Push rods

are 3/8 Comp Cams .080 push rods hi-tech push rods adequate for a BBC blown motor with Comp Cams springs 320# seat pressure?

 

320lbs. and 3/8 pushrods, Sounds a bit light to me, especially if your running a stainless valve.

 

do yourself a BIG favor.....call Terry Manton!

 

I think you'll be fine. I did 3/8 heavywall pushrods on 350# seat no problem. If you get into bigger (7/16) pushrods, the weight of the oil inside the pushrod becomes a force to deal with. Not as much issues on a chevy as there is with a chrysler.

 

Manley make a nice heavy 3/8 and 7/16 pushrod. I think they are .165 wall, I run the 7/16 and love them.

 

pushrods

let me know if you are looking for some. I ran a 10.2 deck for years and have boxes of single and dual taper Smith Bros. push rods. You can always get them shortened. NEVER hurt one. Now the 14* rocker arms left a little to be desired, but maybe it was me. Just never felt comfortable with them. That is one reason I switched to a fat head Hemi. Good Luck Don

 

3/8 vs 7/16 ???

In 1969 GM's L88 came stock with a 7/16 Pushrod! Why would we go backwards?

noel

 

Sure, lets just get the GM part number and ordering up a set? Why would anyone even sell a 3/8 pushrod then?

 

I guess because they know more than Noel Manton? LOL.

 

Look at the time. In my dreams I'm smarter than Darren Mayer, Les Davenport and Dave Leahy. Last post till dawn ?

 

I'm not looking to get into a pissing match with Noel Manton. For a sponsor of a tech question section I sure don't know what the hell his techinical recommendation is when he quoted me with his 1969 technology response. I run Manton equipment in my hemi and they've been decent to deal with in the past (I'll probably get marked up next time I call...).
Noel, you have my number in your data base (Joe Mierkey) from past purchases. If it is your intention to surpress my opinion or censor my thoughts you will not suceed. Please post something of technical value if you really care to help someone out. I learn from information on this site and hope that sharing what I've had luck with will help another. Can you at least expand on your response that you directed to my opinion. Thank you.

 

I have dealt with the Manton's for some time and their parts are second to none. On the other hand I have had parts from other suppliers that weren't so good. Let me detail the scenario- You are running a blown motor- a pushrod or a adjuster fails. That cylinder quits flowing air so the air diverts to the seven cylinders still working. But they only have the amount of fuel allowed by the nozzles for the amount of air divided by eight cylinders. They all go leaner and maybe the one or two leaner cylinders beat the rod bearings out. Soon after the rods exit the block. So the moral of this fairy tale- cheaper, substandard valve gear can cause catastrophic engine failures. Been there, done that. I have a whole "Wall of Shame" in my shop. Broken rods, pistons, and crankshafts from motors I killed. Dave Germain

 

3/8 vs 7/16

First of all I would like to apologize to JM. I had no intention of coming across as condescending or rude when I made the statement about push rod diameter.
JM has asked for an explanation as to what push rod would be correct and why. So here we go.
As an example I will use a push rod length of 8.680” and 9.650”. These lengths are shown in the MANLEY catalog as a stock length for a .400” tall BBC engine using a stock cylinder head.


Critical Load = the point the tube will bend
Static Load = the point of material failure
Natural Frequency = cycles per min.
Approx Mass = grams


3/8” Dia. 8.680” x .080” Wall
Critical Load = 3,403
Static Load = 10,306
Natural Frequency = 27,539 cycles per min.
Approx Mass = 82.8 grams

3/8” Dia. 9.650” x .080” Wall
Critical Load = 2,753
Static Load = 10,306
Natural Frequency = 22,281 cycles per min.
Approx Mass = 92.1 grams



7/16” Dia. 8.680” x .080” Wall
Critical Load = 5,924
Static Load = 12,489
Natural Frequency = 33,007 cycles per min.
Approx Mass = 100.3 grams

7/16” Dia. 9.650” x .080” Wall
Critical Load = 4,793
Static Load = 12,489
Natural Frequency = 26,705 cycles per min.
Approx Mass = 111.5 grams



7/16” Dia. 8.680” x .168” Wall
Critical Load = 7,047
Static Load = 19,771
Natural Frequency = 28,613 cycles per min.
Approx Mass = 158.8 grams

7/16” Dia. 9.650” x .168” Wall
Critical Load = 5,701
Static Load = 19,771
Natural Frequency = 23,150 cycles per min.
Approx Mass = 176.5 grams


The column loading during use at 9500 RPM in this engine, using a typical .500 lobe roller camshaft, a common valve train weight, and a valve spring measuring approx. 350# of seat pressure will be in the area of 3,450 pounds. When the valve train is in surge the loading will be much higher. This tells us that we must have a built in margin, or a safety percentage. Taking into consideration the limits that we have on us here, length, material, and diameter it is reasonable to say that we are limited to a safety percentage of approximately 100%. With that in mind my recommendation would be a 7/16 x .168 wall push rod as a minimum.
If it is at all possible to add diameter to the push rod, no matter what the application, and without regard for overall weight, we will improve the performance of the assembly and at the same time will extend the use full life of all the components of the valve train, including the valve springs.

In response to the question “Why would anyone even sell a 3/8 push rod then?” I would have to say that it is possible these other push rod manufactures may not know what they are selling or the consequences if their part is used in a supercharged application. Call and ask a simple question like, “What is the critical buckling load of your push rod”. The answer may surprise you.

Thank You: Noel Manton
Tel: 951 674-2212

“There are so many variables to consider when choosing a push rod. That’s why I spend so much time with each customer that calls me. I wake up every morning with the responsibility of solving these types of issues for any one that needs help. I’m here for everyone who needs technical assistance”.

Thank You: Terry Manton
Tel: 951 245-6565


www.mantonpushrods.com
www.mantonrockerarms.com
www.mantonengineering.com