No, it shouldn't.

Like so many other things, each person who has been fooling around with engines for a long period of time develops procedures that he/she feels most confident with, I'm no different.

More than 30 years ago, after dealing with several different cam companies and their products, I decided on CompCams as the valve train company to rely on. Naturally, others have chosen a different company and some even bounce all over the map, going from one company to another.

So, basically I decided to follow Comp's advice when a valve train question rears it's ugly head, especially when there are differing views held by others. I fall back on Comp's advice and recommendations.

Based on that, Comp's recommendation is that the roller tip be positioned INBOARD with the lifter on the base circle, CENTERED over the valve at mid valve lift, OUTBOARD at full lift. Then return as the valve begins to close.

As already demonstrated in posts on this thread, there are differing views on how to got about determining correct geometry, which is to expected. But basically, what I do is provide informantion and advice based on what I believe to be the recommended way, since it's what I rely on.

As I regularly say, though, each is free to follow their own chosen path.

Jake

West Point ROCKS! Nation's TOP COLLEGE per Forbes Magazine!! Graduation Day Parade 20 May 2010!!!

 

So what you guys are questioning is that the roller is going so far outbound that it comes off the valve tip? If it does this push rods are too long?

 

How the hell you get a rocker to do that? How did this thread get from a bunch of bent pushrods to this? Do you seriously think that minor valve train geometry will cause mass destruction of pushrods? Lifter preload?? Not unless he tightened them up till the lifter bottomed out. You took a stock set of used pushrods and put them on a cam with a much more radical ramp rate than the stock one along with springs that have more pressure. On top of that it is a no no to run SA rockers with the 918's. I know you say that the washers are not touching the retainers but in your pictures they are pretty damn close. They may not touch it sitting still but at 5000 RPM stuff moves, studs flex, etc. Go get a set of hardened pushrods, GMMP guideplates, and NSA rockers like I said before.

I am not saying that lifter preload and valve train geometry are not important, but not your problem here. And if you didn't deck the heads or block when you installed the new cam or do something else that would have changed your deck height signifigantly then your stock length pushrods will most likely be the correct length. By all means check your geometry when you get it together but I bet you find it is just fine.

 

I'm not questioning your expertise in any way but I'm having trouble envisioning what you're describing. The motion of the rocker tip seems to describe an arc that can only swing from outboard to inboard as the pivot point is above the roller tip ie the clock is running from 3 to 6. If the roller tip were higher than the pivot point as in the clock running from 12 to 3 I could see what you're describing. It's quite likely that the stock stamped steel rockers do what you describe as the pivot point is so low relative to the valve stem tip....

Regards,

 

No, the diagram shown on CompCams" website and in their catalog shows a roller rocker and the movement of the roller tip. Not a stamped, stock-type rocker arm. If it'll help you get a handle on this, you can find the geometry procedure on the CompCam's website. I don't have the URL handy or I'd post it. I can track it down for you, if you want me to - let me know.

Much of what I share has been learned over the years from others, so I can't take credit for this information. I'm just relaying what CompCams says and recommends. Since they're my chosen valve train information source, I heed what they recommend.

When a valve train question comes up, and Comp has a position on the issue, I just pass it along, in the hope of helping others.

But, at the risk repeating myself, (I couldn't spell "repetitious", LOL) each person can walk the path they choose. I don't have a problem with that. Just trying to help.

Jake

West Point ROCKS! Nation's TOP COLLEGE per Forbes Magazine!! Graduation Day Parade 20 May 2010!!!

 

Jake.

I searched the website and didn't find the section you described. I did find the section on pushrod length and how that affects the contact point on the tip of the valve but that's all. If you can find a link would you please forward it?

I may just pull a valve cover and take a look as this is pretty counter intuitive to me....

 

http://www.compcams.com/Technical/FA...inGeometry.asp

 

Yep, that's it. Thanks for tracking it down and posting it pizzi-man.

Jake

West Point ROCKS! Nation's TOP COLLEGE per Forbes Magazine!! Graduation Day Parade 20 May 2010!!!

 

This is about the simplest way I have ever seen and how I do it myself.

http://www.lunatipower.com/Tech/Valv...nGeometry.aspx

Again, unless your rockers are rolling off the end of the valve this is not what is causing the OP's bent pushrods.

 

Great thanks... I see it now. Because the trunnion is below the tip of the valve, the sweep is, indeed, from inboard to ourboard...

 

Even though I'm not able to see how all the valvetrain parts are inter-acting, I tend to agree with you. But even when it turns out to be something else, the pushrod length issue still has to be addressed. Don't you agree?

To the OP, I've been puzzleling my puzzler over this and each time it comes back to coil bind and/or piston to valve interference. If the heads were early, iron L98 heads I'd add the length of the pushrod slots in the heads, but since his heads aren't, that's ruled out.

My suggestion: Buy a pushrod length checker, then determine what the correct pushrod length should be and buy a set. The use one of them to determine the piston to valve clearance and also to check the coil spring clearances at full valve lift.

If all that checks good, set the lifter preload correctly and manually turn the engine and while doing so look very carefully at all the areas where interference can occur. Don't fire the engine until you're absolutely sure there's none.

I can't go much further without knowing what you're doing or have done. Feedback time.

Jake

West Point ROCKS! Nation's TOP COLLEGE per Forbes Magazine!! Graduation Day Parade 20 May 2010!!!

 

The way Jake explained it from Comp is right. Mine are close to coming off the edge at .090 with .080 being the minimum I would let them be(1/4 diameter of the valve stem(5/16) = .078"). I have ran it to 6500 multiple times and put 25,000 miles on it with no problems so far.

 

Other negative side effects are the accelerated valve guide wear it causes.

The wear is cumulative and shows up more and more overtime first showing up as excessive oil consumption, with spark plugs becoming oil fouled.

Later the valve(s) begins not to seat properly, because the stems are wobbling around in the guides, so power drops as the valve seats get pounded out. As valve seating diminishes the valve(s) leak compression. Now, when you do a compression or leak-down test, guess what your numbers will look like.

Valve train noise increases due to the valve stem constantly banging against the guide(s).

Problems continue spiral and increase as will the cost for the eventual needed repairs.

Ever wonder why when you take a pair of heads to a machine shop and the guys say something like "Well, you need all new guides and a valve job and a few new valves". (some not being salvagable)

Best to save yourself all that aggravation and expense and do it right to begin with. Isn't that why all these specs and procedures were developed and recommended in the first place?

Jake

West Point ROCKS! Nation's TOP COLLEGE per Forbes Magazine!! Graduation Day Parade 20 May 2010!!!

 

Well, I have 25,000 hard miles and no problems yet. I think the effects are minimal.

 

Time will tell.

Jake

West Point ROCKS! Nation's TOP COLLEGE per Forbes Magazine!! Graduation Day Parade 20 May 2010!!