Valve spring changing question
Thread Starter
Instructor
Joined: Mar 2003
Posts: 176
Likes: 0
From: Holtsville NY
Valve spring changing question
I am about to swap out my stock LT1 valve springs for LT4 valve springs. I have 2 questions first what is coil bind on the LT4 springs? And second when using the air tool (screws into spark plug hole and puts compressed air into cylinder) how much pressure should I use? Thanks for any info.
Chris
Chris
Le Mans Master
Joined: Jan 2002
Posts: 9,036
Likes: 13
From: Edmonton AB
I don't have a value for the coil bind question but I'd say that air pressure
in the cylinder can be whatever you typically run for the shop. It has
been awhile but I believe I set the regulator at 80-100 psi for this job.
Note that you'll want to have the piston at TDC for each cylinder as you
work on it. Make sure the car is not in gear and that nothing is in the
way of the accessory drive at the front of the engine - applying air
could cause the crank to rotate.
.
in the cylinder can be whatever you typically run for the shop. It has
been awhile but I believe I set the regulator at 80-100 psi for this job.
Note that you'll want to have the piston at TDC for each cylinder as you
work on it. Make sure the car is not in gear and that nothing is in the
way of the accessory drive at the front of the engine - applying air
could cause the crank to rotate.
.
Large Impressive Member
Joined: Jul 2003
Posts: 65,811
Likes: 71
From: Good health is merely the slowest possible rate at which one can die
St. Jude Donor '04-'05-'06-'07
Normal shop air pressure will be fine. What cam are you using? The Hotcam w/ 1.6 rockers pretty well pushes the limits of the LT4 spring for serious performance use. If you're using the stock cam w/ 1.6 rockers, you'll be fine.
Advanced
Joined: Mar 2001
Posts: 89
Likes: 1
From: ca
I agree with having the Piston at TDC on each cylinder as you go. Just follow the firing order and turn the crank 90 degrees each time.
80-100 psi is a no-no unless you want to see that engine spin. Unexpectedly and very quickly.
Try 10 psi. If you bump the stem and loose the seal, it will just drop down onto the piston. Pull the stem back up and re-establish the valve-to-seat seal and continue.
80-100 psi is a no-no unless you want to see that engine spin. Unexpectedly and very quickly.
Try 10 psi. If you bump the stem and loose the seal, it will just drop down onto the piston. Pull the stem back up and re-establish the valve-to-seat seal and continue.
Le Mans Master
Joined: Jan 2002
Posts: 9,036
Likes: 13
From: Edmonton AB
Originally Posted by RichardJ
Try 10 psi. If you bump the stem and loose the seal, it will just drop
down onto the piston. Pull the stem back up and re-establish the
valve-to-seat seal and continue.
down onto the piston. Pull the stem back up and re-establish the
valve-to-seat seal and continue.
The first time I put air on a cylinder, it was at shop pressure and the
piston was not at TDC. You know what happened. After I changed my
shorts, I dropped the inspection pan and made a fixture that engaged
the teeth of the starter ring gear in order to hold the crank in place.
Never had the problem again. Yes, this would take longer.
When I've mentioned the practice of using the fixture before, people
universally say they've never locked the crank and they've never had
a problem. They typically say they use more than 10 psi. In my mind
it would be a bad deal to have the misfortune of the crank rotating at
the same time as losing seal on a valve but I don't know what the
odds of this happening might be.
I like the low pressure approach RichardJ suggests and might try it
some time.
.
Thread Starter
Instructor
Joined: Mar 2003
Posts: 176
Likes: 0
From: Holtsville NY
Just thinking out loud. If you removed all the rockers and left in all the spark plugs except the one cylinder you were working on (at TDC) wouldn't the compression keep the motor from turing?
Could the LT4 springs hold a cam with gross valve lift of .528 ??
Could the LT4 springs hold a cam with gross valve lift of .528 ??
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