BrickBoard Archives
The files contained in this listing have been automatically archived from the active forums. Because the vast majority of posts are now in one place, this archive is considered legacy. You should use the SEARCH feature OR choose your topic and select date tabs within the forum you choose.
Re: Put compressed air to cylinder thru plug[240-260/1980] posted by Randy on
Friday, 29 May 1998, at 4:26 p.m.
>Thanks JohnB, will break out the compressor. Sounds like a good bit of >diagnostics.
My limited experience in this area has taught me two things:
1. You want the piston to be at TDC with both valves seated when you pressurize the cylinder. That's easy to do on #1 by using the timing mark on the vibration damper- not so easy to do on the other three cylinders unless you have a bright light (to observe the top of the piston) and a helper to rotate the crank while you watch the piston.
2. When you pressurize the cylinder the compressed air will act like the expanding gases associated with combustion and will cause the piston to be forced down the cylinder with a lot of force. You would be surprised just how much force with only 100 psi . Figure out a way to LOCK the engine at TDC for each cylinder (Flywheel?) Don't attempt to hold it there with a breaker bar and socket on the crankshaft/vibration damper.
3. Depending how much wear is in the cylinders you may find it hard to get the cylinder to hold pressure for even a short period of time at TDC. Just a little before or after TDC with the valves still closed ( 15-20 degrees either side of TDC- observe the cam lobes to see if the valves are still closed) will have a greater tendency to pressurize the cylinder and allow you to judge the leak down rate of the valves. Rings have a difficult time sealing at TDC in high mileage engines.
Again these are my experiences and yours may differ (but trust me on not attempting to hold the crank in a casual way!)