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Old 04-10-2011, 12:02 AM
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Rockers not sitting true, they are cocked??

I have a 327 punched out .40 over I am really frustrated with this machinist work, not even 200 miles on the motor and the #3 cylinder is bending pushrods and slipping the rocker off the valve tip and making a groove in the rocker stud adding to the problem. It has happened two times, first time I replaced the rocker, rod, rocker ball and rocker stud to only happen again. I contacted the machine shop they told me to bring in the head, but should I be responsible to have to tear everything down since they messed up! Most of the rockers are sitting have cocked to one side. Driver side most are turned towards the radiator and passenger side to the fire wall. Is this normal? I don't think so, they should be square and true on the valve tip, right?
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Old 04-10-2011, 12:16 AM
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If you're bending pushrods, then you have mechanical interference somewhere in the system. Here are the usual suspects.....
1. Piston to valve clearance too tight. Need minimum 0.080" intake valve to piston, 0.100" exhaust valve to piston.
2. Valve spring coil binding at full valve lift.
3. Bottom of retainer hitting valve seal/guide at full valve lift.
4. Rocker bottoming out in the slot where it pivots on the rocker stud.

Rockers should be sitting square and proud on the valve stem tip. This lazy rocker syndrome is either the result of one of the four problems I mentioned above or the tips of the valves have been resurfaced down past the hardness layer and the rocker is just rolling over on the soft material or the rocker studs are improperly located on the head. Are the valve tips nice and square or are they rounded off?

You might not find the culprit and fix it with the heads on the motor. Best to get them out on the bench where they can be figured out. By the way, I have never known a tight valve guide to pinch a valve so hard that it will bend a pushrod, but that's just in the last 50 years that I have been fooling with motors, so I guess it could happen. If it did though, I'd be kicking some machinist's fanny down at the shop.

Get some modeling clay and cut strips to lay on the piston valve reliefs, bolt the heads on without a head gasket (just snug up half a dozen head bolts front to back) and check piston to valve clearance. If there is something amiss with the coils binding, rocker slot too short or retainer hitting the seal/guide, you will see shiny metal where the interference is taking place. If you have had a valve or two hitting a piston, remove the valve/valves and run them in a valve refacing machine to make sure they are running true. Machine additional clearance into the piston eyebrows.
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Old 04-10-2011, 08:07 AM
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Quote:
Originally Posted by chevyrally68
I have a 327 punched out .40 over I am really frustrated with this machinist work, not even 200 miles on the motor and the #3 cylinder is bending pushrods and slipping the rocker off the valve tip and making a groove in the rocker stud adding to the problem. It has happened two times, first time I replaced the rocker, rod, rocker ball and rocker stud to only happen again. I contacted the machine shop they told me to bring in the head, but should I be responsible to have to tear everything down since they messed up! Most of the rockers are sitting have cocked to one side. Driver side most are turned towards the radiator and passenger side to the fire wall. Is this normal? I don't think so, they should be square and true on the valve tip, right?
What ratio rockers are we talking about? 1.5 or 1.6?
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Old 04-10-2011, 12:41 PM
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i am not sure on the ratio sqbox, it is a 327 .40 over with hydraulic lifters mildly built with a cam similar to an rv cam
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Old 04-10-2011, 12:44 PM
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X2 on the rocker ratio and what springs are on the heads also do you have guide plates ?



Cole
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Old 04-10-2011, 01:13 PM
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here are some pictures of the passenger side head
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Old 04-10-2011, 01:38 PM
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they looked lashed down really tight or your push rods could be a bit short.

i would say add some guide plates and screw in studs but you may have deeper issues than that.

do you have specs on the cam? or its just word of mouth that its a rv.

the max the spring can handle is around 480 before i would do some serious measurements to make sure.

also alot of times over the years springs may have been change and the stock arms are only good for stock diameter springs and the arm can contact the retainer and cause problems like this
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Old 04-10-2011, 02:40 PM
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If those are replacement straight shank screw-in studs, are they installed straight?? You might be able to sight along the valvestem to stud to pushrod and see if the studs are tipped to one side.

Were the head locating dowels there in the headgasket face of the block?? Almost seems as if the whole head is to far to one side, like if only the bolts were used to align them and the dowels in the block were missing.
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Old 04-10-2011, 03:02 PM
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cam

turn the engine over by hand and see if the valve springs are bottoming out on full valve lift. that would be a starting place before pulling a head off. but I am with tech inspector1 on this one, make sure you know what you have for clearances between ALL the parts and then decide your course of action. that would mean tearing down the top end though, and maybe the timing cover to check the dial in on the timing gears. talk to the machinist and get the build sheet for the engine as well, ask lots of questions and try to get brand names and specs for cam, rockerstiming components etc. did they use your old rockers or new(possibly got wrong parts by mistake) what did they replace and what did they recondition?
dsraven
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Old 04-10-2011, 04:21 PM
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Since you did not mention it,are you running the early 327 heads or later heads? After 1988 Chevys had self-aligning rocker arms they won't work on the earlier heads,if you had one off so the center slot was visible in a picture we could combine that with the head info to give you an answer.
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Old 04-10-2011, 04:27 PM
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You never said if you changed the valve springs or not, Did you or are they stock ?



Cole
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Old 04-10-2011, 04:53 PM
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Quote:
Originally Posted by JeffB
Since you did not mention it,are you running the early 327 heads or later heads? After 1988 Chevys had self-aligning rocker arms they won't work on the earlier heads,if you had one off so the center slot was visible in a picture we could combine that with the head info to give you an answer.

the chev 327 was only in production from 1962-1970.

the ls 5.3(i assume thats what your talking about late 327)shares nothing with the old 327 including cyl heads and there is no chance of using newer ls slotted rockers on a gen 1 sbc.

im almost certain slotted self aligning rockers were introduced in 93 on the lt engines and no sooner
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Old 04-10-2011, 05:58 PM
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327

1968 327 3914660

gm heads 3917290 also 1968

valves, springs and all valve train is new with this rebuild at the machine shop
mild cam nothing radical not sure on the specs.

I am not sure if they are the stock valve springs with the build or up graded with the motor being bored .40 over

Here are some pictures before the motor was fired up and running rockers look square and true but # 3 exhaust side big problems
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Old 04-10-2011, 06:09 PM
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rocker studs

the rocker studs are pressed in on these heads and not threaded. And what is the norm. with these sbc dowels should they be in the block or the head before to perform correct alignment.
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Old 04-10-2011, 06:16 PM
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Quote:
Originally Posted by chevyrally68
with these sbc dowels should they be in the block or the head before to perform correct alignment.
eather or just as long as they are there.
2 each side
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