Pushrods

[Bruce B.]

What is the length of the push rods in a 365 HP 327?
Do the solid lifter engines use the same length push rod as the hydraulic lifter engines such as in a L79?
Thanks.

[Joe L.]

Re: Pushrods

What is the length of the push rods in a 365 HP 327?
Do the solid lifter engines use the same length push rod as the hydraulic lifter engines such as in a L79?
Thanks.

Bruce------


All original small block pushrods, except those used for 1987+ roller cam applications, were 7.724" overall length. This applies to both mechanical and flat tappet hydraulic lifter applications.

[Bruce B.]

Re: Pushrods

Joe,
Thanks.
Is there any difference in design between push rods for solid lifters and hydraulic lifters?
Bruce B

[Joe L.]

Re: Pushrods

Joe,
Thanks.
Is there any difference in design between push rods for solid lifters and hydraulic lifters?
Bruce B

Bruce------


No difference, at all. The exact same pushrods were used for both applications. However, there were some minor differences over the years.

All 1955-61, regardless of lifter type, used pushrod GM #3837152.

For 1962-63 all engines except SHP continued to use the above pushrod. SHP used pushrod GM #3796243.

For 1964-82 all small blocks used the GM #3796243. The 3796243 also became SERVICE for all 1955-63 when the 3837152 was discontinued in January, 1963.

So, what's the difference between the 3837152 and 3796243? They are both the exact same length which GM variously describes as 7-25/32" or 7.724" (I've never measured one to see which is exactly correct). The difference is that the tube section of the 3837152 is NON-HARDENED. The tube section of the 3796243 is HARDENED. There MAY also be a slight difference in wall thickness but I've never confirmed that. The 3796243 is ABSOLUTELY MANDATORY for engines with guide plates. Of course, no pre-1970 small block ever originally used guide plates.

The 3796243 was discontinued many years ago and replaced by GM #14095256. The latter is a welded ball type pushrod of very high OEM quality. However, it currently GM lists for $18.55 EACH.

[Bruce B.]

Re: Pushrods

Joe,

Thanks.

Bruce B

[Michael H.]

Re: Pushrods

Bruce,

Check out Comp Cams as I used there roller tip rockers and Magnum push rods after one of my original push rods bent due to metal fatigue on my L79 motor. The roller tip rocker arms fit under the stock valve cover with no problem.

Mike

[Duke W.]

Re: Pushrods

Roller tip rocker arms are one of the biggest scams ever perpetrated by the hot rod industry. Even modern Corvettes don't have roller tip rocker arms? They have roller trunnion rockers with plain tips that are curved to "roll" over the valve tip. They don't slide and vintage stamped rockers are similarly configured.

Joe L. previously posted the difference in the various OE pushrods, and the ...243 is the best of the vintage parts. I would not hesitate to install a used set at long as they passed a careful visual inspection - no signs of wear or galling on the tips.

I always recommend the use of OE rockers and pushrods unless you are turning and average of 5000+ revs, which is not possible in a road engine. If legal under the rules, roller trunnion rocker arms should be used in serious race engines.

But not all OE rockers are the same. The current slotted replacements cannot be used on mechanical lifter engines, and I think the best OE SB rockers have an "O" stamped on them and are heat treated to a higher hardness to resist wear, and they may have only been used on mechanical lifters. Joe L. can correct me if I'm wrong.


Duke

[Joe L.]

Re: Pushrods

Roller tip rocker arms are one of the biggest scams ever perpetrated by the hot rod industry. Even modern Corvettes don't have roller tip rocker arms? They have roller trunnion rockers with plain tips that are curved to "roll" over the valve tip. They don't slide and vintage stamped rockers are similarly configured.

Joe L. previously posted the difference in the various OE pushrods, and the ...243 is the best of the vintage parts. I would not hesitate to install a used set at long as they passed a careful visual inspection - no signs of wear or galling on the tips.

I always recommend the use of OE rockers and pushrods unless you are turning and average of 5000+ revs, which is not possible in a road engine. If legal under the rules, roller trunnion rocker arms should be used in serious race engines.

But not all OE rockers are the same. The current slotted replacements cannot be used on mechanical lifter engines, and I think the best OE SB rockers have an "O" stamped on them and are heat treated to a higher hardness to resist wear, and they may have only been used on mechanical lifters. Joe L. can correct me if I'm wrong.


Duke

Duke------


The GM #3974290 stamped "V" were the best of the GM small block rocker arms. Their predecessor, GM #3843359 stamped "O", are OK. Neither have been available from GM in a very long time. The only rocker available from GM is the guided type, GM #10089648.

The best aftermarket version of the non-guided rocker arm is the Crane Nitro Carb.

