The Stovebolt Site Forums The Shop Area Engine Shop 261 oil pressure

Hi there,

I have a question about my rebuilt 261 engine and oil pressure. I'm questioning my gauge at the moment, but want to ensure what's 'normal' on these engines.

I have a rebuilt 1955 261 with no filter. It now has 1700 miles on it. I currently am running straight 30W in it and when it's cold, I will get close to 60lbs pressure in it. When it starts getting warm, it will drop to about 30lbs, and when it's really hot (on our 100 degree days) it will go down to nearly nothing on my 0-60lb gauge when i'm running about 2000RPM. When I rev it up, it does come up off of 0, but barely much - after running it for 30 minutes or more.

The engine had a complete overhaul 10 over on the bottom, new cam bearings, new pistons, new melling oil pump (for better or worse) crank bearings, etc. I am getting oil to the top of the rockers, but I didn't replace the rocker arm shafts. I'm wondering if my shafts are worn so badly it's affecting my oil pressure - and if so - should I replace them? When I got the motor, it had the infamous external oil line run from the side of the block to the passenger side of the head with a 'T' on it.


If replacing the rocker arm shafts is the next step, which rocker arm shafts do I purchase? I have a 235 "848" head on the truck now. I also have the "pinched" return oil line on the rocker arm shaft (NOS)

The motor sounds great and runs just fine - I'm just concerned about the hot oil pressure, valve train is a little noisy, but it's a solid lifter setup and I have nothing to compare it to!

What else can I check (or am I going to have to start checking bearings next)

Thanks

That much hot pressure drop is too much, especially with straight 30 oil. Drop the oil pan and do some Plastigauge checking- - - -I'm going to bet on excessive bearing clearance somewhere, or possibly a weak pressure relief spring in the oil pump. Another trick we used to use frequently was to rig an oil pump with a flex line output in a 5-gallon pail of oil, run it with a drill motor, and pressurize the oil system through the pressure port on the side. Watch the leakage at the rod, main, and cam bearings with the oil pan removed and a big catch pan under the engine. It will be pretty easy to spot where the major pressure loss is coming from.
Jerry

Jerry - Can you school me on the pressure relief spring in the pump and how to check it at the same time? So you think the rocker arm shafts wouldn't cause that much of a drop?

The relief spring is there to prevent the drive gear on the distributor or the tang on the end of the distributor shaft from shearing off due to excessive oil pressure, especially with a cold engine. Most Melling pumps come with two springs- - - -at least the small block V-8 pumps I used by the dozen all did. The fact that your pressure is dropping to near zero with a hot engine tells me you've probably got excessive clearance somewhere. If the cold oil pressure was also low, I'd suspect a weak spring.

The fact that oil pressure builds up at all indicates the pump is moving more oil than the engine needs at the time. If one drop of oil was supplied by the pump to the bearing every time a drop dripped back into the pan, there would be zero pressure. As long as every bearing is supplied with exactly the right amount of oil that it needs, and no more, an engine could be lubricated, theoretically, with no oil pressure at all. The pressure is simply there as a safety factor. It's virtually impossible to accomplish such a feat since there's no guarantee every bearing surface in the engine will get adequate lubrication unless an excess of oil is supplied. In my personal opinion, any pressure above about 30 PSI on a hot engine is simply energy being wasted to turn the oil pump that could be used to drive the vehicle.

I'd suggest checking the relief valve in the base of the pump to be sure it slides freely, and be sure the spring holds it closed firmly. I can't think of a way to check the opening pressure of a particular spring without running the pump against a specific engine, because the volume the pump is required to flow against the bearings, oil filter, and other lubrication needs will directly affect the operating pressure. Just be sure the valve is free to move. A friend decided he needed lots of oil pressure, so he put a stack of washers behind his relief spring- - - -so many the valve couldn't move. The engine would stall from the power required to run the oil pump. When he cranked the engine up and went to full throttle (on a 400+ HP race engine) the oil filter split from top to bottom. I would guess he was getting 300 PSI or more of oil pressure on that one. I happened to be standing right beside the filter when it let go! On an open-wheel dirt track car, that meant I got a bath in 50 weight racing oil!
Jerry

Did they also install new cam bearings?

