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Push rod help
November 25 2001 at 4:04 PM
No score for this post NDSP (no login)
from IP address 205.188.192.172

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I am using early model iron heads (small chambers) and the Ford Motorsport M6250-C460 cam. Its the same cam that comes the the 535hp 460 crate motor. The problem I have is the stock length pushrods seem to short. I have the rocker arms almost adjusted all the way down in order to get the proper clearances. The rocker arm still clears fine, and the pattern on the valve stem is okay (narrow and just off center towards the exhaust). By all the way down I mean almost bottoming on the stud. I was thinking of just geting some 8.7" pushrods. But that might screw up the rocker arm geometry. I have already broken 4 pushrods. Is the cam on a smaller base circle than stock. Or did the rocker stud pedestals need to be milled down to account for the extra hieght of the guide plates. It just seems that I shouldn't have to adjust the rocker until it is almost bottomed on the stud. Any help is appreciated.

Thanks

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Author Reply
George Huff
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205.188.199.31 Pushrod length
No score for this post November 25 2001, 6:19 PM

Valve train geometry is always a factor! You need to get a adjustable pushrod for checking purposes. If the machine shop did not compensate for guide plates, that could cause a problem. Aftermarket cams sometimes cause a promblem also. Let me know if i can help!,George

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Gary
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12.13.226.13 Guide plates
No score for this post November 27 2001, 9:22 AM

When using guide plates on early heads the rocker stud pedestal must be machined down about .250 the CJ heads are the only ones that don't get this done.

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Quintin66
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12.96.65.83 1/4" off Rocker Pedestal?
No score for this post November 27 2001, 5:56 PM

Is that how much must be taken off the rocker base of c8ve heads when you install guide plates for your pushrods? This seems like alot, are the guide plates actually that thick? Thanks...Quintin

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Gary
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12.13.226.18 Rocker Pedestal
No score for this post November 28 2001, 8:45 AM

No the guide plates are not that thick but most after market studs have a much wider radius at the base so the rocker doesn't slide all the way down it's best to make as much room as you can but as I recall about .200 is the lest you can go buy long studs the ones for big block Chevy are about 4 threads short.

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Ken
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165.154.190.1 pushrods
No score for this post December 13 2001, 1:22 PM

fact is the early heads on any 73 or later block requires a longer pushrod. You will find the longest required is on the c8 heads. Each year the port floor was raised as the combustion chamber was moved to accommodate larger combustion chambers and small sparkplug. Almost 3/8" difference measuring from the deck to the port floor.. This also changed the pad height. Th egeometry is NOT correct when the nut is tightened down enough to make it work with stock pushrods. That is why they are breaking. Guideplates make it worse in some cases. My 545 with c8 heads turns 7200 regularily truckpulling and the only pushrod i ever broke was caused from rocker failure.

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Mike R.
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32.97.239.23 Heat treated pushrods?
No score for this post December 13 2001, 1:57 PM

When you added the guideplates did you switch to heat treated pushrods? The CJ/SCJ/PI heads that used guide plates came with heat treated pushrods and that is what's required when using guideplates.

Also heat treated or not, the 5/16" diameter is not the greatest for high performance. Perfect geometry or not, if you switch to 3/8" hardened pushrods, you will never ever break another pushrod.

I've broken several good 5/16 pushrods on these engines. As long as you are running 5/16" with a healthy cam there is never a guarantee they won't break. They will give up on you when you least expect it and put you in very bad situations. Switching to 3/8" hardened pushrods was the best investment I ever made.

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Anonymous
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12.13.226.13 Cure the cause!
No score for this post December 13 2001, 3:12 PM

Cure the cause don't cause the cure I'm running #220-650open springs on My cj heads at .700 lift and know people Who run more if 5/16 push rod failed ether they were junk or something wrong in the valve train.3/8 are just more mass trying to go up and down

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Mike R.
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32.97.239.29 Cure the cause
No score for this post December 13 2001, 3:28 PM

For what period of time have you been running the 5/16" pushrods with those spring? I ran 5/16" for about 5 years with high pressure springs. You may go for 3 years without breaking one, but then out of the blue one will break. One pushrods breakage is too many in my book. You break a pushrod, shoot a lifter out the hole, lose oil pressure, possibly ruin an engine. It's not worth the risk. If you've been running 5/16" with those springs that's great, but talk to me after you've run them consistently for about 10 years with those springs and never broken a pushrod. It may take a while but it will happen.

