What is diameter of push rod in 68/390hp?

[Mark #28455]

3/8" is the way to go

Most of the current racers no longer use the 7/16" pushrods as a good 3/8" chrome moly pushrod has adequate stiffness at a significantly lighter weight. I have used both the 7/16" and 3/8" aftermarket and stock pushrods in my engines and to 7000 RPM with a flat tappet cam and a valve spring with about 135# seat pressure and about 330# open pressure it doesn't seem to make a difference at all.

Be aware, many manufacturers do NOT individually inspect their pushrods. I personally inspect EACH ONE and have found that with the pressed in ends often enough one or two pushrods in a set will have small cracks starting where the end was pressed in place. Although some will complain about the type with the welded on ball ends, at least I have never seen a new one with cracks.

Mark

[Terry F.]

Re: joe were the 65/66/67 ones 3/8"as i

I will use 3/8 inch. Any particular supplier that I should look into. Sounds like Federal Mogal or Elgin are fine as long as long as I use a hardened steel type?? I see the advantage of the ball type push rod. But, given the fact that my engine didn't seem to come with them, I suspect it would do well with the single piece design. Terry

[Joe L.]

Re: here is the deal on the 5/16" push rods

clem------

That's excellent information. That makes sense and also strongly implies that the 3/8" pushrods were carried over into 1968-69 L-36/L-68. If the 5/16" pushrods were actually used in late 1967, as some GM parts references state, then it would be reasonable to assume that they might have been carried over into 1968-69 L-36/L-68. There's no way that they would have used the 5/16" pushrods for early 1967, switched to 3/8" for late 1968 and then switched back to 5/16" for 68-69.

The strange thing is that GM NEVER cataloged a pushrod for 1968-69 L-36/L-68. But, I think that we know now that they were the same as those used for 1968-69 L-71. 1970-72 LS-5 and LS-6 definitely used the same 3/8" pushrods.

[Joe L.]

Re: joe were the 65/66/67 ones 3/8"as i

Terry----

Yes, I really think that Federal-Mogul or Elgin stock replacement 3/8" pushrods will be just fine. They'll be equivalent to what you have now. However, if you inspect what you have and find them to be wear and defect free, why not just re-use them? You want to check these carefully for wear and defects, though. Also, check for straightness by rolling them on a perfectly flat surface.

[Terry F.]

Re: joe were the 65/66/67 ones 3/8"as i

Well, I had this engine apart years ago and reused the push rods. At the time, I found a few with the tips flaking so I replaced them with somemore good used ones. You are right. They would probably work but for the cost of good used ones, I might as well spring for them. Well, now I have to get rid of a nice set of NOS 5/16 push rods Ebay, here they come! Thanks for the help. I will start looking for some nice 3/8 inch push rods. Thanks, Terry

[Clem Z.]

Re: here is the deal on the 5/16" push rods

i ran into the 3/8" to 5/16" change in 396 chevelles because i super tuned a lot more of them than 390/400 HP corvettes. check your chevelle listings. who would buy a corvette 390/400 HP when a few $$$ more bought the solid lifter engine