In a proper competition engine this slop would be very unacceptable while in an engine for the general public it would surely go unnoticed. The simplest way to correct this rocking is to drill the gear and shaft for a second roll pin. This could be a parallel drilling or one at a spaced right angle. For a production machine operation it would obviously be easier to drill two parallel holes.

There exists a Chrysler art department rendering of a 1960 slant six which shows two parallel holes drilled through the distributor gear and roll pins installed. It does not appear that this double drilling was done to engines for the public. It is, however, a fortuitous hint from the past on how modern slant six tuners can improve the stability of their spark timing. As rpms grow this becomes more and more critical, of course.

 

[66aCUDA]

Hey Kevin
I tend to agree that the distributor gear double pined would stabilize the wobble found in the gear. BUT I think that if you are really serious about the HP thing then DIS is the way to go. I am currently experimenting with DIS from a Ford 4.2L V6. And am VERY happy with the results. I also run a remote oil pump so there is NO extra cam loading. This frees up HP and reduces wear on the cam.
Frank

 

[Kevin Johnson]

Hi Frank,

Yes, I agree that there are superior ways to light the fire but there are a lot of owners that cannot afford to get too wild. I got really fed up with a (non-mopar) engine that was running triple sets of points and was forever needing adjustment -- I switched it over to opto-electronic. It looks like some careful work with the standard distributor on the SL6, though, can get you good results.

Good idea to get the oil pump off that gear in any event. I am sure it destabilizes it around 6K.

 

[slantsixdan]

Let the record show that Mr. Johnson has been sanctioned (and repeatedly spanked) on slantsix.org for attempting to pass off as fact what are actually guesses, fantasies, assumptions, hallucinations, misinterpretations, and completely incorrect statements regarding slant-6 distributor and oil pump drive pinions, and for behaving inappropriately towards other board members including moderators and administrators.

Let the record also show that there is no double-pinned slant-6 distributor drive pinion and never has been, nor is one pictured in the airbrushed illustration (not photo) of a slant-6 engine Mr. Johnson thinks he refers to.

He may have some good ideas and valid suggestions, but some of you may want to take him with a grain of salt.

That's all.

 

[lowbudget]

Let the record show that Mr. Johnson has been sanctioned (and repeatedly spanked) on slantsix.org for attempting to pass off as fact what are actually guesses, fantasies, assumptions, hallucinations, misinterpretations, and completely incorrect statements regarding slant-6 distributor and oil pump drive pinions, and for behaving inappropriately towards other board members including moderators and administrators.

Let the record also show that there is no double-pinned slant-6 distributor drive pinion and never has been, nor is one pictured in the airbrushed illustration (not photo) of a slant-6 engine Mr. Johnson thinks he refers to.

He may have some good ideas and valid suggestions, but some of you may want to take him with a grain of salt.

That's all.

Well put. I'm wondering if he ever drilled one of his 3 gears or any gears as per the factory service manual? It worked on my distributor, which is only on a daily driver. I wonder if he has ever double drilled one as per his picture? If Chrysler got is so wrong maybe he can start a distributor shaft/gear double drilling/set up service. Sorry but this was beat to death at .org:-D

 

[Kevin Johnson]

Let the record show that Mr. Johnson has been sanctioned (and repeatedly spanked) on slantsix.org for attempting to pass off as fact what are actually guesses, fantasies, assumptions, hallucinations, misinterpretations, and completely incorrect statements regarding slant-6 distributor and oil pump drive pinions, and for behaving inappropriately towards other board members including moderators and administrators.

Let the record also show that there is no double-pinned slant-6 distributor drive pinion and never has been, nor is one pictured in the airbrushed illustration (not photo) of a slant-6 engine Mr. Johnson thinks he refers to.

He may have some good ideas and valid suggestions, but some of you may want to take him with a grain of salt.

That's all.

I think it is appropriate that I respond to this.

