Valve Lash

[Mulletwagon]

It seems the typical exhaust sound of a Model A is a precise and distinct staccato repetition similar to the sustained report of a .50 caliber M2. My Model A exhaust sounds like a low muffled monotone with an irregular but noticeable wispy puff sound. Sounds like “putt, putt, pfst, putt,pfst, pfst, putt, putt, pfst”, etc. It has an electronic ignition and I just installed Champion W16Y plugs. The PO had the engine remaned by a reputable builder but sadly passed on after the engine was just broken in. I suspect the valve lash was never readjusted after break in. I cannot hear any tappet clacking and am thinking insufficient valve clearance may be a possibility. The engine does not miss but seems to be a little low on power and has a slightly rough idle. I will pull the manifolds and valve cover to check the valve clearance but just curious if anybody can describe the indications of too tight or too loose valve lash.

[Jim Brierley]

First thing to do is check the compression, and maybe even a leak-down test. Also look at the old plugs for color, indicating a rich or lean condition.

[Patrick L.]

I agree with starting at the beginning with a compression check.

The normal Model A sound usually comes from a low idle speed and with the timing retarded until the desired sound is heard. I'm thinking your ignition timing is not adjustable except for base setting.

There is not too much to say about valve lash and exhaust note. The valve clearance is not too hard to check and the manifolds don't really have to be removed.

[katy]

The engine does not miss but seems to be a little low on power and has a slightly rough idle.

Another possibility is a worn camshaft, not replaced or reground when the engine was "remaned".

[Purdy Swoft]

Initial timing .

[100IH]

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And vacuum readings at idle and off idle, jumpy or steady. All good things to establish a starting point.

[1930artdeco]

You can always try the WD40 I think around the manifold to make sure you don't have a leak.


Mike

[Mulletwagon]

OK, did some additional testing. Manifold vacuum is a steady 23 inches - seems a little high. Compression for cylinders 1 through 4 read 65, 65, 75, 70. Does this data tell us anything ? Still have a rough idle and inconsistent exhaust cadence. Thinking about going through the carb next. Engine has just over 1000 miles after high dollar rebuild. Just seems like it should run better.

[old31]

Do you hook the vac gauge up to the intake?

[Benson]

PM sent

[katy]

What kind of camshaft is in that engine? Original, untouched? Reground? New w/a performance grind?

[Mulletwagon]

Connected the vacuum gauge to the wiper vacuum tap at the manifold. Not sure about the cam but suspect it is a regrind. Did the flex tube routine on the carb and determined the fuel level is at 3/4 verses 5/8 inch below the parting line. Should mean the carb is running lean but not obvious considering high speed performance is good and the engine never pings. I will reset the float when I clean the carb. Noticed the plugs were especially clean when I pulled them to do the compression check. Just does not seem to have the classic A idle. The saga continues.

[40 Deluxe]

Originally Posted by Mulletwagon

OK, did some additional testing. Manifold vacuum is a steady 23 inches - seems a little high.

Your vacuum reading is good.
The higher the better (more efficient) unless some one timed the engine using a vacuum gauge (setting the timing at the highest vacuum reading usually results in too much initial advance and pinging and thus bearing damage). Is your distributor original with electronic conversion, or one with centrifugal advance?

[100IH]

Do you have a Motor's or Chilton. If so read about vacuum values and what they tell you. Dry plugs won't cause your idle issue, wet ones will.

[1931 flamingo]

Put about a pint of MMO or ATF in the gas tank and run it. Not going to hurt anything and if a valve is sticking it should free it up. FWIW
Paul in CT

[Purdy Swoft]

Paul makes a good point in post number 15 . When I overhauled the engine in my roadster I installed new original type valve guides and original style mushroom stem stainless steel valves . After a while it started running so badly that I wouldn't trust it out of the drive way . I mentioned the problem here . It was said that the corn gas was probably causing the stainless steel valves to get sticky . When I checked the compression , the gauge would show good compression on all cylinders . When the engine was running I was getting slow valve action because of sticky valves . I first drained the tank and added corn free gas . I then added a small bottle of Marvel Mystery oil to the gas tank and a few ounces to the crankcase . . I then disconnected the vacume line and stuck one end in a bigger bottle of marvel Mystery oil . I started the engine and let the vacume draw the MMO into the intake and to the valves . In a short time it started smoking as the MMO made its way into the combustion chambers . I stood on the passenger side and kept the engine running at a high enough RPM that it wouldn't go dead . When the engine smoothed out and would rev I removed the vacume line from the bottle of MMO and reconnected it to the firewall . I kept the engine running at a fast idle until the smoke subsided and it was good to go for a ride . I now always add at least four ounces of MMO to each ten gallons of gas and have had no more problems with sticky valves ..

[Patrick L.]

Good point. Its been long enough that I didn't give sticky valves a thought even though I've run into this issue.

[Kurt in NJ]

For a while I had a slight "miss" at idle, power was ok, lugging the engine would pull evenly, I finally checked the valve clearance, had 1 exhaust and 1 intake valve at .004, .005 clearance, after adjustment the perfect smooth idle came back
i have original split guides, and original Ford stainless valves

[Mulletwagon]

Originally Posted by Kurt in NJ

For a while I had a slight "miss" at idle, power was ok, lugging the engine would pull evenly, I finally checked the valve clearance, had 1 exhaust and 1 intake valve at .004, .005 clearance, after adjustment the perfect smooth idle came back
i have original split guides, and original Ford stainless valves

Kurt,
Do you recall how much clearance you had on the other exhaust/intake valves ?

PS - Use to live by Exit 13.

[Purdy Swoft]

I run all of my model A intake and exhaust valves with .016 clearance . This includes the ones with 3/4 race cams . Good clearance helps keep the valves cooler and less likely to burn. Snyders recommended a clearance of .016 years ago and it has worked for me . Less clearance may give a fractional amount of lift . I try to stay on the safe side .