Improving Oil Galley Piston Cooling

[Franko6]

Put this one in your 'annal engine build' files under "incremental improvements for assembling a performance engine".

The advantages of an oil-galley piston and tapered (keystone) wrist pins in our opinion, is an obvious benefit and foregone conclusion. Every diesel engine now produced that is turbo charged, has oil galley and keystone pistons. Both improvements are reasonable, cost effective and improve durability of the rod/ piston assembly. However, when modifying the ALH and AHU engines the oil squirts require your attention.

1) Oil squirts are not all the same size hole. We have checked many oil squirts and the smallest oil squirt hole measured with a Numbered drill set shows that the variation of the oil squirts is as small as a #48 (.0760") or as large as a #42 (.0935"). In this case, we think 'more is better'. We re-drill each oil squirt to the #42 hole size.

2) The original pistons on all of the 1Z/ AHU/ ALH and a few of the PD motors are not galley cooled pistons. this means the oil squirt simply sprays the bottom of the 'dome head' piston. The oil squirt is aimed "UP". The oil squirt must be redirected into the oil hole closest the the 'dog house' cutout in the bottom of the piston, as shown in the pistons below.

This is pair of 79.5mm pistons intended for a large variety of TDI engines. We specifically use these pistons with our beveled connecting rods for all 1.9 liter engines, except the AAZ or it's counterparts. The picture for the Left piston is a little deceiving, as the angle makes the oil squirt hole appear quite large, but the Right piston shows the perspective that the oil squirt would be aimed from. The hole is quite a small target.

Here are a piston set showing Before/ After picture where we have made the approach to the galley hole into a funnel.

Our purpose is to make the oil squirt pour oil directly into the galley hole from the bottom of the piston stroke, clear to the top. We weighed the amount of metal removed from creating the funnel (you can see the amount of metal removed in the piston) and it amounts to about .2 grams avg. Without producing this change, there is a rather sharp shoulder that can splash cooling oil away from the intended target, which effectively compromises the cooling ability of the oil galley. The funnel makes the approach easier to hit.
3) The issue of redirecting the oil squirt is important. It is the first thing we do when reassembling the block, as there is nothing in the way to keep us from properly positioning the oil squirt. We have a template of the piston made of cardboard, marked for wrist pin direction and galley hole position. We make matching 'wrist pin direction' marks in the bottom and top of the cylinder bore. After installing the template at the bottom of the stroke, the oil squirt is then bent and positioned to hit the center of the template mark for the galley hole. We then remove the template and install a jobber length #42 drill (or you can use similar sized drill rod) into the oil squirt and move the template to the top of the bore. Without changing the the axis position of the oil squirt at the bottom of the hole, we redirect the angle of the oil squirt, so the oil will hit the targeted oil galley hole. It is a bit tricky and that is why we funnel the piston's galley hole, to allow a bit of 'allowance and error correction'.

I realize there is a lot of dynamics, with pistons and rods flying around at a high rate of speed. The goal is to get as much oil into the target as possible. Taking some pains to make it happen will help the overall cooling of the pistons.

 

[Franko6]

proverbial pin drop...

 

[Dirtracr95]

Cool stuff!

 

[[486]]

Interesting developments, I never thought to check the hole size on mine while they were out
I can't remember if there are pressure valves in ours, if they're there they'd be in the bolts...
mercedes has them for sure, so they don't operate at idle and low oil pressure situations

makes me wonder how it'd react to the overdriven oil pump chain and gears you can get from BRM

 

[Franko6]

486,

The squirts have check balls. I don't know what pressure they open, but if they were to open due to 'too much oil', I don't think getting more to the piston's oil galleys would exactly break my heart.

In response to "...how (the oil squirts) react to the overdriven pump chain and gears from BRM."

Over-driven is maybe the wrong word. I would probably think 'Upgrade', 'Improved' or 'Updated' would be better adjectives.

There have been many unfounded concerns about the upgrade for the ALH and BEW, when using the BRM oil pump sprocket/ chain/ tensioner. Some think the cam followers will over-pressure to cause valve float. Some think you might blow seals. The same oil pump is used in several VW version gasoline engines and in all TDI engines since the 06 BRM, which means all common rail engines have the same oil pump, same sprocket as the BRM.

The smaller oil squirt size is something I only recently discovered, I do think 'more is better' for both the pump and the squirts. However, I do not think the sizing is particularly going to make any pistons melt or seize, unless we are talking outlandish performance, in which case, everything matters.

 

[turbovan+tdi]

Great thread, I'll definately be checking all of this on my ALH build.

 

[GOFAST]

good information.
now I'll certainly use this info for my next AFN.

 

[CakeD]

proverbial pin drop...

That's just the sound of the club processing your latest information bomb. Great info as always.

