14 replies to this topic

[mariner]

A very nerdy question but a recent article on the difficulty of priming a crank mounted Gerator oil pump started ( sorry for the pun) me thinking.

 

Apparently the new Gerotor pumps mounted concentrically on the nose of the crankshaft are much harder to prime than the older "pump in the sump" type installations. Obviously because the pump down in the sump is in the oil but the crank mounted one is maybe 6 inches/15cm above and will initially suck air. 

 

I guess the crank mounted ones make sense when there is no distributor and less extra bits.

 

This got me thinking about priming a dry sump engine. Many a race car has been tow started to build oil pressure but how long does it take?

 

Most dry sump systems have tall tank with an air space for  swirl so the oil can’t drain back to the  pump-less sump on the scavenge side. The tank is usually aimed to be 2/3 full of oil and so the oil level will be well above  any pressure pump mounted at ,or below, the crank centre line- which I think all dry sump pumps are?

 

So with a head of oil int the tall tank above the pump it should prime pretty instantly. Of course, the pressure pump has to fil the filter which might have drained back and the oil has to go round the galleries. 

 

However when I crank over my dry sump engine it usually shows pressure within 10 - 15 seconds even if left standing for days. I do always give two or three 10 second stater bursts to be sure.

 

One caveat some cars have filter installations well away for the pumps and engine with long lines, those I can see needing lots of cranking.

[Greg Locock]

I know it is one more thing to go wrong, but why isn't there a non return valve in the intake to the pump?

[Joe Bosworth]

If you don't mind I will throw my bits of experience into the answer to your question.

 

Absolutely, I make sure that the external sump tank has at minimum level a margin of volume over the pump inlet.  Then, for any first time use such as re-installing the engine after rebuild I loosen the fitting at the pump from the the tank and expel all air in the line until oil comes forth.  It may not be necessary but it assures that the engine has oil pressure at the earliest time when cranking over for the first time.

 

Needless to say, I also remove all of the spark plugs and place a couple of small spoonfuls of oil into each cylinder, this after having poured some oil over the top rockers and valves during assembly..  I then crank the engine over until the pressure gauge shows running pressure.

 

Reinstall plugs, start to idle and check for leaks.  All of this insures that the engine is fully lubricated from first firing.  I have never known the suction pumps to not pick up oil to send to the external tank if I follow the above.  I have never found it necessary to follow these steps unless the engine has not been fired up for many months such as a cold long winter with no racing.  But I also like to fire the engine up about every 4 to 6 weeks regardless.

 

Not asked in the question, I have  some strong beliefs for first running after rebuild.  Do not idle for long.  Get out out the track for a couple of part throttle warm up laps.  When ready give the engine some full torque runs from about 2500/3000 RPM in a upper gear, initially to say 4k RPM and let it run down on no throttle back to 2.5/3K before repeating. Over a couple of laps raise the top revs in 500 RPM increments until you reach red line.  Cruise back to the pits and let the car go back to surrounding temperature before doing your next bunch of static checks.

 

These steps noted in my responses above have never let me down.

 

Regards

 

[malbear]

has anyone had knowledge or experience with electric driven oil pumps ?

[Joe Bosworth]

I strongly suggest that you will not find anyone with knowledge or experience with an electric driven oil pump.

 

It might be that using such to evacuate the internals and return oil to the external sump might make some sense but this load on the engine is really quite small as while the oil return volumes are high the line pressure  to return is quite small.  Thus the power required is low.

 

However, the lubrication pressures are much much higher and do take some useful power from the flywheel.  BUT, and this is a BIG but, the volume of oil required is a function of engine loads which emulate the engine revs.  Low revs need low volumes; high revs need higher volumes.  It would be a bit tricking designing a reliable electric control system. And then you have the problem that any mis-function, even for a split second would have catastrophic results. 

 

So a fully mechanical pressure system based on engine revs is utter simplicity and totally reliable so once you have that there is very little cost and complexity to add the oil return sections to the pump body.

