Pushrod Length

Gailahan · Mar 4, 2008

I'm trying to figure out the pushrod length for my 351w 408ci stroker build and I'm running into a snag. My block has been decked to 9.482" and I am using AFR 205cc heads with Comp Cams Pro Magnum rockers and Comp Cams Endure-X roller lifters. The cam is a custom grind from Flowtech Induction and is a mechanical roller. I am trying to use the sharpie method to get the roller rocker centered on the valve stem. The only way I can get the rocker centered on the valve stem is if I extend my pushrod length checker all the way to 8.75" which is way too long and leaves no threads left on the rocker stud. Ed from flowtech induction told me, "As for the geometry, look for the "smallest" sweep over the valve and call it a day. You may not be able to get it perfectly centered over the valve but the less it swipes, the better." Has anyone else ran into this problem? Here are some pictures to help illustrate what I'm trying to say:

180 Out · Mar 4, 2008

I noticed the missing nuts from the head studs and it makes me wonder if you've got a head gasket in place. A head gasket will add about .040" to the mix, which would knock this same amount off the pushrod length, all else being equal.

Gailahan · Mar 4, 2008

180 Out said:
I noticed the missing nuts from the head studs and it makes me wonder if you've got a head gasket in place. A head gasket will add about .040" to the mix, which would knock this same amount off the pushrod length, all else being equal.

Yeah I realize that. I have a fel pro head gasket with a .041" compressed thickness, but I don't want to ruin the gasket while I'm taking the head on and off.

woodsnake · Mar 4, 2008

It looks like your trunion nut is upside down in the picture. Don't you want the flat side up towards the lock nut?
Otherwise it looks like a really good, thin sweep.

brianj5600 · Mar 4, 2008

I have heard that some rockers need longer studs. That may be your situation.

Gailahan · Mar 4, 2008

brianj5600 said:
I have heard that some rockers need longer studs. That may be your situation.

That's the first thing I checked in to. The AFR 205cc heads use 7/16" rocker studs which come as long as you can get.

Gailahan · Mar 4, 2008

woodsnake said:
It looks like your trunion nut is upside down in the picture. Don't you want the flat side up towards the lock nut?
Otherwise it looks like a really good, thin sweep.

I am confused on what you're trying to say here.

SoCalCruising · Mar 4, 2008

The rocker geometry explanation is at www.mid-lift.com.

69gmachine · Mar 4, 2008

First you need to install a head gasket that's the same thickness as what you will end up with. Buy a cheap set from A Zone if you don't want to re-use your new ones. Make sure the cam is on the base circle for the cylinder you're working on. With the pushrod checker adjusted well down so as not to interfere, drop a rocker down on the stud. Slowly adjust the pushrod until the roller is just a little to the inside of the tip. Tighten the rocker arm nut down until it just makes contact with the rocker. Do not over tighten. Rotate the engine over carefully and watch how far the roller tip moves across the valve tip. This should be the correct length.

Gailahan · Mar 4, 2008

69gmachine said:
First you need to install a head gasket that's the same thickness as what you will end up with. Buy a cheap set from A Zone if you don't want to re-use your new ones. Make sure the cam is on the base circle for the cylinder you're working on. With the pushrod checker adjusted well down so as not to interfere, drop a rocker down on the stud. Slowly adjust the pushrod until the roller is just a little to the inside of the tip. Tighten the rocker arm nut down until it just makes contact with the rocker. Do not over tighten. Rotate the engine over carefully and watch how far the roller tip moves across the valve tip. This should be the correct length.

Why do I need to install a head gasket if I know the compressed thickness? All I need to do is add .041" to the pushrod length. When you say just a little to the inside of the tip do you mean the intake side of the valve stem close to the center? If so, the method that you are describing is the method that I have used, but the roller will not approach the center on the valve stem unless the pushrod is so long that there are no threads left on the rocker stud.

Gailahan · Mar 4, 2008

Comp Cams says that the roller should start at the intake side of the valve stem and then roll to the exhaust as the lift increases. My roller never gets past the intake side.

http://www.compcams.com/Technical/FAQ/ValvetrainGeometry.asp

Has no one else ran AFR 205cc heads with pro magnum rockers? Am I way overlooking this?

brianj5600 · Mar 4, 2008

This is a list of different length 7/16, 7/16 rocker studs from Summit. I would call Ed for advice.

