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Re: 261 with 848 head
bowtietim #1394176 Mon Jan 25 2021 03:46 AM
Joined: Nov 2011
Posts: 11
J
New Guy
Sorry to revive a old thread but I’m running a 1955 261 3733950 and i have a matching 261 head 3836850 from 1954. I want to run a 1962 235 848 head with the steam holes drilled out but it does have different rocker arms. The tube that wraps around the rocker assembly is pitched. My question is should I just use the rocker assembly from the 261 850 head and bolt it to the 848? Or should I just stick to the 850 261 head? The tube on the 850 head is not pinched off.

Re: 261 with 848 head
rgie #1394221 Mon Jan 25 2021 01:57 PM
Joined: Jan 2001
Posts: 5,078
P
'Bolter
I would recommend using the 1954/55 rockers. They should have the groove inside each rocker in the center.


See the USA in your vintage Chevrolet!
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Re: 261 with 848 head
Pre '68 Dave #1394276 Mon Jan 25 2021 08:25 PM
Joined: Nov 2011
Posts: 11
J
New Guy
Thank you!!

Re: 261 with 848 head
rgie #1394706 Thu Jan 28 2021 12:32 PM
Joined: Oct 2014
Posts: 64
J
Wrench Fetcher
Ok after reading this thread I'm confused about my engine. I have a 59-62 261 block and a 59-62 848 head. This engine has the oil line behind the lifter cover and the pinched off tube on the head. It does not have the drilled bolt and the rockers have the offset groves in them. Do I need to change anything about this set up or leave it alone?

Re: 261 with 848 head
rgie #1394713 Thu Jan 28 2021 02:51 PM
Joined: Dec 2017
Posts: 925
D
'Bolter
Leave it alone, you have the correct set up. In 59, GM made the last of the oiling improvements to the 235 and 261 motors. Oil to the rockers came directly from the galley instead of bleeding it from the rear cam bearing, they enlarged the metering orifice in the block that sent oil to the head and rockers, and pinched off the connector/overflow tube. What this did was create a sort of pressurized system. As for the rockers, 58 and earlier rockers had the oil groove on the inside of the rockers set up to intersect the dribble hole on the rocker. Because the 59 and up motors had this sort of pressurized system, GM moved the groove so that it was now offset from the dribble hole so that the rockers would dribble and not spit over the push rods and springs leading to oil starvation and no spring cooling. So if you have a later block and head, you want to use the off set rockers meant for that motor.

The drilled bolt, that is not a factory installed bolt. That bolt was one of two parts you needed to use if you were replacing an early short block with a later service replacement short block. There was also a plug or little cap that you had to use with the bolt. The cap plugged the larger oil passage in the later block, the drilled bolt redirected oil flow through the bolt to the rockers, and metered a little less oil to the the rockers. This was done so that you could use the later short block with an early head and rockers (with the centered groove in the rocker). That way you got the dribble you need for the rockers instead of spiting over the rockers.

The pinched connector was a feature of the 59 and up system, buuuuuut, thousands of earlier loop style connectors were almost routinely pinched off when either the port from the rear cam bearing got clogged, the rear cam bearing became so worn that all the pressure bled out around the loose bearing and no pressure to the steel tube that ran from the rear cam bearing to the center top of the block behind the lifter cover, or the tube just became restricted with build up and would not flow enough. The thought was to not allow any oil to drain away from the loop. So everyone pinched off, or cut off and squashed, the loop to try to maximize oil to the rockers in the earlier motors.

The clogged or worn cam bearing issue was also the genesis of the aftermarket copper tube kits that connected the oil galley at the oil sensor port on the driver side of the block, and directed it through a copper tube to the hex head fitting on the outside middle of the passenger side of the head. That port was a direct feed to the rockers. Some of those kits were just copper tube and some elbows. The best of the kits had an adjustable valve that allowed you to tailor the oil supply. Why? To keep the new supply from being too much of a supply and spitting over the rockers and soli springs instead of dribbling. You could actually adjust the external supply to get the feed to dribble.

Make sense? I think what I wrote makes sense but maybe not, lol.

Last edited by Dragsix; Thu Jan 28 2021 02:58 PM.

Mike
Re: 261 with 848 head
rgie #1394715 Thu Jan 28 2021 03:04 PM
Joined: Feb 2019
Posts: 1,620
P
AD Addict
Here is a good write up from one of our members (Pre ‘68 Dave) on the evolution of the Chevy rocker oiling systems. [LINK] [chev235guy.blogspot.com]


Phil

1952 Chevrolet 3100
Project Journals
‘59 235 & hydraulic lifters
“Three on the Tree” & 4:11 torque tube
12v w/ Alternator
Re: 261 with 848 head
Dragsix #1394718 Thu Jan 28 2021 03:33 PM
Joined: Oct 2014
Posts: 64
J
Wrench Fetcher
Dragsix, makes perfect sense, Thank you.

Re: 261 with 848 head
rgie #1394782 Thu Jan 28 2021 10:00 PM
Joined: Dec 2017
Posts: 925
D
'Bolter
John, re reading your post, your block has a line behind the cover? That is not a 59 and up block, or at least it should not be one with the line. What is the casting number and any chance you can find the casting date?


Mike
Re: 261 with 848 head
rgie #1394785 Thu Jan 28 2021 10:35 PM
Joined: Sep 2001
Posts: 31,055
'Bolter
Find and post the following: [1954advance-design.com]
block casting code
block date casting code
head casting code
head date casting code
engine serial number


Tim
1954Advance-Design.com [1954advance-design.com]
1954 3106 Carryall Suburban [stovebolt.com] - part of the family for 49 years
1954 3104 5-window pickup w/Hydra-Matic [1954advance-design.com] - part of the family for 15 years
- If you have to stomp on your foot-pedal starter, either you, or your starter, or your engine, has a problem.
- The 216 and early 235 engines are not "splash oilers" - this is a splash oiler. [chevy.oldcarmanualproject.com]
Re: 261 with 848 head
rgie #1394795 Thu Jan 28 2021 10:55 PM
Joined: Jan 2001
Posts: 5,078
P
'Bolter
My experience with 261’s is, they do not have the exact time line for changes as 235’s. I believe they kept the line under the side cover a little longer.


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