The Stovebolt Site Forums The Shop Area Engine Shop Lousy Running 235

Over the past couple years, my truck (51 3100 with 1962 235) has run beautifully. Easy starting. Plenty of power and responsive acceleration.

A few weeks back, about the time I was doing a very extensive cooling flush, I noticed it was down on power not running as smoothly as normal, etc. It sure "seemed" like ignition timing, but I resisted the urge to go there right away. Pulled one plug wire at a time to make sure all cylinders responded the same. They did. Stuck the dwell meter on it to make sure the points gap hadn't closed up. That was good as well. Didn't have time to go over everything with a fine tooth comb, so I went ahead and advanced the timing by ear. Idle picked up. Throttle response was snappy. Locked the dizzy collar back tight. A couple of road drives and it felt like my truck again. No issues. Thought it was weird for the timing to have slipped, but figured it was possible.

Fast forward about 2-3 weeks. Been out of town and truck hasn't been driven. Had an appointment for a HS girl to use my truck as a senior pic prop....so went out to start the truck. Other than being a little slower than normal to fire (fuel always evaporates from bowl in that time span)....the drive TO the photo shoot as mostly OK. I'm not sure it was running 100% perfect, but certainly decent-ish. Very hot day here in SE MO. Miserable.

On the ride home (5-10 miles), which included a trip to the gas station, truck was definitely acting up again. Sluggish. Low power climbing hills. Almost exactly how it acted BEFORE I bumped the timing. It was dark by the time I got home, so didn't have time for further diagnoses. One other item of note, it's fairly normal for temp to creep up after shut off (truck still ran at 180 while moving), but the coolant was actually BOILING in the overflow. Checked the inside gauge and it had indeed climbed to 210. Getting hotter after shutdown is pretty normal. I don't recall it ever boiling like that.

Some thoughts on next steps:

1) I have most everything I would need to do a complete ignition tune-up: NOS points. One of Jon's fancy condensers. New plugs. It's probably time for both of those things, anyway. But before I just start throwing parts at it...thought it might we worth sharing this story and seeing where else I might look. Ignition system is just my first hunch.

2) Difference between the trip away and the trip back home last night. All I can figure is that the engine would have been warmer coming home. Could the coil or ignition switch be getting heat sensitive?

3) The (apparent) slippage of timing a few weeks ago, and the way it responded to advancing, has me a little baffled. Especially now that it is acting the same way again.

Just a quick thought but have you checked the vacuum advance canister? This sure sounds like it is timing related.

Edit...if you suck on it, you should see/feel it moving. Usually it doesn't take a lot of vacuum before you start to notice movement.

I did not, but that’s a great suggestion that I will explore. It used to work, but who knows if it still does.

One thing of note, it sure seems like my BASE timing slipped. It responded very favorably at IDLE to advancing it. (Note: I am not cheating with the idle speed screw, ported vacuum should not be a factor at my idle setting)

That said, I suppose a faulty vac advance probably represents a vacuum leak, and would thusly produce a lousy idle.

There should be little to no vacuum at the canister at idle, but it doesn't take much of a vacuum leak to mess with idle. Very little will do it. If you study your throttle valve and the way it covers the ports you can see how a little vacuum could make a difference. If your base timing changed, about the only thing I can think of would be a loose distributor bolt, but I'm sure you had it tight to begin with and all. You know you can set timing and idle using a good vacuum gauge, yes? As for timing, a vac gauge will normally have you go over on timing but if you get it as good as it will be and then back off a bit you should be about right.

Yeah, I’ve done the timing by vac gauge in the past. I know it’s not perfect, but my engine runs like crap if I use the flywheel ball. It wants several degrees more initial timing than that.

Spitballing here:

* Let’s just say I have a vac leak somewhere. Would advancing timing (like I did a few weeks ago) mask that symptom? (That’s not how it works in my brain)

* I’m fairly certain I didn’t leave the clamp loose enough (especially the last time I advanced it) for the dizzy to slip so trying to think of other ways to explain that…

* If memory serves, the dizzy gear is secured by a roll pin. If that sheared, I would think the engine would barely run at all….not just be a few degrees retarted.

* I suppose the dizzy gear and/or cam gear the drives it….could wear to the point that timing slips a tooth or too? Not a big deal to yank the dizzy and explore that theory. But inspecting the cam gear would surely be a little tough.

Cam CHAINS (which you don't have) might skip a tooth when very worn, but if cam GEARS "slip" I doubt they'd last as long as yours has since the first symptom.

Just to be clear, I am talking about the gear mesh between the gear in the middle of the camshaft, and the distributor gear. Not the valve timing apparatus under the timing cover (yes, those are gears not a chain).

But I do agree with your theory of that much wear between (cam gear and dizzy gear) would seem more likely to produce a complete failure, not just slip a bit. Unless one or the other just lost a tooth or two.

Remove your distributor cap, grasp your rotor and turn it back and forth. You should have some play but not a lot...it should be firm feeling. That's a good indication of the gears down there. Please also remember you have mechanical advance (although this almost never fails other than if the weights get rusted and won't move or if one of the springs breaks or pops off and then you will have greatly increased timing at low speeds), and retarded timing will cause your engine to run hot...over advanced timing will cause detonation, etc. And it is interesting if you think about it. You could be driving along on a flat road at 40 mph...maybe 2000 rpm and all is Jake. At that point you may have a total spark advance of 28 to 30 degrees (vac + mechanical). Possibly even a bit more. Then you get to a hill and to keep the same speed you hit the gas. This drops your vacuum from maybe 16 down to 3 or 4 and it knocks your overall spark advance down also. If it is a long hill, you could increase your engine's temperature by the time you get to the top...because your spark is happening at the wrong time during this.

Yes, I expect advancing timing would mask a faulty vacuum advance canister. A vacuum leak might be similar but please remember vacuum advance depends on ported vacuum and this depends on air velocity and to a degree air temperature. It is different from manifold vacuum although if either is messed up, your performance will suffer.