Guest Emil Posted July 8, 2014 Share Posted July 8, 2014 I've been restoring my 1941 pontiac for the last couple of years into a running project.got it up and running last year and had it out for a couple of test drives, but after converting to 12v I noticed the car was running real sloppy when idle, if I rev it up it balances out but since I've never had either flatheads or straight sixes before I can't tell if it's all good.the engine is a 239 cui pontiac flathead from 1941 the original one for the car.so here's the problem: today I started going through the ignition and noticed that it's only running on 3(!) cylinders, I've got compression in two of the non-working ones and the third is all dead. the real weird thing for me though is that the car runs but as soon as I take out any of the sparkplugs from the non functioning cylinders it dies, even if it's the one with no compression. I can see at least one of the valves moving in the non compressing cylinder and the other is at least moving behind the valve cover on the side.all help is much apprechiated! Emil Link to comment Share on other sites More sharing options...
Larry W Posted July 9, 2014 Share Posted July 9, 2014 By "taking out" a spark plug, do you mean you're disconnecting a plug wire from a spark plug? If so, try this instead; peel back the rubber boot from the end of the spark plug wire where it connects to the spark plug. With the engine idling, take a screwdriver and ground the connection to the engine block. Do you get the same result? Does the engine die? Link to comment Share on other sites More sharing options...
Guest Emil Posted July 9, 2014 Share Posted July 9, 2014 By "taking out" a spark plug, do you mean you're disconnecting a plug wire from a spark plug? If so, try this instead; peel back the rubber boot from the end of the spark plug wire where it connects to the spark plug. With the engine idling, take a screwdriver and ground the connection to the engine block. Do you get the same result? Does the engine die?if I take the cable off, nothing changes but if I remove the sparkplug from the engine it dies, it's like it need the compression in the non-working cylinders to run.Emil Link to comment Share on other sites More sharing options...
dictator27 Posted July 9, 2014 Share Posted July 9, 2014 Not related to your question Emil, but why have you changed to 12 volts? I would just leave it as 6 volt. Have you checked your valve adjustment? Flathead engines need less valve clearance than overhead valve engines and a camshaft which is not quite properly positioned can cause valves to be held open.Terry Link to comment Share on other sites More sharing options...
Guest Emil Posted July 9, 2014 Share Posted July 9, 2014 Not related to your question Emil, but why have you changed to 12 volts? I would just leave it as 6 volt. Have you checked your valve adjustment? Flathead engines need less valve clearance than overhead valve engines and a camshaft which is not quite properly positioned can cause valves to be held open.Terryit didn't have enough juice to turn the starter over at 6 volts, opted for conversion since I'm on a budget and had most of the stuff I needed laying around my garage.I haven't checked it, but I have found the intake valve is not sealing on the third cylinder. I have an inspection booked for street use here in sweden on friday so will start tearing this down in a week to check all the valves and cam and all that.after I open the cylinder it gets too much air through that hole and it kills the engine I belive.Emil Link to comment Share on other sites More sharing options...
Rusty_OToole Posted July 9, 2014 Share Posted July 9, 2014 The spark plug is not stopping the car from running, it is something else. I can't tell what else you are doing from 5,000 miles away. It may have to with something you did wrong when you converted to 12V.Can you do a compression test and get back to us? Test dry, then squirt a little oil down each spark plug hole and test again (1 or 2 squirts from an oil can).What is your oil pressure? Link to comment Share on other sites More sharing options...
JFranklin Posted July 9, 2014 Share Posted July 9, 2014 Maybe you have a headgasket leaking between cylinders. if the adjoining cyl. piston is up you could have just enough compression to run and with the plug to that one out tou lose all compression. Just a guess. Link to comment Share on other sites More sharing options...
Guest Emil Posted July 10, 2014 Share Posted July 10, 2014 The spark plug is not stopping the car from running, it is something else. I can't tell what else you are doing from 5,000 miles away. It may have to with something you did wrong when you converted to 12V.Can you do a compression test and get back to us? Test dry, then squirt a little oil down each spark plug hole and test again (1 or 2 squirts from an oil can).What is your oil pressure?the spark plug keeps it running, the intake valve is not sealing which makes the other cylinder suck all the air and fuel out of the third cylinder. if I take out the sparkplug it sucks way too much air in and it kills the engine. (this is atleast what I have concludes thus far)did a compression test, the first two have compression and the third creates a vacuum. the last three are running.oil pressure is good, at least judging from the original pressure gauge. Emil Link to comment Share on other sites More sharing options...
gregchrysler Posted July 10, 2014 Share Posted July 10, 2014 bent valve or valve rod not working no compression worn valve seal put a straw in cylinder see if it moves up and down also bad connecting rod maybe Link to comment Share on other sites More sharing options...