1.300 in.
1.750 in.
1.760 in.
1.765 in.
1.770 in.
1.820 in.
1.850 in.
1.900 in.
1.930 in.
2.000 in.
2.100 in.
2.261 in.
2.350 in.
2.700 in.
3.300 in.

http://store.summitracing.com/egnse...+115&Ne=111091&NeXID=111091&Ntk=KeywordSearch

69gmachine · Mar 5, 2008

Gailahan said:
Why do I need to install a head gasket if I know the compressed thickness? All I need to do is add .041" to the pushrod length. When you say just a little to the inside of the tip do you mean the intake side of the valve stem close to the center? If so, the method that you are describing is the method that I have used, but the roller will not approach the center on the valve stem unless the pushrod is so long that there are no threads left on the rocker stud.

OK, you should be able to just add .041 to your final measurement.

Yes, to the intake manifold side of the tip.

I am using AFR 205 heads and Comp (pro?) magnum rockers just like the ones you have pictured. However, I have a hyd roller cam so my pushrod length will be different from yours. The stock length Ford Racing pushrods for a 94 roller 351W worked perfect for my set up. The roller tips sit just to the inside of the valve stems and the arc of travel is very small. I wonder if you have Ford rockers? Perhaps they were mis-packaged at Comp? I had the same problem 20 years ago with a set of Harland Sharp rockers. They turned out to be small block Chevy rockers and it was impossible to get the geometry right. Do you have a known good rocker to compare with?

EDC · Mar 5, 2008

Gailahan said:
I am confused on what you're trying to say here.

What he is stating is the rocker's trunnion has a flat or small counter bore machined into it for the poly-lock to nest in. If the trunnion is "upside down" the flat will be towards the head and the poly-lock will not nest properly. It's really easy to spot if you look at the rockers and spin the trunnion around.

Also... if you only have a few threads of engagement with the poly-lock, you "can" get longer 7/16 rocker studs from ARP but you have to watch out for the certain aluminum head BBC ones that have too long of a stud length on the cylinder head side. The 351C rocker studs are a possibility to look into....

As for the swipe, the top pictures look DAMNED GOOD! Pictures are not the best way to check things but your swipe mark is small, the location is not running to the edge of the valve tips so all in all, what you have for a length, with that particular swipe pattern, looks perfect.

BTW... I do agree with installing the head gaskets, Even a cheesy parts store gasket for $10-12 is a good investment to check everything the way it's actually going to be run...

BTW... got the Email Jeremy, so I posted here to avoid typing twice.

Ed

Gailahan · Mar 6, 2008

I figured it out

Thanks for all the help guys. The problem was: When I put the rocker on, I took it right out of the box and put it on the rocker stud without noticing that the trunnion was upside down. You wouldn't think this to be that big of a problem, but the hole is actually offset on the trunnion. So, if the trunnion is flipped upside down, the rocker is going to be further to the intake causing the problems that I was having. I was extending the pushrod length checker so far that there was no threads left on the rocker stud, and this was the only way the the roller would even make it close to the center of the valve stem. With the trunnion right side up I have no problems getting a clean sweep on the center of the valve stem without the pushrod being too long, and I have plenty of thread left on the stud. I spent way to much time trying to figure out this dumb problem. I ordered a single pushrod to double check the length before I order the whole set. The funny thing is, the pushrod is the same length as the pushrods in the 200ci straight six that I ripped out of the car (8.350").

Gbart14 · Mar 23, 2008

ProComp Rocker Problem

Guys, I am new to the forum but your thread popped up when I was trying to solve a problem with my rocker trunnion The problem is that the boss (flat) on the trunnion shown in your photo is off center toward the pushrod. If you look at the bottom of the polylock after a few miles and if you have a hefty valve spring and solid lifters, it will beat up where the polylock meets trunnion. The first symptom will be the valve lash opens up. Then if you re-adjust with the same polylock by rotating the polylock to a new position, then it will be sitting on a high spot on the bottom of the polylock and will wear faster.

I think this is a very poor design. Comp says all their Ford steel rockers are all built this way including the high buck stainless like are in the photo. I can also tell you from experience that the ARP locks which are much harder, also will be destroyed. Anyone with similar experience or do I have a unique problem?? FYI I have a message into MEI for advice. FYI, heads are Twisted Wedge, solid roller cam. Thanks

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