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Old 07-26-2010, 01:14 AM
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Pontiac 350 Rocker arms/ push rods?

Changing the heads on my 72 pontiac 350 for 400 heads. Will i be able to use the same rocker arms and push rods? I have the rocker arms for the 400 heads but not the push rods. And also i cant seem to find the rocker ratio's online if anyone can help me out.

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Old 07-26-2010, 05:51 AM
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Same parts

All 1965 throuigh 1979 Pontiac V8 regular production 1.5:1 ratio rocker arms are the same and 1967 - 1979 Pontiac V8 5/16" mild steel pushrods werre 9.137" long. Aftermarket replacement pushrods range from 9.130" to 9.140" in length , depending on the manufacturer. Those different pushrod lengths are within acceptable variance if used with hydraulic lifters.
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Old 07-26-2010, 07:07 AM
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Quote:
Originally Posted by AndersonRacing44
Changing the heads on my 72 pontiac 350 for 400 heads. Will i be able to use the same rocker arms and push rods? I have the rocker arms for the 400 heads but not the push rods. And also i cant seem to find the rocker ratio's online if anyone can help me out.
You will have 1.5 ratio rockers on both sets of heads, unless you stumbled across a set of rare as hens teeth RA IV heads (have rounder, wider spaced center exhaust ports, but that is very unlikely.

If you are going to keep the "net lash" adjustment, the pushrod length is VERY critical.

In the net last system, the rocker arm retaining nut is torqued down to 20 ft/lbs. and that is that.

The problem comes when the heads or block have been milled, a different thickness head gasket is used, different ratio or style rockers are used, or if a different cam is used. Any of these things can change the required length of pushrod, and because it is the length of the p-rod that determines the lifter preload, you can see why it is so important.

The best way to go about this, is to use screw in rocker studs that are not the OEM "bottle neck" studs used in the net lash system. Besides the straight studs being much stronger, they provide for an adjustable valve train- just like a Chevy.

But even then, the p-rod length has to be measured before you will know whether or not the stock p-rods will give you the correct geometry.

If you want, post the casting number of the 400 heads you plan to use. There are a lot of difference in the chamber sizes among Pontiac heads. What you do NOT want is to put too large chambers on your 350. This will lower the CR too much.
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Old 07-26-2010, 08:50 AM
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net lash (preload)

The 20 lb. torque "net lash" adjustment found with stock Pontiac hydraulic lifters will accept up to +/- 0.050" variance in lifter preload. Total GM hydraulic lifter travel is 0.125" and they will function without noise if the plunger is located anywhere within that distance. The optimum adjustment would be 0.063" lifter preload or half of the plunger travel.

In other words, the 1967-1979 Pontiac pushrods do not have to be exactly 9.137" long, as were the OEM pushrods. In theory, replacement pushrods that are from 9.075" to 9.199" will work. Most 1967 to 1979 Pontiac aftermarket stock replacement pushrods are usually 9.130" long.

Net lash (20 lb. torque) lifter pre-load adjustment cannot be used when a high lift aftermarket cam is used that has a cam lobe base circle that is less than 1.330" OD, regardless of the pushrod length. A smaller camshaft base circle will cause the lifter to drop further into the lifter bore, effectively making a stock pushrod too short. Cam grinders can usually make their performance camshafts with up to .450" valve lift (1.5:1 rockers) without changing the cam lobe base circle from the stock 1.330" OD so stock length pushrods can be used.

Last edited by MouseFink; 07-26-2010 at 08:59 AM. Reason: spelling
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Old 07-26-2010, 09:17 AM
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The only way to know what length pushrod to use, is to measure it. This is accepted engine building procedure for ANY pushrod-equipped engine, IMO.

If you try to rely on published figures, and use them to determine what length pushrod to use, you are asking for trouble. That is why Comp and others make tools to measure the correct length with- it IS that important. That's not to say you shouldn't at least try the OEM pushrod to see what the geometry and preload look like, but don't be too surprised if it's off. And it will still have a too-thin wall, IMHO.

A pushrod length checker can also be easily made from an extra pushrod (see thumbnail). Outside calipers are then used to determine the length.

Pushrods usually are stocked in 0.050" increments. If your measurement falls between, go to the next longer number, at least that's what I do. I believe the better pushrod makers will make you up a set to whatever length you ask for. A stock diameter 0.080" wall pushrod should be considered the minimum for strength- those Pontiac pushrods are l o n g!

Good luck.
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Old 07-26-2010, 10:25 AM
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hydraulic lifters

Exact pushrod length is absolutely necessary with solid lifters. .

Explain how you use a pushrod length checker with hydraulic lifters?
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Old 07-26-2010, 10:53 AM
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Quote:
Originally Posted by MouseFink
Exact pushrod length is absolutely necessary with solid lifters. .

Explain how you use a pushrod length checker with hydraulic lifters?
You are kidding, right?
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Old 07-26-2010, 11:05 AM
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No

No Boss, I am not kidding.