I design parts for engine windage control systems. I have designed and made them now for more different engines from more different marques than any other person or company in the world. Because I design parts for many obscure engines that I do not have examples of in front of me I have learned to carefully examine all manner of information sources to try to learn details of engines.

On Slant Six dot org, the logo for the site includes a cutaway drawing of a 1960 Slant Six. A far more detailed version of this picture can be found at Allpar dot com under the Slant Six section. I downloaded this picture as I have with innumerable others and looked at it in a drawing program where I was able to magnify it.

When I mentioned on the Slant Six dot org forums that the distributor gear was illustrated as having two parallel roll pins securing it to the distributor shaft this was immediately attacked and ridiculed. I found this behavior absolutely fascinating.

Two things at least were apparent: 1) that I was the first person to ever look carefully at the drawing that graced the logo of the site; 2) that somehow this information disturbed certain individuals. Perhaps it is because it introduces uncertainty. I just do not know.

There is a page on my website dedicated to this issue which interested people should read. I simply do not have the time to import everything into this thread while trying to cleanse it of references, even oblique ones, to the items I produce.

I am investigating the issue methodically and taking careful measurements and making observations and conjectures.

Here is the thread:

http://www.crank-scrapers.com/Chrysler_slant6_distributor_gear.html

 

[Kevin Johnson]

Well put. I'm wondering if he ever drilled one of his 3 gears or any gears as per the factory service manual?

No, why would I do that? I do not own a Slant Six. I purchased these gears in order to compare them and check Dan's claim that the plastic aftermarket gears are all the same. This might be harmless ignorance on his part save that the differences are significant. Then he is spreading misinformation. It is not malevolent disinformation because he did not know that he did not know.

Apparently what you missed in this presentation is that an official authorized Mopar distributor rebuilder did not follow the instructions in the Factory Service Manual. Why was that? We do not know. That is why we are returning to first principles. There are documentary photographs on the listed thread. Moreover, the distributor gear used in that official Mopar rebuild is significantly different from all the replacement gears checked, which were again all different from each other.

It worked on my distributor, which is only on a daily driver. I wonder if he has ever double drilled one as per his picture? If Chrysler got is so wrong maybe he can start a distributor shaft/gear double drilling/set up service. Sorry but this was beat to death at .org:-D

I am sorry, but when the factory is not following their own rebuild instructions, something is wrong. These types of things are important to some people. Other people seem to stumble through life blindly believing everything they read or are told without checking it out. I mean REALLY -- the one gear had two different sets of instructions and they were both wrong. One set of instructions was even for a Ford distributor gear NOT the Slant Six gear. I caught that.

Thank you for your thoughts.

 

[Kevin Johnson]

Careful examination of the gear pictured in the Dorman parts catalog shows yet a fifth distributor gear variant different from all the others yet noted. The teeth are shifted into still another position with respect to the pilot hole. See the second page (51), fourth row down on the pdf below:

http://www.crank-scrapers.com/sl6/50-52dorpar.pdf

This is important to note, as well, because it establishes that the Dorman/Motormite/HELP! gears historically have supplied at least two different variants.

 

[Kevin Johnson]

Here is the information that interested owners need to determine and hopefully share. I used some information that Willem Weertman supplied in the form of an engineering diagram to Allpar dot com transposed onto the 1960 Chrysler drawing.

The critical measurement is from the shoulder area of the distributor body that rests on the block to the intersecting centerlines of the distributor and camshaft gears. Since it would be very difficult to measure this off of a block absent a CMM, the correct distance will need to be inferred from wear patterns on distributor gears.

http://www.crank-scrapers.com/sl6/225 A.jpg

http://www.crank-scrapers.com/sl6/225 B.jpg

 

[MadScientistMat]

On Slant Six dot org, the logo for the site includes a cutaway drawing of a 1960 Slant Six. A far more detailed version of this picture can be found at Allpar dot com under the Slant Six section. I downloaded this picture as I have with innumerable others and looked at it in a drawing program where I was able to magnify it.