I'm not saying every 460 has to have 3/8" pushrods, but if you're running a healthy cam and some fairly stiff springs it's real good insurance.

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Anonymous
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12.13.226.16 Problems bring on more problems
No score for this post December 14 2001, 10:15 AM

problems bring on more problems push rods that are not up to the job will break a good push rod proper valve train geometry the right valve stem clearness all add up to 5/16 push rods will work and you have the add benefit that they act as a fuse something goes wrong a valve gets hit if the system is ridged a head gets destroyed with a 5/16 a push rod gets bent and by the way I'm in my 25th year of playing with 460!there is nothing wrong with using 3/8 push rods its just not an absolutely have to do don't take it personal.

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Mike R.
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32.97.239.17 Problems...
No score for this post December 14 2001, 11:43 AM

All I can say is I've seen enough 5/16" pushrods break in a variety of 460s (mine and other people's) that I switched to 3/8" and I've never had another problem. However we can agree to dissagree on this point.

With that issue set aside, I believe before he makes any changes to anything he has to verify that he is running heat treated push rods. That's a standard requirement with guideplates. Standard 429/460 pushrods are not heat treated, only cj/scj/pi's had guide plates and heat treated pushrods. You've been messing with these engines for 25 years, so you would have to realize this. If you've ever tried running non-heat treated pushrods with guideplates on one of these engines you would know that they break or are totally eaten up by the guideplate in a very short period of time. Maybe he does have them, but it's not an issue that is redily publicized everywhere, so it would not be uncommon for him not to.

I only mention this because he didn't mention anything to make me believe his geometry is off. The length of the stud and or height of the stud boss with or without guideplates has absolutely zero effect on the geometry. Assuming you have the correct rocker arms, the only two parts of the valvetrain that will change the geometry are the length of the pushrod, and the height of the valve tip. He said the pattern across the valve tip looks good, so there is no reason to believe the geometry is off.

Anonymous, I'm not trying to be rude, but I haven't actually seen you offer a detailed solution to the problem yet.

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Quintin66
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12.96.65.83 When changing ValveTrain, How do you check Geometry of Rocker
No score for this post December 13 2001, 6:46 PM

I have C8V-E heads on original motor-460. I intend on installing 2.19/1.75 valves of stock length. I just purchased a set of roller rockers made by Angus Racing, in original 1.73 ratio. I talked to the cam man at compcams today and he told me that the .530lift magnum cam kit that I want has the cam, lifters, valve springs, locks, retainers, and timing set all in one. The roller rockers come with studs and lock nuts. I understand that I'm going to have to have the stud bosses milled .250. I think that i have a good head for mechanical aspects, and I work as a maintenance tech. for a major manufacturing corp. So if you know anything about valve train geometry, and how to set-up and check the geometry correctly for a setup that I just described, PLEASE, feel free to spill your guts about everything you know. I'd like to know every detail, don't worry about gettin' too technical, I can handle it. And I really really want to know!!! Make that NEED to know.

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Gary
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12.13.226.18 NDSP?
No score for this post December 14 2001, 1:02 PM

Tell us what brand pushrod and what springs You are using? So the Old Timers can maybe help! just poken fun boys.

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Ken
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165.154.190.1 More
No score for this post December 14 2001, 3:31 PM

More. You don't say if you went to longer CJ valves and higher spring hieghts. The fact remains that you also have a different height deck than the original heads. Ford changed the actual stud boss height several times over the years. If you didn't have guideplates before i.e. cast rockers with the rails, then your boss is higher yet. It only takes a couple thou here and there to add up to a lot. By your desription the pattern is actually on the other side of the valve stem than what stock is, or the better part of an 1/8" offset. That is why you are breaking the pushrods. Too much leverage/bind. Idealy it should run to the back of the stem closest to the stud. In any event my experience has shown that a pushrod in the range of a 1/4 inch longer is required.

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Anonymous
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209.226.237.45 Last but not least
No score for this post December 18 2001, 8:50 PM

Most aftermarket cams run a reduced base circle, so even if all other thigs are equal you still need to make up for this reduction in pushrod length, due to the lower seat of the lifter in the bore. One other thing a lot of people don't know is that some solid lifters have an even lower height pushrod seat within the lifter than hydraulic lifters which makes things even worse.

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