Please explain how you can use a adjustable pushrod length checker with hydraulic lifters?

Com'on, I have given yoiu enough time to read up on it.
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Old 07-26-2010, 11:22 AM
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There are times when discretion is the better part of valor. This is one of those times.

I will now bid you auf wiedersehen.
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Old 07-26-2010, 11:47 AM
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I will tell you how.

You can buy replacement pushrod for engines with hydraulic lifters that are the correct length. However, if someone has a little spare time and just wants somthing to do, here is a step by step method to check the aftermarket pushrod length to see if it is within tolerance by using an adjustable pushrod designed for solid lifters on Pontiac hydraulic lifters:

1.) Buy a new or find a used Chevrolet solid lifter. Install it in any lifter bore. Be advised, the Chevy solid lifter pushrod seat is 0.085" deeper at zero lash than a hydraulic lifter pushrod seat at zero preload.
2.) Install a rocker arm and a weak hardware store spring with enough tension to hold the valve closed. DO NOT attempt to use a valve spring because it will fold up the adjustable pushrod like wet spagetti.
3.) Rotate the engine until the solid lifter is on the base circle of the cam lobe.
4.) Install the adjustable push rod and adjust it until slight resistance is felt as you spin the pushrod with your fingers. (Not oily fingers)
5.) Tighten the jam nuts to hold the adjustable pushrod length. That is zero lash for a solid lifter. Remove the rocker arm and the adjustable pushrod.
6.) Measure the adjustable push rod. Subtract 0.022" from that length and that will be the length of the pushrod if used with hydraulic lifters at half-travel or 0.063" preload.

You can just forget all that unnecessary nonsense and install the correct pushrods you bought at the auto parts store.

Last edited by MouseFink; 07-26-2010 at 12:23 PM. Reason: spelling typo
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Old 07-26-2010, 09:22 PM
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This seems like a good thread to ask my question. I haven't adjusted lifters before. I have a Pontiac 400, .040" milled 6x-4 heads, felpro .039" gasket, Summit 2802 cam (lift .465/.488 ) with Summit hydralic tappet lifters. I hope to use the stock push rods.

Reading from http://pontiacstreetperformance.com/psp/rockers.html

"Torquing the adjusting nut per the old Chilton's to 20-25 ft pounds won't work on any heads that have been milled. This is especially true with the high lift cams of today. The valve train needs to be adjustable. Some form of lock nut must be used. I prefer Mr. Gasket's poly lock nuts."

Are lock nuts used in addition to or in place of stock Pontiac rocker arm nuts?

Will I need lock nuts or can I use the stock Pontiac rocker nut? If I can use the stock Pontiac nut should I use Lock Tite thread sealer?

How will I know if my push rods are too long?

BT

Last edited by beertracker; 07-26-2010 at 09:35 PM. Reason: corrected milling value
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Old 07-27-2010, 07:24 AM
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Quote:
Originally Posted by beertracker
This seems like a good thread to ask my question. I haven't adjusted lifters before. I have a Pontiac 400, .040" milled 6x-4 heads, felpro .039" gasket, Summit 2802 cam (lift .465/.488 ) with Summit hydralic tappet lifters. I hope to use the stock push rods.

Reading from http://pontiacstreetperformance.com/psp/rockers.html

"Torquing the adjusting nut per the old Chilton's to 20-25 ft pounds won't work on any heads that have been milled. This is especially true with the high lift cams of today. The valve train needs to be adjustable. Some form of lock nut must be used. I prefer Mr. Gasket's poly lock nuts."

Are lock nuts used in addition to or in place of stock Pontiac rocker arm nuts?

Will I need lock nuts or can I use the stock Pontiac rocker nut? If I can use the stock Pontiac nut should I use Lock Tite thread sealer?
Hey, BT.

You will be using polylocs without any other form of thread lock or jam nut. JUST the polyloc, alone.

Quote:
How will I know if my push rods are too long?

BT
The procedure used by the same Pontiac folks you cited above is HERE.

The method is shown by Bill Boyle is for an engine that's assembled and w/lifters full of oil. On an engine stand, unless you've primed the oiling system this isn't the case, so you'll want to stack small washers (or in some other way) to make a lifter solid. Or just use a Pontiac solid lifter.

This solid lifter is then used to do the procedure to see where the sweep of the rocker arm is, across the tip of the valve. You can add the amount of preload to the figure you get, or you can set up the lifter to have the required preload and use the adjustable pushrod length directly. Either way, your choice.
HERE is a page by Comp Cams that give some more info and insight to the procedure. It is worth reading, IMO.

At first it may seem a little complicated, and it may take a time or three to get a "feel" for what you're doing if you've never set the geometry/pushrod length before. But I assure you by the time you are done you will be a pro at it!

But I WILL say that only the rankest amateur HACK would ever presume to build a performance engine that had not had the valve train geometry verified. And that's all I have to say about that.

