Oil Pressure Question

[JPSmit]

Thinking about the Spridget 50th and the distance. Back in June I drove to Belleville for the MGB register event. When I left, I was getting a really solid 40 or lbs of oil pressure at 70mph. By the time I got to Belleville, (two hours) It was more like 25lb. Once I got into town I stopped at a store for 5 minutes, got back in the car and it was back up to 40 lbs.

any thoughts?

 

[Hap Waldrop]

Oil temp, the hotter the oil, the thinner, the thinner, the more pressure drop. Thats exactly how my MGB engine acted before it took out a rod bearing.

 

[aeronca65t]

25 lbs at 70 mph will work but it's low-ish.

My well-worn 1500 shows 40 lbs at about 4000 rpm after an hour of racing.

I'm running 20w-50 Castrol. What oil are you running?

 

[MCS]

time for a v8

Phil

 

[JPSmit]

Go home Phil.

I'm running 20-50 four stroke Motorcycle oil.

Anything I can do about it Hap?

 

[aeronca65t]

When it's winter, swap rod bearings. While you're at it, thrust washers can be replaced. Not that hard to do and will probably help pressure and add engine life.

While the pan is off, flatten out any grooves or wear on the oil pump cover by sanding against a piece of #600 paper taped to a piece of heavy glass. If the cover isn't flat, you'll loose pressure.

Meanwhile, keep rpm down and be sure you have clean oil/filter.

 

[JPSmit]

all bearing and thrust washers have only 2500 miles on them.

 

[Trevor Jessie]

Oil cooler?

 

[Morris]

Before you get too crazy about doing stuff to your engine, it's worth exploring whether your the issue is not your gauge. It is unlikely that your oil cooled enough in 5 minutes to give you a 15 psi rise in pressure. It is possible that a piece of gunk or some other obstruction got pushed up against the oil pressure tube. This has happened to me once before. In my case, a piece of the teflon tape I used to seal the fitting flapped in front of the opening. My oil gauge behaved kind of like yours for a while before it finally dropped to 0 while I was at a stop light 4 blocks from home. Talk about heart attack.

Take a few more long drives and see if the pattern repeats.

 

[Guest]

JP, I'm a BIG fan of Lucas oil treatment. It doesn't leave behind a mess, increases oil pressure, reduces wear on start up and goes great with chicken.

I ran Castrol 20/50 forever, but recently switched to straight Valvoline 50 "racing" in the Midget.

Why you ask? Because I drains back less when sitting overnight and builds pressure faster on start up. With a .002 out of round crank I need all the help I can get.

 

[aeronca65t]

all bearing and thrust washers have only 2500 miles on them.

OK, you should be good to go with that.

Checking the gauge is worthwhile.

There's an oil pressure relief valve, but I doubt that's it.

20W50 oil could be useful in summer(if you're not already using it)

Eventually it might be a good idea to check the oil pump cover plate and bearing clearances, but for now, I'd just monitor it and see if there's any changes. It's not *that* bad.

 

[skiptune]

If the bearings have only done 2500 the pressure sounds a touch on the low side anyway. Might be an idea to remove the oil pressure relief valve. There will either be a ball bearing or bullet on the end of the spring. Remove whichever it is and clean it. If you still have a problem,, as a temporary measure, you could drill the centre of the pressure relief valve retaining nut ( the 1" AF one)and tap it to take a 5/16th bolt. If you then screw an 1" long bolt through the retaining nut, with a locking nut and place a small washer between the end of the bolt and the spring inside, if the pressure drops screw the bolt in which will increase the pressure on the spring and increase the oil pressure.

 

[MCS]

JP i am camping cant get home until Saturday, you always make me laugh
maybe september will work for lunch with you and the guy with the the thing in the garage
Cheers Phil

 

[JPSmit]

It is 20-50 oil and up until this oil change, I did use Lucas. I'll take a look at the relief valve.

 

[Hap Waldrop]

Go home Phil.

I'm running 20-50 four stroke Motorcycle oil.

Anything I can do about it Hap?

If the gauge is correct, and because they are mechanical, they mostly either work or don't.

Rod journal clearence is the end of the pressure trail, if clearence is too great at the rod bearing, then oil pressure will greatly suffer. We found out building A series race engines that as little as .0005" clearence at the rods could effect oil pressure as much as 20 psi. So if the engine is old and tired, you could install new rod bearing, and that can be done without removing the engine. This is the very reason why I blueptrint every engine I build, I want to control all clearences, and mostly for oil pressue's sake.

Oh and use good tri metal bearing and stay away from the aluminum face bu metal garbage. I'm curently rebuilding a 1275 engine for customer that his egine has aluminum bi metal bearing in it, and the engine only has about 10,000 miles on and the cheap bearing scarred the #4 rod journal, I don't even know why vendors offer us bi metal bearings, since the factory too used tri metal. This one fo the easiest mistake a rookie engine builder can make, it just seems like no one would sell us junk bearings, but they do.

 

[JPSmit]

Hap I rebuilt the engine, and, very much fall into the category of rookie engine builder. The bearings were either Moss or VB - likely VB - would they be bi-metals, and, if so, where would I get tri-metal. Also, I did have the engine block cleaned and measured, don't remember the numbers off the top of my head. Should I assume they need to be remeasured? Do I use plasti-gauge first?

Can you walk me through this a little?

thanks!

 

[DrEntropy]

JP:

Bearings!

