General Category >> Technical Documents/Reference >> "End of the line" Oil Pressure Gage

Message started by Oldfeller on 04/20/10 at 19:52:00

Title: "End of the line" Oil Pressure Gage
Post by Oldfeller on 04/20/10 at 19:52:00

One of the items Verslagen requested out of the Serenity engine project was an inexpensive way of mounting an oil pressure gauge that could detect low oil pressure in the cam bearings.

This was not a super easy thing to do ....  and do it cheaply,  anyway.

(which of course was why he wanted me to go figure out how to do it)

The issue is that you can put an oil gauge into the system lots of places that are relatively easy to get to -- the top of the clutch cover, sticking out of the side of the cylinder jug's vertical oil passage, and lastly a banjo fitting under the head cover screw as shown below -- there are lots of places to put an oil pressure gauge.

The banjo fitting idea was certainly appealing, take off the tank, pop out a long bolt, put in the banjo block and the aluminum crush washers in place with a slightly longer bolt and torque it back down to 120 inch pounds.  

This was so easy to do you could make up a little kit and sell it to the list members for a reasonable price, sure enough.

Almost sounded like a solution it did .... until you think about it a bit.

Well, it was certainly easy enough to do and it almost gets you what you want .... that is until a journal clearance suddenly gets big on you causing an oil volume/pressure drop or a piece of gasket trash gets sideways in the little angled passages up in the head and blocks things up.  

Oops, because you are sensing pressure upstream to these issues they can blind side you with a trashed head while the oil gauge is still happily telling you everything is pressurized & everything is all hunky dory.  

Bad news, that ....  happy gauge but yet another dead head again.

:-?         :-?          :-?        :-?        :-?        :-?        :-?        :-?

Well, where do you have to put the oil pick up to find those suddenly enlarging cam journal bearing gap leakages and that floating trash (generally bits of paper or silicone gasket maker that got loose from somewhere downstream) that is blocking up them little drilled oil passages?  

Where is the magic location?

At the end of everything, of course !!  The very last stop in the very last passage after the very last bearing drop.   That is the only way to sense any enlargements or blockages in the entire system -- go to the very end of  it.

AND THE GOOD NEWS IS THAT IT IS VERY CHEAP TO DO.  Maybe not as easily done as the banjo trick mentioned earlier, but about half the cost for the necessary materials.

Go to Harbor Freight and pick these two inexpensive items up.  Mind you, you can pay more for the pieces (and get better pieces) but this is the low ball way to get it done.

Total cost is around $7.50 for both the items.  Or you can buy a complete oil pressure testing kit for around $16.00 and figure out how to tuck the extra hose away out of sight and put up with the lack of response out of the much higher rated (and physically larger) pressure gauge.  

Or you can spring for a nice oil filled gauge from an American company for an additional $24 -- or you can do any number of different things once you have the basic idea down in your head.

This is just the cheapest way to get it done using the best place to take the pressure from.


Step one -- catch your engine during a top cover tear down

Step two -- while you have the cover off carefully center punch the little dot in the center of the brass plug and drill it out.  You likely already own a 1/8" 27 NPT tap as part of your Harbor freight 40 piece SAE tap set, so you can choose your drill bit by comparison to the tip threads at the very end of the tap.  REMEMBER THE TAP IS TAPERED, so you need to go smaller on the drill hole and don't tap it very deep !!

You want the grease hose fitting to bottom out on the tapered threads before the 1/8NPT fitting shoulder hits the face of the casting and you do not want the male threaded end to go in deep enough to block off the nearby vertical cam journal feed passage.  Too big with the hole or too deep with the tap can give you big trouble, so please don't go there.

Remember to flush all your passages clean with solvent and air blow it out very thoroughly -- then do it all again just to be sure.  Drill chips left in these passage would be a very bad thing -- a pipe cleaner to run through them just to be sure might be a right good idea as well.

Use silicone gasket maker sparingly on the tapered threads to make sure the joint is oil proof as you lightly tighten it up.  Don't get heavy handed with the wrench, the aluminum casting could be jacked apart and busted by the tapered thread action and that would cost you real big bucks for a new head cover (and a new head since they won't sell them separately).  

Easy does it
, let the gasket maker do the sealing, not brute taper lock force like a steel plumbing fixture -- it ain't steel and it ain't very thick either.

The 3000 psi rated grease hose is nice and stiff and it will stay where you bend it so make your routing bends large & generous as you twist it around inside the cosmetic chrome shield going either forwards or backwards as you decide is best for you.

