Cylinder Pressure during rebuild

F

frmhrt

Member
I apologize if I am starting a new thread on an already running/completed topic but I am not even sure how to search for this issue or if it IS an issue. I am a rookie.
Here goes: rebuilding my dad’s 49 ford flathead v8 engine for his farm truck.
Water pumps, crank, rods, pistons, timing gear, valves in and adjusted. Cylinder heads and intake manifold on.
Fuel pump not on, carb not on, exhaust manifolds not on, oil pump not in, oil connections to oil filter canister not connected.
I put in all the plugs except #1. I have #1 piston at top at TDC, valves appear closed via #1 spark plug hole.
I screw into the #1 spark plug hole an adapter to a small hose. I attach suction to the hose. I get air flow, no vacuum is created.
I do the same to #5 cylinder, in the middle of its compression—same result.
I would think that during or at the end of compression, with both valves closed, and piston rings sealing the cylinder, this space would be sealed and I should not be able to create air flow and should create vacuum (negative pressure) by introducing suction to the cylinder.
Is this normal, why and if not, what are potential errors in my re-construction thus far?
I hope I have explained this sufficiently. Any insights/advice/recommendations will be much appreciated.
 
Have you tried oiling the cylinders then give it a try ? Obviously if the oil pump is not in then the pan is still off so you should hear air rushing past the piston.
 
Well, it doesn't sound right, but you are doing some checks I'm not familiar with so no idea what the results should be. Setting the valves up on these engines is a little different than most engines, can you explain how you went about it? How did you establish TDC? How were the valves seated?
 
I think you are doing it wrong. You need a compression gauge.
Do all the cylinders and record what you get.

I just saw you have no oil or pump.
 
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Put pressure in each cylinder with piston at top dead center instead of vacuum. It's a lot easier to locate air rushing out rather than in.
 
This appears to be a test based on your theory that the combustion chamber should be sealed when the valves are closed.
Nice theory, but as previously stated, ring end gap has to be considered.
Unless the rings are solid (no gap) you will not be able to pull and hold a vacuum.
And even with solid rings there would be leakage between the rings and piston.
 
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Sounds like what you want to do is a leakdown test.
That way you can compare cylinders and get a picture of how well rings seal up.
Leak down tester is 2 gauges with a restrictor between them, air in at one side and the cylinder you want to test at the other end.
I use vacuum to test valve to seat sealing but not to good for testing piston to bore.
 
thanks all for your suggestions and insight. I obtained a cylinder leak down gauge and found that on compression and combustion all cylinders seem ok - 25-35% leakdown.

However, during pressurization during the exhaust phases of cylinders 2 and 3, I get exhaust from the exhaust of cylinders 6 and 7, mostly 7 on THE OTHER SIDE OF THE ENGINE and vice versa. Is there a connection in the block between the exhaust ports of cylinders 2 and 3 and 6 and 7?

Trying to figure this out. Would really appreciate feedback and enlightenment on this. Fordbarn is a great resource with generous mentoring. Plus just reading the threads is educational and entertaining.
thank you all.
alan
 
thank you!!
I was anticipating a cracked block.

interesting that exhaust crosses via intake manifold, will wonders never cease.

thx again

alan
 
frmhrt said:
thank you!!
I was anticipating a cracked block.

interesting that exhaust crosses via intake manifold, will wonders never cease.

That exhaust crossover is to heat the bottom of the carb to prevent carburetor icing and to provide better fuel atomization in cold weather. A carb can form ice on the throttle plates and on the outside of the carb up to 55 deg. on a humid day.
Click to expand...
 
Almost all automotive engines had some method of using exhaust heat to preheat the base of the carburetor. Most V8s have a crossover through the intake manifold to the base of the carburetor. If you've ever messed with VW engines it gets interesting is the crossover gets plugged up!
 
Thank you all for your input. This has been very interesting and helpful to me. Fordbarn members are the "institutional memory" of Ford products. thanks again, all.

alan
 
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