Oil pump designs

[Motorbike]

I thought I would post these tidbits for some that do not understand the effects of debri in the engine oil and using too thick of a engine oil for the ambient temp . You will also see that Melling and other manufactures advise using a heavy duty aftermarket pump drive when using any of their High Volume gear to gear oil pumps . The reasoning is not Vi related initially but is due to the additional torsional flex caused by the 30% larger gears . Enter a heavy wt oil and the problem multiplies due to this particular design which has no means to support the gears at the botton end of the pump . Even the stock pumps can and do suffer torsional flex internally and eventually wears the pump rotor housing and end plate as seen here . This type is gear driven off the camshaft and turns 1/2 the engine speed .

pump wear

Here in figure 1 you will see a picture of a Gerotor style oil pump thats driven full engine speed off the crankshaft . It's used in the LS1 , GM 3800 and many Fords along with other makes .

Gerotor

These pumps will not wear as badly when too thick of an oil is used generally because they do not have the support problem the figure 2 design pump has .

The better engine builders blueprint the gear type pumps to reduce internal cavitiation and tighten up the end plate clearance . I've seen as much as .004 gear to endplate clearance in these type pumps ... too much but an easy fix .

Abrasives in the engine oil lead to premature pump wear as well especially since many engine now come with soft aluminum housings instead of the cast iron which are a bit tougher in terms of durability . The GM 4.3 is an example of a engine that uses an aluminum oil pump housing w/ gear to gear type oil pump . These used a bronze bushing in the pump housing to support the main internal gear shaft thats ran by the drive that meets the distributor .

Distributors can and do suffer some of the same torsional stress but to a lesser degree if it's the type using a non-sealed bushing in the lower part of the distributor housing and is fed by pressurized oil .

When an oil pump gets worn an engine has a problem . Usually the top end " hydraulic lifters " is still tight but the oil pressure is low making for the need to run a thicker oil to gain some oil pressure back but the lifters don't much like it as evident by both cold start noise and the viscous caused clack that various in severity due to the thick oil even when at hot idle.

I always thought it funny to see an engine builder give a bottom end race clearances then run hyperuetectic pistons and flat tappet hydraulic lifters ... kinda screws with the oil choices in a streeter .

but that deserves another topic .

Anyway cleanliness is godliness to a good engine builder ,

Keep good oil filters on those engines and keep them internally clean by whatever means available !

Ask Terry Dyson about how a clean engine benefits in terms of lenght of time it will last as opposed to an identical engine that's ..... filthy . Even the merits of keeping the ring pack clean and moving freely effect how long the lower end can last and that includes the oil pump

[ March 07, 2004, 08:54 AM: Message edited by: Motorbike ]

 

[JohnBrowning]

The Georotor is vastly supior so long as indexing is not a problem and radial runout at the crank nose is not a problem! If geared right off the crank nose then the drive is as thick as the nose of the crank! I prefer for then not to use a bushing at all.

 

[dickwells]

I was watching a cable show this morning where they were building a small block that eventually put out 660 hp. (for the street no less). At any rate they used a standard volume oil pump and made the comment that one reason was the drag on HP while another one was that all the oil could end up in the upper end at very high RPMs. Makes sense to me.

 

[JohnBrowning]

dickwells, It is common on street rods to use an oem volume and pressure pump but to either shim the bypass valve or to remove it entirely. You can easily shim and and rplace the spring on most stock pumps to arive at a 100PSI bypass from a system that was once a 65PSI bypass.

 

[427Z06]

quote:

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Originally posted by JohnBrowning:
You can easily shim and and rplace the spring on most stock pumps to arive at a 100PSI bypass from a system that was once a 65PSI bypass.

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Isn't anything over 75PSI over-kill on anything but a specialized race engine?

 

[JohnBrowning]

No, many OEM use oil pressures bypass's set this high or higher! 100PSI would not be adaquate for a true race motor. Dodge and Toyota run this high or higher on their newer engines. The most durable engine that GM has kept in production is the 3.8V6. The 3.8 V6 has a higher oil pressure system then the Gen III blocks.

The great thing about shimming a bypass is that it does not affect the dynamic pressure curve of the pump at all. It only effects the psi at wich bypass happens. So even if you do this your oil pressures at what would be considered normal RPM's is not going to significantly change from pre-shimmed. The only time you would notice a difference is at higher then normal RPM's as the pumps displacment is the same for every revoloution. To get higher pressure you need to increase rpm's. SO by doing this you can easily get your 25-35 PSI at idle minimum and 10 additional PSI per 1000 rpm's above idle.

With the stock set up no matter how high the RPMs climed you would begin to bleed off presure at what ever the factory preset was. So even if you were able to exceed the factory recomended RPM limit you oil pressure and volume would not follow suite!

P.S. Just so everyone knows. THe old rules of thumb of 25-35 PSI at idle and 10 PSI per 1000 RPM's above idle allowed for a catastrophic failer like rod hemorage. Most engines that have stuck with this guideline have proven to be very durable.