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Pushrod problems

6K views 25 replies 6 participants last post by  stroked385 
#1 ·
I have a chevy 383 stroker with 230cc dart pro 1 heads, 1.6 comp cam rockers, 7.8000 pushrods, comp cam number 12-250-3, gross valve lift intake .507 and exhaust .510. My rockers are hitting the head studs, are my pushrods too short? Or do i need offset rockers? Im also having a problem with keeping the rockers centered on the valve stem, the rockers go off to the left and the right...why is it doing this? How do i fix these problems, please help!!!
 
#3 ·
Yes the guide plates are in and they are roller rockers. No i have not checked the length or pattern of the pushrods, i am in the process of doing that but the pushrods dont seem to sit straight between the lifter and the rocker. Also, the rocker seems to go left and right on the valve stems. I have had the motor built by a shop a few years back, the motor sat for a little while before i used it and i had come faced with this problem with the rockers hitting the head studs while i was doing a valve adjustment. The pushrods that came with the motor are 7.8000, do i need the bigger pushrods? I appreciate your response and help thanks.
 
#10 ·
The Dart heads you have use +0.100" valves, IIRC. This usually means the p-rods need to be longer as well. The exact length can be determined easily; this is covered in the link, "Valve train geometry" below.

If you have roller rockers, the roller trunnion takes the place of a long slot in a stamped steel type rocker. All the roller tip rockers I know of are also 'long slot', but it's easy enough to check the clearance w/a paper clip inserted between the stud and rocker if you have rockers w/a slot.

Also it's important to have the lifter preload set correctly before assuming there's a problem. If the rocker nuts are too tight, this will throw off what you're seeing and it'll look bad when it may not be bad at all.

To check the pushrod length the checking lifter need to be either a solid lifter w/the same pushrod cup-to-foot length as the hydraulic lifters you're going to use, or stacked full of small washers or filled w/grease to make them un-compressable. Using a checking spring can make things easier, but isn't mandatory.

Most times the supplied pushrod guide plates will be all you need. This isn't always the case when you get into some of the off shore head castings, but w/your Dart heads you should be fine. That said, you still have to check the alignment along w/the other critical areas to be sure.

More info on setting up the valve train:

Valve train points to check
Valve train geometry
Valve spring installed height
Adjusting hydraulic lifters
 
#5 · (Edited)
Thanks for your advice! Could you possibly be able to get me the part number for the long slot rockers i need and whether i should use 1.5 rockers or the 1.6 rockers that i currently have? Here's my comp cam number 12-250-3. What size pushrods do i need or should i keep the 7.8000 ones? I also already have the adjustable guide plate the same one as the link.
 
#8 · (Edited)
My i ask why u dont like to use extreme energy cams ?
An internal combustion engine is an integrated compilation of parts that work together toward a common goal. Easy up, easy down flat tappet camshafts have been used for years by the OEM's and those who rebuild engines because they are cheap and will work in most applications if certain precautions are taken at pre-installation, installation and post-installation.

There is a quality of camshaft lobes known as hydraulic intensity. That's the rate at which the camshaft lobe interacts with the crown of the lifter to initiate lift. There is a point of lift per degree of rotation of the lobe beyond which the whole mess comes to a grinding halt and some of the camshaft grinders, CompCams in particular, have run the hydraulic intensity right up against the wall with their "Extreme Energy" grinds. Any more lift per degree of rotation of the cam could result in the crown of the lifter digging into the lobe and the game would be over. I dislike anything that's designed to run on the ragged edge if it's intended for a motor that should last for a while, like in a street or street/strip motor. Full tilt race motor? No problem. Balls to the wall is fine because of the inspection and replacement of parts on a regular basis. But a street driver does not need the extreme hydraulic intensity. It needs longevity with a less intense lift and seating of the valves in my opinion. For the street, I prefer a cam with a difference of advertised duration to 0.050" duration of at least 60 degrees. (for instance, 280 degrees advertised, 220 degrees @0.050").

And i have a graddle for the rockers should i still use them?
Like the old Sergeant used to say, "smoke 'em if you got 'em".
 
