Hi all. Had to take my truck in to get it's annual inspection (several months overdue) the other day, and to make a long story short, the garage messed with my timing and now it doesn't run like it did before I dropped it off. They claim they did it in attemp to get it to pass emissions. I chewed 'em out something fierce when I discovered how bad it runs. They basically looked up the correct timing for a 71-71 351C, which according to Chilton is 6 BTDC. Of course, it didn't pass emissions....thanks for nothing. I didn't want them messing with it any more, so I just drove it home as is.

My truck is an 86 F150, which I've posted about on this board before. I bought it with the 351C already installed, and it ran great. The motor is, to the best of my knowledge, an original 2bb mill with what I believe to be the stock cam. It's got headers and a 600 cfm Edelbrock AVS with an MSD 6A ignition system. The rear gear is a 3.08, and the auto trans is also stock (no perf converter). I like it to run strong through the mid-range. Not knowing what the timing was before the shop monkeyed with it, I've attempted to get it back to where it runs best. Right now, it's running at 30 BTDC....I had it at 20, and it felt pretty good, but it still wasn't quite right so I set it where it is now. I'm not too convinced it's right, though, and I don't want to damage the motor, so I've come here for some expert advice.

I know this isn't the easiest thing to answer, seeing how every engine is different, but do y'all think I've got it right, or even close? What timing setting would y'all recommend, based on the info I gave above?


I can say one thing...lesson learned. Next time, when I buy another late model vehicle, I'll take note of things like this before I ever tinker or let anyone else tinker with it.


Thanks for any input guys.




Rob.

 

i'd try around the 10* -16* range and see how it runs. are you saying 20*and 30* initial? 20 would be a lot and 30 would be a REAL LOT. you prolly want to shoot for about 36*-38* total. a timing tape on the balancer takes alot of guesswork out of it, or a timing light with an advance dial on it.

 

To my chagrin, I must admit that I never really understood the difference between initial and total.

I just hook up my timing light, start the engine, get it idling @ 500 or so, and read what it's lining up on. Right now, it's right on 30...My light doesn't have an advance wheel, so I surmise that what I see is what I've got?





Edit: Reading some other posts on this board, I'm kinda getting the idea that my cam is not stock.



Rob.

 

Initial timing refers to the base timing. Your timing can't drop any lower than the initial setting because it is determined by the distributor body's position relative to the rest of the engine. Total timing refers to initial plus advance. Timing is advanced with a vacuum advance to compensate for load, and a centrifugal advance to compensate for RPM.

Usually, initial timing is all you see at idle.

I think 30 is way to high for initial timing and I'm surprised you're not hearing any spark knock. Set it to what your emissions label says, but if that's gone, your Chilton's manual will give you a ballpark. However, I wouldn't be surprised if you had to bump it up some, especially if you're running an aftermarket cam.

 

When you say you just start it up and check the timing, are you saying then that you do not disconnect the vacuum advance line from the distributor? You need to disconnect it and plug the vacuum line, and then check the timing.

 

Also, your vacuum advance should be running to ported vacuum; they might have moved this around also.

 

Thanks for all the replies, guys. I appreciate all the info, but I think everyone's missed something I wrote above. It's an MSD distributor, pn 8580.

There is NO vaccuum advance on it. This is why I didn't mention plugging that line up. Sorry I didn't make that clearer.


Rob.

 

does your timing light have a dial on it?

 

No, it doesn't.


I found a .PDF file on MSD's website which gave me a pretty good run-down.

It's a mechanical advance distributor, which is why there's no vaccuum line. Advance is controlled by one of four color-coded bushings, each of which sets a different amount of advance, ranging from 18-21-25-28 degrees.

