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Observations after modifying a sgl relief case
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Alstrup
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PostPosted: Mon Jul 26, 2021 3:29 am    Post subject: Observations after modifying a sgl relief case Reply with quote

Hello.
Not sure if this is the correct place to put this. If not, the moderator can maybe move it to the right place.
Anyway, here goes.
About 3 weeks ago I got a "2 hour" 1600 sgl port industrial engine in to get ready to go into a bus. It had sat for over 16 years so I did not dare to start it without taking a look inside, and good that I did because the rod bearings were not that nice. the rest was fine. not even much corrosion behind the main bearings. So basicly good.

Now, since it was going in a bus, and since we had it apart I enlarged just about all the oil galley routings to "dual relief"size and did the Hoover mods too. Normally I would increase the oil pump size from 21 to 26 mm too with this mod, but since this pump was brand new we decided to flow optimize it and use it.
Everything was checked. Crank balance, fair, rods and pistons, good. Back together. Topped off with a set of dual 34 Solex.
Fast forward to the engine and vehichle on the road. Already after the initial runs we noticed low oil pressure below approx 1600 rpm. and even at only 80 C. the pressure would occasionally drop below 0,45 bar. The engine had a nice quality 15W40 mineral oil at the time. We checked with 3 different sensors, all the same result. Interesting! So the increase of the oil galley size along with the Hoover mods simply flows more oil than the 21 mm pump can supply at a 15w40 viscosity. Since the engine is in the car and the guy wants to go camping I used the redneck method of increasing viscosity to a 20w50 oil. That took care of the low pressure issue at idle, but also increased oil temps by almost 10 degrees on cruise.

Come winter and the engine will of course get a 26 mm pump. But it was a little interesting to experience how much increase in oil flow these mods gave.
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oprn
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PostPosted: Mon Jul 26, 2021 6:02 am    Post subject: Re: Observations after modifying a sgl relief case Reply with quote

Thanks for that! It confirms a couple things, first off that the Hoover mods do lower oil pressure all else being equal. Second is that thicker oil is not a cure for higher oil temps!

I am curious about a couple points. How low was the oil pressure? What exactly was wrong with the rod bearings?
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PostPosted: Mon Jul 26, 2021 7:10 am    Post subject: Re: Observations after modifying a sgl relief case Reply with quote

Did you also install the larger dual relief pickup tube? I have done this on two single relief engines.
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Alstrup
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PostPosted: Mon Jul 26, 2021 7:11 am    Post subject: Re: Observations after modifying a sgl relief case Reply with quote

Upon startup I did notice a relatively low oil pressure. Only about 40 psi max. but that is within factory specs, so I wasnt worried. But during start up I only had about 65C oil temps so I didnt see the pressure drop with warm oil until the engine got on the road.
I knew that, but the Hoover mods do take a little pressure. not a lot though. The main reason for the pressure drop is 95% certain that the oil galley has very little restriction compared to stock, so the bearings etc simply consume more oil.

The rod bearings had scuffing marks. most likely due to the engine being turned over on a regular basis, and at some point there was simply not enough lube between the crank and bearing.
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PostPosted: Mon Jul 26, 2021 7:51 am    Post subject: Re: Observations after modifying a sgl relief case Reply with quote

a straight 30 or 20-30 may be what it needs to have the better pressure and lower highay temps some,but I do agree with a biger pump when possiable to do so. I have a duel relief case that was machined for single relief from vw. someday Ill go over it good and build something. I havent a clue how the relief system works in it.never looked at it close to see,I bought it cheep years ago almost looks like new. I was quite supprized to see the unmachined flywheel end relief hole, then stuck it on a shelf.
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PostPosted: Mon Jul 26, 2021 11:13 am    Post subject: Re: Observations after modifying a sgl relief case Reply with quote

Alstrup wrote:
Hello.
Not sure if this is the correct place to put this. If not, the moderator can maybe move it to the right place.
Anyway, here goes.
About 3 weeks ago I got a "2 hour" 1600 sgl port industrial engine in to get ready to go into a bus. It had sat for over 16 years so I did not dare to start it without taking a look inside, and good that I did because the rod bearings were not that nice. the rest was fine. not even much corrosion behind the main bearings. So basicly good.

