Distributor stop pin bushing dimensions

This site may earn a commission from merchant affiliate
links, including eBay, Amazon, Skimlinks, and others.

D

ducktapeguy

10 Year 15 Year 20 Year
Joined
Jan 6, 2003
Threads
64
Messages
1,204
Does anyone have a picture of, or preferably dimensions, for the stop pin bushing in the distributor that limits the mechanical advance?

Mine is missing and I want to make a replacement. I assume the ID is approximately 4mm x 6mm high, I can only guess that the outside diameter is somewhere between 6mm and 8mm. Also, is it held on with a E-clip or is it press fit?

Thanks in advance.
 
I dunno the dimensions, but those pins also had a plastic bushing on them to control the advance. They're almost always cracked and gone. Jim C. puts some kinda brass wrap on those pins when he rebuilds, to serve the same function. Difficult to see with all the dissy stuff installed so I can't get a pic or measurements...
 
ducktapeguy said:
Does anyone have a picture of, or preferably dimensions, for the stop pin bushing in the distributor that limits the mechanical advance?

Mine is missing and I want to make a replacement. I assume the ID is approximately 4mm x 6mm high, I can only guess that the outside diameter is somewhere between 6mm and 8mm. Also, is it held on with a E-clip or is it press fit?

Thanks in advance.
Click to expand...

For a job like this I would just ship it out to Jim C......


Zack
 
So, after speaking with Jim C a couple times I felt confident enough to do a basic rebuild of my dizzy. By basic I mean that I do not have a distributor machine to read and diagnose the specific tolerances and advance curve, or lack there of, of my dizzy. Therefore, no real assurity that the springs are still providing a proper advance curve. And, of course, my stop pin bushing was long gone.
But, with everything cleaned up all seemed to work fine until under heavy load, i.e. truck loaded with plenty of weight and headed up 6 miles of mountain highway in 4th@55mph/2500rpm or 3rd@55mph/3300rpm. In 4th the knock was mild but in 3rd it took my foot right of the gas.

Looking at the MSD #8464 advance kit, there are three bushings to choose the max mechanical advance (and consequently idle retard limit). So, I picked up a threadless aluminum bushing w/#8 I.D X 1/4" O.D. X 1/4" H (#8 is slightly larger than 4mm) that appeared proportional in size to the smallest bushing in the MSD kit. It pressed right on with moderate pressure and doesn't move a bit. The very top of the pin that the bushing sits on is slightly larger in dia. than the rest of the pin and holds tight.

There is a marked improvement in heavily loaded uphill ass-haulin'. Just did 9 miles up 8-9% grade driving like I stole it without even the hint of a knock or worse, pre-detonation.:smokin:
During the 3 upper miles cylinder temps should've been about as high as they can get, with all things working well enough to say that the truck is running well, except that it's not summer.

May not be the perfect solution, but I think it's a lot more right than no bushing at all.

C
__________________

tmp_20131222_165455-1317729067.webp
 
CLove said:
So, I picked up a threadless aluminum bushing w/#8 I.D X 1/4" O.D. X 1/4" H (#8 is slightly larger than 4mm) that appeared proportional in size to the smallest bushing in the MSD kit. It pressed right on with moderate pressure and doesn't move a bit. The very top of the pin that the bushing sits on is slightly larger in dia. than the rest of the pin and holds tight.
Click to expand...

CLove, where did you end up getting this bushing? I've been hunting around local hardware stores and can't seem to find anything in the ballpark to these dimensions...

Thx.
 
Slow Left said:
CLove, where did you end up getting this bushing? I've been hunting around local hardware stores and can't seem to find anything in the ballpark to these dimensions... Thx.
Click to expand...

I picked it up at the local home improvement center. It was in the specialty drawers amongst the clips, knobs, pins, caps, etc. I could always send one or more your way, they're pretty light and about $.20 a piece. Though I'm sure they're around somewhere in NY.

At this point I'm pretty confident that the dimension is close to what I need, as my total MAX advance is 32º on the dot at >3000rpm. Of course, I forgot to read the max adv. before I installed the bushing. Here in CA we burn only the crappiest of gasahol, so don't want 38 or 42º advance. If my calcs are correct then the bushing limits the mechanical adv. to roughly 18º, w/o it 28.25º, that's crank degrees. 2.325mm or .1inch in the dizzy makes a significant difference @ the crank.

IMO, this has the best cost/benifit ratio, as well as literally being the cheapest thing I've done to my cruiser. For our older motors this minor restoration is crucial to protecting from knock and ultimately pre-ignition as our gas refiners continue to :censor: us with their "research" (M+R/2 my ass). C
 
CLove said:
...as our gas refiners continue to :censor: us with their "research" (M+R/2 my ass). C
Click to expand...