My 261 after 25 years would still get 60 lbs cold start, and even in 100+ degree weather and warmed up the oil pressure at idle would be around 25psi at idle, and would jump back up to around 35 to 40 going down the road at 55mph.

Be amazed how much oil pressure is lost due to cam bearings that are worn.

And as Hotrod Lincoln suggest, time to check the lower end too. It should have better pressure than that hot at idle.

Yup - It had brand new cam bearings installed on the build. So I guess nobody's buying my theory on rocker arm shafts?

No, though they may make it drop some. Where is your oil pressure gauge hook to the engine? If it is off the main gallery on the drivers side of the block then I wouldn't think the rocker arms would be that much of an issue.

My bet is the lower end has too much clearance.

Pplummer,

If you want to check your idea about the rocker arm shafts, you could plug the port feeding the shafts, and then run the engine and see what it does. You could have someone dribble oil over the shafts while you did this to make sure they are getting a little oil.

If you need a hand, I'll come over and help.....

Kurt

The rocker arm shafts themselves have nothing to do with pressure. There is a restriction somewhere on the feed to the shaft that linits the flow. The shaft is a hollow very leaky tube.

Hey Kurt, thanks for the offer. I'm working on the truck at my friends shop on Glennwood ave using his lift to get access to my fuel sender.

The gauge is connected to the oil galley port on the drivers side of the engine. I was going to connect an additional gauge tonight on the passengers side in the head and compare pressures on the gauges.

If I had that much clearance on a bearing, wouldn't I hear it knocking if it was leaking that bad?

You can have low pressure from bearing wear before you get knocking.

I ran my last 1954 235 that had 15psi cold oil pressure and 0-to-5psi when warmed up. It had no knocks, but most likely it was just a matter of time. I took that engine out because I did not want to gamble on a failure on a long trip.

My 1960 261 with full-flow oil filter holds it pressure at 30psi at all RPMs. My gauge might be off or my pressure relief spring might be different, because other people with tight 261s say their engines stay at about 45psi. The 1959 Shop Manual shows 35psi @2000rpm

I agree with the speculation that you have bearing wear. And, my uneducated guess of probability of which bearings would be in this order: rods, mains, cam. It really does not matter which bearings - the engine is showing significant wear. If you are mostly driving short distances, drive it until it knocks. Let it warm up before revving it and don't push it to high revs.

A rebuild/replacement might be near at hand and you might want a rebuildable block (a thrown rod might bring you to tears).

With only 1700 miles on a fresh rebuild, you've got serious problems somewhere. I'm going to guess your machine shop made a mistake on the crankshaft regrinding and put WAY too much clearance in there, on either rod or main bearings, or possibly both. Did you do any kind of clearance checks during assembly, such as using Plastigauge? Ideally, the oil clearance should be about .0015" (1 1/2 thousandths). If the clearance is over .003", you'll have hot oil pressure problems unless a very high-volume oil pump is also used. On the round trackers, we used very wide clearances and high volume pumps, but those engines were "worn out" after less than 1,000 miles. The clearance was built in to allow high RPM with very low drag, and if the bearings got pounded out after a short time, we replaced them after a few high speed laps. It was time for new rod bearings after 800 racing laps, about 400 miles at speeds of around 7,000 RPM.
Jerry

Pplummer,

PM me if you want some help or company tonight. Les (Roadmarks) is also just a shout away, although I think he is lay'd up recovering with his new knee...

Kurt

I'm optimistically thinkin' he may not have the proper restriction in the supply tube to the rockers. I think he said he replaced it....

I know the shop where he had the work done, and they are a way oldtime automotive machine shop, family owned. My dad had his 230 rebuilt there in the late 60's, and they have done work for me on my 235 in the 70's and 80's, and most recently they did a little machine work on the engine of my '37 John Deere.

But anything is possible, and they do mostly build race engines these days....

Kurt

I guess I should check that the relief spring is also not stuck open too

I had low oil pressure as you describe in your first post with my 235.

A new oil pump cured my trouble. The gears on my old pump were scored badly, but perhaps the spring was just knackered, either way, the $95 pump solved the oil troubles. (Although my engine is still a bit worn out!)