When I mentioned on the Slant Six dot org forums that the distributor gear was illustrated as having two parallel roll pins securing it to the distributor shaft this was immediately attacked and ridiculed. I found this behavior absolutely fascinating.

Two things at least were apparent: 1) that I was the first person to ever look carefully at the drawing that graced the logo of the site; 2) that somehow this information disturbed certain individuals. Perhaps it is because it introduces uncertainty. I just do not know.

This is one of the things that led to your getting sanctioned. There's a lot of people who are quite knowledgeable about the parts that actually were put into production, and there are no known examples of factory double-pinned distributor gears. So it is possible you may not have been the first to notice this, but it does seem like you have been the first to argue it meant anything significant instead of the work of a careless illustrator, or an ink spot on the drawing. Insisting there had to be something serious there based on a single artist's drawing is going to come across as, at the very least, something of a know it all.

Kevin appears to have deleted or edited a large number of his own posts on slantsix.org just before coming here, so it's hard to find exactly where he mentioned that theory and how exactly he came across it.

 

[Kevin Johnson]

This is one of the things that led to your getting sanctioned.

Yes, let's look at that:

1. Do not bring up other marques, or refer to systems or engines that are not slant sixes.

I am sorry but this is just laughable.

As I mentioned many times, the designer of the slant six used other engines to design it -- so what is that?? He brought that up in an interview and was proud of it.

In the 1960 drawing from Chrysler (an aluminum block engine) the main webbing is shown as reaching down to the cap registers. Yet in aluminum production pieces the webbing is straight across with an abrupt step. This is because aluminum casting technology was not advanced enough at the time to avoid a high rejection rate and so the molds were adjusted. This is what plagued Buick and Olds with the alloy V8 they were producing at the same time. When iron blocks were made they returned to the original design. That was wise because -- as I pointed out -- the bay to bay gas flow exchanges needed because of the particular pattern inherent in the six center bay were being obstructed. This center piston pair was positioned directly above the unshielded oil reservoir to send double pulses of air directly at it.

Look, I was being gentle. I could have mentioned that Renault stuck it out with the technology and developed the R16 and its fully alloy engine about a year later. Colin Chapman was impressed enough to nab them and the alloy transaxles for the Lotus Europa after flipping the ring and pinion. Rover stuck it out too with the Buick V8.

When I lived in Dearborn and owned a business in Detroit I used to pass by a large S.A.E. building quite often. That is an organization that has been around for a very, very long time -- even prior to the slant six, just imagine --where the engineers from different automakers get together and discuss general technical issues.

I know people grow fond of certain engines but please do not get delusional and imagine that they popped into existence as independent entities sharing no engineering or issues with other engines whatsoever.

Yesterday I wrote about how you have to be careful about cryogenically treating subassemblies with interference fit parts. It can cause microcracks. That was erased because it came up in an engineering class and unfortunately did not involve a part from a slant six. Oh well, let people find out the hard and expensive way.

... There's a lot of people who are quite knowledgeable about the parts that actually were put into production, ...

Yes, there are. But they are not knowledgeable about all parts that were put into production as this current research exercise demonstrates. What the REALLY knowlegeable people on slant six dot org admitted, is that it was possible that what I conjectured was correct but they had not seen evidence of it. When I was growing up (living in Park Forest, IL -- have to throw that in for the benefit of one person) there was a "testor" of a Chrysler Turbine car a few houses down. When Chrysler was done with that test they collected the cars and almost all were destroyed. The destruction of test parts and cars was a common industry practice at the time -- research it. I might speculate that the illustrator was looking at real parts, real parts from a factory competition engine that was never released to the public. If he was not looking at real parts then why the hell would he or she draw two roll pins? I am assuming this was not his or her first dalliance with illustrating distributors.

Why don't you ask Lotus Group if there were any one-offs when they were working on the Corvette engine for GM? Why not just read about the published history of that engine. I know, tragically, that this involves effort.

