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Old 04-17-2020, 03:10 PM   #1
Ol' Ron
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Default Bearings vs oil pressure

Bearings vs oil pressure
O.
Notice that all the clearances in a stock engine are very tight. Main and rod bearings run from .001/.002". Cam bearings even tighter, but no more than.003". An important one Rod side clearance, .006/,010. Now you know where all the pressure comes from, resistance to the oil pump output.
Now trying to shove some heavy oil through these clearances, forces the relie valve to open. The relief valve is only so big and can't reduce the pressure below #50 if the oil is too thick, thus forcing this heavy oil through the small spaces. However the pressure of the oil coming out of the small spaces is much higher that 50 or 60 lbs. More like several hundred lbs. THis is the principal of waterjeting, cutting steel with hi pressure water. This high pressure also contains small particles which blast the bearings and surrounding materials. One thing we've forgot is: why we put oil in the engine anyway? I have a hit & miss engine that doesn't have any oil in it, but a drip system for the cylinder and rod. Yes, it lubricates the bearings and most everything else. But it also cools the bearings by removing the heat generated by the force of the connecting rod being driven down by combustion pressure. To cool these bearings we need flow, the more flow the better. In fact all the bearing mods are designed to increas flow.
WE do this by increasing the bearing clearances to .oo23/0027,both crank and rods, and ncreasing the rod side clearance to .010 for hot street to.o15 fro racing and to cool the bottom of the piston
I'll end this now, Food for thought. If you're contimplating building a 276/284/294, this might be the way to go. Next: the allout compiyion, blown, nitro burning beast???? Now you know why I don't like a heavy oil in a stock engine.
ramps
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Old 04-17-2020, 03:56 PM   #2
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Default Re: Bearings vs oil pressure

Thanks Ron!! I run syntec full synthetic 5w30 in my 8BA(no leaks,no oil lost) and all my other 4 stroke engines(2006 HHR,2008 Subura,87 305,in my 1937 chevy truck,19 HP Kawaski mower,12 HP Briggs snowblower,8HP Briggs generator) Pete
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Old 04-17-2020, 06:11 PM   #3
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Default Re: Bearings vs oil pressure

Yup. too much oil pressure is not good thing. Excellent explanation, Ron.
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Old 04-17-2020, 07:05 PM   #4
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Default Re: Bearings vs oil pressure

For the larger clearances. I use 40w racing oil
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Old 04-17-2020, 07:48 PM   #5
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Default Re: Bearings vs oil pressure

Excellent explanation Ron on the reality of oil flow related to clearance, pressure and flow.
The loose is fast clearance numbers for my blown on gas engine is a lot more for sure using the large Melling high volume M-21 oil pumps pressure readings will go above 100 using VR-1 oil at 6 thousand RPM.
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Old 04-18-2020, 08:26 AM   #6
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Default Re: Bearings vs oil pressure

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Also remember just increasing the pressure heats the oil which is counterproductive to the purpose of removing heat.
As Ron mentioned about running the wider clearance for racing engines remember those are not made to be dependable for thousands of miles. Some of them, one race and they're being torn down.
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Old 04-18-2020, 08:42 AM   #7
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Default Re: Bearings vs oil pressure

Hey Ron, I have an 8BA that has over 50# when running down the road but drops down to 2-3lbs at an idle. It has about 5k on it after a total rebuild. I guess if it made it this far it'll be ok, but when I look at that gauge it makes me sick. I have a reground cam, and standard cam bearings, I never checked the clearance on them, could that be the problem? Thanks Chuck.
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Old 04-18-2020, 11:25 AM   #8
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Default Re: Bearings vs oil pressure

Quote:
Originally Posted by chuck stevens View Post
Hey Ron, I have an 8BA that has over 50# when running down the road but drops down to 2-3lbs at an idle. It has about 5k on it after a total rebuild. I guess if it made it this far it'll be ok, but when I look at that gauge it makes me sick. I have a reground cam, and standard cam bearings, I never checked the clearance on them, could that be the problem? Thanks Chuck.
I would find the problem and fix it. What weight oil, I don't like any that
say 5 20/40 is good. I have seen the pressure drop after warm up do
to the pressure relief valve in the oil pump relief valve or the valve up
in the front of the intake manifold leaking. The pressure starts to drop
ang goes way down. When the engine is restarted it usually comes back
up and drops off again. This is a week spring in either of the relief valves.
Don't stretch the spring make a spacer out of 1/4" pipe about 5/16" long.
Spin the engine, plugs out on 12 volts and the oil pressure you see is
what you will have at 35 MPH. Adjust the spacer length for max pressure.
These pumps will put out over 100 lbs. Look in old posts for a plastic tube
fixture for adjusting oil pumps. G.M.
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Old 04-18-2020, 01:06 PM   #9
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Default Re: Bearings vs oil pressure

