Rocker arms: To shim or not to shim? That is the question

Discussion in 'Fox 5.0 Mustang Tech' started by vnmsgt, Dec 19, 2006.

  1. I recently bent a valve on my 347 and since got a new valve installed and installed the head back on but I was asked if I shimmed the valves and rocker arms before because on my GT40 heads one valve stem tip sits a little higher than the other on all the valves including the other head and I said I did not when I built the motor. I have a set of aluminum 1.6 PRO-FORM rocker arms that are bolted on as stock replacements, nothing special and it never said anything about shimming them and in any of the stang mags it never said anything. I just bolted them on and that was it. Do you really need to shim these stock replacement rockers or on these ford heads do I just bolt them on like I did before? I think if I shim the rocker arms to get the clearance I was told (which I forgot already) It will push the valve further down into the combustion chamber and it will be more likely to bend a valve again since the clearance will be less. What should I do? To shim or not to shim
  2. You may need to shim them, but need to check preload to know for sure.. Make sure the valves are closed on the clylinder you are working on. loosen the rocker arms up and proceed to "0" lash, then from there tighten the bolt to specified torque( around 18-21 ftlbs) The bolt should torque to the specs within a 1/4 to all most a full turn. Personally I like them to torque within 1/2- 3/4 turn.

    To obtain "0" lash, with the valve closed and the rocker arm bolt loose, tighten it until there is no up & down movement of the pushrod, and a slight drag on it when you spin it. Then thats when you torque the bolt down.
  3. I know I have to have the valves closed when I do. So what you are saying is if I am tightening the rocker arm bolt and it tightens all the way down to torque specs and the pushrod still has some slight play up and down OR does not drag a little when I spin it I would have to shim that particular rocker arm?
  4. once you have the valve closed and tighten the rocker arm to tq specs. and the pushrod is still loose you need longer pushrods. what size pushrods are you running now and how much play is in them when you torque them down?
  5. I have the stock pushrods right now. I do not have anything fancy in the motor (stock block and GT40 heads and the rocker arms bolt on exactly the same as the originals so I do not see why I would need different size pushrods. I have not yet tried reinstalling the rocker arms yet. Even if I did have a little play isn't that what the shims are for?
  6. you wont need the shims if the pushrod has play when the rocker arm is torqued down, you only need them if the desired preload ( 1/4 to 3/4's turn past zero lash) is not met before torquing. when i put the 1.7's on the 89 i had to get 6.400 pushrods to compensate for the stock shorter pushrod. might also check to see if they are bent , that could cause a little shortness to not allow them to set right.
  7. how much longer is the new valve? if the valve is .100" taller than you need to shim that rocker .100". but you will also need a pushrod that is .100" longer. i dont see why they would put a longer valve in the head. doesnt make much sense to me since you can get valves in just about every length you need
  8. Good info on that link
  9. im still wondering why they installed a different size valve. also, you might want to check that the installed height of the spring is the same.
  10. The valve is the same size as the old one. The new valve is not the only one that has the tip of the valve by the keepers at a different installed height, ALL the valves are like that on each cylinder (one valve in each cylinder is slightly taller at the tip and it is the same valve on each cylinder. I bought the heads brand new and fully assembled in the box and they only have 800 miles on them. You would think the installed height on all the valves would be the same but they are not. They were like this when bought them.
  11. If you bent a valve then you most likely damaged the valve seat. When you cut the valve seat, the valve will sit higher in the head thus causing your problem. Measure the difference in stem height to the other ones and have the difference taken off the tip of the problem valve. The machine shop should have done this for you so take it back and see what they say.
  12. i have a 1989 5.o i installed a trick flow stage one cam 499/510 lift 275/279 duration. i didn't replace the lifters, push rods or rockers. i did add gt40 heads with a 3 way valve job, had the heads surfaced and the trick flow spring upgrade kit installed at 1.800" as the paper said (those were done at the shop) first i didn't know anything about shimming so i just bolted the rockers down the car had a little bit of a high idle and ran a little warm didn't overheat though well i drove it for around 50 miles while trying to find the idle problem. them it started popping in the the intake towed it home and the number four cylinder had bent both push rods and broke the rocker arm bolt on the exhaust side next i replaced all push rods and ordered shims i shimmed all rockers with .30 shims runs great and at normal temp so i'm guessing without the shims the valves were open a little all the time but now i have a ticking noise so i checked that and on some the rockers a loose and wont get to 0 lash but without the shim it gets to tight before the bolt even gets hand tight any suggestions? Thanks.
  13. i have kinga the same problem on my gt 40s one valve on each cylander is taller than the other the post above tells about my problem

