So whoever set up the valvetrain over tightened the rockers. I take it it is a Hyd. Roller? So now you have to adjust all your rockers. That is a free fix and the finding of a lot of lost power. Won't you be a happy camper when all is said and done!!!! Good luck.
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I believe the stock rocker arms are torque down and go. At least they were on my '81 300. But, if some headwork has been done, rocker arm studs have been modified, etc. then you have to adjust them manually.
One thing to consider is the pushrod length. Most any competent builder will check this, but not everyone's competent. If you rebuild the motor, resurface the heads and block, etc. you remove metal. This reduces the distance between the rocker arm and the lifter. If you use stock pushrods, the pushrods are going to bottom out the lifters. You have to get shorter pushrods.
If you loosened your rockers and the compression went up, something is adjusted wrong in your valvetrain and needs to be addressed.
If your rockers are adjustable, the best way I've found to adjust rocker arms is to do it while the engine's running. It's messy (oil likes to go everywhere), but it works great.
For this job, I also created a valve cover that's open, which reduced the oil splash by about 99%.
![Automotive tire Motor vehicle Coil spring Automotive exterior Electrical wiring]()
When it's running, back off the rocker arm nut until it starts to clatter. Tighten it back down slowly until the sound goes away. Then give it one more 1/4 turn and lock it into place.
Go through all of the rockers like this.
If you don't want to go this route, you need to rotate the engine and go through each valve. Make sure the valve is 100% closed. Loosen the rocker arm until you can move the pushrod up and down. Slowly tighten until the pushrod suddenly can't move up and down. Some say to spin the pushrod and tighten until you can't spin it easily, but I don't like this method as some people's grip is a whole lot stronger than others. Moving it up and down is much more reliable. Once it can't move up and down, give it a 1/4 turn and lock it. Go through all the rocker arms.
Again, you'll need to be sure your pushrods are the right length before doing any adjustments.
One thing to consider is the pushrod length. Most any competent builder will check this, but not everyone's competent. If you rebuild the motor, resurface the heads and block, etc. you remove metal. This reduces the distance between the rocker arm and the lifter. If you use stock pushrods, the pushrods are going to bottom out the lifters. You have to get shorter pushrods.
If you loosened your rockers and the compression went up, something is adjusted wrong in your valvetrain and needs to be addressed.
If your rockers are adjustable, the best way I've found to adjust rocker arms is to do it while the engine's running. It's messy (oil likes to go everywhere), but it works great.
For this job, I also created a valve cover that's open, which reduced the oil splash by about 99%.
When it's running, back off the rocker arm nut until it starts to clatter. Tighten it back down slowly until the sound goes away. Then give it one more 1/4 turn and lock it into place.
Go through all of the rockers like this.
If you don't want to go this route, you need to rotate the engine and go through each valve. Make sure the valve is 100% closed. Loosen the rocker arm until you can move the pushrod up and down. Slowly tighten until the pushrod suddenly can't move up and down. Some say to spin the pushrod and tighten until you can't spin it easily, but I don't like this method as some people's grip is a whole lot stronger than others. Moving it up and down is much more reliable. Once it can't move up and down, give it a 1/4 turn and lock it. Go through all the rocker arms.
Again, you'll need to be sure your pushrods are the right length before doing any adjustments.
As far as I know, you can only shim pedestal rockers. But even then, shimming them is not to correct the geometry. It's to put them at correct height.
The geometry has to be correct and that's done with pushrod length. If the pushrod is too long or too short, the rocker arm tip will ride on the outer edges of the valve stem, which will eventually wear out the valve guides. The pushrod needs to be the correct length so that when the engine's rotating, the rocker arm is centered on the valve stem. You can test this by covering the valve stem tip with a dry erase marker, properly install the rocker arm, and roll the engine over a few times. It'll rub off where the rocker is touching. If the wear mark is on the side of the pushrod, it needs to be longer. If it's on the opposing side, the pushrod needs to be shorter. Centered is just right. A pushrod length checker is a pretty cheap tool for this.
