Steve, i agree and glad to see we have narrowed it down to one thing to persue at this time, Peeoot, i would try resetting the valves with engine running, first loosen lock nuts if that style of rocker, then bend feeler guage, makes it more accessable past exhaust, just slip feeler in and note any rpm changes, and loosen or tighten rocker, my lingering thought earlier was worn rocker tip giving wrong setting and once warmed up may tighten valve clearance,be on lookout for that misss as it warms up and you may be able to localise it. i know its just a thought and we await your pleasure.

  AussieBill            YYYY    Forever Y Block     YYYY

 Down Under, Australia

If you are trying to isolate the problem cylinder would removing one spark plug wire at a time and run the engine not tell you which cylinder is the problem?I seem to recall reading the instructions on the Vacuum gauge and there was something along those lines when trying to locate a cylinder causing vacuum to drop.If the plug is not firing you would not get the reaction at the tail pipe.Does this suggestion make sense?

  

Greenbird, what exactly do you do with your gloved finger, and how can you tell whether it's on the verge of clicking? I do not have excessive valvetrain noise.

aussiebill, are you saying you leave the feeler gauge in between the valve and rocker with the engine running? Wouldn't that deform the gauge? I have always wondered how people check clearance on a running motor.

oldcarmark, I'm not sure whether that would help or not. If the paper towel sucks into the exhaust right before the miss, it would suggest an exhaust valve hanging open temporarily during some or all of the intake stroke. That way, the intake draws in some inert exhaust gas, weakening the charge strength to that cylinder. As the compression stroke begins, the sticky valve is forced shut, giving good compression numbers, and the weak charge is burned. It completely accounts for the symptoms. So as long as the valve is still sticking, even with the plug wire disconnected I should see the temporary suction at the pipe end created during the intake stroke.

There are at least 2 exhaust valves sticking because the dual exhaust pipes are separate and I get misses out of both of them at different times (not simultaneous).

Do you think if I can isolate the offending valves, I might be able to resolve the issue without pulling the head? If so, my next task will be to find the trouble! May be able to see it with the timing light, because if the cylinder is too lean it might not fire at all.

1954 Crestline Victoria 312 4-bbl, 3-speed overdrive

Try this link.

http://www.y-blocksforever.com/tech/html/valvelash.html

It was written by one of our members that is no longer with us. The directions are simple and it takes the wear out of the equasion. Chuck

Y's guys rule!
Looking for McCullouch VS57 brackets and parts. Also looking for 28 Chrysler series 72 parts. And early Hemi parts.

MoonShadow, 292 w/McCulloch, 28 Chrysler Roadster, 354 Hemi)
Manchester, New Hampshire

I'm thinking that the sticky valve can be felt with your finger on the rocker tip - the clearane gap will go excessive and a touch will silence it.

 
 Steve Metzger       Tucson, Arizona

[quote]peeeot (6/29/2013)

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Greenbird, what exactly do you do with your gloved finger, and how can you tell whether it's on the verge of clicking? I do not have excessive valvetrain noise.

aussiebill, are you saying you leave the feeler gauge in between the valve and rocker with the engine running? Wouldn't that deform the gauge? I have always wondered how people check clearance on a running motor.

YES, just see how easy it goes in, generally if tappet is loose or correct ,feeler will go in relativly easy as compared to hard to ease in re being tight gap, but point is to try and note differences, you just do it for a moment, doesnt hurt anything.

  AussieBill            YYYY    Forever Y Block     YYYY

 Down Under, Australia

Peeot:

You mentioned a couple pages back you would look for a shop with a scope. Did you find one? If so, the scope would likely be equipped with a cylinder leakdown tester. With that tester, properly used, they can evaluate each valve in each cylinder for proper sealing. They can also check the rings and for leakage into the cooling system. If they find a bad valve, there will be no fix except to pull the head(s) and grind the valves.

John - "The Hoosier Hurricane"

Hoosier, I have not yet located a shop equipped to scope my ignition system. That doesn't mean there isn't one within reach, there just aren't many places that work with the old stuff anymore.

Moonshadow, those instructions are the ones I followed to set the valves most recently.

