VCCA Home Forums TECHNICAL - 1945 AND EARLIER 1933-1936 Oil pressure; Oil distributor

I'd like to start a discussion about oil pressure in a 207 cu.in. engine. Like most, mine runs at around 7 psi when warm. I know the key to lubrication is delivery, not pressure, so my concern is how the oil gets distributed to the front and rear rocker arms.
The brass distributor sends what looks to be 90% of the oil to the front arms and severely restricts the flow to the rear arms. (I think I have that right). The oil flow is notably different to each set of rocker arms. My question is has anyone tried to enlarge the small hole in the brass distributor to increase oil flow to the rear? Would this reduce the oil pressure further? Can the flow to the front arms be restricted? Does anyone have any experience or advice?

If it ain't broke don't fix it! just make sure the lines and orifices are clean and free of crud, I understand that the engine may be lower in the rear, and the oil will run toward the back?
Come on Gurus help me out here!

Hi Coachhill,

Your engine is designed to do exactly as you describe. Don't try to modify a correct design.

You mention 7 lbs. of oil pressure when hot.At what engine speed is this????.If its at idle its great.

If the shaft and bushings are in good condition then there will be sufficient pressure and flow to the rear rocker arms. All it takes is a few drops of oil every once in a while to lubricate the rocker arms.

Yeah, I figure if the Wheels are A'Turning and A'spinning, Windshield is A' Shielding and rockers are A'rocking and the tappets are A' tapping and Nothin' ain't A'Squeekin' and The Pistons are.......A'Slapping and A'going up and down and the rods are A'splashin' and the Motometer is A' meterin' The old thing is A' doing OK!

Ok guys...I get the idea. With all due respect it still appears the rear shaft is "underlubricated" especially in comparison to the front. If you've ever seen the rockers operating while the engine is running you might be concerned too. When I had the rocker assemblies apart the rear shaft was more heavily worn than the front, indicating insufficient lubrication.
Well, maybe I'll just try the modification and report back in a while. The goal would be to maintain oil pressure and maybe even out the oil flow to both halves of the rockers. It may take a little time to get back in the garage so be patient!
I welcome all other thoughts and comments!

We may not have enough "given" information to provide you with an intelligent reply. For example: Have the rocker shafts been removed from the engine recently? Has the plug been removed from the rear rocker shaft? Any modifications to the center connection where the oil is fed to the rocker arms. The sleeve in this distribution device has a restriction to the rear shaft. Perhaps this small hole in the sleeve is plugged with debris and has completely stopped the flow of oil to the rear shaft. Check that the distribution device has a vent hole at the top of the curve. This vent is necessary to keep the oil from being siphoned out of the shafts when the engine is not running and returned to the pan/sump leaving the rocker shafts 'dry'.

Chevrolet was concerned that too much oil would be diverted to the rear rocker shaft as a result of the inclined engine mounting. That is why the restriction is in the sleeve that provides the oil to the rear shaft.

Worn rocker arm bushings also can reduce the oil flow to the rears.As the bushing wears the center grove becomes more shallow-decreasing the flow of oil.This will cause more oil to flow to the front.

The "rear half" on my '34 recieves almost as much oil as the front-the difference is hardly noticeable.I had replaced both the shafts and arms (20,000 miles ago)

Also, if the over flow tube is flowing to much oil it will starve the shafts. In the old days the over flow tube would be pinched to restrict flow forcing more oil through the shafts. If everything is new (shafts and bushings) you should have oil splashing at all of the rockers after the engine has run for a few minutes.

Mike :)

Ok, I'll try to fill in a few blanks. The engine was completely rebuilt years ago and stored but kept loose and oiled. I installed the rockers 2 years ago when I first got the engine running and the oiler, shafts and distributor were all clean; they are used, showing signs of wear, but usable. Gene could be on to something with the grooves wearing down and not letting oil through. Still, with a little play between the rocker arms and the shaft I would think the oil would find its way through. Mike, the overflow tube is pinched but to what degree I don't know. Is there a spec for the "pinch"? Ray, the oil distributor sleeve is clean, unplugged and as yet unmodified.
Looks like I have some things to check. I have a spare engine so I can swap out rocker shafts and rockers to see if that makes a difference. Failing that, I may still try to enlarge the small orifice ever so slightly and see what happens. I may also do another visual check this weekend and see what happens at slightly higher engine speeds. At idle the rear half of the shaft just doesn't seem to get much oil at all.

Thanks to all for the interesting posts and advice. I appreciate your collective wisdom!

If all is as "it should be" there should be an adquate supply of oil without pinching off the overflow.Restricting the flow could result in an oversupply to the valve train at higher engine speeds.If you see an ocasional drip around the arms at idle its sufficent.The lack of a groves seals off the oiling hole on the bottom of the rocker shaft-also check again to see if the shaft is perfectly clean inside.Also a worn shaft will have a raised grove-reducing the flow.

The oil directed up to the valve train is not under much pressure as its taken from the low pressure side of the oil distributor valve.

Here's this weekend's update. Once again I took the rocker arm assemblies apart and recleaned them. As expected everything was clean. The most notable problem was that 3 of the 6 rear pushrods had no oil in the top socket where the rocker arm fits. In fact it was rusty! I think this pretty well confirms oil starvation to the rear shaft. I ran the engine with the valve cover off and watched as the front shaft is soaked in oil and the rear gets only a little. Also, I think Gene may be right on the right track about the oil passages in the rocker bushings being worn and further limiting oil flow as there was some evidence of that. I mixed and matched rockers with spares from my other engine to use the best ones.
I took a spare oil distributor and enlarged the orifice that feeds the rear shaft. The original hole was only 1/16", so I opened it up to 5/64". The results were the same; limited oil the rear shaft. I then took it out to 3/32" and it appears a little more oil is flowing aft. I may run it like this for a while and see what develops. I checked oil pressure and there appears to be no effect on what little pressure there is in these engines.
Next step may be to make a restrictor for the front shaft and open up the orifice for the rear.
Thanks again for all the input!

Just one question did you check the oil line for restriction from the connection up to the rockers?

Coachhill ,If there is such a thing as one rule, I guess it is..."There is always an exception to the rule!"
What ever works for you!

MrMack, the oil line is free and clear (except for the "pinch") and oil flows freely to the front rocker shaft. It's just the rear that looks under-oiled.

Just checking, We have found that the line coming up sometimes got plugged with crud, this was before high-detergent oils become common place, and several engines we have put into service had not been run since the 50s and 60s. The old crud was often almost impossible to clean out and new lines had to be fabricated. Likewise the early Chevrolet V/8s were found to have much crud, rust, and plain old dirt in the water jacket and often the rebuilders never pulled the soft plugs and rodded it out, boiling often didn't get the job done.

One other comment on under oiled rocker arms. When I got my '35 22 years ago it had badly worn rocker shafts. The rocker arm bushings were installed incorrectly. From what I remember, there is a notch on one side of the bushing and it should go towards the rocker shaft support stand. This is going from memory so someone may have more thoughts on this. I have had no more rocker arm problems in almost 60,000 miles of driving the car since.