Checking boost system for leak?

I do agree that heat and speed will self destruct the turbo, and many times you can windmill them without any (noticeable) damage. But its the last time you let it windmill that will get you.

Because the turbines are optimized to spin at the hint of exhaust expansion, at nearly frictionless conditions, at speeds over 100,000 RPM, with tolerances of less than 0.002, spinning within a soft brass bushing set... its not a bet I'd be willing to take on someone else’s truck I gave advice for.

 

If I understand correctly, you will be back feeding the turbo (forcing air into the boost side)? <--Yes that will spin the turbo backwards. And you also will not have any back pressure to test for your leak.
Put a cap on the air cleaner inlet side of the turbo and you might find what your looking for.

 

With what northern mech said. I agree, to test the rest of system real simple. Before you unhook any tubing just start truck and idle at or above 1500 rpm. Then squirt windex or soapy water on all conection and look for bubbles. You will only make about 1 or 2 lbs of boost but it is enough to see a leak.

 

Valve overlap, allows the air through intake valve to exit the exhaust valve. Your theory is true in a single cylinder engine, the piston will rest at the bottom of its power stroke when turned off. But all opposed engines no matter 2,4,6, or 8 cylinders will have a single piston resting near TDC of its exhaust stroke, thus you get valve overlap.

I truly, don't know what kind of RPM's a turbo will spin, off a single cylinder @ 30psi?, but I figure better safe than sorry.

 

If your talking about the elbow that has two bolts with two pc of flat metal, there is two o-rings in there. Just pry the elbow out and replace. Word of advise spray wd-40 in there to lube the o-rings so it slides out a little easier. Dont beat on it with a hammer, just be paitient.

 

It will (wiggle) that is normal. doesn't mean they are leaking. Those o-rings that go in there are purty robust.