Oil Pressure - Rocker Arm Assemble

Posted by: Ted's Inline 6

Oil Pressure - Rocker Arm Assemble - 11/06/13 03:05 PM

I'm building a 1954 261 engine and there is a 1/4" oil line (copper piping) from the main oil galley on the side of the block to the inside of the hollow bar the rocker arms pivot on. The pipe brings oil into the interior of the rocker arm assembly and also goes past the assembly and dumps oil onto the top of the head, under the rocker arm cover.

The end of the pipe on my stock 261 was wide open.

I've taken four 235 engines apart in the last 6 weeks and the 261 is the only engine with that oil line open. All of the others have had the pipe crimped to some extent to restrict oil being discharged on top of the head. One of the 235 oil pipes was bent over completely to force all of the oil into the rocker arm assembly where it would eventually surface onto the top of the head and splash onto the pushrods.

Can anyone help me understand what is going on and what I should do as I assemble the engine? Is this an effort to keep the engine's oil pressure as high as possible?

All help appreciated,

Thanks,
Posted by: stock49

Re: Oil Pressure - Rocker Arm Assemble - 11/06/13 07:56 PM

 Originally Posted By: Ted's Inline 6
One of the 235 oil pipes was bent over completely to force all of the oil into the rocker arm assembly where it would eventually surface onto the top of the head and splash onto the pushrods.


Hi Ted . . . not sure why you've found these other anomalies as the top oil line is supposed to run past, up and over the rocker shaft with 'overflow' discharging down into the lifter bay:
1954 Chevy Truck Shop Manual

This design is essentially unchanged from the stovebolts. The line is intended to provide pressurized oil to the hollow rocker shaft. The shaft is drilled to allow oil to lubricate each rocker arm. The pressure in the shaft is governed by the fit/clearances of the rockers on the shaft.

I don't see how crimping the end of this 'overflow' line could materially affect the the main bearing or rod bearing pressures - the line is peripheral. Not unlike the reasoning that caused some engine builders of yore to peen over the oil holes in the big end of the connecting rod (which Chevy put there to oil the cylinder walls - another peripheral use of pressure). Besides, this rocker oil line is fed from the camshaft on a 261 so it is already one hop away from the mains.

I think that attention to main, rod and camshaft bearing clearances is the best way to assure maximum oil pressure in these areas - which in turn will provide maximum pressure to the peripheral uses of oil.

regards,
stock49

Posted by: Ted's Inline 6

Re: Oil Pressure - Rocker Arm Assemble - 11/07/13 09:06 AM

Hi Stock, thank you for the quick response and the reference to the shop manual. I went to the book and read the passage

"....connector pipe between the two hollow rocker arm shafts, then distributed to all rocker arm bearings. A bleeder hole in each rocker arm supplies oil for lubrication of the valve stems and push rod sockets."

The entire rocker arm assembly in the 261 was and is in great shape; no discernible wear on the hollow shafts or the rocker arms (I didn't know there were bearings for the rocker arms) and my intent is to reuse the entire assembly as it is.


All additional information / comments are appreciated. I truly appreciate your help.

Thanks,

Ted
Posted by: stock49

Re: Oil Pressure - Rocker Arm Assemble - 11/08/13 07:26 AM

 Originally Posted By: Ted's Inline 6
The entire rocker arm assembly in the 261 was and is in great shape; no discernible wear on the hollow shafts or the rocker arms (I didn't know there were bearings for the rocker arms) and my intent is to reuse the entire assembly as it is.


This is consistent with my experience on stovebolts and jibes with the shop manual - where there is no discussion about checking for wear or clearances in this assembly - just a recommendation on cleaning to remove "gum & sludge" to make sure oil flows.
Posted by: panic

Re: Oil Pressure - Rocker Arm Assemble - 11/08/13 10:48 AM

If there are bushings inside the rocker arms, they were either rebuilt (RAS etc.) or much older than the engine.
Posted by: Whitedog

Re: Oil Pressure - Rocker Arm Assemble - 11/09/13 09:18 AM

There's actually a couple different designs for the rocker shaft oiling. The 56 and earlier had drain back port. It was common practice to crimp in shut. It was a thought that it helped the outer rockers get more oil, and it helped with engine oil pressure.