Just an observation, if I pull a spark plug wire, I get a steady miss out of that cylinder's exhaust pipe, and if I hold my paper towel at that pipe it sucks in steady with every miss. I thought that the paper towel sucking in was a definite indicator of sticking valves, but if that's the case, then why does a KNOWN, intentionally caused ignition miss cause the same result (sucking in at the tailpipe)? Also, if the valves are sticking, why does bypassing the resistor eliminate all misfiring?

1954 Crestline Victoria 312 4-bbl, 3-speed overdrive

Here is the latest update.

First, still trying to find a shop that might be able to solve this. I found one with a scope nearby but they are not experienced with old car technology.

Second, have redone some old tests and tried some new things, each time recording what I did and what affect it had. Here they are, not exactly in the order performed:

SYMPTOMS: hot engine develops intermittent random sputter/misfire below approx 750 rpm. Hot engine stalls immediately when shifted into gear. Hot engine will not remain running below 650 rpm for an extended period of time in any gear.

1. Installed Edelbrock 1405 carburetor. Regardless of how I adjusted it, I was unable to produce any improvement on the symptoms.

2. Tested for vacuum leaks. I tried creating a vacuum leak at the vacuum pump, which increased the engine speed, and I tried hand-choking the engine, which slowed the engine down. In the past, soaking the intake and lower carb with water did not affect engine running.

3. Checked coil current draw. 4.0A engine stopped, 2.7A engine running about 700rpm. Rechecked current draw on cold engine, engine stopped, no change. Specs are 4.5 and 2.5, stopped and at idle, so I see no problems there.

4. Increased dwell angle from 26 to 29, no change in symptoms.

5. Checked voltage to coil with analog meter and confirmed coil always sees at least 9 volts, even during trouble symptoms.

6. Checked resistance from starter relay to resistor; was negligible.

7. Advanced timing as far as 22 degrees initial, vacuum advance plugged. Engine ran faster and better with all of that advance but ultimately symptoms persisted. Retarding timing below 10 degrees exacerbated all symptoms.

8. Checked for accuracy of damper markings by hand-turning engine with my pinky against the cylinder wall and top of piston. Marks accurate within 2-4 degrees.

9. Repeated hot compression test, numbers all within 2 psi of last time I ran the test, most exactly the same. Worst cyl 155, highest at 167, rest 160-162.

10. Ran with battery charger attached, no improvement

11. Ran with gas cap off, no improvement

12. Ran with 0.6 ohm resistor installed, no improvement

13. Ran engine with valve covers off, feeling each rocker arm and then each spring cap looking for signs of a sticking valve. Nothing felt at all out of the ordinary. No unusual noises, or more pronounced clicking, or "double seating" of valves (by which I mean, once the valve came back up it didn't move anymore, and the motion from closed to open to closed was smooth and regular on every valve)

14. Listened with hose at tailpipes and intake as engine was spun with ignition disabled and throttle open for evidence of valve irregularity. I wasn't sure that I heard anything unusual.

15. Held paper up to tailpipes as disabled engine was spun over; there was some sucking in but I am not sure whether that means anything

16. Checked manifold vacuum as hot engine was spun over; reading fluctuated between 4-4.5". Was not rock steady.

17. Loosened all valve screws a small amount twice; based on calculations, probably opened them all up 2 thousandths or more. They got noisier but engine running was not improved.

18. Watched timing light with pickup coil on coil to distributor ignition wire. Ignition signal was 99% perfect. Tried retarding timing, leaning mixture, putting car in gear, stalling the car by each method a few times while watching the timing light, and the signal was strong to the finish every single time.

19. Verified the presence of fuel in the carburetor bowls at time of trouble.

As I understand it, to run an engine needs compression, fuel and air in the right mixture, and a spark at the right time. I have done everything I can conceive of to confirm the presence of all of these elements. In my experience, vehicles which have tested worse in every category have been able to succeed where this one fails.

If I am unable to find a shop or get this resolved for a reasonable cost, I will abandon this drivetrain, if not the whole project. What a bummer.

1954 Crestline Victoria 312 4-bbl, 3-speed overdrive

Is the exhaust butterfly valve (if still fitted) opening?

Have you tried a different intake? A crack into the exhaust crossover passage could cause problems.

Man, I think I would have given up by now...


South Australia