Route it forward and you can put the gauge along side the clutch cable with a black nylon pull tie or two to keep things stable.  You can read it while you roll down the road that way ....  it may be upside down and small & hard to read accurately, but you sure can put it there if you want to.

Route it backwards and you can have the gauge hang down by the fuel tap and carburetor area if you take the mindset that you just need to know what the oil pressure is at idle and at partial throttle settings while you have the engine in neutral on the side stand.  These are the speeds that would indicate potential trouble as full speed just tells you the direct drive (no overpressure valve equipped) oil pump is working a lot harder than it needs to.  

This routing has another benefit, the gauge is in the normal upright reading position hanging down from the tank, it is all sheltered from the elements too.


BTW, if you do go with the $2.99 cheapie gauge you will have to twist the little chromed plastic dingus off with your fingers and you may have to clip off a little protruding brass post with a pair of dykes before joining the gauge to grease hose with an 89 cent 1/8" NPT coupling from a hardware store.  

(Note: there are 3 types of this cheapie air gage that Harbor Freight sells in rotation, some with brass posts, some without -- just make sure there are 1/8" 27 NPT threads under that plastic cover piece or it won't work out for you at all).


Are improvements to this idea possible?

Sure !!

As many as you have imagination and dollars to cover.  

Look at flexible under sink hoses at Lowes in the plumbing section -- the braided steel ones would likely work out jest fine and you would get to pick your length by 4 inch increments to put the gauge anywhere on the bike you want it.

Better made, oil filled bottom or back mounted pressure gauges with faces up to 4" large are available if that's what trips your trigger.

But, for less than $10 this proves out the principals involved and correctly identifies the place to take the pressure from.

And that's what Verslagen had asked for -- the main trick to doing it cheaply while covering all the failure modes that we know about.

Title: Re: "End of the line" Oil Pressure Gage
Post by verslagen1 on 04/20/10 at 20:19:14

Hmmm... that's a good place.  I was thinking the other side.  
But there you could mount a gage permanent like.
I was thinking schrader valves so you can take a reading just like on a tire.
And not have to worry about oil squirting all over.
and oil type valves are available.

Title: Re: "End of the line" Oil Pressure Gage
Post by Oldfeller on 04/20/10 at 20:36:48

Well, if you do the spark plug door mod so you can get to it then you can put that little piece in the same spot with the appropriate tap.

Where can you buy the little metal spud?  
T'ain't no good if we don't know where to go get it.

One of the tricks the hose does is to get the gauge away from hot head zone.  The 3,000 psi grease hose is built plenty rugged enough to take it but the cheapie pressure gauge likely wouldn't care much for burning hot oil.  Since the oil doesn't circulate the oil out by the gauge would be at ambient temperature for wherever you mounted it.

Title: Re: "End of the line" Oil Pressure Gage
Post by verslagen1 on 04/20/10 at 20:40:15

Only place I could find a direct listing...

of course plenty of listings for spud guns.   ;D

gonna try berg hardware when I get the chance.

trap door? do you mean I gotta put it back on? 8-)

Title: Re: "End of the line" Oil Pressure Gage
Post by Oldfeller on 04/20/10 at 20:47:33

Yes, most of us still use the chrome glory covers 'cause they're purty and all shiny looking.

Neither you nor Lancer have any use for the wasted ounces of weight though .... yeah, I know.

But yer mod has to assume normal list members with covers in place, ergo the heavy construction durable hose extension part of the trick.

Title: Re: "End of the line" Oil Pressure Gage
Post by verslagen1 on 04/20/10 at 21:00:41

'others'  :-? ooooh yeah... others.    ;)

hey found it in fleabay cheap so I got a couple.

Title: Re: "End of the line" Oil Pressure Gage
Post by Oldfeller on 04/21/10 at 05:16:54

You may have to locate the special viton hi-temp oil proof rubber spring insert piece to go inside the brass shrader body that you found on Ebay.  

It has to be able to live a long time mounted up there on the head cover (constantly sitting in the heat) so the normal rubber inner spring unit may need to be swapped with a high temp oil proof viton seat inner spring unit.   Parker makes them, so somebody sells them.

With shipping your cost is about the same as my method and your pressure reporting is only gonna happen when you push a separate air gauge up against the spud instead of constantly reporting the ever changing pressure as revs rise & fall.