Personally, I like using blue machinists paste (below) to use on the valve tip instead of a Sharpie, but that's me- you may have no problem using the Sharpie/Magic Marker 'method'.

Hopefully some guys w/real engine building experience besides myself will add to what I've offered here- there are tricks guys use that work for them and some of those may help you w/your task at hand.

Good luck and feel free to ask whatever you want if something comes up.
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Old 07-27-2010, 08:08 AM
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Pontiac lifter pre-load

Toss the stock Pontiac adjustment nuts. You must use poly-locks when you install most aftermarket camshaft, especially those with higher valve lifts. In other words, aftermarket cams require a fully adjustable valve train. Stock Pontiac rocker nuts are not locking nuts. You can use 3/8"-24 Chevy locking rocker nuts but I don't recomend it. The clinch type (prevailing torque) Chevy lock nuts eat up the rocker stud threads and are only for one adjustment. Adjust and forget, which is seldom the case with high performance camshafts.

If your heads still have stock Pontiac 3/8"-24 sholdered screw in rocker studs, replace them with BB Chey 7/16"-20 sholderless rocker studs, or use ARP replacement rocker studs for a BB Chevy. The top of the ARP studs are flat with a dimple to hold the nose of the allen lock screw. Stock Pontiac screw-in rocker studs have 7/16"-14 lower threads just like a BB Chevy rocker studs and are a direct replacement. When using poly-locks, you can easily adjust the lifter pre-load with your fingers and then lock the adjustment with the set screw. With a fully adjustable Pontiac valve train, you adjust the lifter pre-load just like you would a Chevy.

Your stock Pontiac pushrods will be too SHORT if you have installed an aftermarket camshaft with more than 0.450" valve lift. Cam grinders use stock cam cores and they can grind up to 0.450" valve lift and still leave the cam lobe base circle at 1.330" OD. The diameter of the cam lobe base circle is one of the two factors in determining the push rod length and the year series of head you have is the other factor. The two series of Pontiac V8 heads are 1955-1967 and 1968-1979. If you can manage to measure one of your camshafts lobe base circles through the lifter gallery, subtract that measurment from 1.330" and divide the remainder by 2. Add that figure to 9.137" when using 1968-1979 heads. The sum of those two figures is how long the pushrod must be. If the figure you added to 9.137" is less than 0.050", don't worry about it, the lifter pre-load adjustment will compensate for that. If you want your push rod length dead-nuts on, you can order pushrods made to your specifications from Comp Cams or from most other cam grinders.

For example a Lunati SPC-297 camshaft with 0.570" valve lift and a 1.220" OD cam lobe base circle:
1.330" - 1.220" = 0.110"
0.110" / 2 = 0.055"
9.137" + 0.055" = 9.192" is how long the push rod should be for that camshaft. Therefore, a Comp Cams pushrod that is 9.200" long would be preferred which is the next highest 0.050" increment. Never choose a shorter increment than what is needed.

Comp Cams has off the shelf 5/16" High Tech chromemoly steel 0.080" wall pushrods in 0.050" length increments. Stock pushrods are 0.060" wall, plain mild steel and should never be used with more than 280 lb. open valve spring pressure. .

Last edited by MouseFink; 07-27-2010 at 08:30 AM.
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Old 07-27-2010, 08:34 AM
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Quote:
Originally Posted by MouseFink
Your stock Pontiac pushrods will be too SHORT...
The cam base circle is but ONE of many reasons the pushrod length needs to be checked and the valve train geometry verified, as any engine builder is well aware.

Instead of posting incomplete or erroneous info, why not take a few minutes to VERIFY the info BEFORE you post it?

Quote:
Originally Posted by mf
If you can manage to measure one of your camshafts lobe base circles through the lifter gallery, subtract that measurment from 1.330" and divide the remainder by 2. Add that figure to 9.137" when using 1968-1979 heads. The sum of those two figures is how long the pushrod must be.
This is NOT how to measure for the correct pushrod length/valve train geometry!

To the OP and to Beertracker: There are well known and practiced procedures that making measuring for the correct pushrod a relatively straightforward procedure. I would implore all to research using these well-understood methods.

PLEASE- do not get sidetracked by nonsensical postings- just adhere to what is KNOWN to work, and work well.

Quote:
Stock pushrods are 0.060" wall, plain mild steel
Stock Pontiac pushrods that come w/heads that have guide plates- which are the VAST majority, BTW- are NOT "plain mild steel".

They, in fact, ARE hardened, for use w/the guideplates.

Last edited by cobalt327; 07-27-2010 at 12:53 PM. Reason: Trying to maintain proper decorum.
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Old 07-27-2010, 09:07 AM
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Have you verified that the 350 and 400 heads in question are the same combustion chamber size. I have seen the same casting with a 20cc variation in CC volume, I suppose for use in different applications. I would measure and calculate the compression ratio and make sure it is no less than 9:1.
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