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By alanfreeman - 11 Years Ago
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I have an engine problem that has stumped me and I also brought the car to a local "oldtimer" mechanic who also cannot figure out the problem. I have a 1961 292 in my '54 Mercury. I am still running a 6 volt system. I put a "B" intake manifold on the engine and a new Holley Model 4160 465 CFM carburetor. The exhaust manifolds are '54 Ford Police/Mercury accessory duals. The distributor is the stock original. The compression is 140-150 lbs in all cylinders. The points, wires and plugs are new. The point gap and valve lash has been set per specs. The timing is advanced a few degrees beyond the factory 3 degrees. The engine sounds good and has lots of power while driving. There is no noticeable engine miss. The intake tested negative for vacuum leaks. The problem is a very rough idle. The exhaust coming out of each cylinder bank through the dual exhaust system has a very unusual loud and distinct "put...put...put" sound rather than the usual; soft exhaust pattern of the other Y-Block engines that I have in my two other cars. The weird exhaust "put...put...put" sounds the same coming out of both exhaust pipes. Anyone have a clue as to the cause for the rough idle and weird exhaust pattern? Thanks, Alan S. Freeman
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By 56_Fairlane - 11 Years Ago
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I'm wondering if the exhaust manifolds have something to do with it. The Ford and Merc engines in 1954 were only 239's and 256's and the manifolds might be too restrictive for a 292 with a Holley 4 bbl on a B manifold.
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By Hoosier Hurricane - 11 Years Ago
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You say the distributor is stock original. It is a stock '61 or a stock '54? The '54 distributor would be incompatible with the later carb. Do you know for sure what camshaft is in it?
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By Daniel Jessup - 11 Years Ago
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Check Hoosier's comment first, but if the engine "has lots of power while driving" then I would imagine that your distributor is from 1961. That being said, I would look to that carburetor and the idle screw adjustments. What happens (happened) when you adjusted those after initial warmup? Are you sure that the timing pointer/crank dampener is correct? You know how people talk about the sleeve in the dampener that gets loose and the outer ring spins and all. Why not time by ear just to satisfy your curiosity?
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By alanfreeman - 11 Years Ago
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The distributor is the '61 which came with the engine. The mechanic checked the carburetor idle mixture adjustment and told me that it is o.k. On exhaust restriction theory, this is interesting. However, I would think that the early dual exhaust that I have on the engine has to still be less restrictive than the single exhaust/crossover exhaust that Ford used on 292 truck engines until 1962. Could I test this theory by removing both exhaust manifolds and running the engine without exhaust to see if it runs smoother at idle? Alan
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By Daniel Jessup - 11 Years Ago
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If the engine has good power as you drive and put it under more load (thereby increasing exhaust flow and pressure) then I would be unsure how the exhaust manifolds could be so restrictive at idle (when there is very little need for good flow, etc) but then give you good power as you drive...?
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By Pete 55Tbird - 11 Years Ago
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From reading your post I get it that the car is still 6 volt positive ground. What coil are you using and is there a ballast resistor in you system? Do some more trouble shooting by checking you engine manifold vacuum reading at idle. If the vacuum is low ( camshaft) that can cause the power valve in the carb to spill fuel into the intake. Try to get some more information if you can. It is nothing to do with the exhaust manifolds, forget that. Pete
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By 56_Fairlane - 11 Years Ago
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Pete, that does make more sense than my far fetched idea. I was just thinking in that direction because of the description of the strange combustion sounds. Sometimes the old-timers can be a bit off too.
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By alanfreeman - 11 Years Ago
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I am using a new standard 6 volt coil. I thought that all 6 volt coils were basically the same. Am I incorrect? I thought that ballast resisters are only used on 12 volt and not 6 volt systems. On the manifold vacuum, what is an acceptable reading at idle? I would like to check it but I have no idea of the readings I should have. Thanks, Alan
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By Ted - 11 Years Ago
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At the top of my list of things to look at would be low voltage to the ignition system at idle. This could be verified with a volt meter connected across the posts at the battery. Beyond that, then a steady vacuum gauge reading at idle without any irregular blips taking place would at least point to an engine that is in good mechanical condition. Any irregularities in the vacuum reading can point to electrical or mechanical problems.
