Intermittent valve sticking

[40-A Twins]

After installing new valves & guides plus new 5.5 head, the motor is still not running well. Compression was around 60 for all cylinders cold. Starts up easy, but starts smoking and it stinks like its running too rich and has little power. I was watching the exhaust while it was running at high idle and there are intermittent muffled pops that seem to coincide with smoke output. Now I am thinking this might be sticky valves. New valve guides are modern type that are interference fit, and I did not ream them after installation. Is this the root of the problem ?
Kevin

[Synchro909]

I very much doubt they are the cause of the problem. I have used those press in guides, never reamed them and had no trouble. I think you'll find the cause elsewhere.

[Oldgearz]

Dump some (1/4 cup) MMO into the tank and run it awhile.

[Mulletwagon]

Originally Posted by Oldgearz

Dump some (1/4 cup) MMO into the tank and run it awhile.

Also squirt some MMO directly into the carb at elevated RPM. If valves are sticking, that will cure them immediatly.

[johnneilson]

If the new guides do not have the ~.100 step, you may not have enough valve spring pressure.

John

[40-A Twins]

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I will pick up a bottle of MMO and give it a try.
The modern style valve guides are a straight bushing without any feature that contacts the spring like the original style does. The online "A" parts houses don't list spring sets designated for original or modern style guides. Is there a design flaw here ?
Kevin

[johnneilson]

not a design flaw, it is progression of manufacturing.

You can make spacers to shim the springs back to proper seat pressure.

The proper procedure would be to measure installed spring height and then measure pressure at that compression.

The standard spec is 40-45#
You will not hurt anything if it gets up to 60 or so as long as the springs are not coil bound at valve full open.

J

[40-A Twins]

I bought some MMO and poured a little in the gas tank while the motor was running and watched for any changes in smoke or popping. It still smoked and popped. After a while the motor quit, so I checked for spark, OK, checked timing, OK, and after a lot of cranking and pausing, it finally started. It ran fine for around 1/2 hour and stopped again. This time I removed the carb and cleaned it out. Again, it took a lot of cranking and pausing before it started up. During all this cranking, it did not bark at all, even after spraying some starting fluid in the carb. All I can conclude is that adding MMO to the gas makes it very difficult to start.
Kevin

[nkaminar]

My guess, and it is only a guess, is that the original problem was not a valve sticking but a problem with the ignition system. Adding the MMO probably has noting to do with it not starting and the root of the problem is the ignition. If you did not get a response from the engine with the starting fluid then that would confirm an ignition problem.

[Patrick L.]

Originally Posted by nkaminar

My guess, and it is only a guess, is that the original problem was not a valve sticking but a problem with the ignition system. Adding the MMO probably has noting to do with it not starting and the root of the problem is the ignition. If you did not get a response from the engine with the starting fluid then that would confirm an ignition problem.

I agree

[Synchro909]

Originally Posted by johnneilson

not a design flaw, it is progression of manufacturing.

You can make spacers to shim the springs back to proper seat pressure.

The proper procedure would be to measure installed spring height and then measure pressure at that compression.

The standard spec is 40-45#
You will not hurt anything if it gets up to 60 or so as long as the springs are not coil bound at valve full open.

J

Are the springs that come with that kit the same as the others or are they made with a little more tension to compensate for the longer length?

[katy]

Originally Posted by johnneilson

The standard spec is 40-45#

At what length would that 40-45# be?

[40-A Twins]

I didn't record spring measurements before installing them. There was something else I didn't think to mention before, but after it stopped running the first time, the ammeter did not register any current when the key switch was on. I pulled the dash panel off and checked everything with a multimeter looking for a loose connection, checked for power at the coil, but did not find anything wrong. Later, after it had cooled down some, the ammeter moved while cranking the motor. I will swap the coil for another 6v coil today and see if this will cure the problem. I don't suspect the condenser at this time, (modern upper distributor plate with 1957-1974 Ford condenser) but have another on hand.
Kevin

[40-A Twins]

I swapped out the USA made coil for another USA made coil and motor still would not run for very long. Then I robbed the condenser from the other car and installed it. Had to set timing again because the breaker spring came loose while loosening the electrical connector nut. I don't think the description for this "modern upper plate" quite lives up to its description: "Improved Upper Plate uses modern Ford Points & Condenser. Keeps Condenser away from extreme heat and the points can be changed without re-timing".
The now installed condenser was marked RF-914, and it looks like a 57 T Bird condenser. I will look for a NOS condenser now because I can't trust a shiny new imported unit to work for very long.
The motor starts up and keeps running now, but still smokes and pops same as it had before. I poured some more MMO in the tank and see what happens.
Kevin

[Patrick L.]

As long as you didn't loosen the points hold down screws and only the contact leads you shouldn't have to re-set the point gap or the timing. Just keep the point block lubed.

As long as the 'modern' upper is a wired unit, which it looks like it is, and the wire is in good shape that upper plate will work just fine. The wireless units are troublesome.

A NOS Ford V8 condenser and points set are good things to have hanging around.

Yep, the new stuff made from chinezeium is pretty much junk.

[nkaminar]

Congratulations on getting your engine running. Now on to the smokes and pops. What lash (gap) did you set the valves at? Did you use the old springs? What method did you use to set the valve lash? How tight were the valves in the new guides? Did the valves just drop in or did you have to push them down? Are the old guides also the press in kind or do they have a lip for the springs?

As others have indicated the springs may not be right for the press in guides.

[johnneilson]

Hard to say on spring preload
Don’t hold me to this, something like 2.25 or 2.312
I don’t use std springs, usually V8 or small block Chevy springs
John

[40-A Twins]

Valve guides were installed with a 11/32 valve guide driver that measured a little undersize which allowed the guide ID to deform undersize the same amount. I ran a dill bit down the hole just enough to open up the deformed area. A reamer would have been better. I thought the valves fit the guides fine. I don't recall any sticking when cold.
Lifters are adjustable type, and valve lash was set using a feeler gauge, which I think was .012.

[Patrick L.]

.012" lash on intakes is OK, but, a bit tight for exhaust.

[nkaminar]

The other thing that I can think of is problems with the carburetor. A lean mixture can cause skipping and popping in the exhaust and a funny smell. Assuming you have a Zenith carburetor this site may be helpful: https://model-a.org/default.html. Or an air leak in the intake manifold system or at the throttle shaft. Also see here: http://modelabasics.com/carberutor.html