Overhead Valve Train Design.

Started by Ralph Messina CLC 4937, December 08, 2015, 05:08:51 PM

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Ralph Messina CLC 4937

This is a question of why both Ford and GM designed new OHV engines using two different hydraulic valve lifter designs. When Ed Cole and company designed the ’49 Cadillac engine, they chose nonadjustable valves. That is the action of installing the assembled rocker shaft on the head preloads the lifters through the rocker and pushrods. Because of the preload, the push rod  always contacts the end of the rocker arm. When Cole headed up development of the Chevy small block for ’55 he chose to have adjustable valves. The proximity and loading of the push rod/rocker interface must be controlled by an adjusting nut on top of the rocker. (usually called valve lash adjustment.) This method requires more parts and labor and likely higher cost. What was the desired benefit â€" performance, cost, durability etc. - of one design over the other? Cole already knew how to preload the lifters. There’s also a parallel example at Lincoln between’52 and the mid 60’s. Earlier and latter engine designs had nonadjustable hydraulic valves but the mid-fifties  Lincolns had the hydraulic valve lash adjustment requirement.

Any thoughts
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The Tassie Devil(le)

I believe the Chev design was far cheaper to produce than the Cadillac style.

The Chev design makes it easier to add performance parts, and one has to remember that the Corvette was getting the engine and it would have been too costly to produce a lot of non-adjustable parts to suit different Camshafts for the same engine.

Plus, even if they saved $1.00, the numbers produced with the Chev was far greater than the Cadillac.

Bruce. >:D
'72 Eldorado Convertible (LHD)
'70 Ranchero Squire (RHD)
'74 Chris Craft Gull Wing (SH)
'02 VX Series II Holden Commodore SS Sedan
(Past President Modified Chapter)

Past Cars of significance - to me
1935 Ford 3 Window Coupe
1936 Ford 5 Window Coupe
1937 Chevrolet Sports Coupe
1955 Chevrolet Convertible
1959 Ford Fairlane Ranch Wagon
1960 Cadillac CDV
1972 Cadillac Eldorado Coupe


Hello Ralph,

When I first started working on engines, I worked on small-block Chevy V-8s.  Later, when I had a chance to see the 50's Cadillac V-8s, I remarked how similar the Caddilac engines were to the Chevrolet engines.  Of course, it is the other way around.  The small-block Chevy is derived from the '49 Cadillac OHV engine.  Chevrolet, being the introductory GM division, had to keep the cost of the new (in '55) V-8 competitive.  Ford was always a concern for Chevrolet, but Cadillac did not have the same competitive pressure.

I am not sure that the Chevy valve train is more costly to produce than the Cadillac's.  Cadillac used valve guides whereas Chevy did not (cost advantage to Chevy).  Cadillac mounted the valve rocker shaft on four pedestals in each cylinder head whereas Chevy used eight valve rocker studs in each cylinder head (cost advantage to Cadillac, maybe - machining the pedestals in the Cadillac may only have been a little less expensive than drilling and pressing in the Chevy's rocker studs).   Cadillac used 16 rocker arms that are much more precisely machined than the steel stamping rocker arms used by Chevrolet (cost advantage to Chevy).  Cadillac used a shaft and springs to mount and locate the rocker arms, Chevy did not (cost advantage to Chevy).  Cadillac did not use a ball and adjuster nut, whereas Chevy did (cost advantage to Cadillac).  My guess is that when the production engineers at Chevrolet were trying to develop a reliable, but less expensive, valve train based on the Cadillac OHV engine, the valve train that was introduced with the small-block Chevy in '55 proved to be the solution.  So much so, I would suggest, that Cadillac adopted a hybrid version of it in '67 when the 429 engine was equipped with pedestal mounted valve rocker arms.

Respectfully submitted,
Christopher Winter
Christopher Winter
1967 Sedan DeVille hardtop



Is are the heads different on a 67 429 then earlier 429's 64-66? They have the same head as the 390 don't they
I got myself a Cadillac but I can't afford the gasoline (AC/DC Down Payment Blues)

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1962 Coupe Deville


Agreed the stamped rocker SBC design seems cheaper to produce vs the Cadillac shaft system.

The other reason may be that many engines based off of the SBC architecture were offered with solid lifter camshafts which require adjustability.  (whereas Cadillac would be all hydraulic lifter)

Ralph Messina CLC 4937


Thanks for the responses. We’ll never know the exact reason because we don’t have access to GM cost data. The Chevy design does appear to have a cost advantage; but not as much as a smaller number of parts might suggest. Stamping and secondary operations to finish the repetitively stressed parts would be more expensive than the simplicity of the rocker suggests. I have a sense that suggestions above that Chevy’s desire for a flexible design and increased future performance output may have been the deciding factor in the design process. The fact that no one suggested a performance difference, and that history shows excellent durability over time, means Cole’s design was more genius than accident.

Daddyholic: The ‘49-66 heads and rocker systems were rockers on a shaft derived from first OHV design. For ’67, the head and rocker design was changed to the pedestal type rocker used on the 472 but mounted to the 429. In ’68 the engine beneath that new head was completely redesigned yielding the “full” 472 package.

1966 Fleetwood Brougham-with a new caretaker http://bit.ly/1GCn8I4
1966 Eldorado-with a new caretaker  http://bit.ly/1OrxLoY
2018 GMC Yukon

Dr. John T. Welch

As Alfred Sloan said, "General Motors is in  business to make money.  We also make cars".

No one ever went into a committee meeting at GM to announce that they were going to increase costs. If they did, they walked  out of that committee meeting without a job. Ed Cole had a long career with GM.

Stamped rocker arms, ball pivots, studs and friction lock nuts are cheaper at high production volumes than cast rocker arms with machined bores, precision ground  rocker shafts, pedestal mounts and the associated close tolerance machining of  cylinder head deck and pedestal mount surfaces.
Multiply that cost savings by the vast difference in engine unit volumes Chevrolet vs Cadillac and you begin to see the profit picture.

GM does things for one and one  reason only:  to save money or make more of it.

Now , if  I could just get the ignition switch in my '05 Impala to stop turning the engine off every time I go over a speed bump.........
John T. Welch
CLC   24277

Philippe M. Ruel

When both Cadillac and Oldsmobile OHV V-8s were released in 1949, Buick OHV inlines had been using the proven rocker shaft design for decades, whether with adjustable mechanical lifters or non-adjustable hydraulics.

Individual stamped steel rockers may have seemed quite a novelty on early SBC engines. Although requiring individual adjustment, stamping is much cheaper on a large scale than casting/machining. If they could make stamped camshafts or engine blocks, they would - not sure no one has ever tried to.
1952 60 Special in France.