No. 7 Cyl never gives evidence of a power stroke on '46 Flathead

[Jack E/NJ]

Mike>>>intake valve not opening??....no gas mixture to fire>>>

I'm leaning this way, Mike, if the plug is dry. May also ***partially*** explain the slower cranking vs faster running pressures ***if*** the gauge check valve is responding properly in both cases. Jack E/NJ

[Jack E/NJ]

37cab>>>That is why you remove the check valve. >>>

I can see why this would make sense too. Just have to watch the gauge while it's running or cranking. Jack E/NJ

[ronchamblin]

I just fast-read the input. Looks good, will read more slowly when I get to Ford later today. I had to work yesterday, and am this morning. I "did" purchase a leak-down test unit yesterday. However, last night after work, I ran a cold pressure check on all cylinders (forgetting to open the throttle I might say), and they were all around 110 lbs, including No. 7. BTW, my checking the pressure at idle speed was an "experiment", being desperate for info, on No. 7 and two other cylinders, just to compare. All were the same at 45 lbs.

I then warmed up engine, again verifying that No. 7 has no power stroke (by removing wire). To verify the integrity of the plug and the wire and the spark intensity, I switched plugs, and laid a spare plug on head, attaching various wires. All, including No. 7, had good spark.

At this point (I will do further testing this afternoon, using the fine suggestions from everyone), I focus on the following: 1) The valve action is good, as the compression is consistently as in other cylinders. 2) The ignition, plug, and spark is good. Conclusion: The cylinder is getting plenty of air, spark, and compression, but "no" fuel. Why? The only thing that comes to mind at this point is that air is entering the combustion chamber via the intake valve, but not via the intake manifold (which would be great because it would have a fuel mix with it). Air lacking fuel is entering via a leak past the intake valve seal perhaps ... in other words, the air is coming from the plenum wherein lies the cam ... which .. if it has a little pressure, will encourage air past the seal. Maybe the assembler failed to install the intake valve guide seal. Does this seem a viable scenario?

I must get a little work done. Really appreciate everyone's info, and will use it later today to gain more into. I now have a leak down tester, and will perform the moves suggested by some posters above to gain more info.

[edhd58]

just for kicks and giggles, maybe put a little gas in the cylinder and see if it fires until the fuel is gone??

[flatheadmurre]

You get good compression with the horseshoeclip missing on the valve assembly.
but on the intake stroke it suck exhaust into the cylinder lifting the guide and valve and doesn´t fire.
That´s why i asked if the plug got real wet from fuel as it should....
Same for taking a leakdown test, looks great but the valve is not going to do it´s job when running.
Take the intake off and have a peak...don´t take that long if the plug doesn´t get wet.
Run one known good cylinder and the suspect one without ignition cables attached then compare them, if the suspect seems dry in comparsion...

[ronchamblin]

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After work, I got some firm data. As I said earlier, the plugs, wires, and spark verified as good. I warmed the engine and checked pressures at cranking speed with throttle open (I forgot to do this before). All cylinders are 140 to 145 lbs, "except" for No. 7, which was 115 lbs. Also, a very interesting thing is that while all the other plugs were wet with fuel upon removal after the warm up, No. 7 was completely dry. I spayed again the intake manifold area with starting fluid to determine if the RPM would increase .. indicating a leak. The RPM did not change.

I used my newly purchased leak-down gauge ... being able to put only 20 lbs into the unit however. On 5,6, and 8, I was able to get a non-leak "silent" condition. No. 7 always gave sound of leaking, although all readings on all cylinders showed only a "very slow leak" condition. At one point I was able to place my finger over No . 8 and the sound stopped. At another point, on a later repeat of the test on No. 7, the leak sound came from No. 6, until I closed the plug hole with my finger. Inconclusive data with leak-down unit at this point ... no time tonight. I will take more time later with the leak-down unit.

Conclusion so far ..... No. 7 cylinder is getting some air, but no fuel, as evidenced by the dry plug. No. 7 never has shown a power stroke since I installed the engine just 60 miles ago. I would think that it would fire on 125 lbs pressure. Perhaps the other cylinders, with greater vacuum, are taking all the fuel/air mixture. I think its time to pull the intake manifold ... as someone suggested earlier on this forum.

[40 Deluxe]

Originally Posted by ronchamblin

Conclusion so far ..... No. 7 cylinder is getting some air, but no fuel, as evidenced by the dry plug. No. 7 never has shown a power stroke since I installed the engine just 60 miles ago. I would think that it would fire on 125 lbs pressure. Perhaps the other cylinders, with greater vacuum, are taking all the fuel/air mixture. I think its time to pull the intake manifold ... as someone suggested earlier on this forum.

125# is more than enough to fire. Look at all the early engines that ran with less than 50#. It's extremely doubtful that the other cylinders could "steal" mixture from #7! Don't be surprised if you find a shop rag or other blockage somewhere in #7's intake tract. A brother-in-law of mine once overhauled an old Harley and could not get the front cyl. to fire, no way-no how. Finally pulled it apart and found a rag stuffed in the port. It was a long term project and he forgot he stuffed a rag in there to keep it clean.

