Camshaft timing - valve timing question

[matts70]

OK, I've been chasing a timing issue for a while now (http://classicbroncos.com/forums/showthread.php?t=155660) and have received some great help and ideas from lots of people here. I thought it would be better to start a new thread for this question because it's more specific.

My compression in all cylinders is 130-150 psi. Can I still have a valve timing/camshaft timing issue? If the timing gears are off a hair (1-2-3 teeth?) could this cause the initial ignition timing to be advanced 30* (600 RPM, no vacuum), but still maintain good compression in all cylinders? Is it even possible for the timing gears to be misaligned on a 302 with stock timing gears?

I've done the following while trouble-shooting this situation: rechecked idle mixture on carb, installed a new dizzy, checked TDC on #1 cylinder, ensured rotor is pointing right at the right plug wire at the right time, checked timing chain play (OK--5*), replaced the damper, checked the timing marks on the damper, checked proper voltage to the coil, checked compression.

 

[73azbronco]

what are the conditions; is it a new motor, rebuilt, comp ratio? Is it a new or old timing chain, damper, new or old cam? What cam? What timing set?

 

[Viperwolf1]

Yes. If the cam gear is off timing by just one tooth it advances or retards the cam 10 degrees (20 crankshaft degrees). My guess is it would be retarded. Why not get a dial indicator, pull a valve cover and measure the cam timing? Easy to do without taking much apart.

 

[av bronco]

have you determined true tdc?
http://www.jegs.com/i/JEGS/555/80524/10002/-1

 

[NYLES]

have you determined true tdc?
http://www.jegs.com/i/JEGS/555/80524/10002/-1

X2 and how old is your HB, if HB has spun all your timing #'s are off!

Whats compression got to do with timing?

 

[Viperwolf1]

Guys, he's verified the balancer marking is correct at TDC but can't get it to run without 30 degrees of initial advance.

 

[NYLES]

Okden...180 out?

 

[blubuckaroo]

Are you calling the correct cylinder #1? Don't laugh. Lots of people learn on Chevys and just assume #1 is on the front driver's side.

 

[av bronco]

If you are gonna degree it in the bronco you have to get the small wheel
http://www.jegs.com/i/Comp+Cams/249/4790/10002/-1
The large one wont clear the crossmember.

 

[DirtDonk]

Whats compression got to do with timing?

Nothing, if you're talking about the static compression ratio and cam timing.
But with dynamic cylinder pressures (as in a "compression check"), it can have an effect depending on where the valve timing events are.
Think overlap and/or early or late valve opening/closing events.

Paul

 

[DirtDonk]

My compression in all cylinders is 130-150 psi. Can I still have a valve timing/camshaft timing issue?

I would think that those reasonably good readings wouldn't completely rule out an out-of-time camshaft. But I don't know. They seem pretty "normal" (and pretty good) for a stock Bronco engine.
But we'd have to compare the same engine and cam to a specific degree timing, with the same setup at a different degree setting to be sure.
Maybe someone with more experience with this aspect would know that, generally speaking, given a specific engine and cam, you should have, say, 175 psi, so your 150 could indicate an advanced/retarded cam.
I just don't know in this case. To me they seem like normal pressures.

If the timing gears are off a hair (1-2-3 teeth?) could this cause the initial ignition timing to be advanced 30* (600 RPM, no vacuum), but still maintain good compression in all cylinders?

If I'm reading you right, you're asking why it runs better when you set initial ignition timing at 30° than it does with it set at the more normal 10° or so?
I'm only getting this because I think that's the question that started your other thread.
Is that basically correct? If not, let me know.
If so, then I'd say "maybe", but probably not. Then again, I don't know for sure anything other than that these things are dynamic and have a mind of their own.
There, How's that for vague?

The orientation of the cam-to-crank relationship does not change the location of your spark-to-piston physical location. In other words, your 30° spark advance is still the same 30° it would be on any other engine. It's how it interacts with the engine that "could" change with the cam-timing.
But my feeling is that it would not change it that much unless your cam was way off. A few degrees either way would maybe make the engine prefer a different ignition timing factor, but only a few degrees either way.
Not 20 degrees!

In general terms, advancing your cam timing a few degrees lowers the torque curve. Retarding it raises the curve. Your engine make the same peak power (within reason), just at a different rpm level.
So a stock-car racer might retard a cam to make the engine more efficient in the upper rpm range. A truck owner might advance the cam to give the engine a lower effective rpm range and better off-idle performance.
Assuming of course that neither one had a cam tailored exactly the way they wanted them and had to "make-do" with an existing cam that was close to what they wanted.

Is it even possible for the timing gears to be misaligned on a 302 with stock timing gears?

Yes, it's possible to mis-align any gear/chain (or gear/gear) combination. All it takes is moving one gear, one tooth over in the chain link and you're off by x degrees. In this case, 10° for one tooth off the cam gear according to what Viperwolf said.

I've done the following while trouble-shooting this situation: rechecked idle mixture on carb, installed a new dizzy, checked TDC on #1 cylinder, ensured rotor is pointing right at the right plug wire at the right time, checked timing chain play (OK--5*), replaced the damper, checked the timing marks on the damper, checked proper voltage to the coil, checked compression.

What was the original problem again? Other than the off-base timing, how is the engine actually running now? Was it you that had borrowed an old beat up timing light that wasn't giving consistent readings? If so, did you replace it with a good one and re-check?
How's it running now, ignoring the timing for the moment?

