I had just rebuilt (with help) my 427 in May and had run into oil leaking problems in the oil pan, I changed the gaskets twice with no luck. Now I’m being told that I am experiencing blow by in some cylinders due to some top rings installed upside down and that I would need to do a “Leak down test” does this sound right? Can I do this? And How?

 

Any help would be appreciated.

 

Thanks

IF the rings are in upside down it can cause the problem.   A leak down tester is a dual gauge (in most cases) pressure measurement.  You turn the cylinder to top dead center on the compression stroke.  Then connect air to the leak down tester.  Zero the gauge at 100%.  Now shut off the air, and connect the tester hose to the spark plug hole, and reconnect the air.  You will get a reading of somewhere less than 100%.  If it is over 90% all is great.  90 to 80 is good.  80 to 70 is okay, but worthy of a closer look, maybe.  Below 70% is a definate problem that needs attention.

While the tester is still connected and has air pressure check for leaking air from the engine.  If air is leaking from the intake, the intake valve is leaking.  From the exhaust the exhaust valve is leaking.  From the crankcase the rings are leaking.

If the engine is not at top dead center when you apply air pressure, the engine will turn.   So be carefull.

But you can also check for excess blowby by removing the oil fill cap and running the engine at different speeds.  Hold you hand over the fill cap areas and get a tight seal.  If you feel pressure after running for a minute or so, you have too much blowby and need to do the leakdown check.  If you find a slight vacuum, all is good and forget the leakdown test.  If vacuum is not present, and you have pressure, that will cause leaks.  With vacuum, there is another reason the gaskets leak.  It could be intallation procedures, or a warped pan, or dirty or uneven sealing surfaces.

Thanks Ken

 you da man

Ken two questions:

1, where can I get a dual gage (can I rent one?)

2, Do I leave it at TDC to check all cylinders?

[QUOTE=RHeyboer]

Ken two questions:

1, where can I get a dual gage (can I rent one?)

2, Do I leave it at TDC to check all cylinders?

[/QUOTE]

2   you must take each cylinder to its TDC.. 

Ken, I have completed the leak down test and all cylinders check over 90%. Is it possible that the cam I have instaled (EDL-5062 Cam and Lifters, Hydraulic Flat Tappet, Advertised Duration 302/304, Lift .527/.553, Chevy, Big Block, Kit from Summit) has next to no vacuum until 2000 rpm thus unable to relieve the pressure???? this might also explain why my wiper door stays open until about 2000 rpm.

Do I install a second PCV?

Do I need a second source for the vacuum?

Please anyone chime in as I 'm so frustrated over this issue.

 

 

[QUOTE=RHeyboer]

Ken, I have completed the leak down test and all cylinders check over 90%. Is it possible that the cam I have instaled (EDL-5062 Cam and Lifters, Hydraulic Flat Tappet, Advertised Duration 302/304, Lift .527/.553, Chevy, Big Block, Kit from Summit) has next to no vacuum until 2000 rpm thus unable to relieve the pressure???? this might also explain why my wiper door stays open until about 2000 rpm.

Do I install a second PCV?

Do I need a second source for the vacuum?

Please anyone chime in as I 'm so frustrated over this issue.

[/QUOTE]

you only install one PCV..  and have to have a breater on the other side..

to run your vacuum accessories you should get an electric pump.. and take them off engine vacuum with that cam.

Ken and others;

Not to horn in on RHeyboer's thread however, I'm about to build up this 350 for my 80.  How do I ensure I don't get the rings upside down.  It has been about 27 years since I pulled one down and rebuilt it and I don't want to make any more mistakes than I absolutely have to.

Are the rings marked in some fashion?

DNV, the top ring is marked.

cthulhu, I do have breather on one side and a PVC on the other but cannot stop this thing from leaking.

With a 90% on a leak down test, the rings are not the problem. 

Check the breather that is the air INLET to the crank case.   If the inlet is not up to snuff, the PCV can't do it's job.  Make sure the PCV is the correct one.  It may look right, but not have enough flow.

High crankcase pressure is not affected by or will it affect engine vacuum.  The engine vacuum is a result of the cam, and a electric pump would help that issue, but it will not affect crank case pressure.

Or the other possibility is the crank pressure is okay, and there is another reason for blowing the gasket.  The pan could be warped, or the gasket not up to snuff. or installed correctly.  You might want to try one of the FelPro gaskets that have a steel center that prevents it from blowing out.