  14. Pedestal rockers aren't my favorite. I'm running the GT-40X 58cc and had similar problems. This is a combination of information I could find that was helpful for me.

    Ford recommends a preload of 0.02 to 0.06". This means that once you set the pre-load and the oil pressure in the lifter bleeds down - there should be a gap of about 0.02 - 0.06" between the top of the oil cup/pushrod and the wire retainer. Basically the cup on top, inside the lifter, should be pushed down 0.02 - 0.06".

    The 5/16-18 bolt on the pedestal rockers. One complete turn of the bolt will move down the rocker fulcrum 0.056". One half turn of the bolt will give 0.028". One quarter turn will give 0.014".

    It also depends on the ratio rockers being used. 1.7s will be slightly different than 1.6s when the lifter bleeds down.

    1.7 ratio: 1/2 turn gives 0.016" at the lifter. 3/4 turn gives 0.025". 1 turn gives 0.033". 1 - 1/4 turn gives me 0.041". 1 - 1/2 turns gives me 0.049".

    1.6 ratio: 1/2 turn gives me 0.018" at the lifter. 3/4 gives me 0.026". 1 turn gives me 0.035". 1 - 1/4 turn gives me 0.044". 1 - 1/2 turn gives me 0.053"

    The procedure for pedestal is a little different than stud. With studs you bring it to "0" lash then turn anywhere from 1/4 to 3/4 depending on your preference. With pedestals everything is a positive lock once bolted down. There is no small adjustments aside from shims or pushrods.

    The consensus on the preload is 0.02 to 0.06". That would be anywhere from 3/4 - 1 - 1/2 turns from "0" lash.

    I used a clicker torque wrench to around 13 ft. lbs., and a beam torque wrench to final torque. I do the lower torque at first so that I know how many turns until everything becomes firmly seated. Meaning the rocker fulcrum, pedestal, any shims and bolt is tight to the head. I don't care at first how much further it takes to get to full torque spec. I only care about the amount of rotation to get everything seated.

    I tighten the 5/16 bolt by hand while using my fingers to spin the pushrod. As soon as I feel resistance on the pushrod I stop turning the bolt. That is my "0" lash. With the clicker torque wrench set to 13 ft. lbs. I put the torque wrench at 12 , 3 , 6 or 9 o'clock. Turn until everything is seated. If I got a 1/4 turn or less then I have too many shims. Removing the thin shim will bring the valve to within 1/2 - 3/4 of a turn. If I have a little more than 3/4 of a turn, adding a thin shim will bring it up to around 1/2 a turn. Once its set I torque to final spec of around 22 ft. lbs. with a beam type torque wrench. A little note. The FRPP pedestal shim kit. The shims actually measure 0.02" and 0.04". I guess the 0.03" and 0.06" has something to do with geometry and not the actual shim size.

    I did each cylinder by firing order. 1-3-7-2-6-5-4-8. I have read a bunch of different ways. I looked in my Ford service manual for the 93 Mustang H.O., but couldn't find anything. Nothing on lifter preload either.
    #15 jAEded, Aug 12, 2013
    Last edited: Aug 12, 2013