[Joe R.]

Re: Pushrods

Roller tip rocker arms are one of the biggest scams ever perpetrated by the hot rod industry. Even modern Corvettes don't have roller tip rocker arms? They have roller trunnion rockers with plain tips that are curved to "roll" over the valve tip. They don't slide and vintage stamped rockers are similarly configured.

Duke

Hi Duke:

I learned from your earlier posts that the stock rocker arm doesn't really slide across the valve tip. Rather, it sort of walks across the valve tip the way a shoe walks across the floor. I found this quite interesting and I agree that a roller tip rocker does not really decrease friction compared to the OEM design.

However, I also recall from some of your earlier posts that that you determined that as a result of the rocker "walking" across the valve tip, the stated nominal rocker ratio of 1.5 actually varies from about 1.35 at low lift to about 1.5 at maximum lift (I can't recall the exact numbers you cited). This makes perfect sense considering how the OEM rocker walks across the valve tip.

In comparing the contact patterns of stock rockers to roller tip rockers, I find that that the roller tip rockers create a much narrower contact pattern than the OEM rockers. This suggests to me that with a roller tip rocker, the actual effective rocker ratio remains closer to the nominal ratio throughout the valve lift range compared to the OEM rocker. So, a roller tip rocker with a nominal ratio of 1.5 yields closer to 1.5 at low lift than an OEM rocker.

So, while roller tip rockers do not help much with reducing friction, they do a better job of maintaining the nominal rocker ratio throughout the full range of the valve lift. In this respect, they do offer a tangible benefit over the OEM rocker.

[Duke W.]

Re: Pushrods

My measurements, dating to back to the seventies, yielded a lash point small block OE rocker ratio of about 1.37:1 and about 1.44:1 at full lift with about a 0.3" lobe. No conventional rocker are system has a constant ratio through the cycle because the effective lever arm on both the valve and pushrod side vary through the cycle.

Rocker arms "roll" across the valve stem due to their curvature - like a cylinder rolling on a flat surface as long a valve train geometry is in the ballpark, which can be affected by head and block deck milling and pushrod length.

Like all other conventional rocker arm systems, roller tip rocker ratio will vary through the lift cycle. I don't know if the roller tip has much effect on this, but if it does, it's likely minor to noise level. Anyone can find out by doing the simple measurement using a couple of dial indicators - one on the center of the rocker arm pushrod socket and one on the valve retainer. A solid lifter should be used to prevent any effects from hydraulic lifter bleed down and several should be measured to ensure consistency of the data.

Anything other than an accurate data set is pure speculation.

There is a broad based misunderstanding that OE rocker ratio is not consistent... that it varies from rocker to rocker. This is a complete misconception. If you take a bucket of any type of rocker arm and measure the ratio variation through the lift cycle all will show essentially the same ratio variation behavior through the lift cycle. The "variation" is through the lift cycle, not from part to part and is consistent for all parts of the same design.

Over the years GM Powertrain has made dozens of improvements to the modern small block to reduce internal engine friction that improves vehicle fuel economy in addition to increasing output. Roller trunnion rocker arms go back to the original LS1, and have been on all subsequent small blocks. They have conventional curved tips as do the Gen 1 stamped rocker arms. If roller tips offered any advantage GM Powertrain would have gone with that design years ago.

Duke

[Joe R.]

Re: Pushrods

Hi Duke:

I agree that the roller tip has almost no effect on friction compared to the shoe-type tip on the OEM rocker.

However, based on some observations of the contact patterns, I think that the roller tip does have less variation in the effective rocker ratio.

Attached are two photos that compare the contact pattern for an exhaust valve using the LT1 cam. The wide pattern is from an OEM shoe-type rocker, while the narrow pattern is from a stamped steel rocker with a roller tip.

It seems to me that the effective rocker ratio increases as the contact point moves across the valve tip. The effective ratio is lower with the contact point being toward the rocker stud, and higher with the contact point being toward the exhaust manifold. So, based on comparing the contact patterns, the narrower contact pattern of the roller tip suggests that the effective rocker ratio has less variation than the shoe-type tip.

I believe the min-max variation in the effective rocker ratio increases when the maximum valve lift is increased. So, the reduced variation of the roller tip might be more important for high lift cams.

Given that we pay a lot of attention to cam specifications that differ only slightly in terms of lift or duration, it's important to keep in mind that the rocker arm's job is to translate the cam's lobe profile into a valve lift profile. Any variation in the effective rocker ratio will have the effect of altering the intended valve lift profile. So, a rocker that has a smaller effective ratio at low lift than at high lift will have the effect of making the actual duration at the valve smaller than what was intended with the selected cam lobe.

