compressed air method to change seals

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like_A_pike

that's not factory
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quick clarification question; Do I have to hand crank each piston to TDC before pressurizing the cylinder I'm working on? thanks in advance
 
I have done it becore with a length of thin rope. Put the piston down in the bore. Feed the rope in through the spark plug hole (tie the loose end onto something so it doesnt all drop in......) and then turn the crank so the piston comes up and the rope pushes onto the valves. You can now safely remove the valve keepers and springs.
 
If you brought it up to TDC, when you put the air to it it would move the piston back down. The best way is the rope in the hole like Dave said to do it that way if for some reason you lose air pressure when the keepers are off, you wont drop a valve.
 
I have used air pressure many, many times. It is ideal to have piston at TDC in case you somehow knock the valve hard enough to break air seal, so valve won't drop. Not always possible to keep piston at TDC, like another member stated, but if you leave all other plugs in, and can regulate the line pressure, I've found you can do it. Don't really think you would have an issue with sudden air pressure loss. Much easier and quicker method.
 
Since the rocker shafts are off....all the valves are closed...as said...just leave all the other spark plugs in and the engine will not move went you hit the cylinder air
 
TDC for each, leave other spark plugs in as you go. Enough regulated air pressure to hold the valve up, and a way to lock the engine to prevent the air pressure from forcing the piston down helps big time
 
I have changed many valve springs with compressed air. I have never worried about tdc. I have unseated the valve seat on accident but it immediately reseated itself when I took pressure off the spring.
 
What I am beginning to understand is that the spring will close the valve when I take the rocker off. So when I apply the air pressure, I may compress each spring, remove the keepers, and the valve stays put. If the 90 psi is enough to push the piston then does it matter if it's actually at its highest point or not, just as long as whatever space in there is maintained at pressure? Along with leaving the other spark plugs in, do folks brace the crankshaft to stop any rotation that would allow air to escape? Do you think a 10gal compressor that can maintain 5cfm at 90 psi work for this?
 
I'd just give it a go, hold off on pulling valve covers, pull a plug on a cylinder at tdc, apply the air and see if it stays put or pushes it down. You'll also hear the air blowing past the rings to whatever extent. 10 gallon tank I'd think would do fine. I once used a small nail gun compressor and it worked, but with the blowby and such it ran continuously.
 
Pressure is pressure regardless of volume so not being at TDC should be fine. As mentioned, being at TDC just adds a safety factor that the valve does not drop. I use the rope method, due to the fact that sometimes you have to tap the retainers pretty hard to break the keepers looses, and no way the valve is not going to move when you do.

I dunno what harm it does if the crank moves..... there is no propeller attached to it.
 
rope. so much easier and no fittings to worry about. also use a magnet to fish the keepers out with, very easy compared to needle nose pliers.
 
hi, it can be done without air or rope. run piston to #1 tdc, remove springs, valve will drop 3/16 of an inch. piston stops it. also, can change # 6 same time. rotate 90 deg, do # 8 & # 5, rotate to #4, can do # 7 also. rotate # 3 can do #2 same time. I've changed valve springs this way many times. when you're at the races, you don't have air. # 1&6 , #8& 5, #4&7, #3&2. simple.
 
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