I have read several times about some arm on the mechanical advance on the stock single point distributors. Something like 16L and or 10L.... Sound familiar?? I am going to wait on putting in the Mallory Unilite that I bought (used) and send it in to get it gone through just to ease my mind. I called Mallory and got an estimate on this and they said as long as I didn't need any major parts that it was usually about 45 bucks with a three week turnaround. How much play should a stock dizzy have as I am afraid mine is getting worn beyond it's limits... If it is, I will probably just get a remanned one at NAPA and run it for a while.

Thanks,
JC

 

Actually that 10L and 16L that you refer to are slots in the reluctor post or if you have points the post that has the cam on it.

At the bottom is a plate that has those slots in it and they limit the mechanical advance according to the number that is stamped on the plate.

To change it just rotate the post 180 degrees and you hve now changed from 10L to 16L or vice versa.

When you change the post you also in essence made the distributor 180 degrees out.

Tmod

 

So will I then need to pull the dizzy up and get it spot on again?

 

Well either that or change the wire locations on the cap to match the 180 out.

I always just pull the distributor up and rotate it.

I also modified my slots by welding them shut more to limit the mechanical advance even more then is available with the factory slots. You can also find different reluctor posts that have different timing slots in them.

Tmod

 

OK, how much side to side (like if the dizzy were installed in the engine) freeplay should the shaft have? The Unilite I have doesn't have near as much (by feel anyway). Wouldn't sticking a dwell meter on these and reving the engine tell you if the dizzy was worn (dwell would jump around)?

 

Ok, upon dissasembling the stock dizzy I see what you are talking about. Mine has 13L and 18L. It is on the 13L notch which is a shorter notch/slot than the 18L (hence the lower number). I just picked up a remanned dizzy from NAPA and I will have to take it apart to see what it has. The remanned one doesn't have a thin shim between collar above the gear and the housing of the dizzy, will that really matter? The remanned one doesn't have as much side to side play as my used one.

 

I have yet to have a distributor with that shim on it. My units have been running fine without it.

Does the reman one have a bushing at the bottom of the housing? Most electronic version's come without a bushing at the bottom and I end up machining the housing and a oilite bushing to put in there.

Tmod

 

The remanned dizzy has the same 13L and 18L settings and is on the 13L setting. It does look like it has a bushing at the bottom but it isn't the usual copper color (it's black). Don't I have to remove the collar and the gear (wish I didn't) to get those slots out of the dizzy so that I can add some metal to them???... Or does the cam pull off of the shaft?

 

The cam will lift out from the top.

What you need to do is look in the middle of the shaft and you will see a felt wick, Just remove that and you will see a little snap ring with the tabs facing upward.

Take two picks and go in between those tabs and push them apart and try and lift the snap ring out of there.

After that just lift the cam out and do whatever you need to do and re-install.

How much metal are you looking at adding? And why?

Tmod

 

Wellllll, wouldn't that limit the amount of mechanical advance??.. I wanted to limit it so that I could run vac. advance too. On the old dizzy with the same settings, I had to disconnect the vacuum advance to get the total timing down to 32 degrees total. Are you suggesting that I maybe change one or both of the springs?

 

Yes it does but I was just asking.

Here is my setup on my 390. I can run regular 87 octane without any pinging.

Distributor Timing Specs:
Initial Timing Advance 16 BTDC @ 800 RPM
Full Centrifigual 8 BTDC @ 2500 RPM
Initial & Centrifigual @ 2000 18 BTDC
Vacuum Advance @ 5" 0
Vacuum Advance @ 10" 3
Vacuum Advance @ 15" 14.5
Vacuum Advance @ 17" 18
Centrifigual Starts @ 1800 RPM
Total Initial & Centrifigual 24 BTDC @ 2500
Total Timing @ Idle 800 RPM 34.5 BTDC @ 800 RPM

Also here is the dimensions of what you need to close the slot width down to for a particular timing limit.

10 degrees centrifugal advance = .280"
12 degrees centrifugal advance = .306"
14 degrees centrifugal advance = .332"
8L slot = 16 degrees centrifugal advance = .358"
9L slot = 18 degrees centrifugal advance = .384"
10L slot = 20 degrees centrifugal advance = .410" Total slot width
11L slot = 22 degrees centrifugal advance = .436
12L slot = 24 degrees centrifugal advance = .462"
13L slot = 26 degrees centrifugal advance = .488"
14L slot = 28 degrees centrifugal advance = .514"

Oh and yes change the springs as the weights will slam and bounce with the stock springs.

Tmod

 

But wouldn't changing to heavier springs make the advance come in later...??? resulting in lower performance off the line and at lower rpms.

 

The stock springs are the heaviest that I have seen so I was suggesting that you put lighter springs in the distributor.

Just buy the Crane Vacuum Advance kit and it will contain a new vacuum canister and some springs.

Tmod

 

Mine has one lighter spring and one heavier spring. I already have that Crane kit so... You obviously know more than I do on this, but should I just put the lightest spring in the kit from Crane on the dizzy or should I have a combo (one heavier than the other)? I believe if I remember right that the springs are color coded in the Crane kit.

 

If memory serves me correct you have silver and yellow springs in the kit.

Which one is there two of? Been awhile since I did mine.

I want to say use one yellow and one silver.

I think there are two silvers in the kit.

After installing the springs bend each outer ear out about 1/32" of a inch.

That setting should get you pretty darn close to the same timing curve that I have.

Now if you have a hand vacuum pump just have the engine running at idle and adjust the vacuum canister until your vacuum timing matches my settings.

You will now have a good baseline if not a great timing curve that matches the 87 octane as well as performance and fuel mileage.

Tmod