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I figured out the pushrods- used ARP lube on valve tips, and found an 8.8" pushrod worked best and gave the centermost line across valve tip. Ordered Trick Flow 3/8" dia pushrods to save $50 and will be degreeing this thing next week! Thanks everybody for your help. Rod cap problem was easily fixed too.
8.800" sounds awefully long for most BBF cylinder heads. Which heads are you using? What is your valve spring installed height? Most all custom BBF builds use different length pushrods on the intake and exhaust. And where the roller tip rides on the valve has literally nothing to do with vavle train geometry.Quote:
Originally Posted by parpart
Paul
Maybe you should call up CompCams and tell them that this article they wrote is all wrong.:eek:Quote:
Originally Posted by Paul Kane
http://www.compcams.com/Products/CC-'Pushrods'-0.aspx
There are many different theories as to what is correct valve train geometry, such as mid-lift geometry, jesel geometry, the roller-tip-in-the-middle-of-the-valve theory (R.T.I.M.O.V.), etc. Similarly, there are as many different beliefs, or final conclusions, by the end user as to which one is best to adhere.Quote:
Originally Posted by techinspector1
Choose whichever you want. Just remember that where the roller tip rides on the valve has literally nothing to do with valve train geometry. In fact, giving priority to "putting the roller tip in the middle of the valve" in order to establish good geometry makes all kinds of dangerous presumptions about the combination of valve train components being used, and actually can (and usally does) throw off geometry and thereby cost horsepower because the valves don't receive the linear information correctly translated by the radial sweep of the (incorrectly positioned) rocker arm. So instead of having a given amount of valve lift for the 30*, 40*, 50* of crankshaft rotation, instead you have less, and/or the valve train is imposing greater frictional loads than it should be, etcetera, all of which costs horsepower.
In a properly engineered valve train, made of valve train components which are properly engineered for the specific engine appplication, and when set up with properly evaluated and optimized valve train geometry, will usually allow the roller tip to fall in the "correct" location. But trying to get there from the reverse approach (which the practice of R.T.I.M.O.V. theory is) may or may not get you in the ballpark...depending on the combination of parts used since all rocker arm manufacturers make rocker arms as they see fit (there is no standard for rocker arm design).
Making sure the roller tip is on the valve stem where you want it basically just locates the roller tip on the valve where you want it to be, making optimized geometry secondary. :whacked: But with excellent valve train geometry the roller tip may be positioned just about anywhere on the tip of the stem that you want and the engine will run fine, even if outboard or inboard of the center of the stem. Why? Because contrary to popular belief the rollerized tip's primary purpose is not friction reduction as most people think (the needle rollers in the fulcrum provide the big friction reduction). The purpose of the roller tip is to provide a second pivot point that is constantly aiming the loads directly in-line with the valve tip's contact surface so as to maintain direct force in line with the valve stem over the course of the rocker arm's radial sweep.
The best example of this that I can give is this: imagine extending your arm out straight as though your shoulder is the pivot point like a rocker arm trunnion and your closed fist is the roller tip's axle. Now, from your closed fist hang a weight from a piece of string and consider the weight at the end of the string to represent the roller's diameter contacting the valve tip. As you move your arm up and down radially, the weight and string remains vertical and unchanged in vertical positioning (and force) even though the radial motion of the rocker arm is changing direction.
I recently rebuilt a sportsman drag race engine that had a 7600 rpm shift point. The engine had been together for 7 years before it kicked a rod out of the pan. We gave it a new shortblock. On this engine, the rollers were on the absolute ousde edge of the stem tips. How much guide wear after 7 years of roller cam spring pressures? ZERO, ZIP ZILCH, NADA. Why? Because the combination of valve train components were prepped with optimized valve train geometry which correctly loaded the valve train. :)
Paul
Paul, Im using Edelbrock 60679 75cc heads, along with their head gaskets (.048 thick torqued) ARP head bolts tqd to 137#s, and Id post pic of the valve tip line if I knew how on this site- the line is about 1/3 of valve tip wide, centered. Installed height, I do not know- can I measure with stick end of caliper? Where to where? I did read Comp's article prior to doing the measurement- also, the machine shop barely removed any surface material from my block- DIVE-6015-A2B. Id have to measure, which I can, the piston to deck- maybe an 1/8". Rockers I purchased some years ago, still new, Ford Motorsport, marked A460. I'm always up to learning, and the help to avoid a catastophic mistake is greatly appreciated.
The cam is Comp- 34-250-4. Reading articles with 460's and alum heads, I tried 8.550, 8.575- up .025 each time, until I found that "centered line" the best at 8.800". Used pushrod length checker Comp Cams 7703-1. It measured 7.8220 to start with. Heads are torqued, and Ive re-lubed cam lobes after each 2 revolutions. The lifters are Comp hydraulic, soaked in 30W for about 5 minutes; I used the Comp Degree kit 4796 instructions of 0 lash + 1/2 turn. Rockers feel loose, with side to side movement possible when valve not depressed- I believe this will go away when lifters "pump up" on start up.?
This is the photo of intake valve #1. Line in center is roller tip contact through 360 deg revolution with 8.8" pushrod/ using Comp cams length checker
This is mock up, and also the car it's going into- in case you're curious!
Is the 0 lash+ 1/2 turn correct? I can loosen the perma locs by hand (without the set screw tightened). This seems odd, and with rocker arm side to side movement after returning to TDC, I have my doubts. I have only used factory type rockers on engines before. Of course Perma locs are not lock nuts though, and need the set screw to secure them. Should a person use say blue loc-tite on the set screw?
i use smiths or trends push rods most of the time.i use the set up checker from jesel and T&D and then use the ferry mild lift tool for fine tuning from there.i set every thing at mild lift. every thing works fine that way for 10 over years .the roller tip comes in the play on the size of the roller and how long is the valves and where the rocker stud sets to the valve guide angle if the same and other things as well . i will not going to get in to all of it on here other to say some rockers geometry is better then other s rocker arms. i have posted on here about the poor value of roller tip rockers with stock ball trunnions. i have stuff out there with over 350 on the seat and 1075 open alot of builds going past 7500.rpm and still living the way i do it.on shaft rockers it can take over a days labor some times to get them right
Got it degreed, bottom end finished up + all valves adjusted. Thanks everybody- very much. Gene
The engine looks nice.
Sorry but I cannot make an educated judgement call on your valve train geometry based on the image of the valve stem tip; it tells me nothing relative to what I believe matters when setting up a valve train.
Oh my god is that ever true! And the application of mid-lift geometry clearly reveals which rocker arms have horrifying engineered geometry in them.Quote:
Originally Posted by pat mccarthy
In the past, I have had others ask questions about why they can't seem to make sense of why their geometry seems to be so far off, usually because they are trying to get the roller tip in the middle of the valve via absurd pushrod lengths. In the discussions, they mention the rocker arm brand and I already know that brand to be poorly designed. AND SO, after exhaustively educating them on engineered rocker geometry, installed valve train geometry, and the theory of mid-lift geometry principles, they apply the mid-lift principles and return to the forum thread, saying, "so what I've just realized is that my rockers are crap." :3dSMILE:
Paul