new eng only fires on 2cyl

[steven a]

New eng.ran for abuut 15 min. put up for 3 mo's ,now only fires on back two comp is 100 0n 1-4&3 none on #2 . seems like I should have it fire on 1 if I have compression and fire which I do. No water in oil It;s a H/C finned head. Anybody got a clue?

[JoeWay]

Sounds like stuck valves to me. Can you see the valves through the plug holes in this head? If so, pull the engine through the firing order and check the valves at TDC for each cylinder to be sure they are closing. One of the #1 valves may be closing quickly enough at cranking speed to show compression, but not fast enough to allow combustion at running speed.

Marvel Mystery Oil or other penetrating lube may cure your problem.

Joe

[BRENT in 10-uh-C]

Steven, you say you have compression on 1, 3, & 4, --but no compression on #2. When it is running, do you hear a"popping noise" out of either the exhaust or carburetor?

While Joe and I think alike on this, one thing that is critical is re-torquing the aluminum heads until they 'settle in'. While you only specified it was a finned H/C head, this may apply here too.

Might I suggest you do a cylinder leak-down test. If you do not have one, but do have a way to pressurize the cylinders, I would put an air hose on it with about 35#-40# of pressure and listen for leaks. If you need an adapter, they can be purchased, --or fabricated by welding a quick-change air fitting to a "hollowed out" spark plug.

[Tom Wesenberg]

I agree that it probably is a stuck or slow to close valve or valves. !5 minutes may not have been long enough to warm the engine thoroughly enough to get all the moisture out. Years ago I ran a low mileage 63 Studebaker Lark and my low mileage 29 Chevy for a short time and left them for 6 months. When I tried to start them 6 months later, both egines were seized from too short a run time.


A vaccum guage would be good to check for stuck or slow to close valves.

[Mitch//pa]

agree with above to do a cylinder leak down test. years ago i had a vehicle that the fuel tank was so tarnished and bad fuel almost to a syrup and when i fired up the motor it stuck all the valves real bad to the point i had to pull the heads back off..

[Tom Sieffert]

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I would also check the gap between your rotor and the distributor body on each of the four contacts to the spark plugs. I believe it should be .020.

[Mitch//pa]

Originally Posted by Tom Sieffert

I would also check the gap between your rotor and the distributor body on each of the four contacts to the spark plugs. I believe it should be .020.

that would'nt cause no compression

[2manycars]

Your intake valve is stuck open on number 2 cylinder. This causes number one to also not fire. You may be able to free it up by taking off the side cover and working it with a large screw driver and some penetrating oil. If not, take off the head and tap it down with a soft face hammer while someone cranks the engine. running a new engine, then putting it away without oiling everything will cause new, tight parts to stick.

[Tom Sieffert]

@ Mitch//pa

Originally Posted by Mitch//pa

that would'nt cause no compression

Correct but it might explain why he is not getting any firing on #1 where he is getting compression. And he states that he is not getting any firing on #1 & #2 indicating that the rotor may not be coming close to the distributor body at all on the front side of the distributor - a possible alignment problem in his distributor. Just something that is easy to check.

Thanks! Tom

[JoeWay]

Originally Posted by 2manycars

Your intake valve is stuck open on number 2 cylinder. This causes number one to also not fire.

Why would a stuck valve on #2 keep #1 from firing?

Joe

[2manycars]

Originally Posted by JoeWay

Why would a stuck valve on #2 keep #1 from firing?

Joe

Because the open valve of number 2 blows the charge back through the manifold when the piston comes up, and number one is supposed to be getting the fuel/air charge. The result is a very lean charge that will not fire in number one. I know it sounds odd, but I have had it happen often, last summer it was a customer's model T, and that exact thing happen.

[tamagrouchy]

Yep, the A has 4 exhaust ports, but only 2 intakes, 2manycars nailed it I believe.

[JoeWay]

I ran that scenario through my mind before posting the question. Seems to me if #2 didn't fire, the cylinder would be full of standard air/fuel mix, which should combust just as easily in #1 as the same mix drawn from the carb.

If both valves in #2 were stuck open, it might draw in burned exhaust from #3 and then pass it to #1. That wouild definitely cause a lean mix in #1, but it looks to me as if it would take two stuck valves to do it.

Am I missing something?

Joe

[BRENT in 10-uh-C]

Originally Posted by tamagrouchy

Yep, the A has 4 exhaust ports, but only 2 intakes, 2manycars nailed it I believe.

Ummm, I tend to disagree also. Take a moment and think the firing order through... #2 draws AFTER the #1 will. Because #2 does not explode, there is little (if any) spent gasses, --but even if it did draw just a tiny amount, there would be plenty of fresh air/fuel available from the intake when it is time for #1 to fire again.

[2manycars]

You guys can postulate all you want, but from 45 years of experience, I still say it is a stuck intake valve on number 2.

[Mitch//pa]

since #1 and #2 intake valves share the same runner and say if #2 intake valve is stuck open when #1 is drawing in air it would also be drawing in extra air from #2 cylinder causing a lean mixture thus a miss. it would act like a large vacuum leak. the key to this thing is 1 and 2 intake valves share the same port..