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86 Brc 351W XLT HO, had rebuilt 2 yrs ago. Was looking for low to mid torque, installed msd box & Dist, fast EX 2.0 never could get it to run RIGHT. Efi is back in it's coffin running one wire dist. Running ok but compression 78 - 92psi on all cyls?? Pulled all plugs, loosened 1 & 2 piston rockers comp 150 & 150 ? Running roller cam and lifters?
 

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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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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.
I will have my Mech readjust and let you know! Thank You Steve
 

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Doesn't mean he adjusted them "Right" either. Do your own compression test again and see whatcha get, then take it from there.
 

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Mech adjusted lifters, still no power?
When the engine was rebuilt did they do a valve job on the heads? New springs for the new cam? Sounds like cam might need to be degreed...or tthey got the chain off a tooth...
 

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Doesn't mean he adjusted them "Right" either. Do your own compression test again and see whatcha get, then take it from there.
I'm a dummy when it comes to Ford valvetrain but aren't you supposed to just run the nuts all the way down on ford rockers? I know on a chevy you have to use a feeler gauge and adjust the lash accordingly but when i rebuilt both my fords (both flat tappet) i was told to run-em-down...and i did..and so far its been great. Maybe different for roller cam engines?
 

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I always make sure the lifters are at full pump up/hitting/contacting the snap ring then tighten the nut till there is pressure on the pushrod then tighten the nut 1/2 a turn lock it in then move on to the next. You also have to have the correct length pushrods installed. Grant it I never built a Ford V8 but did swap the head out on a Ford inline 6 in a 66 mustang and it ran great after that. My specialty is Mopar V8's and Turbo Buick V6's, Oh and one SBC with Rhoads lifters in a boat.
 

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I always make sure the lifters are at full pump up/hitting/contacting the snap ring then tighten the nut till there is pressure on the pushrod then tighten the nut 1/2 a turn lock it in then move on to the next. You also have to have the correct length pushrods installed. Grant it I never built a Ford V8 but did swap the head out on a Ford inline 6 in a 66 mustang and it ran great after that. My specialty is Mopar V8's and Turbo Buick V6's, Oh and one SBC with Rhoads lifters in a boat.
Well, and small chevy's are the same as you described, set it to a certain preload then go another 1/2 a turn and lock it in, but on MOST of these windsor ford's (some exceptions are out there) they have a non-adjustable pedestal mount rocker arm, and provided everything is factory original, you just torque them bad boys down and you're done...which was odd to me but it works.

If using roller rockers or other push rods, then i believe doing it the way you described is necessary.

Said all that to say this...if he has non-adjustables and they are torqued down correctly, he's losing compression for some other reason...which sucks. Got me thinking bad timing gear or something.
 

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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%.

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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.
 
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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.

Again, you'll need to be sure your pushrods are the right length before doing any adjustments.
So is this where rocker arm shims would come into play? instead of changing the length of the pushrod you change where the rocker arm bottoms out at.
 

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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.

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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.

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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.

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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.

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86 Brc 351W XLT HO, had rebuilt 2 yrs ago. Was looking for low to mid torque, installed msd box & Dist, fast EX 2.0 never could get it to run RIGHT. Efi is back in it's coffin running one wire dist. Running ok but compression 78 - 92psi on all cyls?? Pulled all plugs, loosened 1 & 2 piston rockers comp 150 & 150 ? Running roller cam and lifters?
As Stated above OP said he loosened 1 & 2 piston rockers so I just assumed they were Adjustable. The Big block Mopars have Shafts for the rockers and they do make Shims if the Block and or Heads have been Milled to correct for what was removed, but I also mentioned having the correct length Pushrods installed in post #8. Let's let the OP, @RAFA, chime in on this!
 

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86 Brc 351W XLT HO, had rebuilt 2 yrs ago. Was looking for low to mid torque, installed msd box & Dist, fast EX 2.0 never could get it to run RIGHT. Efi is back in it's coffin running one wire dist. Running ok but compression 78 - 92psi on all cyls?? Pulled all plugs, loosened 1 & 2 piston rockers comp 150 & 150 ? Running roller cam and lifters?
Is the engine still drinking a quart of oil every month as you had said in an earlier post?
 

