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Single vs dual diaphragm distributor 72 Q Code
#21
the total timing could be adjusted on any distributor.

one method is making your own plate, you weld up the gap in the mechanical plate then you cut out the gap just as you need it.
it requires measurement and testing and usually lots of adjustment.

another method is bending the end points on the mechanical advance. to shorten the gap..

my method,, i stuck a piece of rubber hose on the stoppers to make the gap smaller.

the total timing being high isn't necessarily the nail in the coffin for what happened in your case.
there could of been multiple factors. remember even with mechanical advance locked to 34 degrees total you can still have the vacuum advance kick in and drive the advance over 54 degrees this is normal under low load. you most likely just had too much timing coming in too quick and were running hot and lean then that would of nuked the pistons.

as for the L on the plate.
it stands for Limit pin.

L15 would be 15 degrees but it really means 30 because the distributor spins half speed of the Crank.
so you multiply by 2 to get the total mechanical advance.
L10 is 20
etc...

most distributors have have 2 positions on the mechanical advance L15 and L10 are common.
if you happen to be set on the larger number say L15 then you could turn the distributor 180 and use the L10 position.

so you need to pull the distributor out of the engine, move the mechanical plate to the smaller number say L10 and now the distributor will be 180 degrees out. so you need to spin the rotor 180 and reinstall back in the engine with the #1 at 1 o'clock position.
  Reply
#22
72HCODE;246165 Wrote:the total timing could be adjusted on any distributor.

one method is making your own plate, you weld up the gap in the mechanical plate then you cut out the gap just as you need it.
it requires measurement and testing and usually lots of adjustment.

another method is bending the end points on the mechanical advance. to shorten the gap..

my method,, i stuck a piece of rubber hose on the stoppers to make the gap smaller.

the total timing being high isn't necessarily the nail in the coffin for what happened in your case.
there could of been multiple factors. remember even with mechanical advance locked to 34 degrees total you can still have the vacuum advance kick in and drive the advance over 54 degrees this is normal under low load. you most likely just had too much timing coming in too quick and were running hot and lean then that would of nuked the pistons.

as for the L on the plate.
it stands for Limit pin.

L15 would be 15 degrees but it really means 30 because the distributor spins half speed of the Crank.
so you multiply by 2 to get the total mechanical advance.
L10 is 20
etc...

most distributors have have 2 positions on the mechanical advance L15 and L10 are common.
if you happen to be set on the larger number say L15 then you could turn the distributor 180 and use the L10 position.

so you need to pull the distributor out of the engine, move the mechanical plate to the smaller number say L10 and now the distributor will be 180 degrees out. so you need to spin the rotor 180 and reinstall back in the engine with the #1 at 1 o'clock position.

I'm learning more every day. I'm sure many others are also benefiting form these posts.
As I said, the engine is going back to the shop and will not be going back in the car until I KNOW it's set up correctly. Your obvious knowledge on this issue is a great help and I thank you so much.
I've asked many people if they know what that 'L' stands for and no one was ever able to tell me...... even those who are supposed to know!! Amazing. Now I know.
As for fuel mixture, when the car was on the dyno, I had O2 bungs inserted in the pipes so they could install the sensors. Fuel mixture was seen to be right on and plug read would support that. I can't get anymore technical than that.
I now have the info I need to get where I need to be with this, so thank you one and all for your invaluable help.
Geoff.
  Reply
#23
Stanglover;246092 Wrote:
barnett468;246059 Wrote:.
exactly what is your timing problem?

any ford distributor can be set to whatever spec you want.

if you cam and/or compression is no longer stock, the factory setting no longer applies.

as i mentioned earlier, you can probably get more power by setting your timing curve for your particular engine . . failure to do this and just assuming the factory setting is best is doing a great disservice to yourself.

