Valve Job??

A

ampico-kid

Senior Member
Hey gang. I've got the Town Sedan that had the Stop/Stall issue that was discussed on another thread. I've worked through all of that, discovered that the compression on cylinder 3 was low (about 35psi) and found evidence of exhaust leakage in the coolant by using an exhaust detecting chemical that is blue, turning to yellow when it detects exhaust gases in the water/antifreeze. Well, mine didn't turn yellow, it turned green indicating some exhaust was detected. I've now pulled the head, couldn't see any evidence of the blown head gasket, but I'm having the head machined and will reinstall it with a new head gasket. I'm hoping that will get the compression on #3 back in the range of the other three, which are all in the mid 60s psi.

My question is...since I have the head off, and manifold out of the way, should I consider a valve job? If so....how difficult of a job is it? I've been around machines and engines most of my life, but have never done a valve job. I haven't pulled the valve access cover off yet, so I don't know if it has been converted to adjustable tappets. Seems like removing the springs and retainers would be pretty difficult? If I was able to removed the valves, what next? The car is disabled, so I can't take it to a shop for any kind of work. Would I just have to "lap" the valves or do they have to be "cut"? I assume cutting them is something a "pro" would have to do with some specialized equipment? Please fill me in on the procedure and your opinions please. Thanks.
 
I would start by pulling the manifolds and looking for evidence of water leakage in the exhaust valve pockets that would allow exhaust gases into the water jacket under pressure while running and from the water jacket into the manifold while the engine is not running.

This was what I found after dealing with water loss combined with exhaust in the coolant. I found a pinhole sized opening half way down in the #3 exhaust valve pocket on the forward side of the pocket.
 
In general, you want the repair job to be proportionate to the problem, so what symptoms are leading you to want to re-do the valves? There's a big difference between, e.g., checking clearances and sealing, and replacing the valves or re-cutting the seats.

Also did you check the block deck for flatness and what was the outcome?
 
alexiskai said:
In general, you want the repair job to be proportionate to the problem, so what symptoms are leading you to want to re-do the valves? There's a big difference between, e.g., checking clearances and sealing, and replacing the valves or re-cutting the seats.

Also did you check the block deck for flatness and what was the outcome?
Click to expand...


The reason I was thinking about "valves" was because of the low compression in cylinder #3. I was actually thinking more like just checking #3 valves. I figure low compression can come from leaky valves, blown head gasket, or piston ring issues. Since I'm already planning on replacing the head gasket, I thought maybe I should check out the valve possibility while I have access to them. Not necessarily thinking of doing all of them. How do you check the block deck for flatness? Lay a straight edge on it? Thanks.
 
ursus said:
I would start by pulling the manifolds and looking for evidence of water leakage in the exhaust valve pockets that would allow exhaust gases into the water jacket under pressure while running and from the water jacket into the manifold while the engine is not running.

This was what I found after dealing with water loss combined with exhaust in the coolant. I found a pinhole sized opening half way down in the #3 exhaust valve pocket on the forward side of the pocket.
Click to expand...


The manifold is off of the car. I took a good look into the exhaust ports (and intake) and I don't see anything that would lead me to believe there's a water leak. All of the exhaust ports have pretty much the same coloring and soot consistency. Likewise the two intake ports appear to be the same. I would think it would have been pretty hard to spot a pinhole size leak. You must have pretty good eyes. If the manifold on your car was off, and the car was also off, could you see the water dripping into the exhaust manifold port? Maybe that's how you spotted it?
 
You can check the valves by squirting some solvent on the valves when they are closed. If you see the solvent in the ports then the valves have some leakage. More solvent, more leakage.

Lapping the valves can be a fairly straight forward job, depending on if you have the original valves or not. Take the valve cover off to see what you have. The vendors sell a spring compression tool that allows you to lift the springs to remove the keepers. You may have to gently tap the valves down to break loose the keepers. If they valves are the modern type they will just lift out. If original type you will have to pound out the guides with a special tool. Keep track of the valves by drilling 8 holes in a board and labeling the holes 1 through 8. Look at the valves and seats. If they are not worn excessively you can lap them using a lapping tool available from the vendors and valve lapping compound. When you get a shinny ring all around the valve and seat stop and clean up all of the lapping compound. Lube the stems and install the valves. Put the springs back. Adjust the valves (0.012 inch is typical). If you have the original style valves then you will have to carefully grind off the end of the valve to get the required clearance, which is a huge pain to do and special tools are needed.
 
