timing a recurved distributor

[moknbrd]

I have a 72 Scout II with the Holley aluminum distributor w/o gov. Or tach gear.

Recently I bought a re-manufactured distributor for my 345 and sent it to the philbin group to get a performance curve installed. I also sent them the specs for my new isky cam that has 256/262 duration profile. When rebuilding the engine, I also picked up a new set of timing gears that remove some of the built in retard in the setup by using a non-emission pattern. I think they're r70s or r90s? I can remember now.

When I got the distributor back, put a pertronix II in it, and then installed it in the engine. I didn't get anything back from philbin stating what the curve profile now was or how it had been modified.

Questions:

1. When setting the timing, do I use the same specs as most everyone else (5-10 btdc)?

2. Does my change in cam timing affect my setup for ignition timing?

Thanks

patrick
albuquerque nm

 

[Michael Mayben]

Welcome to the forum patrick!

And you have asked the right questions, you are paying attention really well!

Did you actually "degree in" your cam at install...or just set it "straight up" with the provided timing marks on the replacement gear set? Did you by chance use the gear set offered by isky that provides for alternative cam timing???

Actual base timing for your or any other engine is not affected by the "recurved" distributor. And neither does the cam specs really affect the timing point. So if you are gonna use a timing light initially, I'd go with 6>8* btdc for a starting point. You are timing the engine to what it needs as a total running package, not "to a cam" or "to a carb", or "to a compression ratio".

Once the engine/cam are broken in, then do the "power timing" thing I've described elsewhere. Then shoot it with the light if you want to know what the actual timing reference point is for your understanding. That is the base timing your engine likes...not necessarily anyone else's! Don't be surprised that you can run up to 12*btdc at your altitude in albuquerque.

I pretty sure of the curve specs that philbin uses...if ya wanna figgr it out on your own later on, then ya need an accurate "shop tachometer" and a "dial back" timing light (some folks refer to those as a timing advance tester). Maybe I need to post a stickee about how to do this in this sub-forum??? Doing so is also an excellent method for determining the mechanical condition of any distributor without having to use a distributor machine such as philbin has to set up/test distributors.

 

[moknbrd]

In general, is philbin recurving their distributors with lighter or heavier springs?

I didn't dial in my cam, I just used the dots on the gears. However, I do have to replace the timing cover in the future so maybe I could redo it then.

Didn't know isky had an alternative gear set. I think I got mine from IHOnly...they're IH gears but are pre-emissions. I'd have to go look at some old emails to get part numbers, but essentially they're supposed to take out the built in retard in the gearset that was originally in my motor.

 

[Michael Mayben]

We're working with isky now on some timing gear sets they have done in the past (many years ago when there was a market for that stuff). They are identical to the gears we supply from ihon, but have had some custom machining performed to offer some alternative timings. Problem is they need to be heated to install properly...and they have no puller holes for removal for alternative timings so it's a tedious operation for someone not used to doing this kind of work. More to come in the future about that.

Philbin, me, and any distributor tuner uses a combination of springs, advance weights, and bushings for making the curve do what we want. It's not "just the springs" and it depends upon which distributor is being built and what it's original curve is/was.

There was a time when we could easily obtain an adjustable vacuum can for a Holley distributor from crane...but those went away many years ago. We can still find adjustable cans for delco distributors however, very common item.

 

[moknbrd]

Ok, I'm headed to the shop to work on my Scout today so I'll make sure I:

-set my base timing between 6-8 btdc
-ensure the vac advance is working
-verify idle is at what is specified in the manual and tranny is in n.
-ensure my pertronix is is set to .030"

 

[Michael Mayben]

ok, I'm headed to the shop to work on my Scout today so I'll make sure I:

-set my base timing between 6-8 btdc
-ensure the vac advance is working
-verify idle is at what is specified in the manual and tranny is in n.
-ensure my pertronix is is set to .030"

Great detail! Yore on it!

 

[moknbrd]

-ok, got my initial timing set to 8-9 btdc
-set my air gap on the pertronix using a feeler guage to .030.
-idle is at 725

I think my vac advance is broken, did the suck test and it didn't advance. Pulling the distributor this week to see if it's just stuck or whether I'm going to need a replacement.

 

[Michael Mayben]

-ok, got my initial timing set to 8-9 btdc
-set my air gap on the pertronix using a feeler guage to .030.
-idle is at 725

I think my vac advance is broken, did the suck test and it didn't advance. Pulling the distributor this week to see if it's just stuck or whether I'm going to need a replacement.

Philbin should have verified the vacuum advance unit as functional or not and then if it was dead, rebuilt or replaced the can with a unit that worked. That was imperative regarding a "recurve" job!

The vacuum advance you are dealing with will begin to move when approximately 5"hg>7"hg of vacuum is applied...and will provide 5* of movement/rotation of the breaker plate. If you turn your vacuum can upside down, you will see a digit which is either "5", "6", or "7" stamped on the arm. That is the "value" of the amount of movement that unit provides and is read as "degrees".

When philbin "rebuilds" those cans, they can change the calibration to whatever they wanna use.

If the vacuum nipple on your can is connected to a "ported/timed" vacuum source (which is oem), there will be somewhere between 0"hg and 6"hg of vacuum at that point at correct curb idle speed and idle mixture setting. So at "idle" the vacuum advance unit is not functional, that is how it's supposed to be! Not enough vacuum present to make it actuate! So if you apply the suk test to the advance can, ya gotta give it more than 6>7"hg. That is why the correct test for that item involves a mityvac with a high resolution gauge so that the exact point of actuation can be read for diagnostics as ya use the pump to provide an "increasing" level of vacuum applied.