Inliners International Forums General Discussion Engines 261 push rods

Is their a difference in the length of push rods for mechanical lifters and hydraulic lifters? Does anyone have the lengths?

Thanks
Warren

Hi Warren . . .

The Master Parts Catalog has stock lengths (0.426):
TOCMP: Parts Master 1929-57 - page 141

Hydraulic lifters are typically shorter then solids so push-rods are correspondingly longer.

If you are using after-market lifters you might need to order custom length push-rods (to get the rocker-geometry right).

regards,
stock49

I am looking at installing a .510 lift cam and using stock solid lifters. The engine is a 1961. Did anything change from 1957? The rockers are stock.

Thanks
Warren

I guess I am not following you.

When rebuilding/modifying an engine there are several factors that can alter rocker-arm geometry which in turn drives push-rod length. Milling the head, sinking the valves, not compensating with shims under the rocker perches, zero decking the block all add to changes from stock length.

Next comes the variables of a reground cam with a smaller base circle and higher lift. Which is why most mock-up assembly and measure for length.

Is there a measurement you are perhaps already shooting for?

There's a good chance that .510" intake lift will not clear your (stock?) piston dome during overlap.

The original rocker geo was not "valve stem 90° to the rocker pivot axis @ 50% lift", and selecting components or making adjustments to achieve this is contrary to GM engineering.
The shaft center is located below this point by about 33-50% of lift to reduce scrub and extend stem tip and rocker pallet life.

A common remark "proper geometry places the rocker arm pad exactly in the center of the valve stem tip”. Not important, not a valid goal.

The total decking and milling is about .115, the intake valves were sunk .125, the valve stems were cut .125. I am currently running a McGurk roller cam with a .460 lift along with Smith Bros. push rods made to McGurk specs. I am running flat top pistons but have been considering Ross pop ups. I realize the piston may have to be notched. I also ave a NOS new set of solid lifters. I am not telling here, I am asking. I will take all this important input and anymore that may come to try and make a valid decision. I am working with a retired builder who built many 235s for circle track racing. The questions I ask are answers he cannot provide, but we will plastgauge and notch where necessary. Another thing, I have just changed my carb setup to three Holly/Webber 32/32s from Tom Langdon.

Thanks
Warren

I assume that's a steel cam? That permits fairly stout valve springs, heavier than the usual 250-280 lb. open. Did McGurk make a spring recco?
Are those rollers .990" or common auto with bushed tappet bore? What do the links look like?
3 X 32/32 as semi-IR (3 manifolds with minimal vacuum balance) or plenum?

McGurk supplied a steel cam, .990 roller lifters, dual valve springs and push rods. One of the inner springs broke and subsequently that push rod bent. The push rods were replaced with Smith rods but are the wrong length for solid lifters. No other damage. I replaced the intake valves with PG units and installed dual Buick 455 springs rated at 320 lbs. The three carbs are mounted on a Offy intake (plenum). The rollers only have about 3-4 total run time and look brand new although it is my intention to use new flat tappet solid lifters.

Thanks
Warren

???
On the same cam?

That would not be a happy place . . . on a two fronts. First the 261 is after the transition from steel to cast-iron cams - so the lifters are to soft to run on a steel cam. Second, a roller cam blank is designed with the lobes centered on the lifter bores - whereas a cam blank designed for flat-tappets has the lobes off center to the bores (so that the lifter rotates on the lobe).

No, as stated earlier, I am having a flat tappet cam ground.

Warren

As far as I know the '53-55 PG push rod - part number 3836260 measuring 11 13/32" was then used on all 6s from '56-62.

But with all the variables you have at play I would plan on measuring to be sure.

After this discussion and all the variables involved, I think it would be wise to verify the push rod length before ordering new ones. All I see on line are 7" to about 9" measuring tools. Has anyone seen one in the vicinity of 11" to 12"' Thanks everyone for your input and a Happy New Year.

Warren

The low-cost ones seem to target the ubiquitous V-thing market . . . hence they are too short.

The one's made for a professional engine builder require a bit more of an investment:
Jegs Pushrod Length checker


And the guys over at OE Pushrods have an interesting cross-reference table online: Application Chart by Length

Yeah, a little pricey, almost the same price as a set of push rods from Smith's. I will definitely measure before ordering, but going through the charts and all the chatter on line, very little distinction is made between hydraulic and solid liter assemblies. The most common mention is either 11.263 or 11.406 but never associating them with the lifter style and/or year. It is incredible that these engines were so popular in circle track racing at one time, yet the documentation is so scarce.

Thanks
Warren

That's because the transition period was over from a stock part perspective. The early 50's saw a lot of change in the Stovebolt lifter department:

with a variety of push-rods to go along with it. Chevy used the 3836260 push rod on both the '53 and '54 power-glide cars - and then standardized on the part in '55 for both solid and hydraulic lifters. It was used through '62.

The only other lifter change occurred in '58:

when the solid lifters were relieved to allow for a new top-end oiling system for the rocker arms - as documented here at the:1954 Advanced Design site. But the change did not affect lifter height or pushrod length.

The 11.263 dimension shown at the OE Pushrods site is a compromise. The vintage Chevy Parts Master Catalog shows the original parts and dimensions. The OE pushrod is longer than the 3835777 original and shorter than the 3836260 original - yet claims to replace both.

Welcome to the repair part party . . .

I dug out my circa '06 Dana Clevite cross reference - it shows the same collapsing of parts onto a single replacement pushrod:
Dana Clevite - 215-4010 <----------
Cross-references:
Old Clevite - 21-3020
McQuay Norris - RP110
Manley - PR32
Sealed Power - RP1218 and RP3020
Wolhert 2206L among others . . .

This of course makes no sense because the Factory original lifter and pushrod packages all vary (as evidenced by the Chevrolet part numbers and dimensions).

But again consulting the Dana Clevite cross reference on the lifters and sure enough all three of the Chevrolet hydraulic lifters depicted above collapse onto a single Clevite replacement:
213-1630 <---------
Cross references:
Johnson Hylift - A-761
TRW - VL6 and VL46
Sealed Power 761 among others

This can make for a somewhat maddening assembly process when mixing NOS Chevrolet parts with after market replacements from differing eras during the obsoleting and collapsing of repair parts over time.