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on Pedistal style rockers arms that most of our trucks use. you tighten the bolts till there is no more slop yet no preload in the pushrod. then it should take 1/4 to 3/4 of a turn more to reach torque spec. this sets correct lifter preload. when the valvetrain has been changed in any way (new cam, resurfacing, valvejob, ect) then the stock pushrod might not be the correct length. it might need a shorter/longer pushrod to be used but it also might need the rockers to be shimmed to get proper preload. cant really change the geometry on pedestal rockers.

compression tests are very basic and dont tell you much other than that there is an issue. instead of checking compression you really need to be doing a leakdown test. that will tell a much better story of whats the issue. it will identify if its rings leaking, intake valve, exhaust valve, headgasket.
 

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on Pedistal style rockers arms that most of our trucks use. you tighten the bolts till there is no more slop yet no preload in the pushrod. then it should take 1/4 to 3/4 of a turn more to reach torque spec. this sets correct lifter preload. when the valvetrain has been changed in any way (new cam, resurfacing, valvejob, ect) then the stock pushrod might not be the correct length. it might need a shorter/longer pushrod to be used but it also might need the rockers to be shimmed to get proper preload. cant really change the geometry on pedestal rockers.

compression tests are very basic and dont tell you much other than that there is an issue. instead of checking compression you really need to be doing a leakdown test. that will tell a much better story of whats the issue. it will identify if its rings leaking, intake valve, exhaust valve, headgasket.
How would that work? On a pedestal rocker, you just bolt them down. There's no adjustments, tightening until preload, 1/4 turn, etc. It's just like bolting any other part onto the vehicle. The bolt doesn't do any adjusting, it just keeps it from coming off. But otherwise, yes, shims would help with setting the preload correctly.


I'm still guessing that his valvetrain is messed up. If he's getting low compression when it's put together, and higher compression when he loosens the rockers, that's telling me that his valves are being held open by the rockers and compression is seeping past the valve seats.
 

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I went through some of this when I set up the valvetrain for the ‘91 460. It uses a 5/16-18 bolt to hold the rocker onto the head. My book advised me that anywhere from 3/4 to 1-3/4 turns of the bolt from pushrod axial slack removed to the rocker arm bottoming out on the pedestal would set the lifter in an acceptable, near-center position (which says 0.090” collapsed, although the rotations don’t fully support that). I reused all valvetrain components and found it easiest to bleed the rockers down in a vise to reduce bolt force resistance and get a better feel for when the rocker made contact with the pedestal. I also attempted to look at lifter movement. I had around 0.005” shaved off the heads but no block work done. Valves were redone and I’m not sure what all was required there. Regardless, my numbers were pretty consistent at right around 1 turn to go from no slack to no lifter movement. At 18 TPI this is 0.055” and seemed to be in range of what the book says and I’ve read. I also checked a couple valves with well-bleed lifters and was near 0.100” lash which is also in range.

All that said, engine still on the stand and it’s the first one I’ve ever built.

I agree the leak down test could point you in the right direction. But it does sound like your valve timing is either off valves held open. I suppose if your lifters are stuck solid in the fully extended position that may keep valves off seats as well, although I’d consider that a lower probability than an incorrect timing or set up.
 

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How would that work? On a pedestal rocker, you just bolt them down. There's no adjustments, tightening until preload, 1/4 turn, etc. It's just like bolting any other part onto the vehicle. The bolt doesn't do any adjusting, it just keeps it from coming off. But otherwise, yes, shims would help with setting the preload correctly.
it would not be for setting preload, it would be for checking preload. since the only way to chnage it would be different length pushrods or shimming. that is why i said "then it should take 1/4 to 3/4 of a turn more to reach torque spec". anything out of that range would indicate an issue
 

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Oh, gotcha. I misread that. (y)
 
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