... and there are no known examples of factory double-pinned distributor gears.

There probably would be no known examples of 1960s era SBC DOHC cylinder heads direct from Chevrolet if Smokey hadn't taken pictures of them and published same.

Right?

Or the single photo of a prototype cast aluminum deep sump for the SBC similar to what Mercedes was producing for its V8 engines.

Or canted head valves...

Should I go on... ?

... So it is possible you may not have been the first to notice this, but it does seem like you have been the first to argue it meant anything significant instead of the work of a careless illustrator, or an ink spot on the drawing. Insisting there had to be something serious there based on a single artist's drawing is going to come across as, at the very least, something of a know it all.

I think it is really sad that it took me going out and buying vintage slant six parts and holding them in my hand to notice that the factory replacement gear would have substantial slop -- causing spark scatter -- and this is probably why the second pin was introduced. I seem to recall at least one person saying that he had held hundreds of slant six distributors -- but this was the same person who acknowledged that it was possible that the illustrated part did exist.

For those that cannot discern the dual roll pins in the illustration, I can only thank the Lord that they were presumably not involved in any sort of analysis of defense imagery sonst wir ja alle Deutsch sprechen würden.

Kevin appears to have deleted or edited a large number of his own posts on slantsix.org just before coming here, so it's hard to find exactly where he mentioned that theory and how exactly he came across it.

Most of those threads were deleted ["removed for review"] by moderators.

After receiving the amusing missive asking me to refrain from speaking about anything other than slant sixes at "our pool" I went through each and every post I made on slant six dot org over the past six years and tried to remove any mention that I had made that referred to other engines or engineering other than the slant six. I try to be consistent -- often failing nonetheless.

Now, perhaps (?), the thread can return to its stated useful task for actual slant six owners who want to be able to massage their OEM distributor system ??

If you don't like me or how I write or my attitude or just because my name is Kevin, hey, fine. Somehow I will learn to live with that. Sheesh.

 

[Kevin Johnson]

But hey, look at that cool collar over the dual pinned gear. Wild guess is that it has set screws to allow it to be set for the correct clearance.

Billet, man. Rad. Far out. Groovy. Sick. The bees knees.

Oh, forgot: it's a Duesie.

I guess those old fogies knew their ****, eh?

 

[66aCUDA]

So Kevin
I read the info on your website. It looks good and certainly warrants some questions about the modern drive gears and the differences that one can encounter.
I have always just re drilled the gear to match up with the hole in the shaft. I really havent had to do that too much as the gears dont fail that often. Have you seen any difference in the points VS Electronic dizzys?
BTW when you decide to get rid of the slant six parts let me know and Ill send you my address.
I will be down the first part of next month to Charrlie's house. Maybe we can talk windage trays then.
Frank

 

[Kevin Johnson]

So Kevin
I read the info on your website. It looks good and certainly warrants some questions about the modern drive gears and the differences that one can encounter.
I have always just re drilled the gear to match up with the hole in the shaft. I really havent had to do that too much as the gears dont fail that often. Have you seen any difference in the points VS Electronic dizzys?
BTW when you decide to get rid of the slant six parts let me know and Ill send you my address.
I will be down the first part of next month to Charrlie's house. Maybe we can talk windage trays then.
Frank

Hi Frank,

I have not examined electronic distributors so I could not say whether that critical length would be the same. If it is not it implies that the blocks are machined differently, i.e. have a physically different distance from the cam centerline to the mounting face. I would guess that this being different is not the case but one never knows for sure.

Sounds good -- I have not been up to see Charlie in a long time now.

 

[Charrlie_S]

Personally, I think this distributer gear thread is "much ado about nothing". It is not a "critical" issue. Take the new gear, install it on the shaft, with a little clearence between the gear and the distributer body, drill a new hole in the gear, right in line with the existing hole in the shaft, install the pin, done.
There is so little loading on the gear, especially, with the electronic distributers, gear failure is not a problem. The only gear failures I have seen, are old brittle gears, or where someone did not install the cap/rotor properly, and they jammed. This is not "rocket science".