It does save a couple of ounces of weight though, and I know that weight is real important to you and Lancer as you build them stripped down race bikes of yours.


But that is two fully functional methods to get your oil pressure reported from the correct spot for less than $10.   That ain't bad.

Who has another, even slicker & better method to tell us about?

Title: Re: "End of the line" Oil Pressure Gage
Post by JohnBoy on 04/21/10 at 13:44:49

Very nice work!!!

How much pressure are we talking about, and how much drop before things start going south?

Title: Re: "End of the line" Oil Pressure Gage
Post by Oldfeller on 04/21/10 at 14:04:49

We keep talking about how critical it is to keep your idle RPM over 1,000 RPM for a good reason.

At idle, with fully warmed oil the end-of-line pressure is around 1-3 psi, assuming you have normal cam shaft bearing gaps and no leaks in any of the gasket junctions at crank shaft, clutch side cover, base gasket, head gasket, cover gasket, etc etc -- all of which detract from the volume and pressure measured up at the head.

If you have a gasket leak or an enlarged journal gap, your pressure is reduced accordingly.

:o         :(        :P        :-/        :-[          :-?    

Guess what happens if it gets down to zero?  Your cam shaft journals hit the soft aluminum in the head and begin to increase those leakage gaps by simple friction & wear.   (this occurs at every engine startup, btw)

The head death spiral begins then -- more gap = lower pressure from then on.

The test bed we are using to develop these tricks died twice from "unknown at the time" low oil pressure.   It happens.

The intent this time is to have a reporting method in place that will allow me to shut it down if the oil pressure swings low after the next time and money consuming complete rebuild.

This engine isn't being rebuilt for speed -- it is being rebuilt for "tight" instead.   Cam journal gaps are less than a thousandth, gasketing will be meticulous and I am hoping to see some oil pressure when I crank it up ....

Title: Re: "End of the line" Oil Pressure Gage
Post by Oldfeller on 04/26/10 at 16:09:00

OK, you guys keep PMing asking about the cautions written above concerning the drilling & tapping steps.  Apparently I wasn't detailed enough when I wrote it originally, so I'd better break it out in a bit of detail so it is clearer.

This is what I mean about punch marking the center of the brass plug, put a ding mark in the very center so a 1/16" drill bit will find a clearly defined centered spot to start in.

You have to drill the plug out with increasing size steps until you can see a picture like this in the bottom of the hole.  That last bit was a 5/16" bit and it stops biting about half way through the cam bearing vertical feed drop hole.

At 5/16" you should be able to start the longer version of the pipe tap, the one with the long nose on it.   Pay some attention to starting the pipe tap straight and true since it can and will start crooked if you let it.

Pipe taps are tapered and cut on all threads at all times -- expect to have to pull it and clean it a lot.  The aluminum is very soft and gummy, so use lots of oil when tapping to keep the tap from sticking or loading up (smearing) the soft aluminum.

The long pipe tap bottoms out on the back of the hole before getting big enough to admit the fitting to the right depth, so switch over to a bottoming tap and enlarge the hole all the way to full depth.   Stop and check things periodically, making the tapped hole too large is one of the ways you can mess this thing up big time.

(yes, Rigid makes a 1/8" NPT-27 bottoming tap if you want to go buy one.  But if you don't want to spring the $$ for one simply shorten the tap you just used until it will cut wide enough to admit your fitting.  That's what I did)

You gotta verify you haven't blocked off the last vertical oil passage with the fitting, so stick a drill bit butt first down the hole and put the fitting in and tighten it up lightly.  If the bit still moves freely in the vertical hole you are OK for not blocking the passage.

This is what the final product looks like.   You route the hose either forwards or backwards to park the gauge where you want it to be.


I will restate and make VERY BLASTED CLEAR before you bolt things up you have to make durn sure you don't have any drilling or tapping chips in the oil passages.  

Go buy a pipe cleaner from an artsy craftsy store (girls use them to make little figurines) or go to a pipe store and pick one up and USE IT along with many blasts of carb cleaner (running the red tube down deep inside each passage) and blow everything dry with an air hose to make sure your passages are grit free and clean.


EASY DOES IT !!!   The aluminum walls of the tapped hole are thin, so do not get heavy handed when tapping or when installing your fitting.   It would be very easy to jack that tapered fitting into the hole and BREAK YOUR HEAD CASTING.

That would be a   :-[  $300-$400  :-[  major major f*ck-up so please, let's not go there !! » Powered by YaBB 2.2!
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