Number One Cylinder Isn't Helping

[Dollar Bill]

I'm new to Model A's but have some experience with 8N's. This is a new to me car and I'm having trouble with number one cylinder not playing well.

With the engine warmed up and idling, short out the first cylinder and the idle doesn't change a bit. Shorting the second one makes a slight difference in the idle but not as much as 3 and 4.

Car has been converted to 12 volts with modern style Remund (PerLux) distributor with electronic ignition and auto spark advance.

It has great spark to all four cylinders. Spark will jump about a 1 inch gap. Have swapped plugs between cylinders (Champion W18) with no difference in symptoms.

Had to wait several days for spark plug adapter to arrive and it came today. Was anxious to see what the compression readings were so I did not follow the correct procedures for doing a compression check. I only pulled the first plug and took the first reading of 50 psig. Gave it 4 squirts of oil and got the same reading.

Pulled the second plug and got 55 dry and 55 with oil.

Pulled the third plug and it read 60 dry and the same with oil.

Pulled number four and it read 60 and 65 with oil.

Now that I had all four plugs out they read: 60/65/65/65 from front to back.

I was really expecting different readings particularly on the one and two cylinder. Now I'm not sure how to proceed??

[George Miller]

Leak in the intake manifold gasket.

[Mitch//pa]

what George said...
spray around the intake gasket with carb cleaner while running and see if it makes a difference in the miss.. also make sure your wiper vacuum does not leak but usually that is so small it wont kill a cylinder unless someone modified the port bigger...

[1930artdeco]

What about the valves being out of adjustment?

Mike

p.s. Welcome to the barn.

[ponymare]

I would think a leak in the intake gasket would cause a lean burn, not a miss, I agree with 1930artdeco, either too tight or got one that's starting to burn.

[Dollar Bill]

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WOW! Talk about response time - You guys are quick!!

Interesting you mention lean burn as all of the plugs are blindingly white and I do have to run it with GAV about a half turn off the seat or it overheats.

After work I'll spray around the intake and post the results.

I've done the skeeter smoking procedure a couple of times thinking of sticky valves or rings - This was before I took the compression readings.

Not ruling out sticky valves and I'm planning on a valve adjustment as several are a might rowdy.

[Patrick L.]

With compression readings like that, the valves are at least closing. So, that shouldn't be an issue.
If you have good spark all the way thru to #1 sparkler, then you should be good there.[ just ruling out a tracked/cracked cap]
Then I agree that you could very well have an intake gasket issue, especially if both #1 and #2 sparkler are burning lean. So, as mentioned spray it well while running. I usually use ether/start fluid.

[Marshall V. Daut]

It sounds as though everything is o.k. inside the engine with those favorable compression readings. That's good news! If it's an external problem, it'll be less expensive to repair than digging into the engine. It's unlikely that a sticking valve would co-operate for a compression check, but then stick when the engine is running. So, you can probably rule out that out.
Try a simple test: switch #1 and #2 spark plugs and try the shorting out test again. You already know that #2 plug is functioning properly, so use it as a benchmark for troubleshooting the problem in #1 cylinder. If swapping spark plugs doesn't help, can you try a different plastic distributor body? There may a problem inside the plastic body, especially if it's an older repo from the 1980's that tended to crack inside and short out the spark to the plugs, especially in cold or rainy weather. To check the plastic distributor body's functionality, lay a KNOWN good spark plug on the cylinder head, still connected to #1 distributor body electrode. Disconnect the other plugs to be sure the engine doesn't accidentally start. Not probable like a Model T, if all the stars are in proper alignment, but the engine could start, even with #1 plug removed. Turn on the ignition key. Hand crank the engine until the rotor inside the distributor is at the 4:00 position at TDC. You want to crank slowly so that you can stop at TDC when the plug should fire. If you can't see a strong electrical arcing at the plug's electrode, the plastic body is bad internally.
Try these simple tests before panicking.
Marshall

[tbirdtbird]

"With compression readings like that, the valves are at least closing."

ya for sure.

Plugs that white are too lean and watch out else you will burn the valves.
Should be a dark tan color
If the car overheats so easily = late timing
Valves on 1 & 2 might be too loose not getting enough lift. On a good day the most lift you will get from a stock A cam is only .302 . Even .025-.030 less than that will be noticeable

Those compression numbers are acceptable.
What George said and easy to check.
Check lash on all valves. Use .013-.015 on both I&E not less
Be certain timing is correct, go here:
http://www.abarnyard.com/workshop/timing.htm

most cars that arrive in this shop have late timing

oops Marshall types faster, what he said, too

[Marshall V. Daut]

Hmmm..,. I see that the original post specified that a Nu-Rex distributor has been installed. Does that mean a modern cap and rubber plug wires are in place instead of the original plastic "wing" distributor body and brass connectors? If so, then my comments about an internal short do not apply. Also, you have swapped plugs. I guess my comments can't help here. I need to read and type slower.
Still, this is a mystery...
Marshall

[700rpm]

Your GAV at 1/2 turn is about right.

[Dollar Bill]

Well folks, George wins the prize for being first with the correct diagnosis of a vacuum leak. There was a considerable gap between top of intake port and gasket on both intake ports but it was worse on the front. It amazes me that it ran as well as it did.



Upon closer examination, I find the intake and exhaust manifold doesn't bolt together properly to allow all of the ports to be level. The intake is lower than exhaust.


Intake looks to be original, exhaust is obviously newer. I'm thinking both manifolds have to be bolted together - Right?

I was thinking of egging out the two bolt holes on the intake to allow it to move up but there is a raised shoulder for the bolts. Once I remove enough material for proper alignment, the two bolts will be about half way off the shoulder. I am trying to show with this photo how far off the mating bolts would be when the intake is in the correct position.

I'm thinking of rolling the dice on another exhaust manifold. Is the mismatch in runner height a common problem?

Also, which way does the flange go on these gaskets - I'm thinking they should go into the manifold. Problem is the diameter is too great to fit in the block or in the manifold.



Thank you folks for all of your help!!

[Mike V. Florida]

Thank you for posting the result, many don't.

[George Miller]

Bill it was easy, because you gave a good account of what was going on. The only other thing it could have been is a broken or weak valve spring. That would have been a long shot.

[1931 flamingo]

Looks like your gasket has the gland rings built in. Do yourself a favor and get the late 31 copper gaskets that slip down over the attaching bolts. No need to remove manifolds if the gaskets need to be re-replaced. FWIW

Paul in CT

[Purdy Swoft]

I also use the late 31 manifold gaskets, they were the last revision, cover more area and give the best chance to avoid leaks .

[Dollar Bill]

Thanks for the tip on the late 31 gaskets - I'll get a set my next parts order.