If there were a "like button" I would push it. LOL.

Good information too! I'm kind of amazed to see that much of a difference, but not surprised (huh?).
 
Found these online:

http://www.widgetco.com/size-8-aluminum-spacers

Think I'll give it a try and see what happens...

EDIT: So I have purchased, received and installed the following bushing
Part Number: 10-8-250-AS
Fits screw size: #8 or M4
Dimensions: .170" ID x .250" OD x .250" L

In metric units, the height of the bushing is (0.25") 6.34 mm
OD (0.25") or 6.34 mm
ID (0.170") or 4.18 mm
Wall (OD-ID)/2 (0.042") or 1.08 mm

In order to get the bushing to fit over the stop pin, I had to file down material from the inside of the bushing using a small, round file. Got it to fit snugly over the pin; the height is good.

According to this website:
http://www.globalsoftware-inc.com/coolerman/fj40/dizzyfaq.htm
I should expect to see:
23* of mechanical (centrifugal) advance
18* of vac advance
6* of HAC (High Altitude Compensation) advance - but I'm at sea level (well, probably 3 stories, so 30', above sea level...), so I shouldn't see much here.

So total max advance according to Factory Specs should be 41* at sea level!??!!

Here are the ignition advance curves I measured (I used tape on the fly wheel to mark out approximate markings by measuring the distance between the TDC line and 7* BTDC punch factory marks already on the flywheel, so the accuracy of these measurements isn't so great, maybe +/- a couple degrees. If I can get my hands on a timing gun that measures both timing and RPMs, I will retake the final curve and post.) - this is for a stock 12/1981 FJ60 with all emissions components working properly:

Without the Stop Pin Pushing Installed & Vac Advance Lines connected
RPM Measured Advance
Idle (650) 7*
1000 11*
1500 17*
2000 42*
2500 42*
3000 42*

Without the Stop Pin Pushing Installed & Vac Advance Lines disconnected
RPM Measured Advance
Idle (650) 7*
1000 11*
1500 17*
2000 21*
2500 21*
3000 21*

With the Stop Pin Pushing Installed & Vac Advance Lines connected
RPM Measured Advance
Idle (650) 10*
1000 10*
1500 16*
2000 41*
2500 41*
3000 41*

With the Stop Pin Pushing Installed & Vac Advance Lines disconnected
RPM Measured Advance
Idle (650) 10*
1000 11*
1500 16*
2000 21*
2500 21*
3000 21*


I should note that after installing the bushing, I didn't make any changes (like rotating the distributor cap) before taking measurements for the curves with the stop pin bushing installed. So the base timing for all these measurements were at 7* BTDC WITHOUT the stop pin bushing installed (so the difference between 7* base timing WITHOUT the busing installed and 10* base timing WITH the bushing installed is purely a result of the bushing itself, and not having adjusted/rotated the distributor cap).

Installing the bushing advanced the base timing 3*but doesn't seem to affect the max total advance. After having recorded these curves, I have reset the base timing to 7* BTDC, but don't have the curve measurements for that. I would assume that it shifted at least the lower end of the curve down 3*, but don't know if it reduced the top end (higher RPMs) total advance down into the 30*s...

It also appears that the vac advance kicks in at higher RPMs, and is responsible for the higher RPM advance.
I have measured the vac at the distributor (t'ing off the distributor vac advance diaphragms) to see how it changes as RPMs change. The vac max's out around 5 inHg (I watched to see how high it got up to 3000 RPMs) and is 0 inHg at idle. Makes sense, since the vac to the dist diaphragm is ported into the sidewall of the primary barrel, probably so won't create vac until the throttle plate moves to a minimum position. This is enough vac to move the actuator arm that moves the breaker plate (goes from dist diaphragms to connect to breaker plate), since with the engine off, I tested with a hand held vac to see how much vac it took to actuate the arm and it was under 5 inHg.

I think the way to shift the mechanical advance peaks (and smooth out the rate of advance) is going to have to be done with springs and weights... but for now, I'm going to run and adjust the base timing and idle mixture and idle speed screws to see if I can dial it in better under the current conditions with the new bushing installed...

I'm also thinking about looking into addressing these possible issues:
checking/replacing the teflon inserts upon which the mechanical weights rotate
lubricating the weights/springs
replacing the vac advance diaphragms (available from Advance Auto or NAPA for ~$130 USD)

I'm wondering if fatigue on the teflon inserts or the need of lubrication (or a combination of both issues) is causing the weights to open suddenly and completely, instead of gradually. This could be the reason why the advance comes all at once. The other reason could be that the factory springs and weights behave this way normally.
With regard to the vac advance, it also seems to arrive all at once around 2000 RPMs. Although I have checked and convinced myself that the vac advance is working (vac is actuating the arm that connects to the advance plate), I wonder if the diaphragms are just old and if replacing them might add some more "elasticity" to the curve...
 