 

Regards

[gruntguru]

I believe there are some electric scavenge pumps out there. Also electric pumps for turbo oil return where turbo is low or remote monted.

[GregThomas]

There are some - very limited - circumstances where an electric pump might be used. In my experience, one is for the scavenge side of a roadrace sidecar outfit or where a motorcycle engine and box are used in a car.. Bear in mind that 99% of motorcycle engines now are wet sump - and damm hard to drysump. 

You generally have the choice of an electric waterpump or an electric dry sump pump. Usually the only practical place to put an engine driven scavenge pump is where the water pump would live so it's a straight choice. Which way you go depends on the layout of the support systems and how much space is available..

 

To adress the self - priming aspect, a scavenge pump or pumps  usually has more than sufficient capacity for oil return and hence pumps quite a lot of air, Such that crank seals for example often have to be reversed as the crankicase may run at a negative pressure. Even early, relatively crude motorcycle scavenge pumps seem to self prime quite happily.

On the pressure side, late model bike practise is to run deeper, narrower sumps to a/ lower the oil in relation to the crank and b/ cornering clearance.

This has seen the oil pump migrate lower in the cases. Gear drives have given way to chain drives to span a longer distance.

Edited by GregThomas, 06 February 2022 - 20:24.

[mariner]

Ive heard of electric water pumps , sounds like they make sense for saving power and fine-tuning engine temperature tothe  exact combo. of load and road speed - but not an electric oil pump.

 

It would let you pre lube but not a big advantage vs the failure risk I think!

 

Speaking of priming “pump in sump" is easier when engines had distributors as by removing the distributor you can spin the pump down below with a drill and attachment

 

 You can spin a dry sump pump if it has a cogged belt drive by removing the belt and winding it with socket on the pump end nut. However, it means loosening the pump  mounts to remove the belt which makes re tightening rather important!

 

 

Speaking of dry sump pumps and belts I remember a comment by Hugh Chamberlain,who ran many Le Mans teams, that when running the big Vipers he had to tell the drivers NEVER to re start the engine after going into the gravel traps without opening the bonnet and making sure no gravel was trapped in the pump belt.

 

The pump was so low that every time the car went into the gravel it got rocks in the belt so as soon as the driver runs the starter the belt came off, he revved up to re-join the race bang no oil pressure

[Joe Bosworth]

After adding my comments in reply #3 to Mariner's query regarding IC engine dry sumps I will jump back in with one more comment.

 

I think we have put to bed the issue of reliability etc being paramount which precludes using an electric pump for pressure lube we can concentrate on how much sense it takes for electric applications for the sump evacuation.

 

I have done some back of envelope engineering calculations and for evacuation realms.  Using between 1 and 3 stages it is about impossible to calculate that more than about 2 HP is required to get the job done.  Most applications will be fractions of 2 HP but that is about the top side.  It is hard to believe that anybody will try to save less than 2 HP at the crank at the cost and complexity of installing a battery powered system.

 

As a reality check I have perused the availability of such pumps.  I have Demon Tweeks (UK race bits supplier) and Summit Racing (US supplier) catalogs and find practically nothing that makes sense for use in other than dif cooler type applications where battery power makes good sense.

 

Regards 

[malbear]

thank you all for such relevant comments  cheers 

[Greg Locock]

a 2hp electric pump would be a fair old lump of hardware, pulling over 100A at 12V

[Greg Locock]

Turns out gerotor style pumps were only about 20% efficient in the 90s.. SAE 912407

[gruntguru]

Off the shelf electric oil pumps.

https://www.emp-corp.../advanced/OP80/

[Lee Nicolle]

I raced a drysumped engine for 20 plus years. I read the Smokey Yunick book on mounting and plumbing. 

Which these days so many 'Pro' teams totally screw up. 

A. Tank outlet must be higher than the pressure stage. And to me tank should be about 6" in dia. Larger ones must suffer from oil surge in the tank

B. Must be close as possible to the engine. So you see all these 'pro' idiots with them in the boot of the car. Nascar Stupidcars etc.

