Hello, hoping to get some verification on this. I'm rebuilding the engine in my 1949 3100 - its not the original engine and I've discovered that the block and cylinder aren't matched in age either. So if my research is correct on the 235 they used the copper line from the rear cam bearing to take oil up to lubricate the rockers behind the push rod cover until 1957, then in 1958 they used a channel from the front and rear cam bearing that supplied oil to the rockers via a drilled channel in the center of the block under the push rod cover, and in 1958 there was a 1/16" orifice to mimic the restriction that would have previously been provided by the copper tubing. Then in 1959 they changed that orifice to 11/32" and moved the oil groove in the rockers over by 1/4" and got rid of the bypass loop on the center sleeve to provide a pressure system. My question is what is the proper rocker set to use with this 1958 block with the 1/16" orifice, mine had the later versions with the oil groove offset but they were also worn out so perhaps that's why? My thinking would be to use pre 58 rockers but I would appreciate it if someone with more experience and wisdom could give me a yay or nay. Thank-you
Just a slight correction to the above post. It is not the head that makes a difference, but the block. So up to and including 1958, center groove rockers would be used on a 1958 block.
True, if you are not concerned with the head's date casting.
Not sure what you mean? The oiling path did not change between 1953 and 1962 on 235’s in the head. It is only the block, rockers and rocker connector that changed through the years.
Thanks for your replies, that's what my thinking was as well. I have a set of center groove rockers that came from a 1952 235 that are in great shape and seem to bolt up nicely, was there a change in 54 on the rocker assembly and would it be a bad idea to use these ones?
The drilled head bolt gets used when you are running a 59 and later block, but using 58 and earlier head and rocker assembly. The head is not really the issue but the center groove rockers are and looped overflow on the rocker connector. Btw, it’s not just the bolt, but a plug also.
"True, if you are not concerned with the head's date casting."
Example: A mint condition unmodified 1962 Chevrolet truck with a 235 engine would have 59-62 rockers but not installed on a head with a 1956 casting date.
"Adding CFM to a truck will only help at engine speeds you don't want to use." "I found there was nothing to gain beyond 400 CFM."
I think it’s easier to explain why the head is not the real issue by explaining the reason for the bolt and plug in the first instance. So if you had say a 55-57 car or truck, and the motor went bad, bad rings, bad bearings, whatever, and you were at the dealership in say 1960, the dealer would order a service replacement block. Those fitted blocks are unusual in that they were cast with various motor mounts that would allow those block to be installed in 55-60 vehicles but those blocks were in fact the later 59-63 design blocks.
In other words, you were swapping the later design block for the earlier design block, and reusing all the other parts, including the head. So if you were swapping the new block and you were using the rest of the earlier parts, rockers and head included, you installed the bolt and plug to cut down on the oil flow to the earlier center groove rockers. If you were replacing a 59-63 block with a late design service replacement block and reusing all the other 59-63 parts, you did not install the bolt and plug.
So it’s not really the head you want to match up with the block but really the rockers. Late block and early rockers, too much oil spitting around, taking pressure and volume from the rest of the motor.
My 54 I purchased in 1988 ,I was new at fixing and decided to get a rebuilt motor the machine shop took my core and ordered a short block and rebuilt the head .Once installed there was no oil going to the rockers ,I went back to the shop and the machinest went to the back and pulled out the tube for the block to head from a box and said they did not think it was needed due to the newer block.I wish they would have used a older block with the waterpump in the proper location but everything works and they gave me a new set of rocker shafts and rockers that I have on hand .
"My question is what is the proper rocker set to use with this 1958 block with the 1/16" orifice, mine had the later versions with the oil groove offset but they were also worn out so perhaps that's why? My thinking would be to use pre 58 rockers but I would appreciate it if someone with more experience and wisdom could give me a yay or nay."
1954-58. The top half of the picture. Some parts made between 1950 and 1958 can be used but I'm not going to expand on that. One way to differentiate is by looking at the oil collector. Unfortunately this is not 100%. I have seen rocker arms mixed. Some old style oil collectors crimped on top.
A common history is that, over many years, sludge builds up in the tubes and passages and eventually blocks oil from making it to the rocker assembly. Back in the mid 60's I remember a old farmer was fussing because his engine was making a racket. Ed, the mechanic, pulled the valve cover off. He shouted well no wonder, it's bone dry. Ed cleaned up the oil returns and poured oil over the rockers. It was not as noisy as before but still no oil was making it up to the rocker assembly. Ed told him how much it would cost to fix the problem. The farmer laughed and said, nah. I'll drive it like it is. You can bet the farmer kept a can of oil in his truck after that. These old trucks were mistreated in the worst way but they kept on running.
Last edited by buoymaker; 03/28/202211:57 PM.
"Adding CFM to a truck will only help at engine speeds you don't want to use." "I found there was nothing to gain beyond 400 CFM."
Use the 55-58 rockers with the center groove intersecting the spit hole in the rocker.
Edit. Let me walk that back. What is the casting date on the block? The reason I ask is that the production line for 58 would have shut down like August or September, I forget which, to re tool for the next model year. For example, I had a block cast in like late july or August I want to say of 55. Shooting from the hip you would say its a 55 block but in reality it was a 56 block with the neoprene seal.
So if your block was cast in late 58, it may have been cast for the 59 model year, if so, then you use the 59 and up rockers.
If some of the measurements I've been taking, and the calculations I've been doing for a while come out right, the entire pivot shaft, support brackets, and rocker arm assembly might be able to be replaced by stud-mounted rockers like the 250 engine uses. If so, that could make the entire system obsolete. Initial results are looking somewhat promising. Jerry
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