Now, since it was going in a bus, and since we had it apart I enlarged just about all the oil galley routings to "dual relief"size and did the Hoover mods too. Normally I would increase the oil pump size from 21 to 26 mm too with this mod, but since this pump was brand new we decided to flow optimize it and use it.
Everything was checked. Crank balance, fair, rods and pistons, good. Back together. Topped off with a set of dual 34 Solex.
Fast forward to the engine and vehichle on the road. Already after the initial runs we noticed low oil pressure below approx 1600 rpm. and even at only 80 C. the pressure would occasionally drop below 0,45 bar. The engine had a nice quality 15W40 mineral oil at the time. We checked with 3 different sensors, all the same result. Interesting! So the increase of the oil galley size along with the Hoover mods simply flows more oil than the 21 mm pump can supply at a 15w40 viscosity. Since the engine is in the car and the guy wants to go camping I used the redneck method of increasing viscosity to a 20w50 oil. That took care of the low pressure issue at idle, but also increased oil temps by almost 10 degrees on cruise.

Come winter and the engine will of course get a 26 mm pump. But it was a little interesting to experience how much increase in oil flow these mods gave.


Interesting!

Just looking at it from a pure math direction....maybe we can see something.

Lets say original was 8mm oil galleys. Enlarged to dual relief size is say 10mm?

Lets say we have 60" of galleys (just for conversation)...and we enlarge them from 8mmto 10mm.

The volume of 60" of 8mm galley is 4.68 cubic inches. The volume of 60" of 10mm galley is 7.32 cubic inches.

The 10mm galleys are 36.97% larger in total volume.

The 26mm pump is 19.3% bigger than the 21mm pump.

This may be saying that the 21mm pump...had only a few percent excess capacity over what was really required for its original application.

Other things to think of...or other ways to think about the issue. A pump is a pump...whether its a fan for pumping air, a diaphragm for pumping fuel or an oil pump for pumping oil.
Without getting into massive HP variants of each one (like using a turbo fan engine as an example for a fan pumping air).

They all work by volume.....against a restriction. In open air...pumping from the inlet side on a sealed pickup tube and the outlet side pumping into free air...the oil pump is not going to produce ...even at high rpm....what anyone would consider real pressure. It just moves a LOT of volume.

Without the restriction of the galleys which are very small volume compared to what the pump is capable of moving....you get no pressure.

So going to galleys that are roughly 37% larger (in my crappy example).....you have 37% lower restriction. That will be lower pressure.

Unless the pump was somehow not passing all of the volume it was capable of....and this is more common than one might think....it will generate lower pressure.

The last issue I will mention....and kind of linked to that last sentence ...is efficiency.

We would like to think of any kind of pump...especially a gear pump....as linear...right?

By that I mean...we tend to think of our gear pump as increasing in a straight line by uniform steps....like 10-ish psi at 1000 rpm, 20 psi at 2000 rpm, 30 psi at 3000 rpm etc.

In reality....due to a wide range of subtle issues...ranging from gear mesh backlash, oil shear point, gear end tolerance ...and even smaller flow issues with port shape......they are NOT perfectly linear.

A lot of these gear pumps are not as efficient at lower rpms (bleeding pressure internally at lower rpms)...until high enough rpm and static pressure are generated to lock or prevent internal bleed/slippage.

Likewise....once they get over a certain rpm...they can actually be come less efficient. Not only by robbing more power but through cavitation and foaming of the oil (may have more to do with the oil than the pump).

So ....to combat all of the above the pumps are usually oversized to start with (but by what margin and how is it calculated)...and modulated by pressure relief valves.

Yes....I was moving toward that second pressure relief valve. I think the one on type 1 is smarter....better planned.....but may also be the source of some of this issue you are seeing.

I only make that last statement.....because The one on type 4 engines.....I think is poorly planned and causes variable pressures at low rpm and spikes at high rpm. Which sounds familiar.
I will be doing some testing of type 4 2nd relief (called the control valve in type 4)...coming up in a month or so. Ray
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Alstrup
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PostPosted: Mon Jul 26, 2021 11:46 am    Post subject: Re: Observations after modifying a sgl relief case Reply with quote

Ray, I love it when you can explain what I think, but canīt put into words Cool
But you are spot on I think.
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PostPosted: Mon Jul 26, 2021 2:43 pm    Post subject: Re: Observations after modifying a sgl relief case Reply with quote

The oil pressure at the top end never concerns me as long as it is not stupid low. Even at 18 psi I know that the galleys are still all full and everything is getting oil. It's the low end that worries me. If the pressure drops off close to zero at the low end then the pump is not keeping up with demand and someone somewhere in the oil train is getting short changed! Something is running dry!

