Oil Pressure for B18 engine in Amazon

[Rick Arizona 122s]

What is the appropriate oil pressure for a recently rebuilt B18 engine, after it is thoroughly warmed up? The oil pressure drops quite a bit after the engine has been driven about 20 or 30 minutes.

The mechanic and I mounted an oil pressure gauge under the dash as we were rebuilding the engine in my 1965 Volvo 122s. We put 10-30 oil in the engine. When the engine is cold it has about 21 lbs pressure when idling at about 1000 RPM, and about 42 lbs at 2000 RPM. That seems OK.

After about 30 minutes of driving it drops to about 10 lbs of pressure idling at 1000 RPM, 20 lbs of pressure at 2000 RPM, and and 32 lbs at 70 MPH (113 Km/h). Is that normal for a freshly rebuilt B18 engine?

A new oil pump had been installed. A used crankshaft had been obtained and the rod bearings and main bearings were reground to 0.020” undersize. My original crankshaft was not used because of a badly worn thrust area. With some difficulty, I located 0.020” undersized bearings, and we used a plastic gauge to verify that the clearances were what the machinist said they should be.

As requested, the machinist had the 0.030” oversize pistons in hand before reboring, and he installed a liner in cylinder #3. He also did the valve job. A new C grind camshaft, camshaft bearings, and lifters, were installed. We did not rebuild the rocker arm assembly, or look at it much. Is this normal oil pressure?

[Rick Arizona 122s]

It suddenly occurred to me that it might help to provide my oil pressure numbers in both PSI and BARS. It looks like metric oil pressure gauges use BARS (not PSI).

When the engine is cold I have 21 PSI (1.5 bars) idling at 1000 RPM, and 42 PSI (2.9 bars) at 2000 RPM.

After about 30 minutes of driving the oil pressure drops to 10 PSI (0.69) bars idling at 1000 RPM, 20 PSI (1.4 bars) at 2000 RPM, and 32 PSI (2.2 bars) at 70 MPH (113 Km/h).

The engine does sound and perform as well as I remembered it when driving it back in the 1970s and 1980s.

[Derek UK]

Basic answer, use 20/50 oil. 10/30 is too thin. You'll be changing it after a short running in mileage so give the 20/50 a chance then. You can try 15/40 as a stepping stone if you like to see how that affects the oil pressure but 20/50 is the norm for these old engines, even after a rebuild.

[Ron Kwas]

Rick;

I have to agree with Derek (as is often the case!)...those numbers look a bit low (but not to the point of concern), and could be/are explained by the thinner oil (it certainly sounds like you did all the right things at rebuild time!)...I would expect them to come up a bit after you change to 20W-50.

Cheers from Connecticut!

[Vintagewrench]

The general rule-of-thumb for professional engine rebuilders in the US is 10 psi is needed for every 1000 rpm in passenger car engines when hot for motors built in the era of the 122 and 1800. IE: 10 psi @ idle - 30 psi @ 3000 rpm - 50 psi at 5000 rpm and this works well with a B18 or 20.

It is OK to use 20-50 and I used to. I am a professional vintage engine rebuilder and have changed to 0-30 and 10-30 in my 220 and 1800s without any problems. It is what is generally used today in new cars and causes less of a drag on engine parts and bearings due to its thinner viscosity. The oil pump will also have an easier job pumping the thinner oil and last longer.

With a vintage Volvo engine (B16-B18-B20) that only has three cam bearings, the center cam bearing will also last longer due to less force transferred to the cam and bearing by the oil pump gears with 10-30. When this bearing wears the oil pressure will drop.

If the main bearing clearances are correct and not on the loose side of the specs I have not noticed anymore than normal leakage or oil consumption with these oils if the original felt seals in good condition. I use my cars often and this includes highway use at 75-85 mph w/the engine run at about 3500-4000 rpm w/a 4:56:1 gear ratio over long distances (500-1000 miles) with the overdrive engaged.

When rebuilding, convert the timing gear cover to a B30 (6-cyl.) rubber crank seal or find a B30 cover. Use a B20 oil seal holder in the rear w/its more modern rubber seal. Overall you will enjoy a few more horsepower and get better fuel economy and less leakage of oil.

