Low oil pressure in new engine

[Keoke]

By the way, it turns out the engine was bored .040 over. I don't think that matters, but I previously reported .030.

Probably would smoke a lot more if you had the .030 pistons and rings in the .040 bore, but probably wouldn't affect oil pressure too much

But it sure would increse crankcase pressure!!--Keoke--

 

[Legal Bill]

What's ten thousandths of an inch between pistons and cylinders???

 

[IanIrving]

I've decided to give Dynolite oil a go hasving had it recomended by an old car mad garage owner locally. I put a 25/70 grade oil into engine and gearbox on a recent oil change. My engine was running at 55 psi cold and around 40 psi hot at 2000 rpm. It now runs above 60 cold and 50 hot and the gearshift and overdrive engage/disengage seem much smoother. I'll keep an eye on how it progreeses but sao far looks good. OIl type is AGP40 24W75, can be looked at on the dynalite site

https://www.dynolite.eu/MOTORASP/GB...eFrame.asp?cliprov=SFAKFBHNEEXREPWDUC16:52:05

Still on the subject of oil, what do you guys use for dashpot oil I've hear 20 weight is the same as ATF/hydraulic samper oil. Any comments and how do you add it to the darb piston. I used to do it by lifting the carb piston till the damper oil chamber was visible but that involves removing the air filters which on the BJ8 is a pita.

Ian

 

[Bob_Spidell]

...

Still on the subject of oil, what do you guys use for dashpot oil I've hear 20 weight is the same as ATF/hydraulic samper oil. Any comments and how do you add it to the darb piston. I used to do it by lifting the carb piston till the damper oil chamber was visible but that involves removing the air filters which on the BJ8 is a pita.

Ian

I do it by feel on my BJ8: add oil slowly until you can sense resistance when you stick the (oil) damper pistons back in. If I fill until I feel resistance about one-quarter inch (6-7mm) between the bottom of the cap and the top of the dashpot it seems to stick around longer, and acceleration is smooth. If you think about it, you only need enough oil to just submerge the little 'pistons' on the dampers at closed throttle. Any more either gets blown out or sucked in (there's an oil smear on the inside of the bonnet right over the carbs and when I pull the vacuum dashpots there's a little puddle of oil in the pistons, so I reckon it gets both blown out and sucked in).

20W oil is 'spec.' 3-in-1 oil is 20W. I've tried ATF, engine oil and 'official' SU dashpot oil; didn't notice much difference.

 

[tahoe healey]

I've tried Marvel Mystery oil,great acceleration but too thin and disappeared in a month. Sewing machine oil because it doesn't gum up was okay but I had to top up occasionally. Thirty weight (non detergent) and 20/50 I found no difference between the two. Very cheap and very available. I now use Moss's oil because I had to pad a shipment about two years ago. I got two bottles. Runs well and I've used less than half of the first bottle. Its small size makes it easy to keep in the boot and pour. Pricey, yes, but it seems to last.

 

[Bob_Spidell]

OK, inspired by this thread's info I thought I'd give the '1/4-inch bolt' trick a try. I was not prepared for the result.

Background: my BJ8 has run low oil pressure at idle for as long as I've had it. At startup I get 60psi, but after running on hot days I would register, for all intents and purposes, zero psi at idle. In spite of this, the engine has run and performed well for me for over 100K miles. I use 20W-50 dino oil.

So today I pulled the relief valve and measured the spring at 2 & 11/32"; quite a bit less than 'spec.' So I installed the 1/4-inch bolt and fired her up; 70psi on cold start/fast idle--not too surprising. What's surprising is even after the engine has warmed-up--when I would normally see 20psi, before a long run in hot weather--I am getting 40psi. And the max pressure is still at 70psi; so the effect is max pressure is up 10psi, but the hot idle pressure could be up 10-20psi!

My questions to the forum are: is 70psi too high a max oil pressure? Any explanations for this phenomenon? Should I split the difference with some shims?

TIA,
Bob

 

[Legal Bill]

Well, I have not replaced mine yet. I'll try it this week.

 

[Legal Bill]

So I finally got around to changing the oil pressure relief valve and spring and inserting the bolt to achieve the correct length. When I started the car, the pressure seemed to be a bit higher. After a short run, the idle pressure seemed to be right at 25 lbs. But after a longer highway run, with the engine temp up over 190, the oil pressure at idle fell to about 10 psi. So the relief valvwe and spring are not a significant factor in my application. Of course, if I can keep the engine temp in the 170s, it seems my OP will be higher, so engine temp and oil temp are closely related (as we already knew).

Next step will be replacement of the stock oil filter with the spin on adapter and K&N filter, with a change of oil to straight 50W.