Thanks all for your input. I think I know what I have to start checking. If I get a moment this week, I will tear into it, if not I have a friend who I might get him to take a look too. He's an engine genius, but just really busy with a real job too.

3-4 lbs at idle, 17lbs at 1500, 22 lbs at 3000. Oil pan coming off Sunday if I get a chance. That's with an accurate gauge

The oil pan is off and a few main bearings are out. Something doesn't look right after 1700 miles for sure. If you look at the crank, there is a ridge where the oil galley in the bearing is suppose to ride. The ridge is raised and it feels around .005 There is also some pitting in the bearings as well and there is about a tablespoon of really fine metal in the bottom of the oil pan. It's ground so fine it looks like metallic paint. I haven't had a chance to pull the crank, but at this point I may as well pull the engine. The crank was turned .020/.020 and I did read the bearings and they were stamped 20 over as well, so I'm not sure what happened. Is anybody good at reading bearings? I guess I really won't know until I pull it and start measuring. They certainly don't look oil starved at all. Also, look at the ridge on the edge of the one bearing. My first suspicion - Bad machining, but we'll know soon enough. I hope I can turn that crank again. What's the largest size bearings I can get for these motors?

http://www.flickr.com/photos/45290812@N03/sets/72157630828532764/

Sure looks bad! Out with the engine is right.

.030/.030 is about the smallest undersize that's reccomended, although smaller bearings are available. I'd go shopping for a crankshaft that will finish out .010/.010 if at all possible.

Were any parts cleaned up with a beadblaster? Both the rod and main bearings look like they've been run with some kind of abrasive in the oil. It's very possible to get a tiny bit of beadblast media contamination, and the parts look just like yours when it happens.
Jerry

Jerry - I figured I'd have to go .030 or .040 on the crank. Once I measure it, I will know more. Why don't you think I should go .040 if need be? This crank looks tough as nails.

That's an interesting thought on blasting media. The only thing that was blasted and attached to the motor was the oil pan, the motor was tanked and everything else is new. There is superfine metal in the oilpan though, but I'm not sure where its from yet. I am going to tear it down this morning.

The bearings are multi-layered, starting with a steel backing, followed by a layer of copper, then Babbit, or other soft metal alloys, and finally a flash coat of pure tin to allow for quick wear-in of the bearing to the exact contour of the crankshaft journal. The tin flash coat is very thin, less than .0005". In most cases, the thickness of the steel backing is not increased on very big undersize bearings- - - -more soft metal is added. That makes for a tendency toward more wear or distortion of the soft stuff under heavy load conditions. Back when these engines were daily drivers, most shops wouldn't build an engine with bearings smaller than .030" undersize, and .020" under was preferred. If you don't plan to run heavy loads or do a lot of highway-speed driving, a deep undersize will probably work, but since the 235 and 261 engines share the same crankshaft, they aren't particularly hard to find. The less regrinding the better, IMHO.

The fine metal residue in the oil pan is what wore off the crankshaft. That's a massive amount of wear on the main journals for such a short-mileage engine!
Jerry

Measured the crank. All signs point toward a badly reground crankshaft when I had it turned. I am going to gauge the bearings again, but the crank has almost .005 taper in the con rod journals, and there is about .004 taper in the mains. Also, I had the rods re-done with the engine, but again, they seem out of round with how the bearings are wearing. I haven't measured them yet. I guess I could have had some premature wear from something else, but I don't know what!

Also - I had a small hole in my oil line under the lifter side cover from rubbing against a lifter, but it doesn't seem to have caused my major oil loss issue.

The only result of the oil line hole would be a slight reduction in the volume of oil to the rocker shaft- - - -little if any effect on the oil supply to the crankshaft bearings.