Original type gauge or mechanical?
Are u certain the gauge is accurate?
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Old 04-18-2020, 04:22 PM   #10
Ol' Ron
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Default Re: Bearings vs oil pressure

Yes the cam bearings are getting out of spec lately, I never checked them before , but a friend found them .006" off jad to get a different set, Now I check the old ones before I remove them and if theor OK leae them in, unless I have the block baked, they re install them later. Also I have a friend with an Ardun and his oil pressure is very low at idle, but if oil is flowing through the bearings not to worry It;s Ok at cruise .
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Old 04-20-2020, 04:11 PM   #11
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Default Re: Bearings vs oil pressure

mtt
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Old 04-20-2020, 05:12 PM   #12
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Default Re: Bearings vs oil pressure

Also under high pressure the oil wedge cannot take place and the crank can make contact with the bearing
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Old 04-20-2020, 11:31 PM   #13
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Default Re: Bearings vs oil pressure

There are many people on here that are so concerned about the oil pressure. I just thought they should know alittle about what it does.. Just trying to help.
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Old 04-20-2020, 11:53 PM   #14
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Default Re: Bearings vs oil pressure

This is a great thread you started here, Ron. Very enlightening. Talk to us again about your take on 10W30 oil vs. 20W50 oil in a street engine. I'm using 15W50 Mobil 1 full synthetic oil in the 21 stud engine with Babbitt mains in my '34 - 60 pounds at cold startup, after warmup to 160°, 40 pounds driving down the road and 20 pounds at warm idle....
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Old 04-21-2020, 01:30 AM   #15
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Default Re: Bearings vs oil pressure

What about using synthetic oil on start up on a new engine,
I,m going to be starting my new spare 276 engine in the next week and are contemplating running it on full synthetic oil.
Specially now we saving so much on fuel, 99 cents a litre today
Lawrie
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Old 04-21-2020, 07:47 AM   #16
chuck stevens
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Default Re: Bearings vs oil pressure

Quote:
Originally Posted by RobR'35 View Post
Original type gauge or mechanical?
Are u certain the gauge is accurate?

I have both kinds of gauges, most of the time they are the same, I run 20-50, it makes no rod noises even at an idle, thanks guys.
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Old 04-21-2020, 08:04 AM   #17
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Default Re: Bearings vs oil pressure

Quote:
Originally Posted by Lawrie View Post
What about using synthetic oil on start up on a new engine,
I,m going to be starting my new spare 276 engine in the next week and are contemplating running it on full synthetic oil.
Specially now we saving so much on fuel, 99 cents a litre today
Lawrie
Hi Lawrie, you should always break-in new builds with conventional oil, change to synthetic later if you want.

Just one other tip, try to use oil that has the word "Racing" printed on the label, this tells you all the additives are inside!

In the photo below, on the left, we sometimes use the "Brad-Penn" SAE 30 weight break-in oil, mostly on flat-tappet units!!

Thanks, Gary in N.Y.

P.S. Am keeping my posts a bit short due to some health issues, still only half-way out of the woods so far!
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Old 04-21-2020, 10:40 AM   #18
Ol' Ron
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Default Re: Bearings vs oil pressure

I go along with Gary on breakin oil. AS for low oil pressure at idle, consider the fact that most engines of the past had dippers collecting oil from the pan to lubricate the engine. The Chevy 6 used them into the 50's.
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Old 04-21-2020, 01:09 PM   #19
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Default Re: Bearings vs oil pressure

Thanks Ron...GR8 info. I'll not worry about 8-10 lbs hot idle specially if i'd run her hard.
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Old 04-21-2020, 04:53 PM   #20
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Default Re: Bearings vs oil pressure

One thing We did was install a temp gauge in the oil pan. After a 10 lap race the gauge was pegged. Not very a
hppy with that.
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