The Stovebolt Site Forums The Shop Area Engine Shop Rocker arm question

I have a Canadian 261 Chevy truck engine cast in Dec 1956 with an external oil tube under the push rod side cover. I am using an 848 head, with steam holes, cast in August 1957. Can I use the newer style rocker arms with the offset oil distribution ring and a crimped closed oil tube in the middle of the shafts or must I use the older rocker arms with the oil ring in the center and an open oil tube in the middle of the shafts?

At the rear end of that tube behind the side cover there is a fitting that screws into the block. That fitting has a 1/16” hole in it to restrict oil flow to the rocker.
I think by drilling that restrictor out to around 1/8” you could use the offset rockers and a center supply tube that doesn’t have the loop that allows oil to escape. That style was used up to 1958.
You need what is often referred to as the pinched off style that started in 1959.

Thanks for your response, Dave, I was hoping to hear from you. I will drill the fitting to 1/8th inch and try the offset oil ring rocker arms with a later style center oil tube. It will be a while before I can run this new rebuild due to health issues but I will report back when able.

Get well soon!

Boring to 1/8" is a 300% increase.
Does this affect system oil pressure?

The amount of oil flow through the rocker shaft will be affected by the wear and clearance between the rockers and the bottom of the shaft. Doubling the size of the orfice at the rear cam bearing shouldn't reduce oil pressure enough to cause a problem unless there's an excessive amount of clearance there, and/or the other pressurized bearings such as main and rod bearings are also badly worn. Developing even one pound of pressure at the last bearing in the system indicates the oil pump is supplying more oil than the engine needs.
Jerry

The other issue is there is a restriction in the block itself that was enlarged in 59 to accommodate the direct feed from the main galley to the rockers. The problem with enlarging the fitting at the rear cam bearing boss is that it pulls pressure and volume from the rear cam bearing on the 56 block as opposed to the main galley on the 59 blocks. Really the better way is to use the rockers that were designed for the oiling system for that year motor.

Another alternative to drilling the fitting. Remove the steel line and fittings behind the lifter cover and install 1/8 plugs. Run an oil feed line from the main galley where the oil filter line and oil pressure switch would normally go. If you were using a filter, it would run from that port to the filter and then dump directly to the pan. Instead of funning to the bypass filter, run the line to the side of the head where the hex plug is. Its a direct feed to the rockers, feeding from the main galley, and so that would support use of the offset rockers. You lose the use of the oil canister filter (some of them, maybe all of them have an internal restriction). Dont go crazy with the id of the lines. Too big and you are robbing too much pressure from the mains.


For an oil filter, here you could change out to an after market spin on adapter and a spin on filter, say a Fram PH-8 or 8A for example, use some reducers and some copper or braided Autometer lines, and run the output of that filter (which would be less restrictive then the canaster), to the port on the side of the head. I ran a hot rod 57 235 that way for years because my offy side plate would not fit with the steel line and I only had a set of 59 rockers to use at that time.

How does the ID of an oil line affect pressure?
Jerry

My 235 has the tube behind the cover also if you need to take a look .Out at camp but next time I am in I can check it out if you have some questions

Well, when I was 16 or so, the line behind my cover apparently clogged. I knew very little about what I was doing but was advised that a kit could be purchased to fix the lack of oil to the rockers. Problem, no money. So a friend whose father was an oil heat mechanic got his hands on some of his dad’s copper tubing and some fittings and we made a line up. Only problem, the line was really big, maybe 1/4 or better I don’t really remember it’s been 46 years. We hooked it up and god we had oil all over the head and rockers, leaking out every possible spot imaginable. But the oil gauge was reading no pressure. We robbed to much volume to maintain pressure. A local mechanic fixed all that, with a kit of course, and I paid for that for a good while.

Your problem was the oil clearance between the rockers and the shaft, not the size of the line. With proper clearance on all the parts I can lubricate rocker arms with a 1 inch line- - - -as long as the rocker shafts aren't worn out.
Jerry

I don't disagree that clearance was part of the issue, but that is the case for most if not all 235 motors, especially using less then new rockers. And the rockers themselves, they were spitting, not dribbling and thus not getting the lubrication required. The other issue of course when using a 59 and up set of rockers on a 58 and earlier block is that as the cam bearing wears, the line gets clogged, or the entire system wears, the pressure can dip just because of the wider clearances and clogged lines. The more restricted 59 and up rockers contribute to the problem. I stick to my guns. Run the correct rocker for the block. Sometimes easy is good.

Currently, I'm working on a Torrington roller bearing modification of stovebolt rocker arms, with free floating pivot shafts that won't wear on only one side. Those rockers will be lubed with full pressure by an oil line tapped directly into the main oil gallery. I'll probably use a 1/4" diameter line for that little chore.
Jerry