This probably won't be of any use to the majority of you but here's how you troubleshoot it:
First, the only way that I know of to reliably check the rings and valves is to do a leakdown test on a WARM engine if possible.
A leakdown test is similar to, but different from a compression
test. It uses compressed air from an air compressor
or it could be from an air tank--It doesn't make any difference.
The leakdown apparatus consists of the leakdown gauge assembly and an adapter to fit your engine (it replaces each fuel
injector one at a time).
Now you EITHER need to find someone with both a leakdown tester AND an adapter to fit into your particular fuel
, OR you can build your own with parts
from McMaster-Carr Industrial Supply (my best friend!).
The leakdown adapter: I found somebody on the internet
a year or so ago who sold the adapters for my particular engine (4.107) but they were expensive and I'm cheap
so I made my own. I machined my adapter to have the same lower dimensions as my fuel injectors. Any machine shop competent or not can do this if you don't have access to a metal lathe. I put a quick disconnect (like the ones used for disconnecting air tools) onto the upper end of the adapter.
The leakdown gauge assembly: is easily fabricated using parts
from McMaster-Carr as mentioned above. Instructions for making one are on YouTube. I did it and it's very easy.
Or you can just buy one...but like I said, I'm cheap
So the leakdown adapter gets installed in place of one fuel injector (say #1). Leave all the other injectors in place so that the engine won't turn over from the air pressure. Use a new or annealed copper sealing washer. Directions for annealing copper washers is available on the internet
. Very easy to do with one of those Burnz-O-Matic yellow MAP torches.
Next, rotate the crankshaft until the #1 piston is at Top Dead Center on the compression
stroke (intake and exhaust
valves both closed). If you don't already know how to do this you just remove the rocker cover and rotate the crankshaft until both #1 rocker arms are loose.
Next, you hook the leakdown gauge assembly up to the air source (the compressor
or the tank) and adjust the knob on the gauge assembly until the gauge reads 100psi. You obviously need to have more than 100psi in the tank or available from the compressor in order to get 100psi at the gauge (more on this below).
the leakdown gauge assembly onto the installed leakdown adapter. Any leakage past the rings or valves will result in a something less than 100psi reading on the gauge. The reading will be directly proportional to the leakage, but won't by itself tell you what's leaking. That's where the magic is... (below).
By the way, there is nothing magical about 100psi. If you can only get say 90, then go with it. 100psi is used so that people can talk about things like "5 percent leakdown" which is 100psi at the gauge when it is un-plugged from the adapter and 95psi when plugged in. If you can only get 90psi at the gauge then if you get 85psi on the gauge when plugged in you've got 5.5 percent leakdown (90-85 = 5; 5/90 = 5.5%).
But don't use 20psi or something. You want the air pressure to really push against the valves and the rings.
Now for the "magic" part: Take a McDonald's soda straw--no other brand will do (just kidding), put one end to your ear and the other end into the dipstick hole. If air is leaking past the rings you will be able to hear it--it will be obvious.
Then do the same thing for the #1 intake and exhaust ports
. If either or both are leaking you will be able to hear it.
The louder the noise
the more leakage.
After you're done with #1 AND YOU'VE WRITTEN EVERYTHING DOWN rotate the crankshaft 180 degrees, reinstall the #1 injector, install the adapter in the #3 port (for a four cylinder). Our imaginary engine here fires 1,3,4,2. Other engines may have different firing orders...
Repeat the process for #3, then go on to #s 4 and 2.
And FWIW, you can also diagnose inter-cylinder head gasket
failures by listening in the intake and exhaust ports of adjacent cylinders. Obviously no air should be intruding into the adjacent cylinder ports.
Easy as pie!
Ps: You can also do this with a cylinder head
that is not installed on an engine to check valve sealing BEFORE installing it on the engine. You just need to make a plate with an o-ring seal that will fit around the combustion chamber and drill four holes in the plate to match the head bolt holes for that cylinder. I NEVER rely on the isopropyl alcohol or water leakage test to tell me how good my valve job is...
Jeez, I wrote a freakin' book...
Valiant 40 #163