Let's establish what sort of crank grinding error you're measuring- - -is it "taper", a different diameter dimension from front to rear of the journals, or "out of round", different diameters (egg-shaped) at different places when the micrometer is positioned at various places around the circumference of the shaft? Either one is bad news, but out of round will affect oil pressure more than taper. Taper tends to wear a bearing in a very narrow area, where the diameter of the shaft is the largest, because it's carrying most of the load. Bearings from tapered shafts have a tendency to wear down to the copper, or sometimes even the steel backing, where the clearance is the smallest. At any rate, I'd strongly suggest going back together with another crankshaft, and a set of properly reconditioned rods. If the machine shop is willing to foot the bill, so much the better!
Jerry

Jerry - Looks like you have consensus. From one of the guys on the inliners site

His comments:
Looks like the result of a "soft" crank, hence no wear in the oil groove areas of the crank journal. Very common to grind thru the cranks surface hardness when their ground undersize like this, leaving the crank journals soft and vulnerable to rapid wear. Some cranks are heat treated deeper than others and have no isssues when reground. A sharp crankgrinder operator can usually tell by how the journals "spark" against the grinding wheel whether the crank is soft or not if he is aware of this in these cranks. Regrinding this crank wont make it better unfortunately.

I ordered a 10/10 crank from James Larrowe in Portland today.

Good call! I'd also highly reccomend another set of rods- - -they show up on Ebay pretty often at reasonable prices, either NOS or reconditioned by Federal-Mogul or some other nationwide distributor. A very talented local machine shop can do good-quality rod reconditioning, but it takes a lot of attention to detail to make sure the big end is resized correctly. I ran the rod recon department at a big machine shop for several years, specializing in big Diesel equipment, and we held our work to extremely tight tolerances. Not all shops do that.
Jerry

This time, I am going to have my buddy Kevin Boggs put it back together to his standards and specs. His dad used to race cup cars back in the day and he's well connected with decent machine shops in Charlotte

pplummer,

You mentioned you had the oil pan "blasted"...did they do the inside surfaces? If they did I'd look for a new pan, it's almost inpossible to get all of the grit out of the metal.

When I blast engine sheet metal I duct tape/protect all of the interior surfaces and even after that I wash and wash to get any dust off of those surfaces.

Just another thought...

Mike B

I blasted the pan and no, I didn't do the inside. It's for sure material from the crank. It wore anywhere from .003-.010 on one main alone. Measured it up tonight. The crank wore instead of the bearings. Crazy stuff.

I currently have a "3/4" cam from Patrick's in the engine. Can somebody give me some specs for a decent camshaft for bottom end and torque for this engine (preferably single pattern)? I may want to change the camshaft that's in there now, but i'm not sure what my options are. I have a friend at Lunati and he said he'd grind me whatever I want - but I don't know what I should try!

Patrick's specs are intake 19/53, exhaust 65/19 lift .436. Should I just stick with that or is there something that would give me a little more?

I'd be interested to know what the machine shop says about your crank wearing the way it did. Have you run it by them?

Kurt

Hey Kurt - The hardness was ground through on the crank - that's all. From what I can tell the consistency of the hardness on the cranks wasn't that great back then. Some would be able to handle .020, .030 etc, and some wouldn't. My buddy said that the crank was shot. From what we/he can tell so far, the machine work has been fine, just that the crank wore from being so soft.

Glad to hear at least that the machine work was OK. My office is just around the corner from Boyette's. I've known those guys since the 60's.

Last time I did my crank it was machined .030. That was around '85. Still going strong. I guess I had a good one.

Kurt

A 252/264 degree duration is pretty close to the max for a street cam. It might be possible to increase the intake duration slightly, maybe to 258-260, but there's probably a reason it's biased toward exhaust duration. One specification that's not mentioned is "lobe centerline". Moving the lobe centers closer together will increase low-end torque a little, but unless you're looking for a performance advantage in one particular RPM range, it's probably not worth having a custom grind done. Getting too radical on duration will end up with a very peaky engine with a narrow power band. That's not something you need on the street. If there's a practical way to increase the compression a little, maybe a thin head gasket or shaving the head some, that's probably a better choice than going to a radical cam profile. Just watch piston/valve clearance closely.
Jerry

Hmmm, soft crank journal? Were the bearings worn at all?
Oh the pictures don't work, server down or somthing.
It can be normal for cast iron crankshafts for gas engines not to have hardened journals. With proper lubrication there is no journal to bearing contact, so hardness is not a factor. If it is something that is heavily loaded and there is a chance that the hydrodynamic wedge may break down then there is a chance and that is why most diesel and aircraft journals will be hardened, but still the softer bearing material is what wears first, not a crank journal.
Who originally put it together?