Lotus Elan

Oil pump compatibility?

PostPost by: The Veg » Mon Mar 02, 2020 4:24 am

When I've got the engine half apart, I decided to convert to an oil pump that takes a spin-on filter. I'm a bit ignorant about the finer points of these pumps, and I noticed that the passages are not the same between them. The hole with the spring behind it connects to a lower passage on one but to the upper passage on the other. Does this afftect the compatibility of the spin-on pump?
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PostPost by: Concrete-crusher » Mon Mar 02, 2020 7:00 am

When I changed mine I found two types available, low pressure and high pressure pumps. Most twin cams run the low pressure version. The spring part is a pressure relief valve. I'm not sure if it's position is different, I don't recall it being differnt

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PostPost by: 2cams70 » Mon Mar 02, 2020 7:54 am

The one on the right is the 1973 onward oil circuit pattern pump casting where as the one on the left is the earlier canister type and pre 1973 spin on type pump design.

The one on the right returns oil that has bypassed the PRV direct to the intake of the pump whereas the one on the left returns it back to the sump. The one on the right is an improved design less likely to cause starvation under extreme conditions.

Note that all spin on type pumps also have slightly wider lobes than the earlier canister type pump for improved pump flow rate.

They are all interchangeable but the 1973 onward pump design is the best although knowing the character of this forum someone is sure to disagree - where are you Craven??
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PostPost by: rgh0 » Mon Mar 02, 2020 9:43 am

Yes they are all interchangeable. The removal of the over pressure return to the sump and internal recycle to the pump suction looks more like a cost reduction measure by Ford rather than an improvement. Excessive recycle in the pump itself will lead to higher oil temperatures in the pump and in the supply to the engine which is undesirable but in the push rod sedan engines engines which are unlikely to operate at high temperatures and revs with high recycle for long it is not an issue. i don't believe its been an issue in normal road twin cams and and most competition twinks have oil coolers so not an issue with them either.

Disagreements based on sound engineering principles are to be encourage IMHO as that is the way to truth

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PostPost by: 2cams70 » Mon Mar 02, 2020 10:31 am

Here we go again. All I can say is that those Ford design engineers were very smart cookies and although it's only speculation what the exact reason for the design change was it does not appear to be for cost reduction reasons. All blocks regardless of what style pump was fitted still have the drilling for the oil drain tube and also the drain tube pressed into place even though it's not required with the later 731M pump casting. All the pattern pumps available are based on the later 731M design so this is probably what most people are running in race engines today if it's not a dry sump setup.

The Twin cams, BDA's and push rod engines as standard for equivalent model year all ran the same oil pumps.
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PostPost by: rgh0 » Mon Mar 02, 2020 11:38 am

Yes here i go again. it is just my opinion but .....

The return tube in the later press in pick up blocks (681F and later) had two functions i.e. to hold the suction pickup basket in place and guide its movement as well as return oil ... yes they were smart cookies. Why Ford did not change the block when the pump changed to not use the return tube for oil is probably again cost reduction and backward compatibility .. yes they were smart cookies. The machining lines were set up to do it and it would have cost money to remove it and redesign the pickup and made later blocks not compatible with earlier pumps. Note the earlier screw in 120E style pick up had the return to the sump but without the return tube.

The manufacturing at Ford as in most companies is heavily driven by accounting not only by engineering excellence so I would be hesitant to assign all change to engineering improvements alone.

As a great engineer said to me once, to expand upon the saying on the US dollar note

" In God I trust..... all others please bring data"

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PostPost by: 2cams70 » Mon Mar 02, 2020 11:55 am

rgh0 wrote:The return tube in the later press in pick up blocks (681F and later) had two functions i.e. to hold the suction pickup basket in place and guide its movement as well as return oil ... yes they were smart cookies.


Here's some more data. The return tube was not needed to locate the pickup basket. All the engines with rear bowl sump (i.e in Escorts, Capris, etc.) had a bent pickup totally separate and no where near the oil return tube. Despite this all blocks still retained the return tube regardless of what design pump was fitted.

