Double Checking on My 1940 56S

[Daves1940Buick56S]

In prep for my upcoming trip next week (see here:

) I am going over the car with a fine toothed comb. I noticed a small periodic dip in the vacuum at idle, not much (an inch or less) but it wasn't there before. As part of the process I did a compression test. I haven't done one in about 3 years. As a reminder, the rings and valves were redone in 2014.

 

Compression test results. Starting at #1 going back: 110 105 100 80 100 105 105 110  Notice the dip in #4. I shot some oil in there and it came up to 100. So maybe rings not broken in properly, or my careful ring clocking got declocked somehow, or something more serious? I did a cylinder balance test at idle, and sure enough, all of the others dropped about 50 RPM while #4 only dropped 20 to 25 RPM. I could not specifically tie in #4 to the slight vacuum dip, however. May be 2 different issues.

 

Double checked ignition - spark voltage is the same across 3, 4, and 5. Swapped out the #4 spark plug - no change. Plugs all looked normal including #4. One interesting thing - if I do the balance test at 1000 RPM, the drops are all the same, #4 is good. So it appears it is what it is for the time being.

 

Since I am planning on taking a trip of about 750 miles total, does anyone see any problems in going ahead with this? 20 lb drop in compression is a significant but not huge amount. And the tailpipe sounds clear, no apparent missing. My plan is to monitor, paying attention to vacuum as usual, and maybe doing a quick compression on #4 at about the trip halfway point. I don't see me risking any catastrophic damage by doing this at this point. We all know these engines are very tough.

 

Anyone disagree with my approach? Comments? You can follow me on the trip at the link above to see what happens!

 

Cheers, Dave

[Matt Harwood]

I think you'll be fine--that car will run on 5 cylinders. A long drive might even be good for it if you're thinking your rings might need to be seated. A varied drive over long distances can be good for things like that. I wouldn't worry too much--it's not going to fail in that area.

[edinmass]

I agree........drive it and check it again when you get home. Could be a tight valve. I bet it will be fine.

[Ben Bruce aka First Born]

I believe I would check the valve [ tappet?] adjustment on that cylinder. Can't hurt and will only take a few minutes.

 

  Ben

 

[Daves1940Buick56S]

All:

 

Thanks for the encouragement. I did check all of the valves just last week. Only 1 a bit loose, number 6 intake I think. I tend to leave mine a tiny bit on the loose side as I would rather put up with a small bit of noise rather than risk burning a valve.

 

As far as this being a valve issue, I did do the oil test and compression test which was fine at 100 lbs on #4 so I am thinking more along the rings side.

 

Although I should add that there has been a double tap noise that has been there for a while. I did a post on this last winter I think. It sounds like the tap is coming from down lower in the engine but sounds going through metal can fool you as to location. I did do a remove-spark-cable test on all cyls and the tap did not go away so I don't think it's from a connecting rod. Also the tap seems to be on cam rpm rather than crank.

 

I have a setup where I can detect noise using a vibration to sound transducer and, using an amp and noise cancelling headphones, can really pick out noises in the block. I tried that on the tap but still could not isolate. It sounded a bit like in the cylinder 3 area. Perhaps a dragging lifter. Anyhow, more troubleshooting will have to wait until I get back. I hope that sound I hear isn't whistling past the graveyard!

 

Cheers, Dave

[jenz38]

You have solid (more noises,like mine )or hydr. Lifters ?..(may be a single hyd.Lifter stuck a little).

I would say ,check the valve clearance,

Check for that the Oil pressure is good like always..

Check for no oil smelling (consumption) out of the Exhaust and the for the

Cooling system is ok..,

make a fresh Oil change before you start and then I would go.

So often I see bad running old engines,because of so much cold starts and short distance runs  with low temperature and low Revs.

That's not healthy for old style Carburetor Engines.

They start to build oil crust everywhere  in the Valve seat and Piston area.

They run much better after a long distance run at good operating temperature because of it burned all the crust off.

 

[kingrudy]

Hello Dave,

 

If you have the Carter 474 carb on your Super, I would sure like to see the vacuum line install off of the intake/exhaust manifolds.

 

Thanks,

Mike 

[Daves1940Buick56S]

Actually I have a Carter WCD 663S. My install of the vacuum lines isn't stock so may not help you much. I will see what I can do while on the trip.

 

Cheers, Dave

[Robert Engle]

The tapping noise you hear may be your fuel pump as it cycles at camshaft speed.

 

Bob Engle