Oil pressure itself does not reduce or prevent wear, that is the job of the oil film strength. The oil pump and galleries are just there to distribute the oil and see that everyone gets their fair share.
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PostPosted: Wed Jul 28, 2021 3:56 am    Post subject: Re: Observations after modifying a sgl relief case Reply with quote

didn't the late mexican bugs all have the 26mm pump? Wink
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PostPosted: Wed Jul 28, 2021 4:35 am    Post subject: Re: Observations after modifying a sgl relief case Reply with quote

sometimes volume is just as important, had an old IH diesel, could barely keep the oil light off below 1500 rpm, they rely on volume more then pressure.
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PostPosted: Wed Jul 28, 2021 5:04 am    Post subject: Re: Observations after modifying a sgl relief case Reply with quote

They are directly related. If your pressure is excessive then your pump may be too large. If your pressure is weak then maybe your pump is too small. This of course is assuming all is well in the engine internally and the oil grade is appropriate to the conditions.
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PostPosted: Wed Jul 28, 2021 6:43 am    Post subject: Re: Observations after modifying a sgl relief case Reply with quote

madmike wrote:
didn't the late mexican bugs all have the 26mm pump? Wink


The filterpumps were 30mm, the two "complete OEM longblock" mexican engines I tore down from the late carb era were 26mm.
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PostPosted: Wed Jul 28, 2021 7:44 am    Post subject: Re: Observations after modifying a sgl relief case Reply with quote

RWK wrote:
sometimes volume is just as important, had an old IH diesel, could barely keep the oil light off below 1500 rpm, they rely on volume more then pressure.


Technically.....they are near reciprocal of each other.

Oil pumps (and fuel pumps) ....do not produce pressure. They produce VOLUME against a reatriction....which creates the pressure rise.....identical to putting your thumb over the end of the garden water hose.

So yes.....you are spot on.....volume is key.

But another issue....or a refinement of the issue.....is the ability to keep supplying that volume across a wide range of rpms and usage demands.

This is the same issue that many fuel injection engine owners have....when troubleshooting fuel system problems. They think in terms of absolute pressure only.

Example.....the engine idles fine.....but starves when you rev it or try to accelerate. They look at the pressure gauge at idle and see 36 psi (factory setting at idle).....and think...."ok....getting plenty of fuel ....pump must be fine"......but in reality when they rev it up to say....2500 rpm....where fuel demand has increased.....if they are still watching the gauge....they would see rapid erratic needle movement or dips.

This is because the pump......is not producing enough volume to MAINTAIN stable pressure in the face of higher volume usage.

It can be that the pump is actually fine....but either of the two check valves is leaking (either from a bad valve seat or a weak spring) ....which is the equivalent of the same issue with oil pumps....when either of the oil pressure relief valves have bad sealing surfaces or weak or incorrect spring pressures........or.......if the fuel pump is just high niles or has rust damage.....the internal tolerances may be poor and it can no longer make as much volume.
This is the equivalent of the oil pump that is high mileage....has wear.....and has too much gear lash and/or too much gear to pump wall gap or too much gap between the ends of the gears and the cover plate. It has too much internal cross bleeding of volume to produce higher output volume until rpm rises past a certain point.

And there is still the occasional problem....when comparing fuel to oil pump volume issues.......where someone replaces a fuel injection pump that makes a standard 1 liter per minute at 36 psi......with a cheaper one that produces only 0.75 liter per minute at 36 psi. Again.....it will idle fine.....but as rpm and volume demand increases.....it will run out of the ability to keep volume....and therefore pressure....constant.

