I have a 408 stroker built by a shop in California with Frankenstein Heads, BTR Stage III stroker cam, Fast 102mm intake, Holley drive accessorie setup, 24x reluctor, 411 ECM, all the nice goodies. I've been putting this thing together for about 2 years now and finally got it to where i could fire it up.... or at least I thought so.This is my first time dealing with LS motors and I thought I did everything by the book. Well when I went to start it up all I get is spinning. Did a compression test on it today and there isn't any compression in any of the cylinders. Has anyone ever heard of this or had this problem???? LOST AND CONFUSED!!!😣😢

 

Just curious! How exactly did you do the compression test?

 

Pulled plugs, disconnected ignition and used compression tester for each cylinder.

 

The rocker arms weren't backed off were they? I know some builders that back the rockers off to save the valve springs if the engine isn't going to be used right away.

 

No they weren't. When i blow air into the spark plug holes, air just flows thru. Could this be that the valves are stuck open due to pushrods being too long?

 

Push rods too long would be my guess . It will just spin with no resistance from compression . Hopefully the valves did not touch the piston . If the cam is not to aggressive you are most likely ok . Get a push rod checker and get the proper length .

 

When you blow air into the spark plug hole? How exactly did you check compression? you should have

Disable the ignition system.
Disable the fuel injection system.
Remove all the spark plugs.
Block the throttle plate wide open.
Start with the compression gage at zero, and crank the engine through 4 compression strokes, 4 puffs.
Make the compression check for each cylinder. Record the reading.

If you were blowing air into the cylinder at TDC compression stroke just to see if air was escaping and the air was just blowing out, can you hear it in the crank case, or coming out of the intake manifold or exhaust? Did you check pushrod length before assembly?

 

Sound like the valves aren't closing. I did this once tightening rockers down(sbc) to far and all my valves were hung open. Loosen rockers on one cylinder so your valves are closed and then put the air on that cylinder and see if it holds air.

 

I used pushrod checker and got the same number over and over. I can hear air coming from the crank. I may have tightened pushrod too tight.... hopefully... I will try loosening them over the weekend.

 

You hear air coming from the crank? You mean out the oil filler with the cap removed, for example?

I'd think that when you are introducing (compressed?) air into the spark plug hole, it can escape in 1 of 3 ways:
- intake valve (hear air coming through throttle body)
- exhaust valve (hear air coming out exhaust)
- cylinder (hear are coming out of crankcase/oil filler tube with cap removed)

If you're sure it's the 3rd one above, and it's freely flowing past, what could cause that? Do you still have your new piston rings on your workbench?

 

Loosen or remove the rockers and then try. Let's eliminate one thing at a time.

 

Did you install the rocker stand in between the rockers and head...?

 

Rocker stand installed and air sounds as if it is coming from bottom of motor, The Crank. I will be loosening rockers tomorrow.

 

Your hearing air? Are you performing a leak down test or compression test?

Compression test:

Step 1: Disconnect fuel pump relay and ignition coils and remove all spark plugs.

Step 2: Install compression tester into a spark plug hole and make sure you have it in tight enough to get an accurate reading.

Step 3: Using your keys or a remote starter turn the engine over 5-7 times and watch as the needle climbs. Record the reading of each cylinder. Once you have stopped cranking the engine over the needle will start to drop as the pressure in the cylinder will leak down passing through the rings and the valves that are opened which is normal.

 

Is this the tool your working with?

 

My guess is you are running a healthy cam with a fair amount of overlap and when you send compressed air into the cylinder your pushing the piston down into the bottom of the cylinder and the air your hearing is the air blowing past the rings. On a leak down I would bring the piston to TDC on its compression stroke. Then loosen the rocker arms on that cylinder your testing and take all the pressure of the valve springs. Take your leak down tester and hook it to your air supply and bring in about 100 psi. Open your valve on your leak down tester and transfer the air into that cylinder and then read your second gauge to see how much leak down your getting past the rings. Don't be alarmed if the air pushes the piston down into the cylinder you should still get to see how much leak down your getting. A new motor should be 3-5 percent with 10 being the maximum leak down.

This is a leak down tester! There are you tube videos out there that will show you how to make one fairly cheap.

 

yes that's the tool I'm using for compression test

 

Thats exactly what I did for compression test and had 0 compression for all 8 cylinders

 

That just dose not make any sense to me. Either the gauge is defective or the bleed off button is not working properly and hung open. If you screw the end of the line into the spark plug hole and tie a balloon to the other end of the line when you turn the motor over by hand it should start to blow the balloon up when your coming up on the compression stroke.

 

Thats what i thought but 0 compression. From what I'm hearing it sounds as if the valves are staying open.