If the head gasket was not blown, no obvious pin holes in the ex ports, where do you think the ex gas was leaking into the water? Depending on the gasket, it may heve been leaking without burning completely thru. In addition, these motors are notorious for cracking into the water jacket. Take a real hard look at the deck surface for a crack inside the combustion chamber area. Also rotate piston down halfway, have seen a hole thru cylinder wall.
Hoping for a gasket issue, John
 
I'm afraid you won't like to hear this but from #2 or #3 exhaust valve is the favourite place for Model A engines to crack. The crack heads towards the cylinder and when it gets bad enough, it goes down the cylinder wall far enough that coolant will leak into a port and exhaust gasses into the coolant. It sounds to me that all of this fits your description. I had that happen on one of our outback trips when we were about 2,500 miles from home and we were towing a camper. A proper fix was out of the question so I used some of this https://www.supercheapauto.com.au/p/goss-chemiweld-radiator-stop-leak---325ml/1104.html. I don't know if it is available over there but I am sure there will be something like it. That motor did the 4,000 more miles of our trip and is still going.
That said, the only permanent and proper fix would be a rebuild of a new block. If you haven't touched the surface of the top of the block, a close inspection will often reveal the crack to the naked eye. There is less chance of seeing it if you have cleaned the area.
I don't know how many miles you do but if you are end up having to rebuild an engine, I would suggest one of the new Burtz engines.
 
Combustion gas detectors that rely on coolant color is a dicey reason to tear an engine down, or to link it with a compression loss. Faulty readings are possible when reading ‘tea leaves”… lapping valves is straight forward work , easy to see an issue if that’s the problem.
 
In regards to a valve job, How much time is on the motor? Enough to warrant time spent on a valve job? In looking at the valves, are either one bent or burnt. Check the valve lash. It's rare, but if it wasn't adjusted correctly, it could be allowing the compression to slip past in #3 cylinder. You don't say how the head will be ground, but I avoid those guys who just hold it to a belt sander. I want the guy with the fixture and actually grinds it on a machine made to grind it. The machines are usually Van Norman or Blanchard. As far as the valves go, I had a Van Norman valve grinder that would spin the valve slowly against a high speed wheel with a face angle of 45 degrees. This was to reface the valve ad prepare it for lapping onto the valve seat (This kind of work is becoming rare these days, no one wants to do it anymore) Mike the stem of the valve. It should be .3115 to .3125. then lap it in. The old guys used a valve lapping tool that I see now and then in the flea market and the guys selling the have no idea what they're used for. The tool is a very basic wooden spindle with a rubber suction cup at both ends. Attach the suction cup to the top of the valve and spin it between your hands with a little valve grinding compound on the face of the valve and you will see a visible ring start to form around the face of the valve and the seat. The old-timers used "Prussian Blue" to check the ring, but since no one knows what Prussian Blue is anymore , you'll probably have to use something else. Don't use too much ! Just a stain that will transfer where it contacts! No Blobs that will mark everything! There's more! Some you will figure out on your own, some you will have ask. Go ahead that's what we're here for! But when you do it and get done, you can be dan proud of yourself! Doing a Valve job on a model A is not the easiest thing in the world.
Good Luck!
Terry
 
An automotive machinest I knew went to using magic markers in the 70's for fast checking.I use them on valves,rear axle tapers,water pump tapers,and to find the high points on brake shoes.
 
Since you are already into the engine, lapping the valves is a quick and fairly easy job, #1 priority is to ensure that all...and I mean all, of the lapping compound is cleaned/removed from the engine prior to reassembly.
You'll need the valve tools for the springs and guides, lapping tool and the compound, and lots of rags.
Do not mix the valves and guides up, keep them matched and return to the same place they were removed from.
 
