need 46 cadillac valve informatin

[Dave T]

I had a light miss in my 1946 Cadillac when accelerating that would eventually smooth out at a higher r.p.m.' Also could hear a hollow type sound when decelerating that would smooth out after about about 10 seconds so after checking out the normal compression and ignition test to no avail I decided to remove the cylinder and check out the valves. to my surprise there were no burnt valves. I removed the valves, inspected the valve seats; cleaned and hand lapped the valves. After lapping the valve seats  and valve face   the valves  showed a nice even gray marking that seemed to be in the middle of the valve face and the valve seemed to seat nicely At this point I decided to  assemble the cylinder heads and check the cylinders with air before completing to assemble. I put up to 100 lbs. of air into the spark plug holes to check for leakage. My question is should the valves leak ANY AIR AT ALL  into the valve chambers and if so how much air should escape? it seem like a little more air leaks out of the intake chamber the the exhaust if I put the palm of my hand over the intake port i can feel and hear a small amount of leakage Is this normal to have any leakage and if so how much leakage would be acceptable . any suggestions would be very much appreciated so that I can complete my assembly
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                                  thanks Dave T  CLC 22554

[Doug Houston]

What you have done is not a real meaningful compression test. As thoroughly as you have been, the engine nneeds to be run for a while, to give the valves a chance to seat. Foloowing that, you can get the engine warmed up, remove all plugs, and make the test with a regular compression tester.

As you now have it, the engine should run smooth as silk, but if you still want to check compression, compressed air into the cylinder isn't the way to do it.

[homeonprunehill]

03-10-09
DAVE, After going to the work that you have, I would start it up and drive it like a sweating mule. Then if you want to do a compression test, do so after you have done a tune-up. HTH,Good Luck,Jim

[Dave T]

Thanks guys for the input I did do a normal compression test all cylnders had equal amount of 95 lbs. dry. I forgot to send the photos of the valve and valve seat.
                                                    Dave T CLC 22554

[Dave T]

Sorryy the valve didn't go through

[Paul Ayres #5640]

Dave - I can't ell too much from the photos, but per our phone conversation today, if your valve guides are worn to the extent you mention, you cannot rely on the job you did to get good valve seating, hence the leakage you experience.  Per Doug's comments, you can verify this by doing a cylinder leakdown test ( at least on the side where you have re-installed the head.)  It will undoubtedly show the same leakage you got with the air pressure.  As long as you have the engine this far torn down, I suggest you go all the way and pull it out and do a complete overhaul.  Look at the valve margins, as we talked about, as the guide to whether you will need to buy new valves (which I would suggest in any case, as they are not expensive.)  Paul Ayres

[John Washburn CLC 1067 Sadly deceased.]

Dave,

What I think the original question was concerning the "leak down test", this is when one fills the cylinder, one at at time, with air. Then measures the air leakage.

A special meter is required and it is not an easy test, but is good for what you might think is your trouble.

Find someone with an old SUN Machine, knowledge, and skill to do the test. Works really well.

Good Luck

John W.

[Dave T]

Need some help please from the flathead experts. I have finally isolated the miss in my 1946 Cadillac to number four cylinder. I have tried everything that I can think of to correct the miss, This is what I have done since reassembling the motor all cylinders have equal compression at 100 lbs.leak down test is normal, vacuum gauge reads 20 in. with about 1 in. fluctuation when engine is idling and seems to correlate with the miss. If I remove number four spark plug wire I get a very good arch but the motor does not acknowledge and there is no change in rpms There is no difference in the way the motor runs when I pull number four plug wire Need some suggestions please
                                                                                 
                                                     Dave T CL 22554

[Bill Ingler #7799]

Hi Dave: This might be completely off the wall but have you considered you might have some induction firing, some call it ghost firing between cylinders. As you know induction firing can happen when long plug wires are running parallel and close to one another causing the spark energy from one cable to induce a current in the other which in turn causes two cylinders to fire at the same time. Try switching the position of plug wire 4 with plug wire 6 in the wire loom holder. Do the same thing with 3 & 7 on the other side.  Just a thought. Here is a good article on induction firing.

http://www.jasperengines.com/pdf/SparkPlugCross-FireTB.pdf

[Jeff Hansen]

Dave,

Here is one I can speak to from experience as I just corrected this problem on my '42 last month.  The exact same symptoms you mention I had in cylinder six.  The problem I found is that the upper spring seat was missing on the exhaust valve.  A quick way to test for this is with the valves and springs assembled in the block and the lifters out, try to push up HARD on the valve stem to open each valve in your bad cylinder.  If you can open either valve with finger pressure, that seat is missing and you have likely found your problem.  Attached is an article written by Doug Houston regarding these spring seats and what can happen when 14 of them are missing.

Keep us posted.

Jeff