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

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

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

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?

  

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

Just thinking out loud - when I adjust the valves on the bird, I use a gloved finger on them one at a time to single out one on the verge of clicking or not. would that help isolate the culprit here?

 
 Steve Metzger       Tucson, Arizona

All right guys, I believe I have finally seen what I needed to see to completely be on board with all of you who have pointed to a sticking valve.

I drove the car around and warmed it up and let it idle in neutral, then went out back with a clean paper towel and held it about an inch behind each pipe. Sure enough, right before each miss/spit, the paper towel would suck into the pipe. I wish I had thought to try that a long time ago, as it was very obvious.

Question now is, what do I do about it? I have just added some MMO to the gas and crankcase. If that gets me nowhere, I'm guessing nothing short of removing the heads and having them rebuilt will get me anywhere? Any suggestions?

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

Peeot,

From your vacuum gauge readings, it looks like you have a sticking valve in a valve guide. I would suggest you add a couple of ounces of MMO to your gas tank, this should help. As far as your carburetor adjustment, set the idle screws with the vacuum gauge also. Adjust to get the highest vacuum reading and smooth idle, disregard the amount of turns out on the screws as per the manual. The gas we get today is going to run different than the gas availible in 1957. Since your vacuum reading is 21" at idle, your engine should be real close to be in tune. I hope this helps.

JJ

another thought I agree with bill I would have the mixture screws out a little further than one turn, I know the factory data sheet says that but they can be wrong most carbys like between 1.5 -2 turns out from seated, all carbys are different so I take no notice of the factory data as that is done by engineers in the factory & not under outside influences. the autolite on my 272 has a sweet spot at 2 turns out, in your case at the moment I would screw them in to seated then screw them out slowly until it sounds right & don't worry about the turns out for now. if they run better at 2 turns or even 2.5 then leave them at that for now, remember its only idle mixture, re adjust the idle speed & then that's 2 things to remove from the list.

moz. geelong victoria australia.

graduate 1980, bus, truck, car, hot rod, boat, submarine, hovercraft, hydrafoil, firetruck, mobile home, jet, helicopter, cruise ship, motorcycle, bicycle, santa's sleigh, clock, alloy bullbar, alloy fuel tank, lens, dr who's tardis, matter - anti matter warp drive buffer & y-block lover

hey chuck I forgot to put the wire on the points on a customers car once when tunning it pulled my hair out for hours, I didn't notice it because it was sitting next to the points & not touching them, I only found it when I decided the points must be faulty & went to pull them out.

moz. geelong victoria australia.

graduate 1980, bus, truck, car, hot rod, boat, submarine, hovercraft, hydrafoil, firetruck, mobile home, jet, helicopter, cruise ship, motorcycle, bicycle, santa's sleigh, clock, alloy bullbar, alloy fuel tank, lens, dr who's tardis, matter - anti matter warp drive buffer & y-block lover