It doesn't sound like a valve problem to me. A leak down test would find the problem quickly. A bad valve usually shows 0 compression unless the valve is just barely starting to go bad. Low compression is usually inside they cylinder.

If valves are to be touched, I don't recommend lapping. Grinding/cutting and facing are the proper way.
 
post some pictures of both sides of the old gasket, the valves and top of the block, the coloring of the valves and how they sit in the block can give clues to the problem
 
Kurt in NJ said:
post some pictures of both sides of the old gasket, the valves and top of the block, the coloring of the valves and how they sit in the block can give clues to the problem
Click to expand...

I no longer have the head gasket. I took it to the machine shop that is doing the head so they could examine it. I'll take some pics of the top of the block and the valves.
 
Terry said:
In regards to a valve job, How much time is on the motor? Enough to warrant time spent on a valve job? In looking at the valves, are either one bent or burnt. Check the valve lash. It's rare, but if it wasn't adjusted correctly, it could be allowing the compression to slip past in #3 cylinder. You don't say how the head will be ground, but I avoid those guys who just hold it to a belt sander. I want the guy with the fixture and actually grinds it on a machine made to grind it. The machines are usually Van Norman or Blanchard. As far as the valves go, I had a Van Norman valve grinder that would spin the valve slowly against a high speed wheel with a face angle of 45 degrees. This was to reface the valve ad prepare it for lapping onto the valve seat (This kind of work is becoming rare these days, no one wants to do it anymore) Mike the stem of the valve. It should be .3115 to .3125. then lap it in. The old guys used a valve lapping tool that I see now and then in the flea market and the guys selling the have no idea what they're used for. The tool is a very basic wooden spindle with a rubber suction cup at both ends. Attach the suction cup to the top of the valve and spin it between your hands with a little valve grinding compound on the face of the valve and you will see a visible ring start to form around the face of the valve and the seat. The old-timers used "Prussian Blue" to check the ring, but since no one knows what Prussian Blue is anymore , you'll probably have to use something else. Don't use too much ! Just a stain that will transfer where it contacts! No Blobs that will mark everything! There's more! Some you will figure out on your own, some you will have ask. Go ahead that's what we're here for! But when you do it and get done, you can be dan proud of yourself! Doing a Valve job on a model A is not the easiest thing in the world.
Good Luck!
Terry
Click to expand...

I don't know how much time is on the motor. Just got the car. It was purchased on consignment through a dealer so I never had direct contact with the owner (Who I believe was deceased. Car being sold by his widow). The car was restored some time ago, so my assumption is that the engine was rebuilt at that time. The head is in the hands of an old time machinist who is very highly regarded. It will not be ground on a belt sander for sure. I'm still weighing my options, but from your description the tools and machines required to do a bang up job are not available to me. Thanks for your input.
 
A lot of fellas use Prussian Blue to check for contact area. I just find it too hard too remove when you have to change the placement. So I use a pencil, just a mark every 90* and it comes right off.
 
The open valve appears to have good margin, but, the seats are wide and not in too bad a shape. It doesn't look as though the seats have been narrowed.

What are the valve lash measurements ?
 
These appear to be old style valves because of the two holes on the top that were used to fit into the old style valve lapping tool.

There is supposed to be a margin at the top of the valve. This is a small cylindrical lip at the top. It keeps the valves from burning and allows them to be re machined. Your valves do not have this lip which means that they have been re worked several times. Also the seats are really wide. They should be much narrower. Maybe about 1/16 of an inch. The valves are likely the source of your low compression.

All this means that you need new valves and will have to re cut the seats. Get the modern valves, new guides, new keepers, new caps that mount at the end of the valves, and new springs. Also get modern adjustable cam followers. You will have to pull the cam to install the new followers.

You can buy the tools to re cut the seats.

When you get the new parts and have re cut the seats you will need a light lapping to seat the valve. Just enough to make sure you have 360 degree contact.

If you do the work yourself all this is not all that expensive, especially considering the increase in performance that you will have. If you feel that this is beyond your ability you will have to pull the engine and take it to a shop that can do the work but you will be looking at several hundred dollars of labor.

I would advise taking a peek at the bearings and pistons/rings too.
 
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