View Full Version : Leak Down Test on SBC

01-29-2021, 10:55 AM

I am in the middle of doing a leak down test on a SBC 383. I have the engine out of the car on a four post engine stand. So I had to remove the flywheel to get it to fit on the stand. I found TDC using the hose balloon trick as I don't have a piston stop tool.

Nevertheless, I've tested #1 pretty easily. Now, I'm trying to test the others and can not keep the crank from turning. I had a large ratchet on the front to turn the crank and hold in place. When I turn up the pressure I can see the crank slip (via h. balancer) even though the ratchet didn't move. I switched to a breaker bar and get the same results. I've tried to use a pry bar on the rear by holding it between the flywheel bolts with moderate results.

How can I keep the crank from moving?
Have I messed up the timing gear or something else if the crank moved without breaker bar moving or am I just loosening the crank bolt?


01-29-2021, 02:10 PM
If you put the other plugs back in, then at least the next cylinder that's coming up on its compression stroke (with it's valves closed) will have some resistance coming up to TDC, which should provide some additional reaction force against the cylinder you're pressurizing (which you should bring to TDC when you test it).

02-01-2021, 07:20 PM
Are you just putting a wrench on the balancer/crank bolt?

I would try fabbing up a ~2 foot long piece of scrap metal and bolting it to the rear crank flange using two bolts. Good leverage, cheap and easy to fabricate