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By slick56 - 11 Years Ago
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Ted (7/27/2014)
... a steady vacuum gauge reading at idle without any irregular blips taking place would at least point to an engine that is in good mechanical condition. Any irregularities in the vacuum reading can point to electrical or mechanical problems.
If there is irregular vacuum, here is a great article on pinpointing problems
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By lyonroad - 11 Years Ago
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Thanks Slick. I only wish that there were 12 normal scenarios and 3 bad ones. I don't like the odds.
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By The Horvaths - 11 Years Ago
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Coil wired backwards?
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By 2721955meteor - 11 Years Ago
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all 6volt coils are not the same,some wher neg ground all fords positive ground, the coils must be wired depending on the ground,ford coils usualy say bat that wire comes from ign switch,after market say - and + i cant remember for sure but think - goes to dist,some one hear will remember,older motors manuals tell how it should be hooked up depending on ground. I do know it will efect how the engin runs if in corect. should have a resister as well ,6 0r 12 volt
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By alanfreeman - 11 Years Ago
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Thanks for all of the help, especially that article on interpreting the vacuum gauge readings. I checked the engine vacuum today and it doesn't look good. It is acting close to "Scenerio # 8" in the article. The vacuum at idle rapidly fluctuates between 9 and 13 inches. Increasing the engine speed results in slightly higher vacuum of 15 inches but the needle is steady. According to the article the diagnosis is worn valve guides. Is there any other test to confirm this as the problem short of pulling the heads and taking them to the machine shop? Would worn valve guides make the engine run rough at idle with that distinct "put...put...put" exhaust sound? Thanks again, Alan
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By alanfreeman - 11 Years Ago
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I just thought I would mention that this engine had sat for about 10 years without having been started before I bought the car that it was in. I found the compression to be good and the valve train inside the valve covers was real clean with zero sludge. It looked like the heads had just been done. When I first got the engine running, I had some problems with sticking valves (an intake and an exhaust on one cylinder) which bent some pushrods.. I freed up the valves by soaking them and there have been no bent pushrods in a long time. Alan
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By steinauge - 11 Years Ago
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Check compression.A leaky exh valve will give the symptoms you describe..As rpm goes up the valves will seal better letting the engine run OK under load.
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By lowrider - 11 Years Ago
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The vacuum readings & the sound the engine is making sounds like a valve problem. With the vacuum gauge hooked up & engine running, pull the plug wires off one at a time while watching the gauge. The vacuum gauge should drop as you pull each plug wire off. When you pull a wire off & the gauge doesn't drop that's your bad cylinder. Next step would be to check compression on the bad cylinder. You could also pull the valve cover & check for something out of place (stuck valve, flat cam lobe, push rod etc.).
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By Ted - 11 Years Ago
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alanfreeman (7/28/2014)
...... Would worn valve guides make the engine run rough at idle with that distinct "put...put...put" exhaust sound? Thanks again, AlanYes. A cranking compression test with the throttle opened up would also help to confirm this. There's also the chance that a leak down test would also help to confirm exactly which valve is not sealing but from your description, it would be an exhaust valve.
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By alanfreeman - 11 Years Ago
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I solved my rough idle/fluctuating vacuum problem but I am embarrassed about what turned out to be the cause. This 292 ran great on an engine stand until both valves on cylinder # 6 on the left bank started sticking and I bent a total of 7 pushrods and used a whole can of WD-40 before the problem resolved. I had compression tested the engine before the sticking valves occurred and all cylinders were in the 120-135 range. I retested the compression today and all cylinders in the left bank tested again at 120-135. However, cylinder #2 in the right bank had ZERO compression. I pulled the valve cover and cranked the engine over and the rocker for the exhaust valve of #2 cylinder was not even moving. I pulled that pushrod and it was bent like a pretzel. Inserted a new one and adjusted the lash to .18 thousands. I retested the compression on #2 and it is a bit low at 90 PSI. I am hoping that the low reading is caused by some crud which may have accumulated around the valve seat by running the engine with it not firing???? I started the engine with the valve cover off and ran it for about an hour with no sign of the valve sticking again. It now idles smoothly. Exhaust now sounds normal out of both tailpipes with a light purring pattern. Checked the timing with a light and it seems to run best at about 10 degrees BTDC. Retested the vacuum and it is steady at 20 inches with no bobbing needle. I will run it for awhile and retest the compression in #2 to see if it has improved to normal. Am I being too optimistic? Thanks everyone for your help. Alan
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