C  Mount the pump on the engine out of the way of road debris, if in doubt shield it. Those belts are fairly tuff and should be replaced regularly however.

D Scavenge pickups as low as possible in the pan. And ideally so the oil runs into them. I mounted mine in the floor of the scavenge area

E. Get rid of as many  corners in the lines. Every 90deg bend costs 5 lb of oil pressure. I just love all those fancy 90s stuffing up flow with the "pros' NOT!!  This ofcourse also applies to fuel and water plumbing.

F. After a period of inactivity I used to turn the pump by hand to get oil up. You can feel the resistance as oil psi comes up.

Then crank the engine with ignition OFF until good oil pressure shows then turn the ignition on. After that crank the engine until oil psi shows then fire it.  This really applies to wet sump engines as well, more so with high compression etc

G. All race engines must have a starter switch and a seperate ign switch. You can put a sw in the ign wiring and still use the standard key sw. 

H. word of warning, so much of the shiny hose is very suspect.  For whatever.

Like a few others I used hydraulic hose. Near indestructible. And you can use a hose clamp on it safely. Make certain though you get hose rated at 150C, the cheaper low temp stuff can cause issues. IT is however a bit heavier but lasts decades, shiny **** may last a year. Usually starts to leak about the fittings.

 

With all of the above I never had any oiling issues at all. And for racing wet sump is at best marginal. And the better grip level the more marginal it becomes.

[Lee Nicolle]

Ive heard of electric water pumps , sounds like they make sense for saving power and fine-tuning engine temperature tothe  exact combo. of load and road speed - but not an electric oil pump.

 

It would let you pre lube but not a big advantage vs the failure risk I think!

 

Speaking of priming “pump in sump" is easier when engines had distributors as by removing the distributor you can spin the pump down below with a drill and attachment

 

 You can spin a dry sump pump if it has a cogged belt drive by removing the belt and winding it with socket on the pump end nut. However, it means loosening the pump  mounts to remove the belt which makes re tightening rather important!

 

 

Speaking of dry sump pumps and belts I remember a comment by Hugh Chamberlain,who ran many Le Mans teams, that when running the big Vipers he had to tell the drivers NEVER to re start the engine after going into the gravel traps without opening the bonnet and making sure no gravel was trapped in the pump belt.

 

The pump was so low that every time the car went into the gravel it got rocks in the belt so as soon as the driver runs the starter the belt came off, he revved up to re-join the race bang no oil pressure

Electric  hydraulic power steering,, Far from ideal and uses quite a deal of amperage.

I have seen an electric scavenge, was far from succesful then the pump jammed at about 8000 rpm!!!

Electric pumps have been used for  manual trans and diff coolers. Usually work ok and when they fail not the end of the world. And yes they often fail!

Electric waterpumps??  Never ideal, unless thermostatically controlled temerature will be either too cold or too hot. Normal thermostat is not enough. A fried got this faxation with them, others in his class used them. On his car though apart from charging issues and then alternator failures it boiled in about 12 laps, as the water pumped through too fast so not having time to cool. WHEN the alternator failed and he was forced to refit the waterpump belt it stopped boiling and he could finish a feature race. This engine was on methanol and the factory water pump and alternator were both slowed well below crank speed. Crank speed may be ok for low rpm stop start driving and even the highway but NOT for high rpm constant use.

As for alternators?? On my road race car I have slowed it to about 1/3 of its standard gearing so should be reliable. Using a Crane Multispark ignition and being forced by the events [hillclimbs with traffic jams on the return to [paddock] I do to need fans I need a charging system. I hate alternators, have had several fail over the decades.

My Sports Sedan with HEI ignition and an electric fan for short use [sitting on the grid] I would get a three day meeting from one standard battery.

The classic speedway car with the same has done two events [I forgot to recharge it] with no issues. Meanwhile the opposition are flicking belts off and having alternators sieze. I hate alternators,, or generators as well!  Smokey Yunicks propellor driven alternator for those events was a very good idea.

And both of these cars have the waterpumps slowed to about 80% crank speed.