[ronchamblin]

I agree 40 D, that it should provide a power stroke with the 125 lbs. This morning, while driving to work in other auto, I remembered something I noticed yesterday. Upon holding a piece of paper close to the exhaust, there was the repetitive sucking inward at the pipe, indicating perhaps a cylinder going downward with the exhaust valve open. and this event allows me to suspect that the exhaust valve in No. 7 is not closing completely. This would also explain the dry plug, with no fuel upon it, because the open exhaust valve during the intake stroke would provide the air for combustion, but no fuel. A test this evening might support this idea. I will remove the No. 7 plug and run the engine, determining if the paper continues to be pulled to the pipe. If there is no paper movement as before, the fact will give further support for the idea of an exhaust valve that does not close. We will see.

[chap52]

Ron, I think you may be overthinking this problem. If #7 is not holding air pressure there is a leak. Valve or leak over from the head gasket by an adjoining cylinder would seem to be the probable cause. Why not pull the intake and get a look at the condition of the valves, springs, clips and lifters.
If all looks right it's time to pull the head and look for a leak. For the cost of a couple of gaskets you will eliminate a lot lost sleep laying in bed and diagnosing the problem over and over. This I am sure is a common issue with most folks on this forum.
There have been times when my wife from across the breakfast table will notice a blank look on my face and say something like, "Are you working on the truck?". I figure my "thinking" for each adventure exceeds the actual hands on time by at least ten to one.
I also suggest as has been mentioned on this site by others that you rub down your gaskets with a very light coat of grease before re-assembly. It makes it easier to remove them in the future if you need to and saves on cleaning off an old gasket.
Don't get discouraged. Remember it's a "Hobby".
Your sharing the experience with the right group of understanding folks.
Keep us posted and enjoy the adventure.

[J Witt]

Ron, if either valve is staying open, you get no compression on that cylinder. Do what flatheadmurre suggests.

Best of luck in finding the trouble!

[Capt Kirk]

I have heard that there can be an instance where a spark plug will fire in free air and refuse to fire under compression. If I remember, it's harder for a plug to fire under compression so if there's a weak link in that cylinders ignition, it may not fire. Just throwing this out to see if it sticks.

[ronchamblin]

A friend suggested that the No. 7 valve might be sticking partially open, and suggested that I inject some Marvel Mystery Oil into it. I will try it. However, the following three points allows me to believe that the No. 7 exhaust valve never closes, either because the assembler adjusted the valve on a partial lobe, or there is a foreign object between the valve and the seat, preventing the valve from closing. My belief is because of the following three bits of evidence:

1) With the engine warmed, the open throttle cranking speed pressure test shows all cylinders are 140 to 145 lbs except No. 7, which is 115 lbs.

2) After running engine and removing all plugs, it was found that all plugs were wet with fuel except No. 7, which was dry as a bone.

3) While holding a piece of paper at exhaust, there was a repetitive flick movement toward the exhaust -- presumed to be caused by an exhaust valve being open during piston down stroke.

Therefore, the only conclusion I've arrived at is that the exhaust valve, although moving according to the cam rotation ... never closes. The air drawn into the No. 7 cylinder during the intake stroke as the piston descends comes not from the intake manifold, which has a fuel/air mixture, but it comes from the partially opened exhaust valve, which is only 1/4 inch from the intake valve. A further observation is that the exhaust valve environment actually has a small amount of pressure, thus encouraging air (without fuel) into the combustion chamber during the intake stroke. I might mention that because the adjacent cylinders perform normally on all tests, I can assume that the problem is not caused by a head gasket issue.

What do you guys think? Am I an idiot, or am I probably right?

[ronchamblin]

BTW, the shop that did the rebuild is going to pay for a mechanic to remove the intake manifold and chk the valve setting. He will also check for a foreign object preventing the valve from closing all the way.

[ronchamblin]

In any case, this forum, and all the inputs from everyone, caused me to perform the tests I did perform ... and caused me to think through the suggestions. I am fortunate to have found the forum with such a good bunch of troubleshooters. Thanks. I will let you know the results of manifold (and possible head) removes.

[Jack E/NJ]

>>>believe that the No. 7 exhaust valve never closes>>>all cylinders are 140 to 145 lbs except No. 7, which is 115 lbs.>>>

Nope, still doesn't do it for me. It may never close as well as the others, but it seems to close pretty well at 115psi. Jack E/NJ

[Ross F-1]

I saw a 48 in the shop that was doing the same things. After pulling the intake it was obvious why; when prying against the intake port for that cylinder to release a valve guide clip, someone broke off a chunk of the port at the manifold surface. It was sucking out of the crankcase instead of thru the manifold.

[flatjack9]

Seems to me you have spent a lot of time chasing your tail .Take the manifold off first to see any apparent problems. Then pull a head if needs be.

[ronchamblin]

Flatjack ... I agree. The problem is that the rebuilder insists that I not do the work, as he is responsible, but to let another shop remove the manifold etc. They will not be able to remove the manifold and head "if required" until next week. So ... yes ... I am curious and can't wait for what will be discovered. BTW, I attempted the MMO injection to free up a possible stuck valve, and so far it seems not to have affected anything.

[chap52]

Take a break and wait on the shop mechanic to deal with it. Give them a chance to correct the issue and then go from there. Let him pay for the new gaskets and any parts needed. They may actually get it fixed.
What's another week or so?

[flatheadmurre]

If it´s a horseshoeclip missing running the engine ain´t a great idee since you end up having to knurl the guide to fit if they are alowed to move around for a long time.