In my case, the whole question of roller tips was moot when I built my 383 stroker motor. I decided early on that I would use rockers that have roller trunions, and the aftermarket seems to put roller tips on any rocker that has roller trunions. So, I did not have to give any thought to whether the roller tips were useful. However, based on what I see when comparing the contact patterns of shoe-tip versus roller-tip, I think the roller tips are giving me a more accurate representation of the intended valve lift profile, especially with the increased lift of .560" that I used.

[Gene M.]

Re: Pushrods

Hi Duke:

I agree that the roller tip has almost no effect on friction compared to the shoe-type tip on the OEM rocker.

However, based on some observations of the contact patterns, I think that the roller tip does have less variation in the effective rocker ratio.

Attached are two photos that compare the contact pattern for an exhaust valve using the LT1 cam. The wide pattern is from an OEM shoe-type rocker, while the narrow pattern is from a stamped steel rocker with a roller tip.

It seems to me that the effective rocker ratio increases as the contact point moves across the valve tip. The effective ratio is lower with the contact point being toward the rocker stud, and higher with the contact point being toward the exhaust manifold. So, based on comparing the contact patterns, the narrower contact pattern of the roller tip suggests that the effective rocker ratio has less variation than the shoe-type tip.

I believe the min-max variation in the effective rocker ratio increases when the maximum valve lift is increased. So, the reduced variation of the roller tip might be more important for high lift cams.

Given that we pay a lot of attention to cam specifications that differ only slightly in terms of lift or duration, it's important to keep in mind that the rocker arm's job is to translate the cam's lobe profile into a valve lift profile. Any variation in the effective rocker ratio will have the effect of altering the intended valve lift profile. So, a rocker that has a smaller effective ratio at low lift than at high lift will have the effect of making the actual duration at the valve smaller than what was intended with the selected cam lobe.

In my case, the whole question of roller tips was moot when I built my 383 stroker motor. I decided early on that I would use rockers that have roller trunions, and the aftermarket seems to put roller tips on any rocker that has roller trunions. So, I did not have to give any thought to whether the roller tips were useful. However, based on what I see when comparing the contact patterns of shoe-tip versus roller-tip, I think the roller tips are giving me a more accurate representation of the intended valve lift profile, especially with the increased lift of .560" that I used.

[Joe R.]

Re: Pushrods

Hi Gene:

I think the contact point of the shoe-type rocker starts out on the stud side of the valve tip and progresses toward the exhaust manifold as lift increases. This is due to the way that the shoe walks across the valve tip. The wide contact pattern I showed in my previous post shows the range of contact position as the rocker opens the valve.

I've watched this transition visually by looking directly at the rocker and valve tip as the valve opens. I can clearly see the curved shoe "walking" across the valve tip. Unless I've got my engineering mechanics wrong, moving the contact point across the valve tip changes the effective ratio of the rocker. To the extent that the variation in the contact point can be reduced, the variation in the effective rocker ratio will also be reduced.

[Mark E.]

Re: Pushrods

I've stayed away from roller tip, roller bearing or any arm with more than one piece. More parts and complexity = greater probability of failure. Imagine what happens if the roller tip disenegrates.

Is that risk worth marginally less friction? And now we learn the performance gains may be myth.

The beauty of Chevrolet engine design is simplicity. Stay with that theme.

[Gene M.]

Re: Pushrods

Hi Gene:

I think the contact point of the shoe-type rocker starts out on the stud side of the valve tip and progresses toward the exhaust manifold as lift increases. This is due to the way that the shoe walks across the valve tip. The wide contact pattern I showed in my previous post shows the range of contact position as the rocker opens the valve.

I've watched this transition visually by looking directly at the rocker and valve tip as the valve opens. I can clearly see the curved shoe "walking" across the valve tip. Unless I've got my engineering mechanics wrong, moving the contact point across the valve tip changes the effective ratio of the rocker. To the extent that the variation in the contact point can be reduced, the variation in the effective rocker ratio will also be reduced.

Joe, rocker arm ratio is not the first order of the rocker. I would guess GM had no concern for slight variations in rocker ratio but was major concern for the line of force. Objective to maintain the force pushing down on the valve to be as straight a line of force as possible. You have so many issues that cause the movement on the valve stem. The push rod length, head gasket thickness, deck height of block, the fact that heads are milled or not, position of the rocker stud, spring height, the length of valve stem, seat depth in head, and altered camshaft base circle. Any or all these minute tolerances stack up to exceed design intent. Duke is correct the roller tip on a stock Chevy SB does nothing when it is all assembled correctly. Aftermarket cam lifts outside the originals does disrupt the geometry considerably.

From a pure design objective the roller and axle pin is not dead reliable compared to a solid hardened steel stamping.