guys do i need to turn down the pressure on my compressor to stop the engine from turning over while doing a valve stem seal swap?

my compressor is at 110psi and when i put it into my engine the breaker bar flung over and almost gave me a new set of stitches in my forehead. lol.

i have the plugs out. took them out because didn't want to be reefing on the 5/8's crank bolt. i assume that makes less resistance to turning over.

turn compressor down or what? 20psi? 40psi?

put plugs back in?

 

I did mine at 60psi and only had a little movement on the breaker bar. I also took all the plugs out, not a bad job just time consuming.

Good luck

 

I say we take up a collection for a helmet for VT

 

Somthings wrong.. Once the cylinder is filled w/air the piston shoud'nt budge. I did mine w/100psi

 

i thought the same thing. i just disconnected the air and dislodged the breaker bar. you are saying that once the piston is pushed DOWN then it cant fill it up any more.

and i think u r right. however i read that you WANT the piston at top dead center-ish so if you lose air, the valves will land on the piston and not fall in.

but i was thinking of just doing what it sounds like u did. just fill it up and keep it pressurized. am i right in how u did it?

 

My compressor was between 90 and 120 psi when I changed mine. I would turn the engine by had (all plugs out) until the cylinder I was working on had both valves closed and then attach the hose to the fitting I was using. Never had a issue with the engine rotating. This was on my 85 L98.

 

Put the breaker bar back in the tool box, and let the pistons drop to BDC when you feed in the compressed air. It won't hurt anything, so long as you keep hands, tools, air hose, drop lights, etc, clear of the belts and pulleys while you're working.

Live well,

SJW

 

thanks this seems real simple.

 

mhaha thnx Ant.

the wrench was only one stitch. in and out with no freezing. less than 20 min. i was impressed.

its sssssooooooo important for noobs like me to be overly cautious. im now at the stage where i have 4 ramps for each wheel and then 4 jack stands. even though my three girls think im thor and can lift a house, just cant be too cautious.

so a wrench in the head i can live with, even though i SHOULD NOT have been reefing on that flywheel bolt with the old wrench on a wrench methid pulling straight towards my face.

 

With a manual trans you can put it in a taller gear and set the ebrake, with and auto I'd use the rope trick, feed nylon rope into the cylinder and slowly turn the engine over till it squishes up into the chamber then your good to go.

 

I've done the job a couple of times - and used 90 - 100 psi, and not needed medical attention afterwards.

If the piston is at Top Dead Center or Bottom Dead Center, the connecting rod is perfectly vertical, & the crank pin is directly under the rod - so air pressure won't turn the crank... But if you're even a little bit off the crank will move. BUT - If you chose to have the piston at TDC - the crank will spin 180 degrees or so - if you do the job with the piston at BDC - the crank can only rotate a couple of degrees.

The service manual tells you to do the job at TDC because the valve can't fall far enough to come out of the guide at TDC. That is not true at BDC - the valve can fall out (which means that the head has to come off to get the valve back). But if you have the air pressure to hold the valve closed - that shouldn't be a problem.

I do NOT believe 20 - 40 psi will be enough pressure to do this job. You need to have enough upward force on the valve to allow the spring compressor to break the retainer free of the valve keepers and to counteract any side load that's applied to the valve stem while compressing the spring. If you put 20 psi in the cylinder - that would only equate to about 35 lbs of force holding the exhaust valve in place, and I don't think that's enough to allow the keepers to separate from the retainer.

BTW - if the engine has a lot of mileage on it - this is a wonderful time to replace the valve springs....

 

I HIGHLY recommend using as much PSI as you can. If you drop a valve, well your pulling the head. The lever type valve spring compressors that attach to the rocker stud work well for this. Get a magnetic tool and tray for the keepers. Patience is key to this job. Slow is fast.

 

When I do them I never follow the piston at TDC rule. Because the air always forces it down anyway. I've never had a valve drop. I would recommend removing the rocker arms and then applying air to the cylinder. It will push the piston to BDC and the valves will be closed. Then you can proceed to take them apart. Just don't drop a valve. You want as much PSI as possible.

 

this is exactly what i found.

i did the first one with the piston at tdc. tried the "rope method". garbage.

put my pressure in at 80psi, the crank rotated and away i went.

 

try the old indian rope trick. much safer

 

What was safer for me was to start at #1 TDC where the piston is at max height. Regardless of what you did, the valves would not fall far. Next do 8, 4, 3, 6, 5, 7 and 2. Valves closed for easy adjustment and valve cannot fall far.

I was afraid that if I had rope around me and someone came along with their suggestions on how to do it when things are not going well, I might take the rope, tie a knot in the middle and strangle them with it. No rope, no temptations.