1970 WS 400 stock rebuild
 

I plan to use the Mellings CL-SPC-7 cam and lifter set on this stock rebuild. I want to use the stock rocker arms and push rods but don't know the correct ratio for the rockers or length of the pushrods. Is there a resource here to find this info? Thx.

The rocker ratio would be 1.5 and the push rod lenght stock was 9.130 to 1.935" or so.

Note that the ideal lenght for the push rod due to geometry changes from milling the heads or block may need to change.

Also a valve job being done can change the length of the push Rods needed.

Just do not use stock rods. Not worth the risk and run a forged piston while you are at it. No hyper BS.

Thanks
 

Thanks for the advice and input gentlemen. Dave

The great side benefit from running lighter aftermarket rods, pistons and wrist pins is a engine that revs faster,
This in itself add’s nicely to acceleration performance.

for a stock rebuild... stock rods are perfectly fine. & even stock type cast pistons are fine for a stock build or even a slight 50-100hp increase.

if the OP intends on higher performance or light duty racing or frequent higher rpm use then its a good idea to consider better rods/pistons/other parts, but he said stock rebuild, no need for forged rods & pistons. countless people run stock rods even on higher hp builds for decades, i had a 455 that was abused & saw 6000 rpms daily for 10+ years, plus the 20+ years of life the rods were used before me.

Some folks don’t seem to understand that to be 100% safe even at only 5000 rpm when running stock factory cast iron rods you need to know there history.

Important things like how long they have been run for ( as in cycles) and how high they where ever taken up to rpm wise and even if a motor may have ever seen a overheating condition and if the rods ever had to deal with full throttle fuel knock all make a difference.

These days with the cost of buying and installing new rod bolts and then re-sizing factory rods of unknown history ( like If you have not owned the motor since day one) playing with fire and is also so close to the price of new rods ( under 500 bucks) that making a case for using them is bordering on nonsensically.

I'm going to show my age here and say that before forged rods were available, it was common practice to prepare stock rods by shot- blasting to stress relieve them and then polishing the beams, Both operations improved stock rod longevity. Today, you also have the option of using superior ARP rod bolts. That said, at today's prices, this preparation would likely exceed the cost of new, forged rods.

And as you say, most of us will never know that. Also, depends on how you drive. I like to do lots of WOT runs. That's me. I can't help it. When they rebuilt my RAIII motor they didn't replace any of those parts. Not the rods, rod bolts, valves, springs etc. Even if I was building a stock motor as far as HP output, I'd still replace all that stuff. Heck they also reused the original crank that had a worn snout that resulted in a front main seal leak. All of that is why I have the motor I have now.

So what, means nothing. That block is worth 2500$. Sold one awhile back.
It is too valuable to run cast junk rods.
I would not run them in any engine I cared about and put a bunch of time and money into.
Cast rods are about 50 years old without any real info on cycles or RPM they have been to unless you have been the original owner and the only one to drive the car.
I had a friend that blew 2 cast rods out of the oil pan because he was cheap.
Glad he is out of Pontiacs these days. Only so many left.

Just remember, New doesn't mean good. While I agree the Chinese rods are made of far superior material than the OE rods, and are forged. The machining processes need to be checked for size on each and every rod, big and small ends. Although Eagle stuff is much improved, we are still seeing some that are on the very edge of the tolerance range and even outside by .0001"-.0002". This means some are over .001", larger than the minimum. Have a set of Eagle press pin rods for a Chevy in class. 4 out of 8 had .0005-.0006" press fit. That just isn't enough, even on a .927 " pin. Had to put oversize pins in that set. Not a big deal but please check everything and expect some new parts will need work before installing. Just checked a "balanced rotating assembly" for another Chevy Tuesday. It was out 6 grams on the front and 16 grams on the rear. It would have worked OK like that but it certainly wasn't "precision balanced". No reason to expect Pontiac stuff to be any better.

so what, that also means nothing that your friend had rods break... way too many unknowns as to why that happened. doesnt mean its a common thing for a low power/rpm STOCK engine that will likely rarely see above 4000-4500 rpm or maybe do a little burnout leaving the dairy queen. what about the probably hundreds of thousands of stock rods that dont break? i have lots of friends that have had stock rod engines that are raced & abused, not one has ever had a stock rod break.

i have owned quite a few stock rod pontiac engines like the 455 i mentioned that was beat & abused daily, saw 6000+ rpms countless times before i knew better for 10 years... stock rod bolts too since i was a broke kid doing a cheap rebuild. currently have a W72 400 that didnt have a budget for $500 forged rods nor did i feel they were needed for a 325-350hp street car, but its been drag raced & ran pretty hard on the street for about 12 years now. i trust the rods for that type of use & trust my engine builder that prepped them.

all i mentioned was that when prepared right stock rods are are fine for a stock engine or even a mild build that is kept within a reasonable rpm. with the OPs cam i doubt he has plans for 6000rpm WOT runs at the drag strip or beating the crap out of the car on the street. he was asking about rockers & push rods, then gets you need forged rods or else the stock ones will break... surprised nobody has told him he needs a huge cam & shave/deck the heads/block for 9.5:1 or it will be a turd. :rolleyes:

nothing wrong with using forged rods if/when they are needed, i just dont feel they are needed for a completely stock build but the OP is free to do what he wants. as mentioned above even new rods still need fully checked over & sometimes work done to make them right, prepping & resizing my rods didnt cost anywhere near $500.