As best as I could determine, my bushing, which is under the whole counterweight assembly and is therefore hard to get a good look at, was the silver one which requires a setting of 25 degrees. So, I cranked it down from the 30 I had it at yesterday to the recommended 25, and took her for a spin. It feels pretty good, but it felt better at 30 to be honest with you. However, the bushing for the closest corresponding setting (28 degrees) is RED, and my bushing certainly isn't red. I think I'm gonna leave it where it is now, even though at 30 degrees it didn't produce any knock or other audible problems and it ran just fine. I suppose it's possible that they may have messed with the mixture screws on my Edelbrock AVS...I HOPE not, because that's whole other nightmare.



Rob.

 

the bushings control how much advance the mechanical internals of the dizzy can provide. if you have the 25* bushing in the dizzy and you set the initial at 13*, you will have 38*total. if you set initial at 25*, you will have 50* total which is pretty high. i'm really surprised you aren't getting a lot of pinging! does your dizzy have a "lock-out" feature? this locks the mechanical internals and they do not operate, leaving the timing at the initial setting all the time. maybe the timing is "locked out"?

edit: i looked on the msd site and the dizzy does have lockout capability. it also says that the blue bushing comes installed. i don't think you'd be able to see the bushing while the dizzy is assembled? quick way to see if it is locked out is to hook up the timing light and watch the setting marks as you slowly rev the engine. if the marks move it is not locked out. if the marks don't move it is either locked out or it has VERY stiff springs in it, which could also be keeping it from pinging.

 

It does, and to be honest I'm not sure if it is indeed set up that way. I hear ya on the total advance thing. 50 degrees would be crazy, and it sure doesn't ping at all.


So, let's pretend that it is locked out....the question is, with a permanent (unmodified) setting of 25 degrees by the bushing, and a timing reading of 25 degrees on the flywheel by the timing light @ 500 rpm, am I really at 25 degrees? In other words, I know the timing moves around when I turn the distributor, and I can see what the light is showing on the damper, which right now is 25. With the advance locked in, is what the light reads on the damper a true setting? If that is so, then with locked-out advance on the distributor, my reading on the damper would be my actual total advance, right?



EDIT...To answer that question, I have a small inspection mirror which I was able to stick underneath the weight assembly and by shining a flashlight on the mirror I was able to see the bushing, which clearly wasn't blue. And the springs up top are definitely the heavy silver ones.



Rob.

 

yup, you're getting it. with the vac disconnected and plugged, or no vac at all like yours, at 500 rpm the centrifugal advance should not be doing anything. the reading at the balancer is your "initial" or "base" timing. if the timing is locked out in the dizzy, this will also be your total timing. if the centrifugal advance is operating, the engine has to be brought up in rpm until the advance stops to read the total on the balancer. stock balancers don't read that far so some guys put on a "timing tape" that reads farther than the marks on the stock balancer. aftermarket balancers are marked to be able to read total timing. the other option is a timing light that has an advance dial on it, you set the dial to the total advance and it shows up as "0" on the balancer. the silver thing you see with your mirror could be a sleeve on the pin for the lockout trick? i think if it is in lockout mode there is no bushing? so when can you rev it up and see if the timing is on the move?

 

Could be. I hadn't thought of that.





Well, it'll have to be tomorrow afternoon, as it's just about 10:00 pm here in eastern PA, and my neighbors would have a fit if I started that thing up now.


Thanks for your patience. I appreciate the help. I'll post up tomorrow with the above info.




Rob.

 

Oh, and one more thing I just thought of.


Pretending that all the above is fact, and I do have 25 degrees total advance right now, would it be safe to assume that I do indeed have an aftermarket cam, as 25 degrees is way higher than the 6 BTDC that Chilton recommends?


I ask because, like I wrote way up there somewhere, when it's set at 6 degrees and slightly higher, it runs like absolute crap. Doesn't want to run right at all until at least 20 degrees.


Or am I missing that point entirely?




Rob.

 

comparing apples to oranges. a stock set-up with 6* initial and vacuum advance at idle would be more than just the 6*. a little above idle the vac will really take off and crank in quite a bit of advance. a mechanical only dizzy should want to be set up kinda high for the base timing(to cover the missing vac advance) and only provide enough mech advance to give proper total, like 18* base and the 18* bushing to finish out at 36*