1938 Pontiac 6 cylinder cam question.

[GasWorksGarage]

Ok so the car ran fine went to start it up and it sounded as if it had no compression. So I pulled the pulls to look into the cylinders while cranking nothing moving.

I assumed that i broke the timing chain or gears. I pulled the timing cover only to find everything intact as should be and still in alignment.

Then I think about pulling dist. cap off then crank only to find that the distributor is turning. then i run a compression test no compression. Am I missing something??

 

Thanks in advance.

 

[Bloo]

If the distrubutor is turning, the starter is turning the crank at the rear, which is turning the timing gears at the front, and those are turning the cam, to at least halfway back the engine where the cam drives the oil pump and the distributor.

 

Could it have sheared a key or a pin and slipped time anyway?

 

Pick a cylinder, either #1 or #6, and pull the corresponding side cover, Pick the one thats easiest to get off on a 38. Now remove all the plugs.

 

Pull the distributor cap and watch the rotor. Rotate the crank, clockwise ONLY with the wrench until the distributor rotor gets ALMOST to the OPPOSITE CYLINDER of the oner you picked. For instance if you picked #6, stop before you get to #1 (or vice versa if you picked #1).

 

Rotate the engine really slowly with the wrench while watching or feeling the valves on the cylinder you picked, and watching the timing marks. Are the timing marks on the flywheel on the 38? If so this is going to be a bit like juggling cats. You might have to just feel the bottom of the valvesprings for movement. Use only the wrench to turn the crank. Don't smash your fingers.

 

Now continue turning the crank with the wrench while watching the timing marks and feeling the valves on the cylinder you picked. First you should see the ignition marks come by (probably 2 of them) and then the TDC mark. The TDC mark might be marked UDC or DC.

 

Here is the important part, one valve on your chosen cylinder should open and the other should close RIGHT AS you pass TDC. Go slow and go only clockwise with the crank. The valves are both open for a tiny distance, right at the top.

 

Edited April 26, 2018 by Bloo (see edit history)

[Rusty_OToole]

Has it been siting over the winter? Maybe the valves are stuck. Not unusual in flatheads that have been sitting but it would be unusual for all the valves to get stuck. Try doing a compression test. Squirt some oil around the valves and spin the engine over. If you have enough cylinders working to get it running and warm up, the lazy valves usually start working. It does not hurt anything to turn over a flathead with stuck valves, which is not necessarily true of an OHV.

[Bloo]

1 minute ago, Rusty_OToole said:

Maybe the valves are stuck

 

OOOh... I didn't think of that. Good call.

[GasWorksGarage]

It ran a couple weeks ago. All the valves stuck?? I don't think so. The timing marks on the timing gears are still aligned. 

[GasWorksGarage]

are the lifters in these hydraulic or solid?

[Bloo]

5 hours ago, GasWorksGarage said:

The timing marks on the timing gears are still aligned.  

 

I get that. I was wondering if the cam itself had somehow slipped or got out of sync by breaking a key or a pin. There are only 2 stock cam profiles for this engine family, and both of them have the overlap just about centered on TDC of the overlap stroke, thus my suggestion above. If everything is timed and turning, and the valves are not hung open, and there are pistons in the engine, then what you are telling us is basically impossible, but I guess you already knew that. There HAS to be more to this story. It is hard to guess what from this far away.

 

Even an engine with a crankcase full of gas from a leaking fuel pump, and worn out rings, and flooded from over-choking should register SOMETHING on a compression gauge if the valves are timed and closing.

 

5 hours ago, GasWorksGarage said:

are the lifters in these hydraulic or solid?

 

Solid. The lash might be a good thing to check. Put a cylinder on TDC of the firing stroke and check it. If you find a tight or open valve, I would still be more suspicious of the cam timing. I just don't see any way for a whole bunch of them to get out of whack suddenly. Since it was running recently, and now it isn't, something happened that affected the entire engine.

 

5 hours ago, GasWorksGarage said:

It ran a couple weeks ago. All the valves stuck?? I don't think so.

 

Is the gas in this really old and stinky? You wouldn't believe how tightly valves can get stuck from bad gas. 

 

Good luck, and let us know what you find!

[GasWorksGarage]

I take it that the intake valve is just below the plug opening? If they are stuck what is the best way to go about freeing them up?

 

[Guest]

No the valves are to the side.  The sparkplug is centered over the piston on L-head engines.  Lots of a penetrant around the valve guide might free the valves.  If you were only using the car occasionally the valves would most likely stick again.   Unless you were going to run the engine a lot the only way to correctly free the valves is to remove the head,  remove the valves themselves and clean up both the valve stem and the guides. 

[GasWorksGarage]

I pulled the head found all the intake valves are sticking. I have been spraying carb cleaner and parts cleaning fluid into the valve openings then cranking have 4 out of 6 snapping shut. I will update later. And the spark plug is located over the intake valve on this one. 

[Spinneyhill]

Did it run with old fuel, which can be a bit gummy? Stuck intake valves could be the result....

[Bloo]

Keep after it with the carb cleaner. Once you get the goo cleaned out, there should be a little clearance in the guides. Drip some light oil down them. Get rid of that old gas.

 

 

[GasWorksGarage]

yes the gas is old. 

 

Thanks all!