Years back I pounded stock shortblocks hard high compression and NOS all I can say is never broke a stock rod not saying it doesn’t happen but it’s not going to automatically happen because you make 400hp. Personally if I had a stock set of rods I knew came out of a stock original engine I would have no problem using them in a stockish rebuild. My2¢

The 69-70 RA IV had regular rods, right? I recall CARS magazine impressed how it was still smooth at 6500 rpm.

You can find story after story of guys doing amazing things with stock rods.
Still, I would not use cast rods in a 70 4 bolt 400 block.
And if I had a actual RAIV engine that needed a rebuild it would get some Crower rods.

Smooth when up at 6500 was due to the accuracy of the factory balance job, surly you must understand it had nothing whatsoever to do with cast rods used in the motor.

And just the getting to 6500 cleanly was also in part due to the RA4 motors use of valve springs with a open pressure of 320 PSI .

Back then only solid lifter motors from Chrysler with there Hemi and two Chevys BB motors with solid lifters had more spring pressure.

The problem with building a mild 400 is lack of a good cast piston. Run as far and fast away from HT's as you can, and NEVER use the stock 8 valve relief variety as they sit WAY too low in the holes at TDC providing too much quench and squish area.

Stock rods are OK for mild builds and will probably last forever if you don't hang a HEAVY low-end forged piston on them. I wouldn't be afraid of them with a set of light weight modern forgings pressed in place. Years before we had good affordable forged rods we ran cast rods in 455 builds in full race applications spinning them to and past 6000rpm's w/o any issues. Good thing there is a decent amount of sheet metal between the engine and driver with those builds as I've never been very comforable spinning cast rods that hard in any of these engines.

Stock stamped steel rocker arms are fine for most of these builds and a better choice than many of the aftermarket roller varieties. They are strong, light and fine if you aren't running 450 pounds of spring pressure and .600" or more lift.

About the only roller rockers I'd even look at are Crane Gold Race, Harland Sharp or Crower Enduro. I've burned up, cracked or broken just about everything else that's being offered for these engines, plus they can be a PITA to get under stock valve covers without some work.........

As far as the Pontiac rocker arms, I've never built any engines that I didn't use the stock rocker arms. If they last on a circle track engine, they'll be fine for street use.

Same goes for stock rods, every circle track engine I've built had stock rods in it, they've run for many seasons going to 5-6000 RPM twice every lap. They're more durable than people give them credit for. I've run them in 400s, 428s and 455s, so all stock stroke lengths they've survived. Many of the engines had stock cast pistons in them also, as long as it didn't detonate the cast pistons lasted.

Back in the 70s and 80s, cast rods were all low buck guys had to work with, I was a low buck guy, I still am. If you use cast rods, you want the later rods since 67, they have a stiffening rib near the big end that the earlier rods don't have. These rod were the same rods Pontiac deemed safe for the RA IV engines. Pre 67 rods aren't nearly as robust as later rods are.

I usually did lightly polish the beams to get rid of the sharp edges, and have them reconditioned. My 428 built originally in 1977 ran 3 seasons on the dirt tracks with cast rods, and stock rocker arms, it's still together just as i pulled it out of the race car. BTW, it had the heavy TRW forged pistons too.

When the mildly upgraded rods first came out they were about the same as reconditioning old cast rods, that is no longer the case though. many times the new rods needed reconditioning before installation, so you really didn't gain as far as price goes. reliability was better with forged rods over cast, but for a diary queen cruiser do you really need it?

The way Pontiac built their engines was with really tight clearances on the crank, if left stock these tight clearances were fine for grocery getters, but when you got them hotter than normal the cranks grew with the heat, and took all the bearing clearances out, grabbed a bearing, and spun it. When assembling my engines for racing I always was going for more bearing clearances, that extra oil wedge makes a huge difference. Putting forged rods in won't make a huge difference if you end up with only a thousandth and a half clearance, call it good and send it. It will spin a bearing too.

In my experience it was the bearings seizing and spinning first, then the rod broke due to too little clearances that gave the cast rods the bad reputation.

Good to know, Brad! I have always run stock Pontiac rockers, pushrods, and connecting rods as well. I have always used forged pistons, though. No failures in 45+ years, and the two engines in both of my Pontiacs are still running fine decades later with stock parts.

I had this done to the 389 that is in my '65 GTO when I went through the engine in 1981. Here it is, almost 2023, and that engine is still running strong and hasn't been touched since '81. 50,000 miles on it now.