Rusty_OToole Posted July 10, 2014 Share Posted July 10, 2014 Do you want the damn thing to run or don't you? You have a problem and it's not the spark plugs. Test the compression wet and dry, and notice the oil pressure. You may just need a ring and valve job, you may need a complete engine rebuild. The compression test and oil pressure test will tell you which. Also how many miles on the car. Link to comment Share on other sites More sharing options...
Guest Posted July 10, 2014 Share Posted July 10, 2014 Do you want the damn thing to run or don't you? Link to comment Share on other sites More sharing options...
Rusty_OToole Posted July 10, 2014 Share Posted July 10, 2014 Sorry if I was too blunt. The original post said need help! He got help. Then came a lot of palaver about whether a car will run with the spark plugs out (it won't).I thought the idea was to make the car run right, evidently that wasn't it. I apologize for the confusion. Link to comment Share on other sites More sharing options...
jbbuick22 Posted July 10, 2014 Share Posted July 10, 2014 Sounds like you have several valves stuck open. Remove the head and free up the valves that don't move,(penetrating oil and a small plastic hammer).Be gentile when pushing the stuck valves down. JB Link to comment Share on other sites More sharing options...
trini Posted July 13, 2014 Share Posted July 13, 2014 Changing from 6 volts to 12 volts is not the best deal unless you are a little technically savvy. Most times the reason for doing so is hard starting. The battery cables should be 1 zero or better 2 zero in size with clean connections and grounds. I prefer to have the terminals soldered. Change the ignition coil too to 12 volts. The voltage to the gauges must be reduced to 6 . Do a compression test. There is an inherent problem with flat head motors .If the engine sat for too long the gasket tends to deteriorate between # 3 cylinder and #4 cylinder. Some time the cylinder head bolts passes through the water jacket which helps to speed up malfunction. So you get compression simultaneously in both cylinders. A compression test will determine that. Use a vacuum gauge while the engine is running. The first thing I would try is empty a quart of the engine oil and replace it with transmission oil. Start the engine and run, Transmission oil helps to loosen sticky valve and free passages. If successful drain oil and replace. The alternative is obvious. DO IT RIGHT THE FIRST TIME. Hope this help. Link to comment Share on other sites More sharing options...
Larry Schramm Posted July 13, 2014 Share Posted July 13, 2014 In my book, fix the obvious first! I agree with the others above, why did you change to 12 volt. For hard starting with 6 volt, usually bad connections. 1. I would change back to the original as the cars worked fine when new. 2. Do a compression check.. dry then with a couple of squirts of oil in the cylinders. Compression checks are done with all the plugs out.3. Determine which cylinder if there are any are more than 10% lower than the other/ highest one. 4. Remove the valve covers and inspect the rocker arms and see if they are moving and the valves are going up and down while cranking the engine.5. If one of the cylinders are way out of spec or zero compression as noted above put a straw in the spark plug hole and see if the piston is going up and down.If fortunate enough to have a boroscope put it in the sparkplug hole to see what is in the bad cylinder if there is a bad or low cylinder. Please start here and give us a report and pictures if possible and there is enough knowledge with this group we can fix about anything. Link to comment Share on other sites More sharing options...
trini Posted July 14, 2014 Share Posted July 14, 2014 Hi Rusty,you are right on the ball. There are certain basic steps to be taken for poor running even in modern cars. Check gas in tank and getting to the carburetor, Check for spark at the ends of high tension wire and at plugs outside of engine. THE FIRST AND FOREMOST CHECK COMPRESSION. It is a must for every tune up. HOW ELSE CAN YOU TELL THE HEALTH OF THE ENGINE ? Poor compression ? Start tearing apart. Most electrical problems are because of bad grounds especially on 6 volts system GROUND, GROUND, GROUND. CLEAN, CLEAN. CLEAN. Solder all terminals if possible. Link to comment Share on other sites More sharing options...
Recommended Posts
Create an account or sign in to comment
You need to be a member in order to leave a comment
Create an account
Sign up for a new account in our community. It's easy!
Register a new accountSign in
Already have an account? Sign in here.
Sign In Now