Hi Barnett468, In a nutshell, the engine was rebuilt in late 2012. The builder is a reputable company and overall, they built a very smooth running motor. They used KB177 flat top pistons, which upped the compression to approx. 10.8 and a Melling MTS-2 cam, which is slightly better than stock, nothing radical at all. The rest is factory stock. The problem is the distributor, which was a recent reman. Cardone, was not curved or checked as far as I know. It was fitted with the PertrixIII and timed to 8-10 degrees. The engine was assembled and broken in at the shop on their stand. I've discussed this at length in previous threads. On a dyno, it was seen that the timing was drifting way up to 39+ deg. and not stable. I'm no expert on this, but the tech told me it was a bad distributor from the get-go. Therein lies my problem. The engine is going back to the builder to be stripped and checked. I suspect chipped pistons and scored bores and who knows what else. Needless to say, it will not go back on the road until I know that everything is correct. I am not sure what type of piston I'll use, they all have different pluses and minuses, but it will have a bit less compression at no more than 10:1. Hyper pistons are fine as long as timing is stable and set conservatively. What would your thoughts on pistons be?

hyper pistons are fine but are very sensitive to detonation . . mahle pistons are xlnt.

it sounds like your dyno guy was just a dyno guy and not an engine tuner otherwise he would likely not have let the timing get to 39.

you have some distributor info now but i would do this.

1. you are totally screwing yourself if you use a dual vacuum advance chamber.

2. plug the retard side of the chamber hose with a bb.

3. set initial timing to 10.

4. set the mechanical advance so the limit arm is in a slot that has a maximum of 10 degrees . . if yours says 12, put a thin rubber hose over the limit arm as suggested.

5. check the timing at 22oo rpm . . if it is more than around 24 degrees, i would bend the arm on the heavier spring out a little.

6. check maximum advance . . it should be no more than around 32 at around 2800 to 3000 rpm.

this will be perfectly safe for 10.0 compression if your engine is running at 190 degrees or less.

and install a spark plug that is 1 step colder than stock.
  Reply
#24
barnett468;246238 Wrote:
Stanglover;246092 Wrote:
barnett468;246059 Wrote:.
exactly what is your timing problem?

any ford distributor can be set to whatever spec you want.

if you cam and/or compression is no longer stock, the factory setting no longer applies.

as i mentioned earlier, you can probably get more power by setting your timing curve for your particular engine . . failure to do this and just assuming the factory setting is best is doing a great disservice to yourself.

Hi Barnett468, In a nutshell, the engine was rebuilt in late 2012. The builder is a reputable company and overall, they built a very smooth running motor. They used KB177 flat top pistons, which upped the compression to approx. 10.8 and a Melling MTS-2 cam, which is slightly better than stock, nothing radical at all. The rest is factory stock. The problem is the distributor, which was a recent reman. Cardone, was not curved or checked as far as I know. It was fitted with the PertrixIII and timed to 8-10 degrees. The engine was assembled and broken in at the shop on their stand. I've discussed this at length in previous threads. On a dyno, it was seen that the timing was drifting way up to 39+ deg. and not stable. I'm no expert on this, but the tech told me it was a bad distributor from the get-go. Therein lies my problem. The engine is going back to the builder to be stripped and checked. I suspect chipped pistons and scored bores and who knows what else. Needless to say, it will not go back on the road until I know that everything is correct. I am not sure what type of piston I'll use, they all have different pluses and minuses, but it will have a bit less compression at no more than 10:1. Hyper pistons are fine as long as timing is stable and set conservatively. What would your thoughts on pistons be?

hyper pistons are fine but are very sensitive to detonation . . mahle pistons are xlnt.

it sounds like your dyno guy was just a dyno guy and not an engine tuner otherwise he would likely not have let the timing get to 39.

you have some distributor info now but i would do this.

1. you are totally screwing yourself if you use a dual vacuum advance chamber.

2. plug the retard side of the chamber hose with a bb.

3. set initial timing to 10.

4. set the mechanical advance so the limit arm is in a slot that has a maximum of 10 degrees . . if yours says 12, put a thin rubber hose over the limit arm as suggested.

5. check the timing at 22oo rpm . . if it is more than around 24 degrees, i would bend the arm on the heavier spring out a little.

6. check maximum advance . . it should be no more than around 32 at around 2800 to 3000 rpm.

this will be perfectly safe for 10.0 compression if your engine is running at 190 degrees or less.

and install a spark plug that is 1 step colder than stock.

I know we have got way off track to the original thread posted by nbracken, my apologies to you, but in all there is very valuable info contained here that many of us can and will likely benefit from. Kudo's to those who have offered there time and advice. I for one will be building a much better engine as a result. Can't wait till spring to get it back on the road when I will definitely be posting the remedies and results. Barnett468, your advice will be real help in setting it all up to be a great street driver. Thank you.
Geoff
aka Stanglover
  Reply
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