My only comment would be do you believe there are any gains in bumping up the squirter diameter?

The smaller the orifice the further the oil will "squirt" and at a higher pressure drop/ likely lower volume. This all would be reducing heat transfer. The opposite would be true for a larger diameter orifice. How did you choose #42? Why do you believe there is a difference in factory engines?

 

[Franko6]

Oil cooling is about volume, not pressure. Why the difference is squirter size? I really don't know why, only that the later models are usually larger. The total volume increase is roughly 25%...#48 is .076 and a #42 drill is .096.

 

[BleachedBora]

Nice! Good job Frank

 

[xjay1337]

Interesting post.

 

[Fix_Until_Broke]

Oil cooling is about volume, not pressure. Why the difference is squirter size? I really don't know why, only that the later models are usually larger. The total volume increase is roughly 25%...#48 is .076 and a #42 drill is .096.

FYI that's about a 60% difference, not 25%. Area goes up with the square of diameter

Bigger is better from a cooling standpoint as long as you have sufficient oil pump flow to squirt the oil far enough when it's hot while also supplying everything else with sufficient quantities of oil.

The 0.076" one will flow ~2.3 LPM @ 2 Bar oil pressure
The 0.096" one will flow ~3.7 LPM @ 2 Bar oil pressure or, to flip it around since the oil pumps are fixed flow, not fixed pressure...
The 0.096" one will have 0.79 Bar pressure at the same ~2.3 LPM flow rate.

 

[dieseleux]

Nice thread!

Oil pump are fixe flow but pressure relief limit the pressure, if you have less restriction in oil system, pressure relief valve work less and you have more flow use by engine in overall.
The oil return by pressure relief valve is the good indicator if the pump have good size for the job.


Dieseleux

 

[compu_85]

Mercedes installed oil galleys like this in the pistons of the 86-87 6 cylinder turbo diesels. For some reason they were removed for the 1990 6 cylinder TD (cost perhaps?) going back to the ALH type system where the sprayer was just aimed at the bottom of the piston. However, MB later put the oil galley back in the pistons of the 6 cylinder around 1995. Guess they turned out to be important.

-J

 

[Franko6]

FUB, Point taken about flow volume.... I was thinking linear. Maybe I should think it through again. All that extra oil splashing around may inhibit performance. Not exactly a dry sump...I never thought to check that.

I did not even consider worrying if there was enough volume for the larger orifice for the spray jets. If I am modifying the jets, I am also modifying the pump with the BRM sprocket. So, no worries. As for figuring the drop in pressure at a given orifice, I will leave all that gory detail to you.

Dieseluex, Although I get some talk about supposed disadvantages for using the BRM sprocket on an ALH or BEW oil pump, I don't see how it could be wrong. There are several of the engines in later year models (04- 06) without oil galley pistons. I would think I were cheated if I got the lesser of the pistons VW installs into those engines.

I will admit, I am confused for what both you and FUD say about 'fixed flow', unless you say that the flow is limited by the ability of the engine to pass oil, which would make the flow 'fixed', but it appears to me that this pump, unrestricted, would continue to increase volume with speed, only limiting the volumetric increase from opening a pressure relief valve, in the event there were a flow limitation forced on the system.

 

[Ol'Rattler]

Really great dissertation Frank. Your ability for critical thinking is a gift that most folks will never know.

Something I have wondered about is how do the wrist pins get oiled? Probably pretty simple except I can not find anything that describes it.

 

[Fix_Until_Broke]

Nice thread!

Oil pump are fixe flow but pressure relief limit the pressure, if you have less restriction in oil system, pressure relief valve work less and you have more flow use by engine in overall.
The oil return by pressure relief valve is the good indicator if the pump have good size for the job.


Dieseleux

The pump is a fixed displacement per revolution so flow is directly proportional to engine speed. 2000 RPM will have twice as much flow as 1000 RPM.

The pressure in the system is a result of the restrictions to that flow. As the oil heats up, the pressure goes down, but the flow rate stays the same.

There is a pressure relief in the system like Dieseleux says, however it's set at ~6 bar so 99% of the time it does not open. Only when it's cold or you're at high RPM will this valve open and when it does, the flow to the engine is reduced since some of it is going over this relief valve.

So, when the smaller oil pump sprocket is put on, the pump flow increases by the ratio of the number of teeth on the two sprockets up to the point where you hit the 6 bar relief valve. Again 99% of the time, with the smaller sprocket, you'll be pumping more oil through the engine since the relief is not open.

If all goes well, I'll be changing the oil pump sprocket and not changing the squirters so will be able to see how that changes the oil pressure during normal operation.

