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Excessive oil pressure causing bearing erosion?

2K views 8 replies 4 participants last post by  jtybt15 
#1 ·
I looked around and didn't anything specifically related to bearing erosion due to excessive oil pressure.

Is it an old wives tale?

During the pre-oiling with a electric drill, with a high pressure/volume pump but low pressure spring, it would take a 1/2" drill to turn the pump. I'm not sure how much harder it is to turn the pump with the high pressure spring(65-70 psi). The pressure relief circuit of the OEM type pump only travels about 1 1/2" right back to the input side of the pump body.

I'll be testing the pre-oil pump in a day or two after I get the lifter/valves adjusted on the stand.


Charlie


P.S.
I did extensive mapping of the SBC oiling system and can say I know how the oil travels through-out the engine. (in case anybody is interested)
 
#6 ·
jtybt15 said:
I looked around and didn't anything specifically related to bearing erosion due to excessive oil pressure.

Is it an old wives tale?

During the pre-oiling with a electric drill, with a high pressure/volume pump but low pressure spring, it would take a 1/2" drill to turn the pump. I'm not sure how much harder it is to turn the pump with the high pressure spring(65-70 psi). The pressure relief circuit of the OEM type pump only travels about 1 1/2" right back to the input side of the pump body.

I'll be testing the pre-oil pump in a day or two after I get the lifter/valves adjusted on the stand.


Charlie


P.S.
I did extensive mapping of the SBC oiling system and can say I know how the oil travels through-out the engine. (in case anybody is interested)
The oil pump is there to supply replacement oil for that which is squeezed out of the bearings, the pressure the pump generates, is of itself, insufficient to carry the loads that separate the bearing shell from the shaft's journals. This is done by the formation of a hydro-dynamic wedge that develops as a result of shaft rotational speed. This wedge has an internal pressure of several hundred pounds and does not erode bearing material. So it's safe to say that the pressure the pump can develop won't come close to anything that can erode the surface of the bearing. The pump pressure we see on a gauge is simply the difference between what volume the pump is delivering and how much is leaking out the system and returning to the sump. The maximum pressure arbiter is the pressure relief valve which will after a preset pressure open to bleed pressure oil back to the intake side of the pump or in some designs back to the sump.

By all means publish you oil routing research, all we can learn helps.

Bogie
 
#7 ·
I won't be running at WOT more than a minute or less just to check my state of tune. This is a boat and the ability to actually reach the recommended WOT depends on how ell it's running. Generally, I'll be running between 3200-3500 RPM so I'll leave the high pressure spring in unless the pre-oiling seems to cause excessive load to the drill which means it's putting quite a bit of load on the dist and cam gear.


The primary oiling system of the SBC(older generation block) is confined to what is the rear wall of the block casting and all on the driver half.

The first(vertical) bore from the pump goes straight up to which was traditionally the oil pressure sending port on the rear rail.

Next are two parallel/horizontal bores that go to and come from the oil filter mount. The bottom one also goes into the saddle of the rear main nearing but doesn't oil it as the bearing shell blocks it. The upper bore starts just above the filter mount and stops at the vertical bore. Between these two bores is the plug which diverts all the oil to the filter.

The last bore is a diagonal bore that starts at the passenger side deck of the block(ever wonder what that pipe plug was doing there?) and cuts thru the vertical bore and continues to the rear cam bearing and delivers full oil pressure to what is the distribution point of the whole engine.

Under each of the cam bearings is a groove about 3/16" wide and 1/4" deep(maybe more). They also have a vertical passage that connects the top cam galley with the main bearings. The rear cam groove also has diagonal passages that connect to the lifter galleys. The lifter galleys feed oil forward thru a 1/2" bore to each lifter. Each lifter feeds oil up the pushrods to the rockers and valves.

The cam galleys feeds oil down to each cam bearing thru a vertical passage that also feeds each main bearing. The crank feeds oil to each rod journal thru internal passages.

As stated by bogie, the OEM oil pump pressure relief valve bleeds off excess oil about 1 1/2" right back to the intake port in the pump body.

Last but not often understood is the oil filter mounting adapters by-pass valve.. This has a relatively weak spring that probably bypasses oil around the filter at a low pressure (guessing about 10 psi). This low pressure relief is the difference in pressure the filter is seeing and what the engine needs to lubricate. You see, the by-pass valve is a safety valve in case the filter gets clogged with debris or you have a remote filter system with too restrictive oil lines or fittings, the by-pass valve allows unfiltered oil to continue supplying oil to the engine rather than starving it.
 
#8 ·
jtybt15 said:
I won't be running at WOT more than a minute or less just to check my state of tune. This is a boat and the ability to actually reach the recommended WOT depends on how ell it's running. Generally, I'll be running between 3200-3500 RPM so I'll leave the high pressure spring in unless the pre-oiling seems to cause excessive load to the drill which means it's putting quite a bit of load on the dist and cam gear.


The primary oiling system of the SBC(older generation block) is confined to what is the rear wall of the block casting and all on the driver half.

The first(vertical) bore from the pump goes straight up to which was traditionally the oil pressure sending port on the rear rail.

Next are two parallel/horizontal bores that go to and come from the oil filter mount. The bottom one also goes into the saddle of the rear main nearing but doesn't oil it as the bearing shell blocks it. The upper bore starts just above the filter mount and stops at the vertical bore. Between these two bores is the plug which diverts all the oil to the filter.

The last bore is a diagonal bore that starts at the passenger side deck of the block(ever wonder what that pipe plug was doing there?) and cuts thru the vertical bore and continues to the rear cam bearing and delivers full oil pressure to what is the distribution point of the whole engine.

Under each of the cam bearings is a groove about 3/16" wide and 1/4" deep(maybe more). They also have a vertical passage that connects the top cam galley with the main bearings. The rear cam groove also has diagonal passages that connect to the lifter galleys. The lifter galleys feed oil forward thru a 1/2" bore to each lifter. Each lifter feeds oil up the pushrods to the rockers and valves.

The cam galleys feeds oil down to each cam bearing thru a vertical passage that also feeds each main bearing. The crank feeds oil to each rod journal thru internal passages.

As stated by bogie, the OEM oil pump pressure relief valve bleeds off excess oil about 1 1/2" right back to the intake port in the pump body.

Last but not often understood is the oil filter mounting adapters by-pass valve.. This has a relatively weak spring that probably bypasses oil around the filter at a low pressure (guessing about 10 psi). This low pressure relief is the difference in pressure the filter is seeing and what the engine needs to lubricate. You see, the by-pass valve is a safety valve in case the filter gets clogged with debris or you have a remote filter system with too restrictive oil lines or fittings, the by-pass valve allows unfiltered oil to continue supplying oil to the engine rather than starving it.
When pre oiling, only the pump is spun up, if using an old distributor, grind the teeth off the gear as you don't want to engage the cam gear. Remember when looking down on the pre oiler you want it turning clockwise on a Chevy.
Have someone wrench the engine over in the clockwise direction when looking from the front. Be sure the pre-oiler is engaged and secured like it was the distributor, the left side oil passage is intersected by the distributor's base, if a seal isn't made at that point no oil will flow up the left side lifter passage and the rockers will be dry.

Bogie
 
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