The Stovebolt Site Forums The Shop Area Engine Shop 261 with 848 head

for those of you running a 261 with the 848 head.
what is the set up for rocker arm shaft lubrication?
i have looked in the 59 truck supp and the 54 truck manual
i'm not clear on exactly how the oiling of the rckr shfts is accomplished
i have the special head bolt with the hole in it but does that only work with a 261 head? or will the 848 work?

thanks
rolf

rolf,

Wait to hear from someone (pre68dave) who knows well the differences in heads and rocker-arm assemblies. You will most likely have to ID the style of your rocker arm assembly because the oil fed into the rocker arms by different "plumbing" over the years.

Here is information from Shop Manuals regarding lubrication differences over the several possible years of your 261 set-up.

Good luck,

rolf,
I have a 59 261 in my truck, the oil line is under the lifter side cover and comes from the rear cam bearing up to the center of the block. If you look at the block (in the shop manual) or on the head gasket you will see a spot were the oil will pass up to the head and the tube on the center of the rocker arm shaft the feeds the arms.

Rolf, what year is your 261?

Bowtietim has that setup. See if you can get him on the website.

rgie,

I think that bowtietim has a 1954 261.
He'll let you know the years of his head and rocker arm assembly.

The 261 and the 235 had a least 3 different kinds of head/rocker-arm plumbing between 54 and 63, as shown at the link in my post above. And, I think the "848" head and rocker arms assembly had at least two different kinds of plumbing. I think you will need to know the adaptation needed for the year of your block to the year of your head (and maybe of your rocker arm assembly).

Let Pre '68 Dave know the year of your 261 and he will move you along.

I have a 1954 261 with a 1956 848 head purchased from"wrenchbender ret".I'm running the 1954 261 rocker assembly on it.My oil tube runs behind the push rod cover.My set up does not have that special grooved,slotted head bolt.



Tim

i have a 59 block i'll check the head and get back with you the rocker arms came with the head from the junk yard

ok
to confirm
the block casting# is 3769925 and the date is c289 which i decode as march 28 1959

the head casting is 3836848 and the date is g80 which i don't know how to decode
there are some smaller #s cast into the side above the spark plus B52, 848, 850

out of curiosity what does the CON 9 on the head signify and the CON 2 on the block?

i was going to blow some air down the bolt hole in the block that would have the hollow bolt to see if there was a passage but i forgot
i can always check it later if need be
thanks
rolf

I always thought the CON #s were different conveyors in the plant.

I would suggest you start by reading THIS.
235's made a change in there rocker oiling system in 1958 and again in 1959. 261's seem to have changed slightly later.
To determine which rockers and connecter tube is correct for your engine, you first need to do some checking.
First, does it have a oiling pipe behind the side cover (you will need to pull side cover to know).
Second, if no tube you will need to pull the plug in Fig #4 and check the orifice size. The description on "Rocker shaft full pressure oiling" in this page is also important to read.
After that I can determine which rockers and connecting tube you need.

dave
the orifice in fig 4 on my block is 11/32.
there are provisions for the oil line from the cam to the middle of the block(behind the side cover) but i don't have the line do i need it?.
i have the rocker shaft oil tube and hollow bolt.
i'm guessing that since the head and rocker assy came off a 235 that the shafts are not the correct ones for the 59 261 oiling system.
this block has never been run. i got it from an old guy whose dad got it from the chevy dealer in their town when it closed down about 20 years ago. i got it with cam, crank and pistons only. i have an oil pump for it and valve and side covers
i need an oil pan

Your oil pan and mine are different.You need the late series oil pan 1955.2-1962.your pan will jog out at an angle on one side(gasket surface).
My oil pan is straight on both sides(gasket surface).


Tim

As Tim said, you need a 1955-62 pan for your engine, a 235 pan will work, make sure you get the oil pump pick-up to match the pan.

Now you need to pull one of the rockers off the shaft and see if the groove inside is centered or offset.

Did the drilled head bolt come with the block or with the head?

i got the bolt, rocker oil tube, and the oil pump from a yard out in portland OR.i have seen the two different pans in some of the manuals on line showing a bulge on one side. as a matter of fact both gasket kits i have come with both oil pan gaskets

i have the 235 together minus the water pump and my intent is to put that into the 53 3/4 ton. however if i get the 261 together i may be in a big of a conundrum.

dave , on the 261 block forward of the fuel pump mount there is another oval vertical two bolt boss. is that for the oil filter mount?

That two bolt boss sounds like you are talking about the front side motor mount provision used on 1955-57 car and 1955 2nd -59 truck.

You also will need the m-45 oil pump and not a m-29.


Tim

Is there a pipe plug at the rear bottom?
Is it possible to link a pic of the engine under the side cover?

there is a plug at the rear bottom of the lifter space behind the side cover
i have an m 45 oil pump. the pickup has no number on it
i have pictures. i will work on getting a link to them while at work this week.
you'll also see in the picts that the boss opposite the one in front of the fuel pump is of a different shape. i'm sure you're right dave they are for the front engine mounts.

i'll get the pictures on as soon as i can
rolf

here are some picts of the 261 and my 235

http://s1192.photobucket.com/albums/aa324/rgies/

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.

I would recommend using the 1954/55 rockers. They should have the groove inside each rocker in the center.

Thank you!!

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?

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.

Here is a good write up from one of our members (Pre ‘68 Dave) on the evolution of the Chevy rocker oiling systems. [LINK]

Dragsix, makes perfect sense, Thank you.

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?

Find and post the following:
block casting code
block date casting code
head casting code
head date casting code
engine serial number

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.

There are many 261's out there that are the 54 style water pump design but with a later date code. Warren Foster explained that they were essentially "crate engines" to be a drop in replacement for 216's when they died in larger trucks.

Thanks, Warren

A friendly and a helpful and a most knowledgeable man.

Ok so the Head casting# 3836848, Date code K 30 0, Block casting# 3769925, Date code Con 3 D 20 5 (the 5 could be a 9 it's hard to make out), Ser# F0404LB This engine also has a plate riveted to the block by an comercial engine builder so that may be the origin of the line being installed because there wasn't a hollow bolt in it when I got it. Sooo based on the date codes I don't need the line from the rear bearing or the bolt?

If pre 68 Dave is right, and I have no reason to think he is not, you will need to leave the line in place.

Yes I agree my block casting # is for a 1954/55 “3733950 with a copper line behind the side plate”. My head casting is “3836850” also for 54/55 but the actual casting date for both the block and head are from 1959 a replacement block. Since I am using a 848 head from 1962 I am Removing the rocker arm Assembly off the 3733950 54/55 head and bolting it on my 1962 848 head.

I have seen 261 dated blocks reported/posted from 1954-1962 with the 3836850 casting code .