Oil pump gears are a different story.

 

[Kevin Johnson]

I think for a passenger car engine you're correct and obviously hundreds of thousands (millions?) of stock slant six vehicles have been tooling around for up to 50 years now.

A performance engine is another story. The distributor then deserves special attention. If there wasn't something to be gained you would not see the progression from points to electronic to removing it entirely. A high level competition engine is a collection of special attention to many different areas when tenths or hundredths of seconds are sometimes the difference between winning and losing.

Here is one link for the different thickness shims that are sold to adjust endplay. There are quite a few kits that will work on .500" shafts. http://www.streetperformance.com/part/moroso/distributor-shim-kit/391851-26140.html

The shaft endplay given for a Holley distributor with a metal gear is .024-.035". Since the Mopar authorized rebuilt distributor came in with zero clearance and a plastic gear that expands, the figure given for the Holley seems reasonable to use with the Mopar plastic gear.


Aside: How many guys out there index their plugs? Here's a link to a Mopar fan that did some careful testing and estimates he picked up 3% by indexing: http://dodgeram.org/tech/gas/spark_plugs/s_plug _indexing.htm

As the article states, a lot depends on the combustion chamber design.

 

[Fishthatkills]

WHAT? All I can say is Analysis paralysis! Some live to argue and some argue to live!

John D. Beckerley
Austin, Texas

 

[Kevin Johnson]

WHAT? All I can say is Analysis paralysis! Some live to argue and some argue to live!

John D. Beckerley
Austin, Texas

John, it is not at the level of P vs NP or asking how many angels can dance on the point of a needle. What is suggested is that someone simply measures the perpendicular distance from the mounting surface for the distributor to a tangent on the camshaft gear. Once that is known, a simple procedure can be outlined.

Ford Racing makes the effort to devote a whole page of their performance catalog explaining how to set up the gear properly. Ford Racing does this because there have been so many variations over the decades. It is an industry wide issue at least for vintage parts.

How to do this on an installed engine without doing trial runs of a Sharpie-marked distributor gear? Possible technique is to remove the distributor and then reach down with hemostat held gauze and wipe the cam gear face of oil. Then reach down with a cotton swab with Prussian blue indicating grease and very lightly coat the gear. Take or make a simple depth gauge that extends past the centerline of the gear.

Here is a $4.95 Enco gauge that could be cut or ground to make it fit, if need be:
http://www.use-enco.com/CGI/INLMPI?PMPANO=0515363&PMKBNO=2028&PMPAGE=64&PMCTLG=01

While carefully sliding the gauge flat on the mount surface, just barely brush the outer face of the cam gear. This should give you a blue witness mark on the gauge. Measure from the top surface of the gauge to the middle of the witness mark. That should give you a good approximation of the distance needed. Repeat this measurement at least three times and take the average of the results.


I think then that the Sharpie method could be used to check a gear that is set to the result. I doubt you would even have to run the engine. Just have someone place light finger pressure on the shaft of a temporarily installed distributor while the engine is rotated by hand. I would think that would lightly abrade away the ink from the Sharpie on the distributor gear faces.

 

[Kevin Johnson]

Yes, I obtained a used points distributer from a 70s Dart. Naturally it is a unit from a 1966 automatic and has a service gear installed on it.

I will spare you most of the horror -- needless to say, there is lots of room for improving the spark if you spend a bit of time here.

This gear had wear patterns that walked up and down the teeth as it turns. That means it was wobbling or cockeyed on installation. I would say to seriously think about dual pinning these plastic gears for performance work.

And, I know you're waiting for it, this gear is different from all the others! It is becoming a cosmic question of sorts as to whether there are actually two slant six distributor gears that are the same??

Here's the dirty parameter rundown -- the incredible shrinking slant six gear:

This current (well-used!!) gear OD: 1.020"

New OS distributor gear on Chrysler rebuild OD: 1.013"

New NAPA gear and Borg Warner OD: 1.008"

New HELP! gear OD: 1.001"


Now, useful info.