[Rick Arizona 122s]

After thoroughly warming the engine up today, I got 10 PSI per 1000 RPM up to about 3000 RPM, but beyond that speed, there was no significant increase in oil pressure. When doing 3000 RPM at 55 MPH (89 Km/h) I had 30 PSI (2.1 bars). When doing 4000 RPM at 72 MPH (116 Km/h) the pressure only increases very slightly to 32 PSI (2.2 bars). I do not have an overdrive.

When idling at 900 RPM I only had 6 PSI (0.4 bars), but a fast idle at 1100 RPM brought it up to 10 PSI (0.7 bars).

When the engine was cold I had 60 PSI (4.1 bars) at 3000 RPM, in mild short sleeve weather.

We did not rebuild, or examine, the rocker arm assembly, so I wonder if some pressure could be lost there? I see that both a rebuild kit and an entire rebuilt rocker axle is available for the B18 engine.

We also did not inspect the new oil pump, so I wonder if the pressure relief mechanism could be sticking, or missing the spring?

I watched the mechanic use the plastic gauge as a double check of the gap between the crankshaft and two of the bearings. He did that on one of the rod bearings and also on one of the main bearings. In both cases, that test showed 0.002" clearance after measuring the mark left by the slightly squished plastic strip. That was just a double check for the 0.020 undersized reground crankshaft when used with the 0.020 undersized rod bearings and 0.020 undersized main bearings for a B18 engine.

It sounds like the oil pressure is not too bad and I will probably be able to improve that some by using 20-50 or 15-40 oil. But, I am also hoping to find a problem which can be fixed. All of the advice was very helpful, especially the detailed information provided by Vintagewrench.

[SwallownAmazon]

I remember when I had my first car (Series E Morris 8) 50 years ago, I went to local authority car maintenance evening class to learn how to maintain it and the instructor always referred to the oil pressure gauge as the "worry gauge". So long as the needle moved off the stop with that old side valve engine, that was all that mattered. Higher revving engines clearly need more but it's the volume of oil flowing that is important, not necessarily the pressure.

[blueosprey90]

"and we used a plastic gauge to verify that the clearances were what the machinist said they should be."


I'm new here and I don't pretend to know anything about the Volvo B18 - or any Volvo engine for that matter. But since this is the internet, I'll offer a couple of observations that perhaps someone else can verify or refute.

I understand that the primary cause of low oil pressure in a 4 cylinder pushrod engine is bearing clearance, either main bearings or camshaft bearings. Use of Plasti-Gauge to measure clearances on a rebuild by a professional mechanic is not something that instills confidence. For one, I don't believe you can even use Plasti-Gauge to measure clearances on the camshaft bearings.

The way to measure clearance is with a dial bore indicator and a good set of micrometers. And these are not so easy to use without practice or experience!

For the main bearings, you would torque down the caps and measure the diameter of the bores with the dial bore indicator. Then you would measure the crankshaft journals with the micrometer. Then you would measure the bearing cap thickness with a micrometer, preferably one with a ball anvil. Then you would compare the measurements of the journal and the bearing against the bore to verify your clearance. Only then might you want to use Plasti-Gauge to double check your work. And before using Plasti-Gauge, you need to clean all of the oil off the bearing and journal.

Similarly, you would use the dial bore indicator and the micrometer on the camshaft and the Inner diameter of its bearings.

If the measurements reveal clearances that are out of spec, I suppose a return trip to the machine shop is warranted.

The rocker arm assembly is probably at the very end of the oil pathway, so not likely the problem. Since you have 60 psi when the engine is cold, it is probably not your oil pump. The piston overbore would not relate to oil pressure. The valve job is unrelated to oil pressure.

Hope this info might be of help. Good luck.

[Rick Arizona 122s]

The plastic gauge was mainly just used by me and the mechanic to double check that the undersized B18/B20 bearings which I had purchased were really the correct parts for use with the crankshaft which had been reground for me by a machinist. Both the rod and main bearings were in boxes which said they were 0.020 undersize for a B18/B20.