![Automotive tire Wood Motor vehicle Audio equipment Rim]()
Shimming comes into play on pedestal rockers because they have a set height based on the "pedestal". You just bolt them down into the head and there is zero adjustment on where the rocker sits. If the pedestal is too short, it'll compress the valve spring and/or lifter. Shims will let it sit up a little bit higher and relieve that.
![Tool Gas Electric blue Auto part Machine]()
Stud style rockers are simply held in place by sitting on top of the spring and push rod, so they "float". There's nothing to shim on them. Adjustments to the geometry are only made with pushrod length. The nut on top moves rocker up and down. If it's up too high, there'll be slop, and the parts will clatter and be loose, which will eventually wear them out. If they're too tight then the valves will be held open even when they're supposed to be closed, which will cause the engine to run poorly (AND have low compression since the compression will seep past the valves). If they're WAY too tight, they'll bottom out the lifter and prevent it from coming up all the way. This will bend pushrods and/or chew the lobe off of the cam. When it's the right height, the valve will be fully closed when the lifter is off of the cam lobe and the slop will be taken up by the hydraulics in the lifter.
![Audio equipment Gas Auto part Machine Coil spring]()
The original "torque-and-go" rocker arm studs had a ledge on them that was the correct height for a 100% stock engine. When the nut hit the ledge, they wouldn't tighten anymore, and the rocker was set to the perfect height. Great for an assembly line, and for a completely stock engine that's never been rebuilt. But quickly becomes a pain once you rebuild things, use different rocker arms (like roller rockers), and shave down the heads and block since that set height can't be adjusted, and is most likely wrong.
![Light Motor vehicle Gas Engineering Auto part]()
The geometry has to be correct and that's done with pushrod length. If the pushrod is too long or too short, the rocker arm tip will ride on the outer edges of the valve stem, which will eventually wear out the valve guides. The pushrod needs to be the correct length so that when the engine's rotating, the rocker arm is centered on the valve stem. You can test this by covering the valve stem tip with a dry erase marker, properly install the rocker arm, and roll the engine over a few times. It'll rub off where the rocker is touching. If the wear mark is on the side of the pushrod, it needs to be longer. If it's on the opposing side, the pushrod needs to be shorter. Centered is just right. A pushrod length checker is a pretty cheap tool for this.
Shimming comes into play on pedestal rockers because they have a set height based on the "pedestal". You just bolt them down into the head and there is zero adjustment on where the rocker sits. If the pedestal is too short, it'll compress the valve spring and/or lifter. Shims will let it sit up a little bit higher and relieve that.
Stud style rockers are simply held in place by sitting on top of the spring and push rod, so they "float". There's nothing to shim on them. Adjustments to the geometry are only made with pushrod length. The nut on top moves rocker up and down. If it's up too high, there'll be slop, and the parts will clatter and be loose, which will eventually wear them out. If they're too tight then the valves will be held open even when they're supposed to be closed, which will cause the engine to run poorly (AND have low compression since the compression will seep past the valves). If they're WAY too tight, they'll bottom out the lifter and prevent it from coming up all the way. This will bend pushrods and/or chew the lobe off of the cam. When it's the right height, the valve will be fully closed when the lifter is off of the cam lobe and the slop will be taken up by the hydraulics in the lifter.
The original "torque-and-go" rocker arm studs had a ledge on them that was the correct height for a 100% stock engine. When the nut hit the ledge, they wouldn't tighten anymore, and the rocker was set to the perfect height. Great for an assembly line, and for a completely stock engine that's never been rebuilt. But quickly becomes a pain once you rebuild things, use different rocker arms (like roller rockers), and shave down the heads and block since that set height can't be adjusted, and is most likely wrong.
Oh, gotcha. I misread that. 
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