Paul

 

[matts70]

Hi Paul,
Original problem is that the initial timing is 30*. Setting it at 8* and it will die. The timing light turned out OK--verified the reading with a second light.

How's it running? Good question. It's very tough to get it tuned properly. For example, with initial timing at 30*, it has good idle, acceleration is OK, but as the advance jumps into the 50s and 60s, it's not so happy. Reducing the initial timing gives a poor idle and it will hesitate and jump when accelerating. The best I've been able to get so far is setting initial timing at 10* then connect the dizzy to manifold vacuum full-time.

If all else fails, I'll continue to tinker with it and try to find a combination that best emulates what the engine was designed to do and call it quits, but if possible, I'd prefer to find out what's going on.

Maybe that's just the way this particular motor runs, even if it's unlike any other 302, but I'm exhausting other possible scenarios before giving in. . . and I'm just about to that point.

 

[gearida]

Okay check dampner as stated. How is your idle at idle I think you have the carb too fast and your dizzy is advancing. Do you have an intake or vacuum leak that you are hiding with advancing the timing? Are you checking compression with all plugs out and spinning the motor over only four or five hits? Are you using the correct port for you'd dizzy advance? U think you have something off. What about all the basics, firing order correct? Recheck number one and the dampner first. Carry on and good luck.

 

[DirtDonk]

You just reminded me of a previous question Matt.
When you turn the timing back down to the 10 degree range and hook the vacuum up to ported vacuum source, are you turning up the idle speed screw on the carb, and then re-adjusting the two idle-air mixture screws?
I remember mentioning that the idle always goes down when the timing retards, and goes up when it advances, so you always have to futz with the carb when doing timing.
It's a "system" kind of thing.

Don't remember if you replied to that one or not. So just turn the screw up on the carb and see where that gets you.
Hope that helps.

Paul

 

[matts70]

Yes. If the cam gear is off timing by just one tooth it advances or retards the cam 10 degrees (20 crankshaft degrees). My guess is it would be retarded. Why not get a dial indicator, pull a valve cover and measure the cam timing? Easy to do without taking much apart.

Thanks again, Viperwolf. I'll start asking around to see if anybody has a dial indicator I can borrow before buying one. Never checked cam timing before--what will I be looking for? I'll look for some instructions as well.

 

[matts70]

You just reminded me of a previous question Matt.
When you turn the timing back down to the 10 degree range and hook the vacuum up to ported vacuum source, are you turning up the idle speed screw on the carb, and then re-adjusting the two idle-air mixture screws?
I remember mentioning that the idle always goes down when the timing retards, and goes up when it advances, so you always have to futz with the carb when doing timing.
It's a "system" kind of thing.

Don't remember if you replied to that one or not. So just turn the screw up on the carb and see where that gets you.
Hope that helps.

Paul

Thanks, Paul.
I definitely turned up the idle screw when I set the timing lower. As for the mixture screws, I think I reset them, but can't remember for sure. It became a routine to adjust everything every time I made a change after a while. Regardless, if I end up accepting that this engine runs with a lot of advance I'll have to be sure to reset my mixture wherever it ends up.

 

[Viperwolf1]

Thanks again, Viperwolf. I'll start asking around to see if anybody has a dial indicator I can borrow before buying one. Never checked cam timing before--what will I be looking for? I'll look for some instructions as well.

You'll also need a degree wheel on the balancer. This needs to be zero-indexed as accurately as you can get it with the heads on. The best way to do this is to screw a piston stop into the #1 plug hole. Then turn the engine back and forth by hand to find true TDC.

What you're going to do is find the centerline (in degrees of crankshaft rotation) of the intake and exhaust lobes. It's the point of max lift but more importantly it's the mid-point between valve opening and closing. It's more accurate to measure from .050" lift after opening to .050" before closing because it's hard to tell exactly when opening and closing happens.

Assuming this is a stock flat tappet cam. Intake should start to open about 16* BTDC and close about 48* ABDC, for an intake centerline of about 104* ATDC. The exhaust should open about 57* BBDC and close about 19* ATDC for a centerline of about 111* BTDC.

As I mentioned above 1 tooth off on the cam gear is equal to 20 degrees at the crankshaft so if your centerlines are about that far off you have a problem. It should be pretty obvious if it is.

 

[broncnaz]

Pretty much any timing changes require readjustment of the idle mixture and idle speeds.
I'd probably just pull the timing cover to verify timing marks its a little more work but in the end I think your going to have to do it anyhow. I believe your chain/gears are off. Thats about the only thing that would explain you having a correct TDC reading on the HB but having to run 30 degrees of timing to get it to run. Might also explain why it doesnt run all that great. The cam is probably just to far out of wack to run properly usaully 4-6 degrees is about all cams are usually advanced or retarded.
The only other thing I could see causing issues would be the dist itself. I've seen the roll pin that holds the gear on break and cause the timing to jump off although it shouldnt cause the timing to need to be set at 30 so it really should be a timing chain issue.

 

[NYLES]

Pretty much any timing changes require readjustment of the idle mixture and idle speeds.
I'd probably just pull the timing cover to verify timing marks its a little more work but in the end I think your going to have to do it anyhow. I believe your chain/gears are off. Thats about the only thing that would explain you having a correct TDC reading on the HB but having to run 30 degrees of timing to get it to run. Might also explain why it doesnt run all that great. The cam is probably just to far out of wack to run properly usaully 4-6 degrees is about all cams are usually advanced or retarded.

Id check this!

 

[Vintage Steel]

Car-Craft on how to degree a cam shaft
Not sure if this will help but It's sure cool to know