47 V8 ignition mystery

[Jack E/NJ]

Brian>>tried everything to no avail, culminating with removing the intake manifold and applying grease to both sides of the gasket and rebolting it down which cured the problem!>>

Also a good possibility. IMO, smearing wheel bearing grease on all 4 gasket, block & manifold surfaces is where it's at (except exhaust).



As a quickie test for vacuum leaks --- when engine seems to be missing, try spraying WD-40 or smearing grease on manifold edges around problem cylinders to see if it tries to smooth out.

[slowforty]

There was a story years ago about a Flathead with a strange miss. It turned out to be a blocked exhaust manifold , It was full of carbon. I know this is reaching but just a suggestion.

[dean333]

This has to be one of the longest threads ever

[Jack E/NJ]

Craig>>>I've only got three weeks to solve this problem before I have to put Old Henry in a coma for two years while my wife and I go to serve voluntarily in the Philippines>>>
.
dean333>>>This has to be one of the longest threads ever>>>


Yeah, we only have three weeks to catch up to Vic Piano's 112-page & counting "What I did on my lunch hour" thread.

[Don]

Didn’t one of the early post say he monitered the spark and was missing the spark on a couple cylinders,look like the problem would be in the distributor rather than the engine ?
I have a old sun machine I’ve spun dist up and seen it miss a few flashes,just like it would when on the vehicle,if I remember,the points spring were weak if using a inferior set or older set.I vote for a troubled distributor!!

[Jack E/NJ]

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Yeah. But I think that was before the distributor was serviced/changed.

[cadillac512]

No, still did it after dist service.

[1942deluxe]

I still think in the distributor for what it's worth.

[Jack E/NJ]

Might be? Or cam gear might be worn especially if fiber?

[Old Henry]

I feel like I made a major breakthrough today in the mystery!

As I was driving home from the 3° in Boise today (not in Old Henry) the thought came to me, "What if the stumbling problem of the engine is not an ignition problem? (Several have suggested such and that the ignition problem is just a "red herring") How could I eliminate the ignition as a cause of the stumbling problem?" Then it came to me. It was such a simple idea I'm surprised no one ever suggested it. Here it is:

I would just unplug the wire from the spark plug of the offending #6 misfiring cylinder! If the engine smooths out - that would prove that the stumbling is being caused by that cylinder misfiring. But, if it does not smooth out - that would prove that the stumbling of the engine is caused by something other than the misfiring cylinder!

So . . . I did it. I started up the engine and checked with the timing light that #6 cylinder was misfiring. Then I unplugged the wire to #6 spark plug and let it just hang out in the air. Then I took off for a drive. Much to my surprise, the engine ran just as badly totally without cylinder #6 as it did with it, just a little less power is all. Otherwise - just as rough! After 10 miles I stopped and plugged #6 back in resulting in more power but no more or less stumbling. Another 10 miles unplugged it and another 10 miles plugged it back in with same result. Only the overall power level was affected - not the stumbling!

Is my conclusion accurate that such test eliminates the misfiring cylinder as the cause of the stumbling engine or am I missing something???

[Old Henry]

Originally Posted by Jack E/NJ

Craig>>>Again, the engine worked perfect . . . for a very short time before starting to misfire again.


Still might be sticky valve stems after getting warmed up. Try running MMO thru carb & mixed in tank to see what happens.

Originally Posted by Old Henry

Will do. Thanks for the reminder.

Today I did it. I added 6 oz. of MMO in the 15 gal. gas tank and filled it up. Then, while idling the engine, I drizzled 4 oz. of MMO into the carburetor - both sides. I was hoping there would be some improvement in the 30 miles I drove after that. I thought I sensed some smoothing out at times but not lasting. If my engine stumbling problem is from a sticky valve, hopefully the MMO will fix it and I'll be able to put Old Henry down for his 2 year nap knowing that he'll sleep peacefully.

[corvette8n]

Hey Craig, if you see any old flathead Fords in the Philippines post some pictures.

[Old Henry]

Originally Posted by corvette8n

Hey Craig, if you see any old flathead Fords in the Philippines post some pictures.

Will do.

[Terry,OH]

Does the problem show up after the engine is warm or soon after ? Does the engine run fine when cold ?

[kurt v]

take the carb completely apart and clean it

[Old Henry]

Originally Posted by Terry,OH

Does the problem show up after the engine is warm or soon after ? Does the engine run fine when cold ?

The problem is always there – hot or cold – far or near.

[Old Henry]

Originally Posted by kurt v

take the carb completely apart and clean it

I did that before all of this started and replaced all the replaceable parts but will probably do it again.

[Old Henry]

I hooked up my vacuum gauge and drove the car around looking for anything unusual like bouncing, etc. to indicate a valve problem. All was smooth and normal even though the engine ran as rough as usual.

[Brian]

I've posted this before, but here we go again....some years back my trusty old 35 would fire up on 8 cylinders, but the longer it ran, the more ragged it ran, until it would actually die. i was convinced it was electrical; as the components heat up they misbehave, accordingly I changed condensers, distributors, coils , you name it, all to no effect. Sparkplugs all looked the same, compression test showed all cylinders within 5 psi of each other, vacuum gauge was pretty steady at around 20 in/mercurcury. This went on for months....finally, I pulled the inlet manifold and plugged the heat risers on each side. Put it back together; viola!! what a beautiful thing!! The heat riser passage inside the manifold had obviously blown out, as the engine heated up, the crack would open up and contaminate the incoming fuel /air charge.
I dunno if this is your problem Craig, its way out left field, but why not pull the manifold, replace the gasket with a generous slathering of grease as I talked about in an earlier post, insert a coupla thin shims over the heat riser passages [which can subsequently be removed if this doesn't cure your problem], tighten it all down and try it?

One of the wonderful things about flathead Fords is their basic simplicity, they are basic, aren't they?, until you experience something like this. Ain't it fun?

[Terry,OH]

Watching the flashes from a timing light at idle, (either in line or clamp on type) can indicate which cylinder has a firing problems. Look for missing flashes using a good cylinder as reference. If all the cylinders appear the same, what was your vacuum reading at idle? Should be very close to 20 maybe slightly lower like 18 and very steady. While you have the vacuum gauge attached adjust carburetor idle mixture screws, while enging is warm,g for the highest and steadiest vacuum reading and engine running smoothest. The screws should be about 3/4 to 1 turn out from full close. Small adjustments should make a big difference. If the adjustment can not be gotten or out of adjustment range or screws don't make a difference the problem would appear to be in the Carb. Hard to believe the engine running rough and the vacuum gauge not reacting at idle. While driving the gauge should be moving low and high with acceleration and deceleration IMO Your postings don't seem to give enough information on what your doing or seeing.