 

[Spridget64SC]

Hap and the Dr. are on the right trail. But let me help put some of this in perspective. The pressure the gauge will reveal to the driver is the pressure in the oil galley along the distributor side of the block prior to reaching all the bearings in the engine. The pressure on the gauge is the galley pressure prior to the main, rod and CAM and ROCKER ARM bearings. Don't forget them too. Oil pressure is measured at this convenient location. Clearances and losses all along the oil pressure path determine what the pressure will be at the galley just before what's left goes to the bearings and then drops into the pan to be collected for the cycle to start all over again. The initial and final viscosity of the fluid (oil) affect the losses in the operating temperature range of the engine. Things like STP/Lucas/Motor Honey or whatever the trade name is are pretty much just viscosity improvers, friction modifiers and oil chemistry supplements. They make the oil thicker and slow the clearance loss.

The oil pump itself has clearances and can affect the pressure on the gauge. I have found cracked scrolls on oil pumps that of itself would greatly affect the pressure at the galley.

The face condition of the relief valve plunger can affect its sealing capability and the final oil pressure value once temperature has stabiblized.

Now to bearing clearances. The thrust washers have very little impact on oil pressure as long as the clearance is within tolerance. On an A series engine, this can be up to 0.007" or so for race purposes. However, when approaching this limit, the side clearances of the rods and the clearance between pin boss at the piston and the rod little end need to be checked. Rod side clearance greatly affects oil pressure loss and windage. A good oil pump and low loss piping and filters are a must. Cam bearing, rocker bushes, rod and mains all need to be in specification for the application.

Also, the oil pump needs to be inspected. I have found most oil pumps show up with around 0.006" clearances between scroll and case. And around 0.001" to less between rotor and scroll. I prefer the flat metal back pumps. The MiniSpares performance pumps are good, but I have found a few with not as tight a clearance as I would have expected for selected assemblies. Also make sure the flat sides of the scroll, rotor and pump casings are not scored from debris sucked up by the pump before being filtered. Make sure there are no kinks or flow restrictions in the stock oil path. The oil pump itself is a constant displacement pump. More rpm's, the more displacements and hence you should see more pressure for the same restrictions in the path.

Check your clearances with plastigauge or measurement tools on the rods and mains. Plastigauge is a really good thing. It is a very reliable substitute for using expensive tools. Check your cam bearings for scoring and wear. The center and front bearings will show a ridge in the oil groove area if the bearing is worn. The amount of ridge gives a perspective on wear. Rear bearing does the same, but to a lesser degree. The rockers should be checked for the amount of slop or wiggle with no lash. Also check the journals to make sure you are not on the low side of the range. Same with the rod big ends. Tighten clearances up and I'm sure the gauge reading with improve.

Now, with respect to bearings. I don't have the same adversion to Aluminum alloy bearings as others. Many of the newer Japanese, European and American engines can only use AL based bearings because that is all that is available. These can be raced/used just as reliably. Also, ACL and others have developed some really exotic aluminum alloy overlays to combat the environmental overhead and difficulty using lead or indium materials.

One last suggestion of anyone building an A series engine is to check the alignment of the oil feed hole in the bearing with the drillings/groove in the block. Have seen up to half the hole blocked by the block itself.

Oh, and Cleanliness and Cleanliness. Make sure you clean everything and all the galleys, nooks and crannies where grit and trash can hide.

Resort to additives and high viscosity oils (>50wt) only as a last and temporary strategy. Supplemental ZDDP additives for initial engine operation due to the flat tappet cams is advised, but then should be eliminated and good quality oils with a minimum of 1100-1200 ppm of zinc/phosphorus installed.

HTH
Mike Miller

 

[Guest]

JP, I suspect my 1500 crank is WAY worse than yours. I don't know what my oil pressure is and don't care to know. Why?, cause I don't care to go down the slippery slope and wind up doing a total rebuild. Here's my thoughts on my "build".

My car knocked on cold start since I bought it. Seven years and 10K later I decided that it needed attention. Upon disassembly, the crank looked like it was machine by Ray Charles with a bench grinder and a fifth of George Dickel. I didn't have the money to go completly through it, so I polished off the big chunks and put new bearings in.

I figured:

A. It's run for 10K like this, new bearing can only make things better.

B. The worse that will happen is it will start knocking on a cold start and warn me of impending doom for at least a little while before it frags. ( and that will happen only if I don't listen to what it's telling me.

C. It hasn't blown up yet when the crank looked like it should have, so new bearings should buy me some more time.


Mine is .oo2 out of round on all rods and .oo1 on one main, so I have max allowable spec plus .oo2 depending where the rod is at presently. I run the crap out of my car and it hasn't even started knocking on cold start yet...and I have cheapy bearings.


IMO and experience with a "weak" 1500, I think you're alright for now.

Please understand, I'm not suggesting you go against the professional opinions provided here, I'm saying I think a bit of Lucas and you can make the trip o.k and go through the motor in the winter. That is after all your goal right now, making the trip, right?


Let's look at excatly what your car is. It's a hobby car that belongs to a guy who lives in a place where summer is only sixty seconds long. It doesn't get driven much, often or hard. It's not a race car. With a little juice it should motor happily along "wounded" for the same amount of time and milage mine did, if not more. We're talking about a Triumph 1500, not the space shuttle. The thing wasn't 100% when it was brand new.


All this being said, I'm suprised my car runs as well as it did and currently does. I would never had believed it if I hadn't seen it myself. I wouldn't hessitate to drive MY CAR anywhere... .oo2 out of rouond and all.


Juice it up and if it doesn't make it, there's always AAA.

 

[JPSmit]

so, off to a cruise night about an hour away. sure enough, we started at 40lb and slowly came back to about 25-28. On the way back, it held steady at more like 30-33. the only reason I can think is that it was 5-10 deg. cooler.