Last edited:
Since the bushing is the Max advance limiter I spent some time learning more about spark advance. After searching and reading and knocking on many doors I verified that 32º total adv is the sweet spot for most motors, under and over square, tractor and race. Local Nascar engine builders lock-out the adv. @ 32º on high octane. 35-38º deg is considered dicey. Bad timing can really blow a motor. Chorus of 95%+ of the old guard carb/dizzy techs I spoke with.

So, I marked the flywheel out in 4º increments from TDC to 52º BTDC. Warmed her up. Left All hoses connected. Set up the light and had 8º @ idle. Ran it up to 3200rpms while watching the advance stop @ 40º all the way to 4000rpms. @3200 I adjusted the dizzy up/down to hear the valvetrain at both ends of bad and centered in until I found the harmony my Dad, who was dragin' in the 60s, taught me to recognize, 42º. It is a bit easier to hear at 3000 than idle. Idled & Locked the dizzy down. Timing is now 10º BTDC with VAC adv. hoses removed/plugged per standard procedure. Stock. Adjusted idle. Voila.

Here's the low rpm/high torque great power on 87 octane in CA I've been lookin for! Have been running 87 for about 3 weeks with no issues and actually better performance than before bushing on 91. I intend to pull the plugs in a few more weeks to see what's really happening.

The 2.325mm that the 1/4" bushing, I used, adds to the stop pin narrows the throw in the slot on the advance plate. If my math is correct No bushing = 28.3º@crank. Yes Bushing = 18.1º@crank. So, 42º Max adv vs. 32º.

IMHO, this 1/4"×#8 bushing is a true solution, especially since dizzys are NLA.

HTH,
C
 
Reviving a somewhat old thread, I had to give a huge thanks to Clove and Slow Left. The highway pinging was driving me nuts. For years the only way that I could avoid it was to disconnect my vacuum advance, but I just saw this thread last week and had to try their the fix myself.

74¢ for the bushing at Home Depot (in the small parts trays with other "spacers"), a couple hours work yesterday morning--mostly because I installed the distributor off by a tooth, and had to reinstall it, and the problem is finally solved. I just drove for a weekend ski trip in the Berkshires, 2 hours each way, and didn't ping at all! Plus, with my vacuum advance hooked up again, I got 4 more mpg than I've been getting lately. I still need to tune the engine better, but I'm definitely happy. This really needs to be in the under $50 mods sticky.

A couple observations from my install:

Another view of the pin in question, before installing the bushing.
image.webp

Some pieces of crud that I found inside my distributor. I think they're the remains of the original plastic bushing.
image.webp

It looks like the original bushing was slightly thinner (i.e., smaller outside diameter) than the aluminum spacer. Since the aluminum is pretty soft, it would be pretty easy to file one side or the other down slightly to modify the intial and/or max mechanical advance, if you were so inclined.
image.webp
 
Last edited:
I am deeply grateful to Clove and Slowleft for diggin into this... Any idea whether it matters with regard to high altitude locations?
 
micruz60 said:
I am deeply grateful to Clove and Slowleft for diggin into this... Any idea whether it matters with regard to high altitude locations?
Click to expand...
Actually, Micruz...this is mostly Jim C.'s handiwork, figuring out that the plastic OEM stop pin bushing deteriorates...and replacing it with a more durable one...

If you notice in the pictures above, the stop pin stops the mechanical movement of the governor weights. Without the stop pin bushing installed, the weights will move further than they are supposed to, adding several extra degrees in mechanical advance...throwing off the expected ignition advance curve.

According to this website, the expected ignition advance curve for the OEM system should see:
http://www.globalsoftware-inc.com/coolerman/fj40/dizzyfaq.htm

23* of mechanical (centrifugal) advance
18* of vac advance
6* of HAC (High Altitude Compensation) advance - but I'm at sea level (well, probably 3 stories, so 30', above sea level...), so I shouldn't see much here.

According to my rudimentary measurements on my ignition advance curve, without the stop pin bushing installed, it added an additional 3* in mechanical advance.

Since this is mechanical advance, it will affect all dizzies at all altitudes.

The HAC advance is vac controlled and is supposed to add extra advance at high altitudes.
 
OK thanks for the true attribution to our cruiser whisperer!
Off on a tangent now: if this bushing is awol, would it affect getting dizzy to properly time / align to 7* btdc?
Reason for asking is that my 60 is idling at a lower than usual (450-500 rpm) and the dizzy is turned as far as it'll go towards advance....
 
You must log in or register to reply here.

Share this page

Back
Top Bottom