New timing chain setting?

[diggs00]

Replacing old timing chain and noticed PO had the crank sprocket set to “A” advanced. Should I just match this or set my new chain to “0”.

No clue if he put in a new cam.

Here are pics

https://drive.google.com/file/d/1TKMr1FETJ6w1sdyyudBnMFe8P0N_i5i0/view?usp=drivesdk

https://drive.google.com/file/d/1fk8PCApXL17Q9wMZVXV_vdo-mkrXCMFB/view?usp=drivesdk

https://drive.google.com/file/d/1SUNT2IbOIpdvfgxYbQJCdg5MsNGIQrkf/view?usp=drivesdk

 

[gr8scott]

Yes, set it dot-to-dot ,zero.

 

[suckerpunched]

It's impossible to know why this was done. there might be a number on the front of the cam once the gear is off but I doubt it will answer the question as to how you should set it up. cam make and grind + accompanying info + a degree wheel. will get you close. I guess if it was me and I liked the way it ran, I wouldn't change the timing. setting it to zero may or may not be an improvement, hard to know without more info.

 

[ared77]

My two cents worth %) -

Don't know how long you've had the Bronco but if it's been awhile you probably remember how it ran before the chain stretched out. Use to run good? If so I'd try to replace timing chain just like the one coming out. I'd figure original builder did that for a reason. I would think that putting in new chain at the advanced "A" setting would be my safest option not to have to take it back apart again. That's if your goal is just to replace a stretched chain and get back on the road. Good luck!

 

[DirtDonk]

The other notch says "R" for retard? Or something else?
If you know that the A is for advanced, I'd be tempted to do the same thing. The problem arises that even as precise as manufacturing can be these days, apparently cams and timing gears are not always among those. Seems that when you degree cams with a wheel you find all sorts of discrepancies.
Perhaps the builder found that the cam was retarded so advanced it with a multi-position gear set.
I found the cam for my 400 was already advanced farther than I would have put it, so had to end up using the zero degree mark just to get it "only slightly" advanced. I had known it was a possibility, but it kind of ticked me off anyway.

Or perhaps they just wanted the torque to peak earlier in the rpm range. That's good for trucks and is a universal thing with cams.
The more you advance a cam the lower the torque curve starts and peaks. The more you retard it the higher in the rpm range the torque moves.
This would be true of just about any cam used in one of our engines.

You can do this to simply take a decent cam and give your truck more low-end pulling power. Or you could take an otherwise slightly peaky cam and make it more street-friendly.
It's not always a huge difference, but it can make the difference when you're building an engine that you want specific performance parameters from.

As the others have asked, how did it run before?

Paul

 

[blubuckaroo]

You don't have to take chances or guess when setting up a cam. All the good cam manufacturers will have a recommendation for advanced, neutral, or retard for the setting on your particular application.
If you could come up with a number on the cam, you might be able to sort it out.

 

[diggs00]

thank guys,

The truck ran fine last year, seemed a bit torquey and wanted to get out of first as fast as possible (c4 auto). I drove it from Dallas to Austin (3hours) no issue.

As for finding the cam info, will that be visible one I pull the cam timing gear?

 

[73azbronco]

Probably not, My cam has some chicken scratch on front which does not match anything noted in documents.

Install chain like old one, at least you know it works there.

 

[DirtDonk]

Assuming the same brand anyway. No guarantee that an "A" means the same exact thing between manufacturers. Some might be 2° while others might be 4, or even 6 perhaps.
But like said, those few degrees difference are not going to hurt anything.

I think a lot of the cam manufacturers put their ID numbers on the back boss of the cam, and not the front like we'd hope for an easy identification.
Could still be a stock cam even and they wanted to spice it up down low with an advance timing set.
Lots of possibilities, so you just don't know until you know. Ya know?;D

Oh, and the C4 in Broncos almost always shifts early out of 1st gear. It's been a question many have had since the early days.

Paul

 

[blubuckaroo]

Oh, and the C4 in Broncos almost always shifts early out of 1st gear. It's been a question many have had since the early days.

Paul

Theoretically, advancing the cam will produce torque (and more vacuum) at a lower rpm. With that higher vacuum, the modulator wouldn't delay the shift as long while accelerating.

 

[jckkys]

The part throttle shift points can be raised with a longer pin in the vacuum modulator. I think the stock length is about 1 1/2". Between that and the adjustable modulator I was able to get good part throttle shift points.

 

[Broncobowsher]

Most aftermarket cams have markings on the back of the cam. That is you take the cam out to read them. And the cam won't clear the grill so you are either removing the grill or pulling the engine.

Guessing you are changing the chain because of stretch. A new chain straight up will probably be better that a chain installed advanced (if that is even what the "A" stands for) and has worn into a retarded state.

The really short answer, unless you know more about the parts than you do, just put the chain is straight up. Dot to dot. Put the cover on and run it. Any advancing, retarding, or degreeing of the cam can't be done unless you have the specs on the cam and where it should be at.

 

[diggs00]

Most aftermarket cams have markings on the back of the cam. That is you take the cam out to read them. And the cam won't clear the grill so you are either removing the grill or pulling the engine.

Guessing you are changing the chain because of stretch. A new chain straight up will probably be better that a chain installed advanced (if that is even what the "A" stands for) and has worn into a retarded state.

The really short answer, unless you know more about the parts than you do, just put the chain is straight up. Dot to dot. Put the cover on and run it. Any advancing, retarding, or degreeing of the cam can't be done unless you have the specs on the cam and where it should be at.

The markings are “A” “R” and “0” on the old crank gear. The PO had it set up to “A” advanced at TDC. My worry is if the cam is aftermarket and it required an advanced setting for timing.

I was intending to go for “0” dot to dot on new timing chain/gear. But am second guessing it.

 

[suckerpunched]

I forgot the cam number was usually on the back of the cam. under the cam gear would have been too easy.

 

[DirtDonk]

My worry is if the cam is aftermarket and it required an advanced setting for timing.

The manufacturer often gives a recommendation of advanced, retarded or straight up, but it's not usually an absolute requirement. It's entirely up to the end user/installer in most cases because those few degrees do not create a piston-to-valve interference issue.
With some engines you have interference fits, but with a basic 302 you don't have that kind of issue with only a few degrees of change.
At least none that I know of. Others will know, but I guess it still comes down to the cam.

If it's a radical cam with .600" lift for example, then that might all change.

If by "timing" you mean ignition, cam timing has nothing to do with ignition timing.
Changing cam timing might change where your engine likes the ignition timing set of course, but it in and of itself does not change ignition timing at all.
Timing is timing, whether ignition of valvetrain. And never the twain shall meet...

Paul

 

[ared77]

diggs00, remember you said it ran good last year -

"The truck ran fine last year, seemed a bit torquey and wanted to get out of first as fast as possible (c4 auto). I drove it from Dallas to Austin (3hours) no issue."

And (I assume) it started running worse recently and that's why you are changing the timing chain. Because you started taking engine apart and found that the chain had stretched. If this is all true, I still believe your safest bet (to get it back on the road again) is to install it just like the one one. At the "A" advance setting because that's how the original builder believed it should be set.