I took the average distance on the gear face wear patterns to calculate where the tangent to the cam gear is. This means if you measure down from the surface that is even with the mounting surface of the block to the center of the distributer GEAR itself you should have this value.

The mounting PLATE that bolts to the distributor is .090" thick; distance from this surface: 2.225"

The ledge just NEXT TO the mounting plate is .085" deep: therefore the distance from the surface adjacent to it is .005" further away: 2.230"

These values are for a gear with zero clearance to the thrust washer. Now an important question. The FSM specifies .007" clearance. I suggest INSTALLING the gear at 2.232" or 2.237" with .007" free play. What do you think?

With a right hand bevel gear driven by the camshaft the axial thrust will be towards the cap and should close up the .007" clearance. Bear in mind that OEM rebuilders were using zero, .000", clearance.

Please someone double check the measurements.

 

[Kevin Johnson]

For performance work with the Nylon gear this is a critical operation. I would definitely suggest having a quality drill press that drills square to the table and a proper V type support for the shaft. If you do not have this type of equipment then I suggest contacting a local machine shop.

The reason this is so important is because the thermal coefficient of expansion of the plastic gear is so much greater than that of the steel shaft. There is a large amount of play at room temperature in order to ensure that engines sitting in low temperatures will not have the Nylon cracking. When placed in a normal icebox (~28 degrees F) the Nylon gear has a snug fit.

When placed in a cup of boiling water and then trial fitted on the shaft the amount of play is substantial. With the factory suggested .007" end clearance against the thrust washer this would allow rocking of the gear or movement of the gear back and forth along the roll pin as the shaft rotates.

I would suggest that the most accurate way to do this is to first determine and setup the proper clearancing of the gear. Measure with a set of calipers the distance from the top or bottom of the distributor shaft to a reference point on the gear.

Beware: do not assume that the installed height of the shaft is consistent between distributors. In fact, there was a dramatic difference between the used distributer and newly rebuilt one.

Disassemble the distributor so that the shaft and advance mechanism can be positioned easily in a proper clamp. Have a small ice water bath next to your work area. Position the gear on the shaft the proper distance and carefully submerge the assembly in the ice bath. After it has chilled recheck the measurement and adjust if needed. Carefully keep the assembly chilled. Doing this efficiently means that you should have your drill press and clamp already set up so that the drill will perfectly pass through the center of the shaft. This is important.

Prior to this you will have placed a small mark on the gear in a random location such that it will pass above or below or at right angles to the original hole in the shaft (assuming a used shaft). Another mark should be placed at a suggested right angle to this (versus parallel) but above or below it (obviously the roll pin paths cannot intersect).

Quickly place the chilled assembly on the clamp and drill straight down through the first mark. Install the first roll pin. Rechill the assembly and then drill the second roll pin hole. Allow the assembly to warm and remove the first roll pin. Carefully remove all small bits of metal and plastic from the parts and reassemble the distributor. Recheck your measurements. Small variations can be corrected using thicker or thinner thrust washers.

 

[Kevin Johnson]

The distributor gear in the link below should work in the US slant six. I believe there is a slight difference in the distributor shaft OD that becomes even smaller once the actual OD of the US units is measured.

Certainly with all the gymnastics that need to be done to the plastic gear for performance work this should be considered. What is your time worth? Plus, when all is said and done the bronze gear will be superior. The key issue with the plastic gear is that it will allow more spark scatter.


http://www.pentastarparts.com.au/sunshop/index.php?l=product_detail&p=611

 

[Charrlie_S]

I am not saying Kevin is wrong, just that this is like killing a fly with a howitzer. If the small amount of spark scatter that could/might occur without doing his procedure, is an issue, just switch to DIS ignition. On a "street/strip" motor it is not worth the trouble. On a
race motor the DIS is a better option.