We have a new to us 1931. We have had it for two weeks and we are learning a lot. We have driven about 100 miles. Apparently we have been driving with the GAV fully closed. Is that bad, could we have burnt our valves? I was turning with the hand crank yesterday with key off to learn how things work and i notice that i could make it all the way around pretty easy but then it would get really tough and then easy again. Does that mean anything?
running with GAV fully closed
- Thread starter rfequity
- Start date
rotorwrench
Well-known member
The valves may be stuck but it's hard to say without further information. Squirt some oil in the cylinders and do a compression check on all four. If compression is too low, it would justify removing the cylinder head for further inspection. While the plugs are out, note the coloration. This will tell whether it has been running too lean or other problems.
Running with it closed shouldn't do any damage but it may run a bit stronger with some fuel added by a bit of GAV opening.
Running with it closed shouldn't do any damage but it may run a bit stronger with some fuel added by a bit of GAV opening.
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Check the instruction manual for spark and GAV settings.
http://www.palmbeachas.com/Model-A-Instruction-Manual.pdf
http://www.palmbeachas.com/Model-A-Instruction-Manual.pdf
Read somewhere the stock carb was designed to run a bit lean so it would operate at high altitude. But mine runs best with the GAV closed (at near sea level). Plugs get sooty with it is opened even 1/4 turn.. I think it depends more on how the carb is set up and adjusted.
jayvee34
Senior Member
I run with my GAV fully closed or about 1/8 turn open, makes little difference.
As for you turning the engine with a crank: Easy and then hard. It is normal to turn easy
when the engine is on the exhaust stroke, harder when the engine is on the compression
stroke.
If you have driven about a hundred miles and your engine does not have a miss in it,
I would say you are OK. MO
As for you turning the engine with a crank: Easy and then hard. It is normal to turn easy
when the engine is on the exhaust stroke, harder when the engine is on the compression
stroke.
If you have driven about a hundred miles and your engine does not have a miss in it,
I would say you are OK. MO
john charlton
Well-known member
My 31 BUDD cab p/u is most happy with the GAV closed . MY 29 blindback fordor its a quarter open . My 28 phaeton it is just cracked so most vary car to car .
John in rain stormy Suffolk County England .
John in rain stormy Suffolk County England .
nkaminar
Well-known member
Each car is different with regards to the GAV. It is unlikely that you have done any harm by running the car for 100 miles with the GAV closed. As rotorwrench said, opening it a little may improve performance. The position of the GAV will depending on circumstances, whether you are climbing a mountain or cruising on the flats.
Turning the engine over with the hand crank is an easy way to assess the compression. Each cylinder is a 180 degrees turn of the crank. All 4 cylinders will be felt in two complete turns of the crankshaft (720 degrees). If you are getting variations in each 180 degree pull that would indicate that the cylinders that are easier to pull have less compression. I really good engine will not leak compression and the engine will pop over top dead center.
Low compression can come from various sources. The rings could be leaking, the valves could be leaking, or the head gasket could be leaking. Squirting oil in the cylinders and trying again, as rotorwrench suggested, will indicate if the rings are leaking. If the compression improves then the rings are leaking. You can sometimes hear a leaky valve by listening to the intake or exhaust manifold for a hiss. You have to take the exhaust pipe off to listen at the exhaust manifold and you have to open the throttle to listen at the intake manifold.
Turning the engine over with the hand crank is an easy way to assess the compression. Each cylinder is a 180 degrees turn of the crank. All 4 cylinders will be felt in two complete turns of the crankshaft (720 degrees). If you are getting variations in each 180 degree pull that would indicate that the cylinders that are easier to pull have less compression. I really good engine will not leak compression and the engine will pop over top dead center.
Low compression can come from various sources. The rings could be leaking, the valves could be leaking, or the head gasket could be leaking. Squirting oil in the cylinders and trying again, as rotorwrench suggested, will indicate if the rings are leaking. If the compression improves then the rings are leaking. You can sometimes hear a leaky valve by listening to the intake or exhaust manifold for a hiss. You have to take the exhaust pipe off to listen at the exhaust manifold and you have to open the throttle to listen at the intake manifold.