 

[TDIsyncro]

Good subject Frank. I was not very specific about any of my details when I modified my oil coolers in this post:

http://forums.tdiclub.com/showpost.php?p=4394967&postcount=782

I also created a bit of a funnel at entry, but now that I look at yours I may revisit that aspect. I think I could of done a better job. Good catch! The other thing I did think about doing was to measure flow rate and trajectory from squirters of different hole sizes at different pressure levels. I ended up not doing that do to logistics and timing. It would be a worthy study for someone I think. I am using a dry sump pump and have very high flow volume and pressure. On stock oil pump I would caution that the small check valve (in the squirter) may not flow sufficient to maintain a proper oil jet at high power lower rpm conditions. At the other end of the spectrum, removal of the check valves will cause low oil pressure in main oil gallery at idle and lower rpm ranges. Just to explain a bit more, the check valve becomes a restriction to flow as flow increases, and the nozzle ID is also a restriction. With any restriction, as flow increases, pressure drop increases. If you increase pressure drop at check valve you have less pressure drop available at the squirter tip. The squirter tip is basically nozzle flow. Nozzles convert fluid pressure into velocity. If pressure at tip drops, then velocity drops, and if velocity drops delivery might not reach the upper ranges of the stroke. Some testing would put some good guidelines in place for this. I don't mean to over complicate this but these are some of the considerations that need to he properly vetted.

 

[Franko6]

"Ol Rattler, Thank you. It is nice to be appreciated. I appreciate your vote of confidence.

The amount of oil needed for the wrist pins in comparatively minor. With all the oil flailing around and I expect, easily missing the oil galley entrance hole, there is plenty of splash to reach the top of the connecting rod. In our H-beam rods, we have two slightly offset oil holes toward the top of the wrist pin. Stock rods also have a similar oil hole. The wrist pin gets very little motion. A small bit of oil is all it needs.

FUD, I feel it is a misnomer to call a pump 'fixed', when in fact it's volume is speed based. I think it sounds a bit oxymoronic. But I do follow what you are saying. All-in-all, the main point is to increase oil flow to the piston galley, which I think is a critical element to a highly modified engine. To increase the oil pump volume by decreasing the oil pump sprocket follows suit with my thinking, that the increase volume needed for the oil squirts is well compensated by improving pump speed.

TDIsyncro, I had not seen your previous work. As for the increased volume and size of the nozzle, I have no fear that the pressure and volume will be lost. First, having taken a broken oil squirt apart, the check ball hole is plenty large that the restriction is at the end of the oil squirt. As any orifice, the smallest restriction should be at the aperture. The point we drill out is the point of restriction.

As for the oil jet reaching the galley hole at TDC for the piston, I think that I do not expect it is very possible. The rod and throw of the big end are going to disturb the pattern and direction of the oil, I believe, until the oil jet becomes an oil spray I am sure the rotating mass becomes quite a fan. If any oil hits the hole, and I might add, the higher the rpm, the less likely the aim, I would be surprised.

Please vote.

 

[turbovan+tdi]

The BHW oil pump sprocket mod, I assume the crank gear is the same, just use the BHW chain and gear? How much does it increase the oil pressure?

 

[ryanp]

Increased spring pressure on the check valve would be a good idea, the spring is not stiffer than a ballpoint pen, I'd guess they are working all the time.

Pistons cracking due to excess heat is a big worry and happens a lot to our throwaway race engines. We have a few other issues to address at the same time and it's all heat related!

 

[turbovan+tdi]

Increased spring pressure on the check valve would be a good idea, the spring is not stiffer than a ballpoint pen, I'd guess they are working all the time.
!

That wouldn't really affect oil pressure until you get the rpm's up and from what's been said, higher rpm oiling isn't an issue.

 

[Franko6]

The BHW oil pump sprocket mod, I assume the crank gear is the same, just use the BHW chain and gear? How much does it increase the oil pressure?

The BHW sprocket mod is a bit off topic, but no, BHW crank sprocket is removed (we have the VW modified tool for that to loan) and replaced with the smaller sprocket found on ALH and later 1.9 cranks. The BRM oil pump sprocket, ALH oil pump, BRM chain and tensioner, 1.8 pickup tube, BRM windge tray and a 1/8" pipe plug makes the kit. There are two subframe pins the realign the frame.

I would say that the main objective is not to increase oil pressure, but to avoid several engineering errors with the OEM arrangement. 1) The oil pressure driven chain tensioner is a poor design and bound to fail. 2) The oil pump has a tendancy to shear at the hex drive. 3) the balance shaft portion is virtually worthless. After removing the unit in my own car, I cant tell the difference. 4) The ALH pump, a crescent design, is not only a very good pump, but the same pump is still used in the newer CR vehicles with the same
BRM sprocket and chain, and I think the same tensioner. It is cheaper by a $1000 than the BHW balance shaft module and is more effective.