The machinist told me that my crankshaft had an unusual amount of wear on the thrust area of the crankshaft (used when the clutch pedal is depressed). He said that would require welding on the crankshaft, which was a solution that he was not real fond of. Instead of doing that, I found a used B18/B20 crankshaft which needed regrinding, but which had a good thrust area. The local machinist then took that crankshaft down to a machinist in Phoenix, who specializes in regrinding crankshafts. I had provided the local machinist with several different Volvo Amazon manuals which contained specifications. I do not know what tools or techniques either machinist used to measure things. They decided to regrind both rod and main bearings to 0.020 under.

After getting the reground crankshaft back, I asked the local machinist how to make sure that I had actually received the correct sized bearings. He suggested that the mechanic and I could plastic gauge it. The small packet of plastic gauges contained several colored strips of plastic designed for measuring a specific clearance range. If I remember correctly,the crankshaft was placed in the engine with the small plastic strip between the bearing and one of the caps.The cap was then torqued down. The cap was then removed revealing a colored mark where the strip had been squished to a specific size. A small scale on the package was used to measure the squish mark, indicating that the clearance was 0.002. One of the rod bearings was also measured in a similar way.

Earlier, the local machinist had installed the new 0.030 oversized pistons, wrist pins, and wrist bushings onto the connecting rods. He had also rebored the engine, and installed a liner in cylinder #3. The old wrist bushings were so loose that they fell out of the connecting rods. The replacement wrist bushings available for that engine were also slightly loose, so he had to find some different bushings of the needed size, hone the connecting rod (or something) out to a slightly larger size, before pressing them in. I believe he also had to drill a new oil hole (or two?) in each of the wrist bushings.

The mechanic who assembled the engine probably did not measure either the new C grind camshaft, or the new camshaft bearings. Should those new replacement parts have been measured, before installing them?

I do not know how well the mechanic who assembled the engine did, but most of the measuring had probably already been done by the two machinists.

[blueosprey90]

I should have kept (and should keep) my big mouth shut.

I'm a miscreant from the MG world. Our engines are not exactly similar, but ... take a look at this thread, especially post #10 and #16. http://www.mgexp.com/phorum/read.php?1,2749834,page=2

Two machinists and an engine builder. Maybe too many cooks in the kitchen. And if you only checked one main cap and one rod with the Plasti-Gauge, one might say the job was left unfinished. Live and learn.

From my limited experience, the measuring of clearances is extremely tedious and time consuming. I have a second spare engine** on the stand, partially assembled with new bearings but unknown history, that I am taking down as I suspect metal contamination in the oil galleries. I'm using Plasti-Gauge as I disassemble the rods and mains to try to identify potential problems. It's taken me two nights and I still have one rod bearing to check. I did find one main, however, where the clearance appears out of spec. This is with new, unused bearings in place.

But assuming all is well with your bearing clearances, I saw this on another forum posted by a guy named Phil Singher who perhaps knows what he is talking about.


"I've never done it, but it is possible to pull the pan with the engine in the car. You can't really jack up the engine, though -- what you have to do is support it where it is, and then drop the whole crossmember (subframe) out from under it. Haynes describes this. There's a pipe that runs from the oil pump to the main oil galley in the block. That pipe is sealed with an O-ring at both ends. It's not all that uncommon for one of the O-rings to seat badly when the motor is assembled -- it's a picky operation -- and later back out of place or split. This causes very low oil pressure, because the oil from the pump squirts past the O-ring back into the pan instead of circulating through the motor.

If inspection shows that this is the case, you're only out two O-rings and a pan gasket, plus your labor. If those seals turn out to be good, you have easy access to the oil pump. Remove it, open it up (easy to do), and see if the impeller gears are in good shape. There should be no more than a few thousandths of an inch play between the teeth."



** Just as a side note, and for added fun and amusement of the assembled masses, my main engine and my first spare engine suffered broken crankshafts in September. The main engine was in my car, the first spare was out on loan to my friend who blew up his own engine in April. So now my main engine block and a new first spare engine block are at the machine shop for testing and analysis and I have a new "ghost main" billet replacement crankshaft on order (12 weeks). If both blocks test out, I'll order a second and declare bankruptcy shortly thereafter.