#11 ·
I see not all Pro 1s have +0.100 length valves. Only the heads that came w/1.55" springs come w/the longer valves. But if the heads were bought bare and assembled later, they could be longer valves. If you're not sure, measure them.

The Comp XE284H cam is "lazy" when you compare the lift to the duration. I wonder why it's designated as being an XE cam, maybe there's a lot of lift early in the opening event. In any event, be sure the springs are up to the task- the cam redlines way on up there so it'll take a fair amount of spring pressure to control the valve train. Same thing goes for the pushrods- stock isn't gonna cut it. You may get by w/the stock OD, but the walls will need to be much thicker to stiffen them sufficiently. If it were me I'd be looking for a bigger p-rod- walls and OD.

If you chose 7/16" studs, you most likely won't need a stud girdle. If for some reason you got heads w/3/8" studs, you just might need the girdle.
 
#14 ·
Go w/the p-rod that gives you the narrowest sweep across the tip of the valve, as opposed to a centered- but wider- pattern. Centered and narrow is best, but if you have to choose between a centered and wide pattern or off center a bit but narrower, go w/the latter. Obviously, the rocker roller cannot ride off the edge of the valve tip at any point.
 
#17 · (Edited)
The pattern is made by the combination of the parts involved along w/the exact placement of the rocker stud and valve guide in the casting, but the main thing that drives the pattern is the length of the pushrod itself. Next to that is probably the design of the rocker arm, but most of the time we work w/whatever rocker that is on hand and change the p-rod length to get the narrowest pattern.

If you are handy you can make a checking p-rod from an old p-rod. Click on the image below for details:



Other homemade pushrod length checking tools at HomemadeTools.net

When talking about the pattern of the rocker roller across the valve tip, "wide" and "narrow" are relative. By using an adjustable pushrod, you can see what length gives the best pattern overall.
 
#18 ·
Problem with making a checking pushrod yourself is that different manufacturers measure pushrods differently. Please read this.....
COMP Cams® - Pushrods
Now, pick up the phone and order a checking pushrod from your favorite cam grinder. When you have found the length that works, send it back to the cam grinder so they can make you a set of pushrods to the exact length specified.
 
#19 · (Edited)
The different methods used to measure a pushrod are also covered in the link I provided earlier, "Valve train geometry".

Measuring a checking p-rod is not too much for someone to grasp once the maker's method of measurement is known. And most manufacturers are capable of working w/the length that's provided to them as long as they know it was taken w/a p-rod having oil holes. The only real problem I see is not everyone owns a large enough caliper or micrometer to do the measuring precisely. In that case, I would recommend taking the locked-down checking p-rod to your local machine shop, who would be able to measure it. Then that figure would be given to the p-rod manufacturer or used to select an off the shelf p-rod.

For that matter, the homemade checking p-rod can be sent to the manufacturer just as easily as one supplied by the maker. Granted, $20 for a store-bought checking p-rod ain't likely going to break the bank, and making one may be beyond the ability or too time consuming, etc. If that's the case, by all means- go buy a checker and more power to you. Personally, I would simply order an off the shelf p-rod from one of the several trustworthy p-rod makers based on the measurement taken from the homemade checking p-rod, working w/the way they measure their p-rods. I mean, this ain't rocket science.

Comp has a couple p-rod lines that may work well for you, their Magnum or Hi-Tech. They're available in 0.050" incremental lengths from standard, are thick-walled and are hardened for use w/guide plates. IMO these off the shelf Comp p-rods (or any of the several other vendors like Comp) will be considerable cheaper than custom p-rods, w/o sacrificing durability in your build.

Should you want to go top shelf, here are some high-end pushrod makers:
 
#22 ·
Get an adjustable pushrod as mentioned. One full turn is .050. 1/2 turn is .025

Try at different lengths to get the best pattern. Marking the top of the valve stem with a dry erase marker leaves a good witness mark.

Replace the valve spring with a light checking spring so you can get full lift during the cycle without depressing the lifter plunger.

Post some pictures of your different patterns and them someone will be able to help make a decision.
 
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