Yes they probably still retained the return tube for backward compatibility of oil pumps. That being the case there would have been no cost benefit in the block manufacturing process. I therefore conclude the design change was probably for reasons other than cost reduction.

The change in design would in fact have had a negative impact on the overall cost because new tooling would have been required for the pump itself.
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PostPost by: promotor » Mon Mar 02, 2020 5:00 pm

rgh0 wrote:Note the earlier screw in 120E style pick up had the return to the sump but without the return tube


I'm in disagreement about that - the 120e blocks had a return pipe which was longer than the later type return pipe (ie push-in pickup pipe engines rather than screw-in) and also seems to sit at a different angle to the later type. I've never seen one without the tube fitted here in UK.
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PostPost by: rgh0 » Mon Mar 02, 2020 11:18 pm

Interesting because all the 120E blocks i have dismantled here in Australia did not have the oil return tube fitted so some difference in the Australian assembled engines ?

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PostPost by: 2cams70 » Mon Mar 02, 2020 11:32 pm

My experience in Australia is the same as Promotor. I've pulled apart many Cortina 1500 engines through the years. The earlier 120E engines had to have the oil return in the block anyway because they all ran the early canister type pump which had no PRV bypass to the pump intake.

All the the engines here were imported CBU from the UK in any case and weren't Australian assembled.
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PostPost by: 2cams70 » Wed Mar 04, 2020 4:35 am

Some further interesting information for debate. This explanation seems to make some sense (well to me at least!):

BYPASS OIL RECIRCULATION
Some pump manufacturers like to claim that recirculating the bypassed oil back to the inlet of the pressure pump causes the oil temperature to increase. Well, technically that is true. The problem is that the temperature increase due to recirculation is so small that it is difficult to measure accurately.
Those manufacturers who criticize recirculation claim their products are superior because, instead of recirculating the bypass oil back into the pressure pump inlet, they pump it back to the oil tank (or to the sump).
HOWEVER, sending the bypassed oil back to the tank (or the sump) creates an even bigger problem: The output of the pump at high RPM can be 30 GPM or more, while the engine requires only 8 - 12 GPM. That means that the pump will be bypassing at least 18 GPM through the relief valve to maintain the set oil pressure. If the bypass oil does not recirculate to the pump inlet, then the full pump volume (30 GPM or more) must flow from the tank to the pump inlet through the dash-12 inlet line, with only atmospheric pressure (at best) to move it. The reality is that it can't be done without reducing the inlet pressure below the vapor-pressure of the oil, causing pump cavitation, line collapse, aerated lube oil, and all the engine problems that follow those problems.
NRC pumps provide optimal pumping efficiency by recirculating the bypassed oil back to the inlet side of the pump.

http://nutterracingengines.com/racing_o ... pumps.html

Just conjecture but the rear bowl sump used in the Escorts etc. and hence the longer oil pickup tube probably hastened the design change in 1973 as this pickup would have been more susceptible to oil aeration under high flow conditions
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PostPost by: 512BB » Wed Mar 04, 2020 7:49 am

I''ll bet you're glad you asked the question now Vegetable :lol:
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PostPost by: The Veg » Wed Mar 04, 2020 5:19 pm

512BB wrote:I''ll bet you're glad you asked the question now Vegetable :lol:


More information than I needed, but educational. Much of the deep stuff those guys went into is above my level but it sounds like my new pump is at least acceptable, possibly an upgrade depending on what you value (I value not having to order oil filters from faraway sources).

I'm just thankful that I didn't raise the ire of the purists! :mrgreen:
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PostPost by: 2cams70 » Wed Mar 04, 2020 11:02 pm

It was a good question. Thanks for asking it. I learnt something from it.
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PostPost by: Quart Meg Miles » Thu Mar 05, 2020 12:01 pm

2cams70 wrote:It was a good question. Thanks for asking it. I learnt something from it.

Me too.
I remember Bruce Maclaren made this bypass change on his CanAm engines and it seemed an obvious idea but I had no idea that the later Ford pumps recycled. I fitted one in 1995 to cure low oil pressure but it made no difference, so if anyone wants an original felt element pump with just 200,000 miles use please contact me.
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