The 57 and newer blocks didn't have the drain back port. That was due to changes in the oiling system They had an orifice opened up on the block.

I have 2 235's in my garage right now. The 55 block has the drain back. Whereas the 59 doesn't.

6 cyl. oil flow

More good info. tech tips
Posted by: mdonohue05

Re: Oil Pressure - Rocker Arm Assemble - 11/12/13 09:14 PM

Here is what I have always understood. The 55-57 235 uses the rocker arm connector that loops over itself and dumps excess oil onto the head. The 55-57 motors received rocker oil from a steel line under the tappet cover that pulls oil pressure from the rear cam bearing to a fitting under the cover about the middle of the head. You can see about where this is by looking for the bulge in the cover. This line is notorious for clogging up and starving the feed to the rockers. Lots of owners, when flow was impeded a bit would pinch off the copper loop on the connecter to attempt to keep all of the oil possible going to the rockers. Eventually the line would clog up completely and then you would use an aftermarket external oil line kit to run oil from the driver side of the block
at the oil sender unit, to the square plug on the side of the head which is a direct feed to the rockers. The above may also apply to the 58 motors but I am not positive. For the 59 and up 235 motors, chevy made a slight change in the rocker oiling system. Those blocks do not use a steel line from the rear cam bearing but draw oil from the main galley center bearing up through a drilled passage in the block tonthe head. Gm also enlarged the the size of the feed in the head and used a connector that was pinched off from the get go. This provided a more pressurized sealed system. Gm also altered the rockers so that the higher pressure would not spray oil way over the rockers and springs
instead of the oil running out the rocker spit hole and lubing the rockers, adjuster balls, and springs. They did this by moving the oil grove inside the rocker arms. So if you look at a 55-57 rocker arm, the grove intersects the oil spit hole. On the 59 and up, the grove is offset and does not intersect the oil spit hole as a way of maintaining a little pressure and keep good oil to the rockers.
Posted by: Ted's Inline 6

Re: Oil Pressure - Rocker Arm Assemble - 11/13/13 02:16 PM

Great information guys, thanks to all of you.

From the discussion above there is no disadvantage in a 1954 261 engine to leaving the rocker arm center connector piping, that dumps oil onto the head, as it is. There may be a negligible improvement in oil pressure (advantage) if I crimp off the end of the discharge piping.

As the engine is being built with a "Bulldog cam", will only be driven occasionally on the street, and I'm using 10W-30 oil, I will leave it stock.

Have a great day,
Posted by: mdonohue05

Re: Oil Pressure - Rocker Arm Assemble - 11/13/13 07:51 PM

Stock is fine. I will say this though. The earlier 55-57, and maybe 54, rocker assemblies have not been available new for quite some time. The later 59 and up were made new by sealed power and trw for a lot longer (although I believe production stopped a couple of years ago) so not surprising to still find them new. I have always used a pinched off connector just to make sure that all of the oil goes to the rockers because to have them rebuilt is not cheap. The key to longevity in my book is good oil to keep the shafts from galling and the adjuster balls from wearing out. You might ask if anyone has an extra pinched connector for sale. I think that is the better play. Just a thought.
Posted by: stock49

Re: Oil Pressure - Rocker Arm Assemble - 11/14/13 08:19 PM

Some go so far as to describe this practice of crimping shut the overflow line as 'a used car lot trick':
H.A.M.B.

I guess I would like to hear more about logic behind this 'field' engineering change.

After all the purpose of the line is to provide a certain rate of flow up top. Crimping the overflow restricts the flow rate through the line which in turn will likely promote deposits in the line itself - further reducing the volume of oil reaching the rocker shaft.

Keeping the assembly clean (as the shop manual describes) seems the best plan. Making sure that the overflow is properly directed to the drain hole will prevent excess oil from collecting on the head.

This is the design intention (as I understand it).
Posted by: Ted's Inline 6

Re: Oil Pressure - Rocker Arm Assemble - 11/20/13 01:07 PM

You guys don't make choosing an option easy! I really appreciate everyone's input but am going to stay with the way it was built.

I'll leave the end of the line open and allow the system to function as designed. If I should have a problem I have two rocker arm assembly's from 1959 235s and will install one of them. I should be able to assemble the engine in about 10 days and over the holidays will get it in my '50 sedan.

Happy Holidays!