I think that last one is what Alstrup ran into. He increased volume demand across the board by enlarging galleys......BUT......did not decrease the restrictions.....or outlets for the pressure (the relief valves nad bearing gaps)......so you get some issues down at low rpms.....bit you can get relatively normal running in the middle as pump efficiency catches up......and then sed variability again at even higher rpms.....as pump efficiency starts to vary. Ray
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PostPosted: Wed Jul 28, 2021 8:39 am    Post subject: Re: Observations after modifying a sgl relief case Reply with quote

In making comparisons between fuel pumps for FI systems and oil pumps for engines one must bear in mind that FI fuel pumps tend to run at the same speed regardless of engine speed so pumping losses/deficiencies are more apparent at the high end of demand. Oil pumps on the other hand are connected physically to engine speed so pumping losses show up as a higher percentage of total volume at the low end of the rpm spectrum and become less significant as speeds and volumes increase.
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PostPosted: Wed Jul 28, 2021 8:41 am    Post subject: Re: Observations after modifying a sgl relief case Reply with quote

Yes.
Another thing wrt oil pressure and flow.
Excessive pressure for the given engine kills bearings almost as bad as pressure on the low side.
Oil flow improves bearing life as the volume helps both lubricating of course, but also carrying heat away from the suraces.
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PostPosted: Wed Jul 28, 2021 9:52 am    Post subject: Re: Observations after modifying a sgl relief case Reply with quote

Excessive oil pressure just pre-heats the oil and robs power. There is no upside.
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PostPosted: Wed Jul 28, 2021 10:07 am    Post subject: Re: Observations after modifying a sgl relief case Reply with quote

Yes to both of those last comments.

Alstrup....just so I get your meanung clearly......aside from the problems caused by excessive oil pressure causing cooler bypass....and alsi in some engines ...causing control valve bypass .....how else does excessive oil pressure damage bearings? Interesting!

Ray
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PostPosted: Wed Jul 28, 2021 10:31 am    Post subject: Re: Observations after modifying a sgl relief case Reply with quote

Excessive oil pressure "flushes" the bearings, which initially is good, - to an extend. Excessive oil pressure is almost always also equivallent with high oil flow. Those two things together has a tendency to flush so hard that it actually has the opposite effect. The bearing surfaces get damaged. It basicly "tears" the bearing surface in lack of a better explanation. Udo Becker posted some pictures explaining this exact scenario some time ago. I believe it was on Bugnet. I will see if I can find it.
If you remember, back in the late 80īs and 90īs too where everybody "had to" have 30 mm or even 32 mm oil pumps and run 20w50 oil at the same time, bearing life was generally zilch. Then at some point there were some bright headed people that sort of got the hang of it and began to reduce oil pump size and/or reduce oil viscosity. Then bearing life went up because then the oil pressure didnt tear the main bearings so bad anymore.
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PostPosted: Wed Jul 28, 2021 11:23 am    Post subject: Re: Observations after modifying a sgl relief case Reply with quote

Given enough time running water wears away rocks!
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PostPosted: Wed Jul 28, 2021 12:47 pm    Post subject: Re: Observations after modifying a sgl relief case Reply with quote

Alstrup wrote:
Excessive oil pressure "flushes" the bearings, which initially is good, - to an extend. Excessive oil pressure is almost always also equivallent with high oil flow. Those two things together has a tendency to flush so hard that it actually has the opposite effect. The bearing surfaces get damaged. It basicly "tears" the bearing surface in lack of a better explanation. Udo Becker posted some pictures explaining this exact scenario some time ago. I believe it was on Bugnet. I will see if I can find it.
If you remember, back in the late 80īs and 90īs too where everybody "had to" have 30 mm or even 32 mm oil pumps and run 20w50 oil at the same time, bearing life was generally zilch. Then at some point there were some bright headed people that sort of got the hang of it and began to reduce oil pump size and/or reduce oil viscosity. Then bearing life went up because then the oil pressure didnt tear the main bearings so bad anymore.



Ah...makes sense!

The bearings are made in coated layers near the top...thin layers.

A lot of people have the mental tendency to think of the oil between bearing and journal as static...a hydrostatic film...kept pressurized in that state by the oil pressure coming up behind it....but in reality its ripping through that .001" to .002" gap like a river.

Yep....if a wear spot through the top coating of a bearing starts...just from wear alone....high pressure oil could exploit the coatings. Just like pressure old paint off the brick on the side of your house. Ray
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