I think the reliability of the ALH oil pump is the real issue; Not the oil pressure.

Ryan, The spring is weak by necessity. The orifice in the check valve is only 2.80mm. As best I can tell, there is about 60-65 grams pressure to open the check ball. It would have to be translated to Kpa, as it seems all pressure regulating valves are formulated like that.

If there is someone good with the math, that is enough to calculate the pressure required to crack the check ball. However, there are concerns about flow and pressure drop, which require viscocity, and increased spring tension past crack pressure, which I am not interested in calculating. Otherwise a jig could be set up and run various pressure volume and pressure to determine pressure loss and opening under actual operation. My bet is it would take about 30psi to operate the check valve @ 1500rpm operating temp of 90c.

To finish the answer for a previous question, why the #42 drill? That is .096", or 2.13mm. The squirt is about .7mm smaller then than the check ball orifice. The size differential between the squirt orifice and the check ball is adequate flow and the tube is thinned enough at squirt that I would not push the limits further.

 

[turbovan+tdi]

The BHW sprocket mod is a bit off topic, but no, BHW crank sprocket is removed (we have the VW modified tool for that to loan) and replaced with the smaller sprocket found on ALH and later 1.9 cranks. The BRM oil pump sprocket, ALH oil pump, BRM chain and tensioner, 1.8 pickup tube, BRM windge tray and a 1/8" pipe plug makes the kit. There are two subframe pins the realign the frame.

I would say that the main objective is not to increase oil pressure, but to avoid several engineering errors with the OEM arrangement. 1) The oil pressure driven chain tensioner is a poor design and bound to fail. 2) The oil pump has a tendancy to shear at the hex drive. 3) the balance shaft portion is virtually worthless. After removing the unit in my own car, I cant tell the difference. 4) The ALH pump, a crescent design, is not only a very good pump, but the same pump is still used in the newer CR vehicles with the same
BRM sprocket and chain, and I think the same tensioner. It is cheaper by a $1000 than the BHW balance shaft module and is more effective.

I think the reliability of the ALH oil pump is the real issue; Not the oil pressure.
.

Ok, thanks. It keeps coming up in this thread so just wanted an answer, to which you provided very nicely,

 

[Exenos]

Frank, I got 7.3kPa (~1psi) for the cracking pressure of the squirters. I feel like I'm off by a factor of 10 but either way I think its safe to say that they are operating at all times except for the initial start up.

As a quick note about calling the oil pump "fixed displacement". The "correct" term that I've been taught is "positive displacement".

 

[Franko6]

Turbovan=tdi, You are welcome.

Exenos, I don't know how that could be that low, honestly. Is that calculated or actual crack under pressure load? I thought to set up on a vehicle and run it against a gauge, but it would likely be messy.

What is the formula you are using? The smaller the area, the less spring pressure to resist crack pressure. Getting the spring lift was a very rough measurement, as it would require quite the setup to calculate accurately.

If indeed, the oil squirts crack at that low pressure, then I think it very wise to increase pump flow at low rpm. 4 nozzles blowing oil through a 2.8mm hole becomes quite a volume for idle pressure and I think that could further diminish oil pressure.

My further thoughts are that the older 1Z/ AHU, which also have oil squirts, and the more typical gear drive oil pump will suffer very low oil pressure at idle, if this crack pressure you have come up with, is accurate. That has been a concern for the older engines and we have found aftermarket AHU pumps weak to the point of being ineffective at idle. The bigger point for the AHU's is extremely low oil pressure at idle, for which the oil squirts could be a contributing factor.

On a side-note, we recently found that the 1.8 gasser crowd, which also has the same block arrangement as the AHU in engines like the AEB, AWW, AWD, etc., 20-valve should also be concerned for oil pressure and intermediate shaft bearing longevity. There is a group that is using a similar techinque we use on PD's to cut a radial slot in the intermediate cam bearings to make it oil better. We like it and think it is applicable to the AHU's.

 

[ryanp]

thats why i said to shim them up a little if we open the holes, do we even need them at idle?

1psi sounds low but its not more than a few PSI i dont think

 

[TDIJetta99]

Been modifying pistons and oil squirters since my very first turbocharged engine with galley cooled pistons..

Definitely a good durability upgrade

 

[Exenos]

Frank, I just used the 2.8mm orifice and 65g that you provided to calculate the 7.3kPa.

 

[Franko6]

Exenos, Thank you for your calculations. What is the formula to figure that crack pressure?

I may set up a jig to confirm. That value for check valve for the oil squirts is too low. I definitely would want the oil squirts check ball shut off flow at idle. I think the effect for our TDI's is important, but more so on the weaker oil pumps in 1.8T's.